/*
* Copyright (C) 2009 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.widget;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.os.Bundle;
import android.util.AttributeSet;
import android.util.Log;
import android.view.FocusFinder;
import android.view.InputDevice;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewDebug;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityNodeInfo;
import android.view.animation.AnimationUtils;
import java.util.List;
/**
* 用于布局的容器，可以放置让用户使用滚动条查看的视图层次结构，允许视图结构比手机的屏幕大.
* HorizontalScrollView 是一种 {@link FrameLayout 框架布局}，
* 这意味着你可以将包含要滚动的完整内容的子视图放入该容器；
* 该子视图本身也可以是具有复杂层次结构的布局管理器.一般使用横向的 {@link LinearLayout}
* 作为子视图，使用户可以滚动其中显示的条目.
*
* <p>{@link TextView 文本视图} 类也有其自身的滚动处理，不需要嵌入滚动视图；
* 但二者可以组合使用，其效果与将文本视图放入很大容器中一样.
*
* <p>HorizontalScrollView 只支持水平方向的滚动。 For vertical scrolling,
* use either {@link ScrollView} or {@link ListView}.
*
* @attr ref android.R.styleable#HorizontalScrollView_fillViewport
*/
public class HorizontalScrollView extends FrameLayout {
private static final int ANIMATED_SCROLL_GAP = ScrollView.ANIMATED_SCROLL_GAP;
private static final float MAX_SCROLL_FACTOR = ScrollView.MAX_SCROLL_FACTOR;
private static final String TAG = "HorizontalScrollView";
private long mLastScroll;
private final Rect mTempRect = new Rect();
private OverScroller mScroller;
private EdgeEffect mEdgeGlowLeft;
private EdgeEffect mEdgeGlowRight;
/**
* Position of the last motion event.
*/
private int mLastMotionX;
/**
* True when the layout has changed but the traversal has not come through yet.
* Ideally the view hierarchy would keep track of this for us.
*/
private boolean mIsLayoutDirty = true;
/**
* The child to give focus to in the event that a child has requested focus while the
* layout is dirty. This prevents the scroll from being wrong if the child has not been
* laid out before requesting focus.
*/
private View mChildToScrollTo = null;
/**
* True if the user is currently dragging this ScrollView around. This is
* not the same as 'is being flinged', which can be checked by
* mScroller.isFinished() (flinging begins when the user lifts his finger).
*/
private boolean mIsBeingDragged = false;
/**
* Determines speed during touch scrolling
*/
private VelocityTracker mVelocityTracker;
/**
* When set to true, the scroll view measure its child to make it fill the currently
* visible area.
*/
@ViewDebug.ExportedProperty(category = "layout")
private boolean mFillViewport;
/**
* Whether arrow scrolling is animated.
*/
private boolean mSmoothScrollingEnabled = true;
private int mTouchSlop;
private int mMinimumVelocity;
private int mMaximumVelocity;
private int mOverscrollDistance;
private int mOverflingDistance;
/**
* ID of the active pointer. This is used to retain consistency during
* drags/flings if multiple pointers are used.
*/
private int mActivePointerId = INVALID_POINTER;
/**
* Sentinel value for no current active pointer.
* Used by {@link #mActivePointerId}.
*/
private static final int INVALID_POINTER = -1;
public HorizontalScrollView(Context context) {
this(context, null);
}
public HorizontalScrollView(Context context, AttributeSet attrs) {
this(context, attrs, com.android.internal.R.attr.horizontalScrollViewStyle);
}
public HorizontalScrollView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
initScrollView();
TypedArray a = context.obtainStyledAttributes(attrs,
android.R.styleable.HorizontalScrollView, defStyle, 0);
setFillViewport(a.getBoolean(android.R.styleable.HorizontalScrollView_fillViewport, false));
a.recycle();
}
@Override
protected float getLeftFadingEdgeStrength() {
if (getChildCount() == 0) {
return 0.0f;
}
final int length = getHorizontalFadingEdgeLength();
if (mScrollX < length) {
return mScrollX / (float) length;
}
return 1.0f;
}
@Override
protected float getRightFadingEdgeStrength() {
if (getChildCount() == 0) {
return 0.0f;
}
final int length = getHorizontalFadingEdgeLength();
final int rightEdge = getWidth() - mPaddingRight;
final int span = getChildAt(0).getRight() - mScrollX - rightEdge;
if (span < length) {
return span / (float) length;
}
return 1.0f;
}
/**
* @return 按左右箭头时视图可以滚动的最大值.
*/
public int getMaxScrollAmount() {
return (int) (MAX_SCROLL_FACTOR * (mRight - mLeft));
}
private void initScrollView() {
mScroller = new OverScroller(getContext());
setFocusable(true);
setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
setWillNotDraw(false);
final ViewConfiguration configuration = ViewConfiguration.get(mContext);
mTouchSlop = configuration.getScaledTouchSlop();
mMinimumVelocity = configuration.getScaledMinimumFlingVelocity();
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
mOverscrollDistance = configuration.getScaledOverscrollDistance();
mOverflingDistance = configuration.getScaledOverflingDistance();
}
@Override
public void addView(View child) {
if (getChildCount() > 0) {
throw new IllegalStateException("HorizontalScrollView can host only one direct child");
}
super.addView(child);
}
@Override
public void addView(View child, int index) {
if (getChildCount() > 0) {
throw new IllegalStateException("HorizontalScrollView can host only one direct child");
}
super.addView(child, index);
}
@Override
public void addView(View child, ViewGroup.LayoutParams params) {
if (getChildCount() > 0) {
throw new IllegalStateException("HorizontalScrollView can host only one direct child");
}
super.addView(child, params);
}
@Override
public void addView(View child, int index, ViewGroup.LayoutParams params) {
if (getChildCount() > 0) {
throw new IllegalStateException("HorizontalScrollView can host only one direct child");
}
super.addView(child, index, params);
}
/**
* @return Returns true this HorizontalScrollView can be scrolled
*/
private boolean canScroll() {
View child = getChildAt(0);
if (child != null) {
int childWidth = child.getWidth();
return getWidth() < childWidth + mPaddingLeft + mPaddingRight ;
}
return false;
}
/**
* 表示是否拉伸该滚动视图的内容以适应视口（viewport）的大小.
