/*
* Modifications by Yoni Samlan; based on RealViewSwitcher, whose license is:
*
* Copyright (C) 2010 Marc Reichelt
*
* Work derived from Workspace.java of the Launcher application
* see http://android.git.kernel.org/?p=platform/packages/apps/Launcher.git
*
* 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 com.github.ysamlan.horizontalpager;
import android.content.Context;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.Display;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Scroller;
/**
* A view group that allows users to switch between multiple screens (layouts) in the same way as
* the Android home screen (Launcher application).
* <p>
* You can add and remove views using the normal methods {@link ViewGroup#addView(View)},
* {@link ViewGroup#removeView(View)} etc. You may want to listen for updates by calling
* {@link HorizontalPager#setOnScreenSwitchListener(OnScreenSwitchListener)} in order to perform
* operations once a new screen has been selected.
*
* Modifications from original version (ysamlan): Animate argument in setCurrentScreen and duration
* in snapToScreen; onInterceptTouchEvent handling to support nesting a vertical Scrollview inside
* the RealViewSwitcher; allowing snapping to a view even during an ongoing scroll; snap to
* next/prev view on 25% scroll change; density-independent swipe sensitivity; width-independent
* pager animation durations on scrolling to properly handle large screens without excessively
* long animations.
*
* Other modifications:
* (aveyD) Handle orientation changes properly and fully snap to the right position.
*
* @author Marc Reichelt, <a href="http://www.marcreichelt.de/">http://www.marcreichelt.de/</a>
* @version 0.1.0
*/
public final class HorizontalPager extends ViewGroup {
/*
* How long to animate between screens when programmatically setting with setCurrentScreen using
* the animate parameter
*/
private static final int ANIMATION_SCREEN_SET_DURATION_MILLIS = 500;
// What fraction (1/x) of the screen the user must swipe to indicate a page change
private static final int FRACTION_OF_SCREEN_WIDTH_FOR_SWIPE = 4;
private static final int INVALID_SCREEN = -1;
/*
* Velocity of a swipe (in density-independent pixels per second) to force a swipe to the
* next/previous screen. Adjusted into mDensityAdjustedSnapVelocity on init.
*/
private static final int SNAP_VELOCITY_DIP_PER_SECOND = 600;
// Argument to getVelocity for units to give pixels per second (1 = pixels per millisecond).
private static final int VELOCITY_UNIT_PIXELS_PER_SECOND = 1000;
private static final int TOUCH_STATE_REST = 0;
private static final int TOUCH_STATE_HORIZONTAL_SCROLLING = 1;
private static final int TOUCH_STATE_VERTICAL_SCROLLING = -1;
private int mCurrentScreen;
private int mDensityAdjustedSnapVelocity;
private boolean mFirstLayout = true;
private float mLastMotionX;
private float mLastMotionY;
private OnScreenSwitchListener mOnScreenSwitchListener;
private int mMaximumVelocity;
private int mNextScreen = INVALID_SCREEN;
private Scroller mScroller;
private int mTouchSlop;
private int mTouchState = TOUCH_STATE_REST;
private VelocityTracker mVelocityTracker;
private int mLastSeenLayoutWidth = -1;
/**
* Simple constructor to use when creating a view from code.
*
* @param context The Context the view is running in, through which it can
* access the current theme, resources, etc.
*/
public HorizontalPager(final Context context) {
super(context);
init();
}
/**
* Constructor that is called when inflating a view from XML. This is called
* when a view is being constructed from an XML file, supplying attributes
* that were specified in the XML file. This version uses a default style of
* 0, so the only attribute values applied are those in the Context's Theme
* and the given AttributeSet.
*
* <p>
* The method onFinishInflate() will be called after all children have been
* added.
*
* @param context The Context the view is running in, through which it can
* access the current theme, resources, etc.
* @param attrs The attributes of the XML tag that is inflating the view.
* @see #View(Context, AttributeSet, int)
*/
public HorizontalPager(final Context context, final AttributeSet attrs) {
super(context, attrs);
init();
}
/**
* Sets up the scroller and touch/fling sensitivity parameters for the pager.
*/
private void init() {
mScroller = new Scroller(getContext());
// Calculate the density-dependent snap velocity in pixels
DisplayMetrics displayMetrics = new DisplayMetrics();
((WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay()
.getMetrics(displayMetrics);
mDensityAdjustedSnapVelocity =
(int) (displayMetrics.density * SNAP_VELOCITY_DIP_PER_SECOND);
final ViewConfiguration configuration = ViewConfiguration.get(getContext());
mTouchSlop = configuration.getScaledTouchSlop();
mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
}
@Override
protected void onMeasure(final int widthMeasureSpec, final int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int width = MeasureSpec.getSize(widthMeasureSpec);
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
if (widthMode != MeasureSpec.EXACTLY) {
throw new IllegalStateException("ViewSwitcher can only be used in EXACTLY mode.");
}
final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
if (heightMode != MeasureSpec.EXACTLY) {
throw new IllegalStateException("ViewSwitcher can only be used in EXACTLY mode.");
}
// The children are given the same width and height as the workspace
final int count = getChildCount();
for (int i = 0; i < count; i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
if (mFirstLayout) {
scrollTo(mCurrentScreen * width, 0);
mFirstLayout = false;
}
else if (width != mLastSeenLayoutWidth) { // Width has changed
/*
* Recalculate the width and scroll to the right position to be sure we're in the right
* place in the event that we had a rotation that didn't result in an activity restart
* (code by aveyD). Without this you can end up between two pages after a rotation.
