PullZoomLayout.java

package me.weyye.todaynews.ui.view;

import android.content.Context;
import android.content.res.TypedArray;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.OverScroller;

import com.orhanobut.logger.Logger;

import me.weyye.todaynews.R;

/**
 * Created by Administrator on 2016/11/19 0019.
 */
public class PullZoomLayout extends LinearLayout {
    private OverScroller mScroller;
    private int mTouchSlop;
    private int mMaximumVelocity;
    private int mMinimumVelocity;
    private View mHeaderLayout;
    private View mMainLayout;
    private int mScreenWidth;
    private VelocityTracker mVelocityTracker;
    private float mLastY;
    private boolean mDragging;
    private int mScreenHeight;
    private LinearLayout mRootView;
    private int mOverscrollDistance;

    public PullZoomLayout(Context context) {
        this(context, null);
    }

    public PullZoomLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public PullZoomLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        mScreenWidth = context.getResources().getDisplayMetrics().widthPixels;
        mScreenHeight = context.getResources().getDisplayMetrics().heightPixels;
        mScroller = new OverScroller(context);
        mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
        mMaximumVelocity = ViewConfiguration.get(context)
                .getScaledMaximumFlingVelocity();
        mMinimumVelocity = ViewConfiguration.get(context)
                .getScaledMinimumFlingVelocity();

        mOverscrollDistance = ViewConfiguration.get(context).getScaledOverscrollDistance();
        TypedArray ta = context.obtainStyledAttributes(attrs,
                R.styleable.PullZoomLayout);
        int headerRes = ta.getResourceId(R.styleable.PullZoomLayout_pzHeader, -1);
        int mainRes = ta.getResourceId(R.styleable.PullZoomLayout_pzMain, -1);
        ta.recycle();

        mRootView = new LinearLayout(context);
        mRootView.setOrientation(LinearLayout.VERTICAL);
        mRootView.setGravity(Gravity.CENTER_HORIZONTAL);
        if (headerRes == -1 || mainRes == -1) return;
//        mHeaderLayout = inflate(context, headerRes, null);
//        mMainLayout = inflate(context, mainRes, null);

        mHeaderLayout = LayoutInflater.from(context).inflate(headerRes, mRootView, true);
        mMainLayout = LayoutInflater.from(context).inflate(mainRes, mRootView, true);


//        mRootView.addView(mHeaderLayout);
//        mRootView.addView(mMainLayout);
        addView(mRootView);
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
//        int w = MeasureSpec.makeMeasureSpec(mRootView.getMeasuredWidth(),
//                View.MeasureSpec.EXACTLY);
//        int h = View.MeasureSpec.makeMeasureSpec(0,
//                View.MeasureSpec.UNSPECIFIED);
////        //重新测量
//        mRootView.measure(w, h);
    }

    @Override
    protected void measureChild(View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec) {
        ViewGroup.LayoutParams lp = child.getLayoutParams();

        int childWidthMeasureSpec;
        int childHeightMeasureSpec;

        childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, getPaddingLeft() + getPaddingRight(), lp.width);

        childHeightMeasureSpec = 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 childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, getPaddingLeft() + getPaddingRight() + lp.leftMargin
                + lp.rightMargin + widthUsed, lp.width);
        final int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(lp.topMargin + lp.bottomMargin, MeasureSpec.UNSPECIFIED);

        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        initVelocityTrackerIfNotExists();
        mVelocityTracker.addMovement(event);
        float y = event.getY();
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                if (!mScroller.isFinished())
                    mScroller.abortAnimation();
                mLastY = y;
                return true;
            case MotionEvent.ACTION_MOVE:
                float dy = mLastY - y;
                if (!mDragging && Math.abs(dy) > mTouchSlop) {
                    //正在准备滑动
                    mDragging = true;
                }
                if (mDragging) {
                    Logger.i("-dy:" + dy);
                    scrollBy(0, (int) dy);
                }
                if (dy < 0 && getScrollY() <= 0) {
                    //下拉
                    Logger.i("下拉了");
                }
                mLastY = y;
                break;
            case MotionEvent.ACTION_CANCEL:
                mDragging = false;
                recycleVelocityTracker();
                if (!mScroller.isFinished()) {
                    mScroller.abortAnimation();
                }
                break;
            case MotionEvent.ACTION_UP:
                mDragging = false;
                mVelocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
                int velocityY = (int) mVelocityTracker.getYVelocity();
                if (Math.abs(velocityY) > mMinimumVelocity) {
                    fling(-velocityY);
                }
                recycleVelocityTracker();
                break;
        }
        return super.onTouchEvent(event);
    }

    public void fling(int velocityY) {
        mScroller.fling(0, getScrollY(), 0, velocityY, 0, 0, 0, getScrollRange());
        invalidate();
    }

    @Override
    public void scrollTo(int x, int y) {
        if (y < 0) {
            y = 0;
        }

        if (y > getScrollRange()) {
            y = getScrollRange();
        }
        if (y != getScrollY()) {
            super.scrollTo(x, y);
        }

    }

    private int getScrollRange() {
        int scrollRange = 0;
        if (getChildCount() > 0) {
            Logger.i("mRootView.getHeight():" + mRootView.getHeight() + "-----getHeight():" + getHeight());
            scrollRange = Math.max(0,
                    mRootView.getHeight() - (getHeight() - getPaddingBottom() - getPaddingTop()));
        }
        return scrollRange;
    }


    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            scrollTo(0, mScroller.getCurrY());
            invalidate();
        }
    }


    private void initVelocityTrackerIfNotExists() {
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
    }

    private void recycleVelocityTracker() {
        if (mVelocityTracker != null) {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }
}