ViewGroup的dispatchTouchEvent(MotionEvent ev)

package com.hochan.myapplication3;

import android.content.Context;
import android.support.annotation.AttrRes;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.animation.OvershootInterpolator;
import android.widget.FrameLayout;

public class ZoomViewGroup extends FrameLayout{

    private static final int NONE = 0;
    private static final int DRAG = 1;
    private static final int ZOOM = 2;

    private int mMode = NONE;

    // 初始的两个手指按下的触摸点的距离
    private float oriDis = 1f;

    public ZoomViewGroup(@NonNull Context context) {
        super(context);
    }

    public ZoomViewGroup(@NonNull Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public ZoomViewGroup(@NonNull Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_DOWN:
                // 第一个手指按下事件
                mMode = DRAG;
                break;
            case MotionEvent.ACTION_POINTER_DOWN:
                // 第二个手指按下事件
                oriDis = distance(event);
                if (oriDis > 10f) {
                    mMode = ZOOM;
                    // 在onInterceptTouchEvent返回true之后会往子View传MotionEvent.Cancel
                    // 之后直接调用onTouchEvent
                    return true;
                }
        }

        return false;
    }

    // 计算两个触摸点之间的距离
    private float distance(MotionEvent event) {
        float x = event.getX(0) - event.getX(1);
        float y = event.getY(0) - event.getY(1);
        return (float) Math.sqrt(x * x + y * y);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        View view = getChildAt(0);
        // 进行与操作是为了判断多点触摸
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_POINTER_UP:
                // 手指放开事件
                mMode = NONE;
                view.animate().scaleX(1).scaleY(1).setDuration(200).setInterpolator(new OvershootInterpolator()).start();
                break;
            case MotionEvent.ACTION_MOVE:
                // 手指滑动事件
                if (mMode == DRAG) {
                    // 是一个手指拖动
                   return false;
                } else if (mMode == ZOOM) {
                    // 两个手指滑动
                    float newDist = distance(event);
                    if (newDist > 10f) {
                        float scale = newDist / oriDis;
                        view.setScaleX(scale);
                        view.setScaleY(scale);
                    }
                }
                break;
        }
        return true;
    }

    @Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {}
}