MyYoutobelayout.java

package com.com.mr_wrong.ViewDraghelper;

import android.content.Context;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.ViewDragHelper;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;

/**
 * Created by Mr_Wrong on 15/9/10.
 */
public class MyYoutobelayout extends ViewGroup {
    private ViewDragHelper mDragHelper;
    private int mTop;
    private int mDragRange;
    private View mHeaderView, mDescView;
    private float mDragOffset;

    public MyYoutobelayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        mDragHelper = ViewDragHelper.create(this, 1f, new DragHelperCallBack());
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        mHeaderView = getChildAt(0);
        mDescView = getChildAt(1);
    }

    private class DragHelperCallBack extends android.support.v4.widget.ViewDragHelper.Callback {

        @Override
        public boolean tryCaptureView(View child, int pointerId) {
            return mHeaderView == child;
        }

        @Override
        public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
            super.onViewPositionChanged(changedView, left, top, dx, dy);
            mTop = top;
            mDragOffset = (float) top / mDragRange;

            mHeaderView.setPivotX(mHeaderView.getWidth());
            mHeaderView.setPivotY(mHeaderView.getHeight());

            mHeaderView.setScaleX(1 - mDragOffset / 2);
            mHeaderView.setScaleY(1 - mDragOffset / 3);
            mDescView.setAlpha(1 - mDragOffset);
            requestLayout();
        }

        @Override
        public int getViewVerticalDragRange(View child) {
            return mDragRange;
        }

        @Override
        public void onViewReleased(View releasedChild, float xvel, float yvel) {
            int top = getPaddingTop();
            if(yvel>0||(yvel==0&&mDragOffset>0.5f)){
                top+=mDragRange;
            }
            mDragHelper.settleCapturedViewAt(releasedChild.getLeft(),top);
            invalidate();
        }

        @Override
        public int clampViewPositionVertical(View child, int top, int dy) {
            int topbound = getPaddingTop();
            int bottombound = getHeight() - mHeaderView.getHeight();
            int newtop = Math.min(Math.max(top, topbound), bottombound);
            return newtop;
        }
    }

    @Override
    public void computeScroll() {
        if(mDragHelper.continueSettling(true)){
            ViewCompat.postInvalidateOnAnimation(this);
        }
        super.computeScroll();
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return mDragHelper.shouldInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mDragHelper.processTouchEvent(event);
        return true;
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        measureChildren(widthMeasureSpec, heightMeasureSpec);

        int maxWidth = MeasureSpec.getSize(widthMeasureSpec);
        int maxHeight = MeasureSpec.getSize(heightMeasureSpec);

        setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, 0), resolveSizeAndState(maxHeight, heightMeasureSpec, 0));

    }
    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        mDragRange = getHeight() - mHeaderView.getHeight();
        mHeaderView.layout(0, mTop, r, mTop + mHeaderView.getMeasuredHeight());
        mDescView.layout(0, mTop + mHeaderView.getMeasuredHeight(), r, mTop + b);
    }
}