*
* @return 如果内容需要填充视口则返回真，否则返回假.
*
* @attr ref android.R.styleable#HorizontalScrollView_fillViewport
*/
public boolean isFillViewport() {
return mFillViewport;
}
/**
* 设置此滚动视图是否将内容宽度拉伸来适应视口（viewport）.
*
* @param fillViewport 拉伸内容宽度时设为真；否则设为假.
*
* @attr ref android.R.styleable#HorizontalScrollView_fillViewport
*/
public void setFillViewport(boolean fillViewport) {
if (fillViewport != mFillViewport) {
mFillViewport = fillViewport;
requestLayout();
}
}
/**
* @return 按方向键滚动时，是否显示平滑的滚动效果.
*/
public boolean isSmoothScrollingEnabled() {
return mSmoothScrollingEnabled;
}
/**
* 设置按方向键滚动时，是否显示平滑的滚动效果.
* @param smoothScrollingEnabled 按方向键滚动时是否显示平滑的滚动效果.
*/
public void setSmoothScrollingEnabled(boolean smoothScrollingEnabled) {
mSmoothScrollingEnabled = smoothScrollingEnabled;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
if (!mFillViewport) {
return;
}
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
if (widthMode == MeasureSpec.UNSPECIFIED) {
return;
}
if (getChildCount() > 0) {
final View child = getChildAt(0);
int width = getMeasuredWidth();
if (child.getMeasuredWidth() < width) {
final FrameLayout.LayoutParams lp = (LayoutParams) child.getLayoutParams();
int childHeightMeasureSpec = getChildMeasureSpec(heightMeasureSpec, mPaddingTop
+ mPaddingBottom, lp.height);
width -= mPaddingLeft;
width -= mPaddingRight;
int childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
}
}
@Override
public boolean dispatchKeyEvent(KeyEvent event) {
// Let the focused view and/or our descendants get the key first
return super.dispatchKeyEvent(event) || executeKeyEvent(event);
}
/**
* 需要通过按键事件来实现滚动操作时，可以调用此方法.就像由视图层次结构分派事件时一样.
*
* @param event 要执行的事件.
* @return 若已处理事件返回真，否则返回假.
*/
public boolean executeKeyEvent(KeyEvent event) {
mTempRect.setEmpty();
if (!canScroll()) {
if (isFocused()) {
View currentFocused = findFocus();
if (currentFocused == this) currentFocused = null;
View nextFocused = FocusFinder.getInstance().findNextFocus(this,
currentFocused, View.FOCUS_RIGHT);
return nextFocused != null && nextFocused != this &&
nextFocused.requestFocus(View.FOCUS_RIGHT);
}
return false;
}
boolean handled = false;
if (event.getAction() == KeyEvent.ACTION_DOWN) {
switch (event.getKeyCode()) {
case KeyEvent.KEYCODE_DPAD_LEFT:
if (!event.isAltPressed()) {
handled = arrowScroll(View.FOCUS_LEFT);
} else {
handled = fullScroll(View.FOCUS_LEFT);
}
break;
case KeyEvent.KEYCODE_DPAD_RIGHT:
if (!event.isAltPressed()) {
handled = arrowScroll(View.FOCUS_RIGHT);
} else {
handled = fullScroll(View.FOCUS_RIGHT);
}
break;
case KeyEvent.KEYCODE_SPACE:
pageScroll(event.isShiftPressed() ? View.FOCUS_LEFT : View.FOCUS_RIGHT);
break;
}
}
return handled;
}
private boolean inChild(int x, int y) {
if (getChildCount() > 0) {
final int scrollX = mScrollX;
final View child = getChildAt(0);
return !(y < child.getTop()
|| y >= child.getBottom()
|| x < child.getLeft() - scrollX
|| x >= child.getRight() - scrollX);
}
return false;
}
private void initOrResetVelocityTracker() {
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
} else {
mVelocityTracker.clear();
}
}
private void initVelocityTrackerIfNotExists() {
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
}
private void recycleVelocityTracker() {
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
@Override
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
if (disallowIntercept) {
recycleVelocityTracker();
}
super.requestDisallowInterceptTouchEvent(disallowIntercept);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
/*
* This method JUST determines whether we want to intercept the motion.
* If we return true, onMotionEvent will be called and we do the actual
* scrolling there.
*/
/*
* Shortcut the most recurring case: the user is in the dragging
* state and he is moving his finger. We want to intercept this
* motion.
*/
final int action = ev.getAction();
if ((action == MotionEvent.ACTION_MOVE) && (mIsBeingDragged)) {
return true;
}
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_MOVE: {
/*
* mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
* whether the user has moved far enough from his original down touch.
*/
/*
* Locally do absolute value. mLastMotionX is set to the x value
* of the down event.