*/
Display display =
((WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE))
.getDefaultDisplay();
int displayWidth = display.getWidth();
mNextScreen = Math.max(0, Math.min(getCurrentScreen(), getChildCount() - 1));
final int newX = mNextScreen * displayWidth;
final int delta = newX - getScrollX();
mScroller.startScroll(getScrollX(), 0, delta, 0, 0);
}
mLastSeenLayoutWidth = width;
}
@Override
protected void onLayout(final boolean changed, final int l, final int t, final int r,
final int b) {
int childLeft = 0;
final int count = getChildCount();
for (int i = 0; i < count; i++) {
final View child = getChildAt(i);
if (child.getVisibility() != View.GONE) {
final int childWidth = child.getMeasuredWidth();
child.layout(childLeft, 0, childLeft + childWidth, child.getMeasuredHeight());
childLeft += childWidth;
}
}
}
@Override
public boolean onInterceptTouchEvent(final MotionEvent ev) {
/*
* By Yoni Samlan: Modified onInterceptTouchEvent based on standard ScrollView's
* onIntercept. The logic is designed to support a nested vertically scrolling view inside
* this one; once a scroll registers for X-wise scrolling, handle it in this view and don't
* let the children, but once a scroll registers for y-wise scrolling, let the children
* handle it exclusively.
*/
final int action = ev.getAction();
boolean intercept = false;
switch (action) {
case MotionEvent.ACTION_MOVE:
/*
* If we're in a horizontal scroll event, take it (intercept further events). But if
* we're mid-vertical-scroll, don't even try; let the children deal with it. If we
* haven't found a scroll event yet, check for one.
*/
if (mTouchState == TOUCH_STATE_HORIZONTAL_SCROLLING) {
/*
* We've already started a horizontal scroll; set intercept to true so we can
* take the remainder of all touch events in onTouchEvent.
*/
intercept = true;
} else if (mTouchState == TOUCH_STATE_VERTICAL_SCROLLING) {
// Let children handle the events for the duration of the scroll event.
intercept = false;
} else { // We haven't picked up a scroll event yet; check for one.
/*
* If we detected a horizontal scroll event, start stealing touch events (mark
* as scrolling). Otherwise, see if we had a vertical scroll event -- if so, let
* the children handle it and don't look to intercept again until the motion is
* done.
*/
final float x = ev.getX();
final int xDiff = (int) Math.abs(x - mLastMotionX);
boolean xMoved = xDiff > mTouchSlop;
if (xMoved) {
// Scroll if the user moved far enough along the X axis
mTouchState = TOUCH_STATE_HORIZONTAL_SCROLLING;
mLastMotionX = x;
}
final float y = ev.getY();
final int yDiff = (int) Math.abs(y - mLastMotionY);
boolean yMoved = yDiff > mTouchSlop;
if (yMoved) {
mTouchState = TOUCH_STATE_VERTICAL_SCROLLING;
}
}
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
// Release the drag.
mTouchState = TOUCH_STATE_REST;
break;
case MotionEvent.ACTION_DOWN:
/*
* No motion yet, but register the coordinates so we can check for intercept at the
* next MOVE event.
