GestureDetector+Scroller +scrollBy实现仿viewpager

package com.practice.syd.gesture;

import android.content.Context;
import android.util.AttributeSet;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Scroller;

/**
 * Created by Administrator on 2017/11/16.
 */

class MyViewPager extends ViewGroup {
    private GestureDetector gestureDetector;
    private Context context;
    private float startX;
    private Scroller scroll;

    private int currentposition;
    private float endX;

    public MyViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context=context;
        initview();
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        for(int i=0;i;i++){
            View view=getChildAt(i);
            view.layout(getWidth()*i,0,getWidth()*(i+1),getHeight());
        }


    }
    private void initview(){
        scroll=new Scroller(context);
//手势识别器
        gestureDetector=new GestureDetector(context, new GestureDetector.OnGestureListener() {
            @Override
            public boolean onDown(MotionEvent e) {
                return false;
            }

            @Override
            public void onShowPress(MotionEvent e) {

            }

            @Override
            public boolean onSingleTapUp(MotionEvent e) {
                return false;
            }

            @Override
            public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
                scrollBy((int)distanceX,0);
                return true;
            }

            @Override
            public void onLongPress(MotionEvent e) {

            }

            @Override
            public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
                return false;
            }
        });
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        super.onTouchEvent(event);
        gestureDetector.onTouchEvent(event);
        switch (event.getAction()){
            case MotionEvent.ACTION_DOWN:
                startX=event.getX();
                break;
            case MotionEvent.ACTION_MOVE:
                break;
            case MotionEvent.ACTION_UP:
                endX=event.getX();
                int tempposition = currentposition;
                if(endX-startX>getWidth()/2){
                    tempposition--;
                }else if(startX-endX>getWidth()/2){
                    tempposition++;
                }
                scrolltopager(tempposition);


        }
        return true;

    }

    private void scrolltopager(int tempposition) {
        if(tempposition<0)
            tempposition=0;
        else if(tempposition>getChildCount()-1)
            tempposition=getChildCount()-1;
        currentposition=tempposition;
//        scrollTo(currentposition*getWidth(),0);
        scroll.startScroll(getScrollX(),getScrollY(),currentposition*getWidth()-getScrollX());
        invalidate();

    }

    @Override
    public void computeScroll() {
//        super.computeScroll();
        if(scroll.computeScrollOffset()){

            int x=scroll.getCurrX();
            scrollTo(x,0);
            invalidate();
        }

    }
}