*/
final int activePointerId = mActivePointerId;
if (activePointerId == INVALID_POINTER) {
// If we don't have a valid id, the touch down wasn't on content.
break;
}
final int pointerIndex = ev.findPointerIndex(activePointerId);
if (pointerIndex == -1) {
Log.e(TAG, "Invalid pointerId=" + activePointerId
+ " in onInterceptTouchEvent");
break;
}
final int x = (int) ev.getX(pointerIndex);
final int xDiff = (int) Math.abs(x - mLastMotionX);
if (xDiff > mTouchSlop) {
mIsBeingDragged = true;
mLastMotionX = x;
initVelocityTrackerIfNotExists();
mVelocityTracker.addMovement(ev);
if (mParent != null) mParent.requestDisallowInterceptTouchEvent(true);
}
break;
}
case MotionEvent.ACTION_DOWN: {
final int x = (int) ev.getX();
if (!inChild((int) x, (int) ev.getY())) {
mIsBeingDragged = false;
recycleVelocityTracker();
break;
}
/*
* Remember location of down touch.
* ACTION_DOWN always refers to pointer index 0.
*/
mLastMotionX = x;
mActivePointerId = ev.getPointerId(0);
initOrResetVelocityTracker();
mVelocityTracker.addMovement(ev);
/*
* If being flinged and user touches the screen, initiate drag;
* otherwise don't. mScroller.isFinished should be false when
* being flinged.
*/
mIsBeingDragged = !mScroller.isFinished();
break;
}
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
/* Release the drag */
mIsBeingDragged = false;
mActivePointerId = INVALID_POINTER;
if (mScroller.springBack(mScrollX, mScrollY, 0, getScrollRange(), 0, 0)) {
postInvalidateOnAnimation();
}
break;
case MotionEvent.ACTION_POINTER_DOWN: {
final int index = ev.getActionIndex();
mLastMotionX = (int) ev.getX(index);
mActivePointerId = ev.getPointerId(index);
break;
}
case MotionEvent.ACTION_POINTER_UP:
onSecondaryPointerUp(ev);
mLastMotionX = (int) ev.getX(ev.findPointerIndex(mActivePointerId));
break;
}
/*
* The only time we want to intercept motion events is if we are in the
* drag mode.
*/
return mIsBeingDragged;
}
@Override
public boolean onTouchEvent(MotionEvent ev) {
initVelocityTrackerIfNotExists();
mVelocityTracker.addMovement(ev);
final int action = ev.getAction();
switch (action & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN: {
if (getChildCount() == 0) {
return false;
}
if ((mIsBeingDragged = !mScroller.isFinished())) {
final ViewParent parent = getParent();
if (parent != null) {
parent.requestDisallowInterceptTouchEvent(true);
}
}
/*
* If being flinged and user touches, stop the fling. isFinished
* will be false if being flinged.
*/
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
// Remember where the motion event started
mLastMotionX = (int) ev.getX();
mActivePointerId = ev.getPointerId(0);
break;
}
case MotionEvent.ACTION_MOVE:
final int activePointerIndex = ev.findPointerIndex(mActivePointerId);
if (activePointerIndex == -1) {
Log.e(TAG, "Invalid pointerId=" + mActivePointerId + " in onTouchEvent");
break;
}
final int x = (int) ev.getX(activePointerIndex);
int deltaX = mLastMotionX - x;
if (!mIsBeingDragged && Math.abs(deltaX) > mTouchSlop) {
final ViewParent parent = getParent();
if (parent != null) {
parent.requestDisallowInterceptTouchEvent(true);
}
mIsBeingDragged = true;
if (deltaX > 0) {
deltaX -= mTouchSlop;
} else {
deltaX += mTouchSlop;
}
}
if (mIsBeingDragged) {
// Scroll to follow the motion event
mLastMotionX = x;
final int oldX = mScrollX;
final int oldY = mScrollY;
final int range = getScrollRange();
final int overscrollMode = getOverScrollMode();
final boolean canOverscroll = overscrollMode == OVER_SCROLL_ALWAYS ||
(overscrollMode == OVER_SCROLL_IF_CONTENT_SCROLLS && range > 0);
if (overScrollBy(deltaX, 0, mScrollX, 0, range, 0,
mOverscrollDistance, 0, true)) {
// Break our velocity if we hit a scroll barrier.
mVelocityTracker.clear();
}
onScrollChanged(mScrollX, mScrollY, oldX, oldY);
if (canOverscroll) {
final int pulledToX = oldX + deltaX;
if (pulledToX < 0) {
mEdgeGlowLeft.onPull((float) deltaX / getWidth());
if (!mEdgeGlowRight.isFinished()) {
mEdgeGlowRight.onRelease();
}
} else if (pulledToX > range) {
mEdgeGlowRight.onPull((float) deltaX / getWidth());
if (!mEdgeGlowLeft.isFinished()) {
mEdgeGlowLeft.onRelease();
}
}
if (mEdgeGlowLeft != null
&& (!mEdgeGlowLeft.isFinished() || !mEdgeGlowRight.isFinished())) {
postInvalidateOnAnimation();
}
}
}
break;
case MotionEvent.ACTION_UP:
if (mIsBeingDragged) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
int initialVelocity = (int) velocityTracker.getXVelocity(mActivePointerId);
if (getChildCount() > 0) {
if ((Math.abs(initialVelocity) > mMinimumVelocity)) {
fling(-initialVelocity);
} else {
if (mScroller.springBack(mScrollX, mScrollY, 0,
getScrollRange(), 0, 0)) {
postInvalidateOnAnimation();
}
}
}
mActivePointerId = INVALID_POINTER;
mIsBeingDragged = false;
recycleVelocityTracker();
if (mEdgeGlowLeft != null) {
mEdgeGlowLeft.onRelease();
mEdgeGlowRight.onRelease();
}
}
break;
case MotionEvent.ACTION_CANCEL:
if (mIsBeingDragged && getChildCount() > 0) {
if (mScroller.springBack(mScrollX, mScrollY, 0, getScrollRange(), 0, 0)) {
postInvalidateOnAnimation();
}
mActivePointerId = INVALID_POINTER;
mIsBeingDragged = false;
recycleVelocityTracker();
if (mEdgeGlowLeft != null) {
mEdgeGlowLeft.onRelease();
mEdgeGlowRight.onRelease();
}
}
break;
case MotionEvent.ACTION_POINTER_UP:
onSecondaryPointerUp(ev);
break;
}
return true;
}
private void onSecondaryPointerUp(MotionEvent ev) {
final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >>
MotionEvent.ACTION_POINTER_INDEX_SHIFT;
final int pointerId = ev.getPointerId(pointerIndex);
if (pointerId == mActivePointerId) {
// This was our active pointer going up. Choose a new
// active pointer and adjust accordingly.