*/
mLastMotionY = ev.getY();
mLastMotionX = ev.getX();
break;
default:
break;
}
return intercept;
}
@Override
public boolean onTouchEvent(final MotionEvent ev) {
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
}
mVelocityTracker.addMovement(ev);
final int action = ev.getAction();
final float x = ev.getX();
switch (action) {
case MotionEvent.ACTION_DOWN:
/*
* 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 = x;
if (mScroller.isFinished()) {
mTouchState = TOUCH_STATE_REST;
} else {
mTouchState = TOUCH_STATE_HORIZONTAL_SCROLLING;
}
break;
case MotionEvent.ACTION_MOVE:
final int xDiff = (int) Math.abs(x - mLastMotionX);
boolean xMoved = xDiff > mTouchSlop;
if (xMoved) {
// Scroll if the user moved far enough along the X axis
mTouchState = TOUCH_STATE_HORIZONTAL_SCROLLING;
}
if (mTouchState == TOUCH_STATE_HORIZONTAL_SCROLLING) {
// Scroll to follow the motion event
final int deltaX = (int) (mLastMotionX - x);
mLastMotionX = x;
final int scrollX = getScrollX();
if (deltaX < 0) {
if (scrollX > 0) {
scrollBy(Math.max(-scrollX, deltaX), 0);
}
} else if (deltaX > 0) {
final int availableToScroll =
getChildAt(getChildCount() - 1).getRight() - scrollX - getWidth();
if (availableToScroll > 0) {
scrollBy(Math.min(availableToScroll, deltaX), 0);
}
}
}
break;
case MotionEvent.ACTION_UP:
if (mTouchState == TOUCH_STATE_HORIZONTAL_SCROLLING) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(VELOCITY_UNIT_PIXELS_PER_SECOND,
mMaximumVelocity);
int velocityX = (int) velocityTracker.getXVelocity();
if (velocityX > mDensityAdjustedSnapVelocity && mCurrentScreen > 0) {
// Fling hard enough to move left
snapToScreen(mCurrentScreen - 1);
} else if (velocityX < -mDensityAdjustedSnapVelocity
&& mCurrentScreen < getChildCount() - 1) {
// Fling hard enough to move right
snapToScreen(mCurrentScreen + 1);
} else {
snapToDestination();
}
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
}
mTouchState = TOUCH_STATE_REST;
break;
case MotionEvent.ACTION_CANCEL:
mTouchState = TOUCH_STATE_REST;
break;
default:
break;
}
return true;
}
@Override
public void computeScroll() {
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
} else if (mNextScreen != INVALID_SCREEN) {
mCurrentScreen = Math.max(0, Math.min(mNextScreen, getChildCount() - 1));
// Notify observer about screen change
if (mOnScreenSwitchListener != null) {
mOnScreenSwitchListener.onScreenSwitched(mCurrentScreen);
}
mNextScreen = INVALID_SCREEN;
}
}
/**
* Returns the index of the currently displayed screen.
*
* @return The index of the currently displayed screen.
*/
public int getCurrentScreen() {
return mCurrentScreen;
}
/**
* Sets the current screen.
*
* @param currentScreen The new screen.
* @param animate True to smoothly scroll to the screen, false to snap instantly
*/
public void setCurrentScreen(final int currentScreen, final boolean animate) {
mCurrentScreen = Math.max(0, Math.min(currentScreen, getChildCount() - 1));
if (animate) {
snapToScreen(currentScreen, ANIMATION_SCREEN_SET_DURATION_MILLIS);
} else {
scrollTo(mCurrentScreen * getWidth(), 0);
}
invalidate();
}
/**
* Sets the {@link OnScreenSwitchListener}.
*
* @param onScreenSwitchListener The listener for switch events.
*/
public void setOnScreenSwitchListener(final OnScreenSwitchListener onScreenSwitchListener) {
mOnScreenSwitchListener = onScreenSwitchListener;
}
/**
* Snaps to the screen we think the user wants (the current screen for very small movements; the
* next/prev screen for bigger movements).
*/
private void snapToDestination() {
final int screenWidth = getWidth();
int scrollX = getScrollX();
int whichScreen = mCurrentScreen;
int deltaX = scrollX - (screenWidth * mCurrentScreen);
// Check if they want to go to the prev. screen
if ((deltaX < 0) && mCurrentScreen != 0
&& ((screenWidth / FRACTION_OF_SCREEN_WIDTH_FOR_SWIPE) < -deltaX)) {
whichScreen--;
// Check if they want to go to the next screen
} else if ((deltaX > 0) && (mCurrentScreen + 1 != getChildCount())
&& ((screenWidth / FRACTION_OF_SCREEN_WIDTH_FOR_SWIPE) < deltaX)) {
whichScreen++;
}
snapToScreen(whichScreen);
}
/**
* Snap to a specific screen, animating automatically for a duration proportional to the
* distance left to scroll.
*
* @param whichScreen Screen to snap to
*/
private void snapToScreen(final int whichScreen) {
snapToScreen(whichScreen, -1);
}
/**
* Snaps to a specific screen, animating for a specific amount of time to get there.
*
* @param whichScreen Screen to snap to
* @param duration -1 to automatically time it based on scroll distance; a positive number to
* make the scroll take an exact duration.
*/
private void snapToScreen(final int whichScreen, final int duration) {
/*
* Modified by Yoni Samlan: Allow new snapping even during an ongoing scroll animation. This
* is intended to make HorizontalPager work as expected when used in conjunction with a
* RadioGroup used as "tabbed" controls. Also, make the animation take a percentage of our
* normal animation time, depending how far they've already scrolled.
*/
mNextScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
final int newX = mNextScreen * getWidth();
final int delta = newX - getScrollX();
if (duration < 0) {
// E.g. if they've scrolled 80% of the way, only animation for 20% of the duration
mScroller.startScroll(getScrollX(), 0, delta, 0, (int) (Math.abs(delta)
/ (float) getWidth() * ANIMATION_SCREEN_SET_DURATION_MILLIS));
} else {
mScroller.startScroll(getScrollX(), 0, delta, 0, duration);
}
invalidate();
}
/**
* Listener for the event that the HorizontalPager switches to a new view.
*/
public static interface OnScreenSwitchListener {
/**
* Notifies listeners about the new screen. Runs after the animation completed.
*
* @param screen The new screen index.
*/
void onScreenSwitched(int screen);
}
}