ViewPager滑动后，可移动的Imageview会回到初始化的位置

知乎看到的原文http://www.zhihu.com/question/37398770?sort=created

ViewPager滑动后，可移动的Imageview会回到初始化的位置？

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="180dp" />


    <ImageView
        android:id="@+id/image"
        android:layout_width="160dp"
        android:layout_height="160dp"
        android:layout_below="@id/viewpager"
        android:layout_centerHorizontal="true"
        android:src="@mipmap/a" />

</RelativeLayout>

这是我的布局文件，就一个ViewPager一个ImageView
我在代码中监听了imageview的ontouch事件，重写onTouch方法实现imageview的移动：

private View.OnTouchListener movingEventListener = new View.OnTouchListener() {
        int lastX, lastY;

        @Override
        public boolean onTouch(View v, MotionEvent event) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    lastX = (int) event.getRawX();
                    lastY = (int) event.getRawY();
                    break;
                case MotionEvent.ACTION_MOVE:
                    int dx = (int) event.getRawX() - lastX;
                    int dy = (int) event.getRawY() - lastY;

                    int left = v.getLeft() + dx;
                    int top = v.getTop() + dy;
                    int right = v.getRight() + dx;
                    int bottom = v.getBottom() + dy;
                    // 设置不能出界
                    if (left < 0) {
                        left = 0;
                        right = left + v.getWidth();
                    }
                    if (right > screenWidth) {
                        right = screenWidth;
                        left = right - v.getWidth();
                    }
                    if (top < 0) {
                        top = 0;
                        bottom = top + v.getHeight();
                    }
                    if (bottom > screenHeight) {
                        bottom = screenHeight;
                        top = bottom - v.getHeight();
                    }

                    v.layout(left, top, right, bottom);
                    lastX = (int) event.getRawX();
                    lastY = (int) event.getRawY();
                    break;
                case MotionEvent.ACTION_UP:
                   /* int flag = 0;
                    switch (v.getId()) {

                    }*/
            }
            return true;
        }
    };

运行程序后，imageview可以移动，但是移动之后，滑动ViewPager的话，ImageView就会回到最初的位置，请问一下这是为什么呢？

作者：陈宇轩
链接：http://www.zhihu.com/question/37398770/answer/88058631
来源：知乎
著作权归作者所有，转载请联系作者获得授权。

package fmy.qf.com.mancheng.customview;

import android.content.Context;
import android.util.AttributeSet;

/**
 * Created by Administrator on 2016/10/10.
 */
public class MygifView extends pl.droidsonroids.gif.GifImageView {


    private boolean keepPosition;

    public MygifView(Context context) {
        super(context);
    }

    public MygifView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MygifView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public void layout(int l, int t, int r, int b) {
        if (!keepPosition) {
            super.layout(l, t, r, b);
            keepPosition=true;
        }
    }

    public void moveTiger(int l, int t, int r, int b) {
        super.layout(l, t, r, b);
    }

    public void startKeepPosition() {
        keepPosition = true;
    }
}