// TODO: Make this decision more intelligent.
final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
mLastMotionX = (int) ev.getX(newPointerIndex);
mActivePointerId = ev.getPointerId(newPointerIndex);
if (mVelocityTracker != null) {
mVelocityTracker.clear();
}
}
}
@Override
public boolean onGenericMotionEvent(MotionEvent event) {
if ((event.getSource() & InputDevice.SOURCE_CLASS_POINTER) != 0) {
switch (event.getAction()) {
case MotionEvent.ACTION_SCROLL: {
if (!mIsBeingDragged) {
final float hscroll;
if ((event.getMetaState() & KeyEvent.META_SHIFT_ON) != 0) {
hscroll = -event.getAxisValue(MotionEvent.AXIS_VSCROLL);
} else {
hscroll = event.getAxisValue(MotionEvent.AXIS_HSCROLL);
}
if (hscroll != 0) {
final int delta = (int) (hscroll * getHorizontalScrollFactor());
final int range = getScrollRange();
int oldScrollX = mScrollX;
int newScrollX = oldScrollX + delta;
if (newScrollX < 0) {
newScrollX = 0;
} else if (newScrollX > range) {
newScrollX = range;
}
if (newScrollX != oldScrollX) {
super.scrollTo(newScrollX, mScrollY);
return true;
}
}
}
}
}
}
return super.onGenericMotionEvent(event);
}
@Override
public boolean shouldDelayChildPressedState() {
return true;
}
@Override
protected void onOverScrolled(int scrollX, int scrollY,
boolean clampedX, boolean clampedY) {
// Treat animating scrolls differently; see #computeScroll() for why.
if (!mScroller.isFinished()) {
mScrollX = scrollX;
mScrollY = scrollY;
invalidateParentIfNeeded();
if (clampedX) {
mScroller.springBack(mScrollX, mScrollY, 0, getScrollRange(), 0, 0);
}
} else {
super.scrollTo(scrollX, scrollY);
}
awakenScrollBars();
}
@Override
public boolean performAccessibilityAction(int action, Bundle arguments) {
if (super.performAccessibilityAction(action, arguments)) {
return true;
}
switch (action) {
case AccessibilityNodeInfo.ACTION_SCROLL_FORWARD: {
if (!isEnabled()) {
return false;
}
final int viewportWidth = getWidth() - mPaddingLeft - mPaddingRight;
final int targetScrollX = Math.min(mScrollX + viewportWidth, getScrollRange());
if (targetScrollX != mScrollX) {
smoothScrollTo(targetScrollX, 0);
return true;
}
} return false;
case AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD: {
if (!isEnabled()) {
return false;
}
final int viewportWidth = getWidth() - mPaddingLeft - mPaddingRight;
final int targetScrollX = Math.max(0, mScrollX - viewportWidth);
if (targetScrollX != mScrollX) {
smoothScrollTo(targetScrollX, 0);
return true;
}
} return false;
}
return false;
}
@Override
public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
super.onInitializeAccessibilityNodeInfo(info);
info.setClassName(HorizontalScrollView.class.getName());
final int scrollRange = getScrollRange();
if (scrollRange > 0) {
info.setScrollable(true);
if (isEnabled() && mScrollX > 0) {
info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD);
}
if (isEnabled() && mScrollX < scrollRange) {
info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_FORWARD);
}
}
}
@Override
public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
super.onInitializeAccessibilityEvent(event);
event.setClassName(HorizontalScrollView.class.getName());
event.setScrollable(getScrollRange() > 0);
event.setScrollX(mScrollX);
event.setScrollY(mScrollY);
event.setMaxScrollX(getScrollRange());
event.setMaxScrollY(mScrollY);
}
private int getScrollRange() {
int scrollRange = 0;
if (getChildCount() > 0) {
View child = getChildAt(0);
scrollRange = Math.max(0,
child.getWidth() - (getWidth() - mPaddingLeft - mPaddingRight));
}
return scrollRange;
}
/**
* <p>
* Finds the next focusable component that fits in this View's bounds
* (excluding fading edges) pretending that this View's left is located at
* the parameter left.
* </p>
*
* @param leftFocus look for a candidate is the one at the left of the bounds
* if leftFocus is true, or at the right of the bounds if leftFocus
* is false
* @param left the left offset of the bounds in which a focusable must be
* found (the fading edge is assumed to start at this position)
* @param preferredFocusable the View that has highest priority and will be
* returned if it is within my bounds (null is valid)
* @return the next focusable component in the bounds or null if none can be found
*/
private View findFocusableViewInMyBounds(final boolean leftFocus,
final int left, View preferredFocusable) {
/*
* The fading edge's transparent side should be considered for focus
* since it's mostly visible, so we divide the actual fading edge length
* by 2.
*/
final int fadingEdgeLength = getHorizontalFadingEdgeLength() / 2;
final int leftWithoutFadingEdge = left + fadingEdgeLength;
final int rightWithoutFadingEdge = left + getWidth() - fadingEdgeLength;
if ((preferredFocusable != null)
&& (preferredFocusable.getLeft() < rightWithoutFadingEdge)
&& (preferredFocusable.getRight() > leftWithoutFadingEdge)) {
return preferredFocusable;
}
return findFocusableViewInBounds(leftFocus, leftWithoutFadingEdge,
rightWithoutFadingEdge);
}
/**
* <p>
* Finds the next focusable component that fits in the specified bounds.
* </p>
*
* @param leftFocus look for a candidate is the one at the left of the bounds
* if leftFocus is true, or at the right of the bounds if
* leftFocus is false
* @param left the left offset of the bounds in which a focusable must be
* found
* @param right the right offset of the bounds in which a focusable must
* be found
* @return the next focusable component in the bounds or null if none can
* be found
*/
private View findFocusableViewInBounds(boolean leftFocus, int left, int right) {
List<View> focusables = getFocusables(View.FOCUS_FORWARD);
View focusCandidate = null;
/*
* A fully contained focusable is one where its left is below the bound's
* left, and its right is above the bound's right. A partially
* contained focusable is one where some part of it is within the
* bounds, but it also has some part that is not within bounds. A fully contained
* focusable is preferred to a partially contained focusable.
*/
boolean foundFullyContainedFocusable = false;
int count = focusables.size();
for (int i = 0; i < count; i++) {
View view = focusables.get(i);
int viewLeft = view.getLeft();
int viewRight = view.getRight();
if (left < viewRight && viewLeft < right) {
/*
* the focusable is in the target area, it is a candidate for
* focusing
*/
final boolean viewIsFullyContained = (left < viewLeft) &&
(viewRight < right);
if (focusCandidate == null) {
/* No candidate, take this one */
focusCandidate = view;
foundFullyContainedFocusable = viewIsFullyContained;
} else {
final boolean viewIsCloserToBoundary =
(leftFocus && viewLeft < focusCandidate.getLeft()) ||
(!leftFocus && viewRight > focusCandidate.getRight());
if (foundFullyContainedFocusable) {
if (viewIsFullyContained && viewIsCloserToBoundary) {
/*
* We're dealing with only fully contained views, so
* it has to be closer to the boundary to beat our
* candidate
*/
focusCandidate = view;
}
} else {
if (viewIsFullyContained) {
/* Any fully contained view beats a partially contained view */
focusCandidate = view;
foundFullyContainedFocusable = true;
} else if (viewIsCloserToBoundary) {
/*
* Partially contained view beats another partially
* contained view if it's closer
*/
focusCandidate = view;
}
}
}
}
}
return focusCandidate;
}
/**
* <p>处理按下翻页键时的滚动操作.该方法将视图向左或向右滚动一页，
* 并将焦点设在新的可视领域的最左边或最右边的组件上.
* 如果没有组件可以得到焦点，该视图将撤销焦点.</p>
*
* @param direction 滚动方向：{@link android.view.View#FOCUS_LEFT}
* 向左滚动一页、{@link android.view.View#FOCUS_RIGHT}
* 向右滚动一页.
* @return 若该方法处理了键盘事件，应该返回真，否则返回假.
*/
public boolean pageScroll(int direction) {
boolean right = direction == View.FOCUS_RIGHT;
int width = getWidth();
if (right) {
mTempRect.left = getScrollX() + width;
int count = getChildCount();
if (count > 0) {
View view = getChildAt(0);
if (mTempRect.left + width > view.getRight()) {
mTempRect.left = view.getRight() - width;
}
}
} else {
mTempRect.left = getScrollX() - width;
if (mTempRect.left < 0) {
mTempRect.left = 0;
}
}
mTempRect.right = mTempRect.left + width;
return scrollAndFocus(direction, mTempRect.left, mTempRect.right);
}
/**
* <p>处理按下“home/end”键时的滚动操作.该方法将视图向左或向右滚动，
* 并将焦点设在新的可视领域的最左边或最右边的组件上.
* 如果没有组件可以得到焦点，该视图将撤销焦点.</p>
*
* @param direction 滚动方向：{@link android.view.View#FOCUS_LEFT}
* 向左滚动一页、{@link android.view.View#FOCUS_RIGHT}
* 向右滚动一页.
* @return 若该方法处理了键盘事件，应该返回真，否则返回假.
*/
public boolean fullScroll(int direction) {
boolean right = direction == View.FOCUS_RIGHT;
int width = getWidth();
mTempRect.left = 0;
mTempRect.right = width;
if (right) {
int count = getChildCount();
if (count > 0) {
View view = getChildAt(0);
mTempRect.right = view.getRight();
mTempRect.left = mTempRect.right - width;
}
}
return scrollAndFocus(direction, mTempRect.left, mTempRect.right);
}
/**
* <p>Scrolls the view to make the area defined by <code>left</code> and
* <code>right</code> visible. This method attempts to give the focus
* to a component visible in this area. If no component can be focused in
* the new visible area, the focus is reclaimed by this scrollview.</p>
*
* @param direction the scroll direction: {@link android.view.View#FOCUS_LEFT}
* to go left {@link android.view.View#FOCUS_RIGHT} to right
* @param left the left offset of the new area to be made visible
* @param right the right offset of the new area to be made visible
* @return true if the key event is consumed by this method, false otherwise
*/
private boolean scrollAndFocus(int direction, int left, int right) {
boolean handled = true;
int width = getWidth();
int containerLeft = getScrollX();
int containerRight = containerLeft + width;
boolean goLeft = direction == View.FOCUS_LEFT;
View newFocused = findFocusableViewInBounds(goLeft, left, right);
if (newFocused == null) {
newFocused = this;
}
if (left >= containerLeft && right <= containerRight) {
handled = false;
} else {
int delta = goLeft ? (left - containerLeft) : (right - containerRight);
doScrollX(delta);
}
if (newFocused != findFocus()) newFocused.requestFocus(direction);
return handled;
}
/**
* 处理左右箭头按下时的滚动响应.
*
* @param direction 按下的响应的箭头键.
* @return 若该方法处理了该事件，返回真，否则返回假.
*/
public boolean arrowScroll(int direction) {
View currentFocused = findFocus();
if (currentFocused == this) currentFocused = null;
View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction);
final int maxJump = getMaxScrollAmount();
if (nextFocused != null && isWithinDeltaOfScreen(nextFocused, maxJump)) {
nextFocused.getDrawingRect(mTempRect);
offsetDescendantRectToMyCoords(nextFocused, mTempRect);
int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
doScrollX(scrollDelta);
nextFocused.requestFocus(direction);
} else {
// no new focus
int scrollDelta = maxJump;
if (direction == View.FOCUS_LEFT && getScrollX() < scrollDelta) {
scrollDelta = getScrollX();
} else if (direction == View.FOCUS_RIGHT && getChildCount() > 0) {
int daRight = getChildAt(0).getRight();
int screenRight = getScrollX() + getWidth();
if (daRight - screenRight < maxJump) {
scrollDelta = daRight - screenRight;
}
}
if (scrollDelta == 0) {
return false;
}
doScrollX(direction == View.FOCUS_RIGHT ? scrollDelta : -scrollDelta);
}
if (currentFocused != null && currentFocused.isFocused()
&& isOffScreen(currentFocused)) {
// previously focused item still has focus and is off screen, give
// it up (take it back to ourselves)
// (also, need to temporarily force FOCUS_BEFORE_DESCENDANTS so we are
// sure to
// get it)
final int descendantFocusability = getDescendantFocusability(); // save
setDescendantFocusability(ViewGroup.FOCUS_BEFORE_DESCENDANTS);
requestFocus();
setDescendantFocusability(descendantFocusability); // restore
}
return true;
}
/**
* @return whether the descendant of this scroll view is scrolled off
* screen.
*/
private boolean isOffScreen(View descendant) {
return !isWithinDeltaOfScreen(descendant, 0);
}
/**
* @return whether the descendant of this scroll view is within delta
* pixels of being on the screen.
*/
private boolean isWithinDeltaOfScreen(View descendant, int delta) {
descendant.getDrawingRect(mTempRect);
offsetDescendantRectToMyCoords(descendant, mTempRect);
return (mTempRect.right + delta) >= getScrollX()
&& (mTempRect.left - delta) <= (getScrollX() + getWidth());
}
/**
* Smooth scroll by a X delta
*
* @param delta the number of pixels to scroll by on the X axis
*/
private void doScrollX(int delta) {
if (delta != 0) {
if (mSmoothScrollingEnabled) {
smoothScrollBy(delta, 0);
} else {
scrollBy(delta, 0);
}
}
}
/**
* 与 {@link View#scrollBy} 相似，只是相对平滑的滚动，而不是立刻滚动到位.
*
* @param dx X 轴方向滚动的像素数.
* @param dy Y 轴方向滚动的像素数.
*/
public final void smoothScrollBy(int dx, int dy) {
if (getChildCount() == 0) {
// Nothing to do.
return;
}
long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
if (duration > ANIMATED_SCROLL_GAP) {
final int width = getWidth() - mPaddingRight - mPaddingLeft;
final int right = getChildAt(0).getWidth();
final int maxX = Math.max(0, right - width);
final int scrollX = mScrollX;
dx = Math.max(0, Math.min(scrollX + dx, maxX)) - scrollX;
mScroller.startScroll(scrollX, mScrollY, dx, 0);
postInvalidateOnAnimation();
} else {
if (!mScroller.isFinished()) {
mScroller.abortAnimation();
}
scrollBy(dx, dy);
}
mLastScroll = AnimationUtils.currentAnimationTimeMillis();
}
/**
* 与 {@link #scrollTo} 相似，只是相对平滑的滚动，而不是立刻滚动到位.
*
* @param x X 轴上滚动到的位置的像素数.
* @param y Y 轴上滚动到的位置的像素数.
*/
public final void smoothScrollTo(int x, int y) {
smoothScrollBy(x - mScrollX, y - mScrollY);
}
/**
* <p>滚动视图的滚动范围是其子视图的整个宽度.</p>
*/
@Override
protected int computeHorizontalScrollRange() {
final int count = getChildCount();
final int contentWidth = getWidth() - mPaddingLeft - mPaddingRight;
if (count == 0) {
return contentWidth;
}
int scrollRange = getChildAt(0).getRight();
final int scrollX = mScrollX;
final int overscrollRight = Math.max(0, scrollRange - contentWidth);
if (scrollX < 0) {
scrollRange -= scrollX;
} else if (scrollX > overscrollRight) {
scrollRange += scrollX - overscrollRight;
}
return scrollRange;
}
@Override
protected int computeHorizontalScrollOffset() {
return Math.max(0, super.computeHorizontalScrollOffset());
}
@Override
protected void measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec) {
ViewGroup.LayoutParams lp = child.getLayoutParams();
int childWidthMeasureSpec;
int childHeightMeasureSpec;
childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec, mPaddingTop
+ mPaddingBottom, lp.height);
childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
@Override
protected void measureChildWithMargins(View child, int parentWidthMeasureSpec, int widthUsed,
int parentHeightMeasureSpec, int heightUsed) {
final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();
final int childHeightMeasureSpec = getChildMeasureSpec(parentHeightMeasureSpec,
mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin
+ heightUsed, lp.height);
final int childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(
lp.leftMargin + lp.rightMargin, MeasureSpec.UNSPECIFIED);
child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
// This is called at drawing time by ViewGroup. We don't want to
// re-show the scrollbars at this point, which scrollTo will do,
// so we replicate most of scrollTo here.
//
// It's a little odd to call onScrollChanged from inside the drawing.
//
// It is, except when you remember that computeScroll() is used to
// animate scrolling. So unless we want to defer the onScrollChanged()
// until the end of the animated scrolling, we don't really have a
// choice here.
//
// I agree. The alternative, which I think would be worse, is to post
// something and tell the subclasses later. This is bad because there
// will be a window where mScrollX/Y is different from what the app
// thinks it is.
//
int oldX = mScrollX;
int oldY = mScrollY;
int x = mScroller.getCurrX();
int y = mScroller.getCurrY();
if (oldX != x || oldY != y) {
final int range = getScrollRange();
final int overscrollMode = getOverScrollMode();
final boolean canOverscroll = overscrollMode == OVER_SCROLL_ALWAYS ||
(overscrollMode == OVER_SCROLL_IF_CONTENT_SCROLLS && range > 0);
overScrollBy(x - oldX, y - oldY, oldX, oldY, range, 0,
mOverflingDistance, 0, false);
onScrollChanged(mScrollX, mScrollY, oldX, oldY);
if (canOverscroll) {
if (x < 0 && oldX >= 0) {
mEdgeGlowLeft.onAbsorb((int) mScroller.getCurrVelocity());
} else if (x > range && oldX <= range) {
mEdgeGlowRight.onAbsorb((int) mScroller.getCurrVelocity());
}
}
}
if (!awakenScrollBars()) {
postInvalidateOnAnimation();
}
}
}
/**
* Scrolls the view to the given child.
*
* @param child the View to scroll to
*/
private void scrollToChild(View child) {
child.getDrawingRect(mTempRect);
/* Offset from child's local coordinates to ScrollView coordinates */
offsetDescendantRectToMyCoords(child, mTempRect);
int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
if (scrollDelta != 0) {
scrollBy(scrollDelta, 0);
}
}
/**
* If rect is off screen, scroll just enough to get it (or at least the
* first screen size chunk of it) on screen.
*
* @param rect The rectangle.
* @param immediate True to scroll immediately without animation
* @return true if scrolling was performed
*/
private boolean scrollToChildRect(Rect rect, boolean immediate) {
final int delta = computeScrollDeltaToGetChildRectOnScreen(rect);
final boolean scroll = delta != 0;
if (scroll) {
if (immediate) {
scrollBy(delta, 0);
} else {
smoothScrollBy(delta, 0);
}
}
return scroll;
}
/**
* 计算X方向滚动的距离，以便在屏幕上显示子视图的完整矩形
* （或者，若矩形宽度超过屏幕宽度，至少要填满第一个屏幕大小）.
*
* @param rect 矩形
* @return 滚动距离
*/
protected int computeScrollDeltaToGetChildRectOnScreen(Rect rect) {
if (getChildCount() == 0) return 0;
int width = getWidth();
int screenLeft = getScrollX();
int screenRight = screenLeft + width;
int fadingEdge = getHorizontalFadingEdgeLength();
// leave room for left fading edge as long as rect isn't at very left
if (rect.left > 0) {
screenLeft += fadingEdge;
}
// leave room for right fading edge as long as rect isn't at very right
if (rect.right < getChildAt(0).getWidth()) {
screenRight -= fadingEdge;
}
int scrollXDelta = 0;
if (rect.right > screenRight && rect.left > screenLeft) {
// need to move right to get it in view: move right just enough so
// that the entire rectangle is in view (or at least the first
// screen size chunk).
if (rect.width() > width) {
// just enough to get screen size chunk on
scrollXDelta += (rect.left - screenLeft);
} else {
// get entire rect at right of screen
scrollXDelta += (rect.right - screenRight);
}
// make sure we aren't scrolling beyond the end of our content
int right = getChildAt(0).getRight();
int distanceToRight = right - screenRight;
scrollXDelta = Math.min(scrollXDelta, distanceToRight);
} else if (rect.left < screenLeft && rect.right < screenRight) {
// need to move right to get it in view: move right just enough so that
// entire rectangle is in view (or at least the first screen
// size chunk of it).
if (rect.width() > width) {
// screen size chunk
scrollXDelta -= (screenRight - rect.right);
} else {
// entire rect at left
scrollXDelta -= (screenLeft - rect.left);
}
// make sure we aren't scrolling any further than the left our content
scrollXDelta = Math.max(scrollXDelta, -getScrollX());
}
return scrollXDelta;
}
@Override
public void requestChildFocus(View child, View focused) {
if (!mIsLayoutDirty) {
scrollToChild(focused);
} else {
// The child may not be laid out yet, we can't compute the scroll yet
mChildToScrollTo = focused;
}
super.requestChildFocus(child, focused);
}
/**
* 在为滚动视图设置焦点时一定要小心，不能将焦点设置到屏幕上不可见的组件上.
*
* 这比 ViewGroup 的缺省实现代价更高，否则此代码就作为缺省代码了.
*/
@Override
protected boolean onRequestFocusInDescendants(int direction,
Rect previouslyFocusedRect) {
// convert from forward / backward notation to up / down / left / right
// (ugh).
if (direction == View.FOCUS_FORWARD) {
direction = View.FOCUS_RIGHT;
} else if (direction == View.FOCUS_BACKWARD) {
direction = View.FOCUS_LEFT;
}
final View nextFocus = previouslyFocusedRect == null ?
FocusFinder.getInstance().findNextFocus(this, null, direction) :
FocusFinder.getInstance().findNextFocusFromRect(this,
previouslyFocusedRect, direction);
if (nextFocus == null) {
return false;
}
if (isOffScreen(nextFocus)) {
return false;
}
return nextFocus.requestFocus(direction, previouslyFocusedRect);
}
@Override
public boolean requestChildRectangleOnScreen(View child, Rect rectangle,
boolean immediate) {
// offset into coordinate space of this scroll view
rectangle.offset(child.getLeft() - child.getScrollX(),
child.getTop() - child.getScrollY());
return scrollToChildRect(rectangle, immediate);
}
@Override
public void requestLayout() {
mIsLayoutDirty = true;
super.requestLayout();
}
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
mIsLayoutDirty = false;
// Give a child focus if it needs it
if (mChildToScrollTo != null && isViewDescendantOf(mChildToScrollTo, this)) {
scrollToChild(mChildToScrollTo);
}
mChildToScrollTo = null;
// Calling this with the present values causes it to re-claim them
scrollTo(mScrollX, mScrollY);
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
View currentFocused = findFocus();
if (null == currentFocused || this == currentFocused)
return;
final int maxJump = mRight - mLeft;
if (isWithinDeltaOfScreen(currentFocused, maxJump)) {
currentFocused.getDrawingRect(mTempRect);
offsetDescendantRectToMyCoords(currentFocused, mTempRect);
int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
doScrollX(scrollDelta);
}
}
/**
* Return true if child is a descendant of parent, (or equal to the parent).
*/
private static boolean isViewDescendantOf(View child, View parent) {
if (child == parent) {
return true;
}
final ViewParent theParent = child.getParent();
return (theParent instanceof ViewGroup) && isViewDescendantOf((View) theParent, parent);
}
/**
* 快速滑动滚动视图.
*
* @param velocityX 横向初始速度.负数意味着手指或光标向右移动，意味着内容应该向左滚动.
*/
public void fling(int velocityX) {
if (getChildCount() > 0) {
int width = getWidth() - mPaddingRight - mPaddingLeft;
int right = getChildAt(0).getWidth();
mScroller.fling(mScrollX, mScrollY, velocityX, 0, 0,
Math.max(0, right - width), 0, 0, width/2, 0);
final boolean movingRight = velocityX > 0;
View currentFocused = findFocus();
View newFocused = findFocusableViewInMyBounds(movingRight,
mScroller.getFinalX(), currentFocused);
if (newFocused == null) {
newFocused = this;
}
if (newFocused != currentFocused) {
newFocused.requestFocus(movingRight ? View.FOCUS_RIGHT : View.FOCUS_LEFT);
}
postInvalidateOnAnimation();
}
}
/**
* {@inheritDoc}
*
* <p>该版本的滚动将在子视图的边界处停止.
*/
@Override
public void scrollTo(int x, int y) {
// we rely on the fact the View.scrollBy calls scrollTo.
if (getChildCount() > 0) {
View child = getChildAt(0);
x = clamp(x, getWidth() - mPaddingRight - mPaddingLeft, child.getWidth());
y = clamp(y, getHeight() - mPaddingBottom - mPaddingTop, child.getHeight());
if (x != mScrollX || y != mScrollY) {
super.scrollTo(x, y);
}
}
}
@Override
public void setOverScrollMode(int mode) {
if (mode != OVER_SCROLL_NEVER) {
if (mEdgeGlowLeft == null) {
Context context = getContext();
mEdgeGlowLeft = new EdgeEffect(context);
mEdgeGlowRight = new EdgeEffect(context);
}
} else {
mEdgeGlowLeft = null;
mEdgeGlowRight = null;
}
super.setOverScrollMode(mode);
}
@SuppressWarnings({"SuspiciousNameCombination"})
@Override
public void draw(Canvas canvas) {
super.draw(canvas);
if (mEdgeGlowLeft != null) {
final int scrollX = mScrollX;
if (!mEdgeGlowLeft.isFinished()) {
final int restoreCount = canvas.save();
final int height = getHeight() - mPaddingTop - mPaddingBottom;
canvas.rotate(270);
canvas.translate(-height + mPaddingTop, Math.min(0, scrollX));
mEdgeGlowLeft.setSize(height, getWidth());
if (mEdgeGlowLeft.draw(canvas)) {
postInvalidateOnAnimation();
}
canvas.restoreToCount(restoreCount);
}
if (!mEdgeGlowRight.isFinished()) {
final int restoreCount = canvas.save();
final int width = getWidth();
final int height = getHeight() - mPaddingTop - mPaddingBottom;
canvas.rotate(90);
canvas.translate(-mPaddingTop,
-(Math.max(getScrollRange(), scrollX) + width));
mEdgeGlowRight.setSize(height, width);
if (mEdgeGlowRight.draw(canvas)) {
postInvalidateOnAnimation();
}
canvas.restoreToCount(restoreCount);
}
}
}
private static int clamp(int n, int my, int child) {
if (my >= child || n < 0) {
return 0;
}
if ((my + n) > child) {
return child - my;
}
return n;
}
}