Android view随触碰滑动效果

<?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:id="@+id/relativeLayout" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.xingyi.moveviewwithtouch.MainActivity"><ImageView android:id="@+id/imageView" android:layout_width="40dp" android:layout_height="40dp" android:background="@android:color/black"/></RelativeLayout>

package com.xingyi.moveviewwithtouch;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.view.MotionEvent;import android.view.View;import android.widget.ImageView;import android.widget.RelativeLayout;public class MainActivity extends AppCompatActivity { ImageView imageView; RelativeLayout relativeLayout; int heightRL,widthRL; int halfHeight,halfWidth; boolean first=true; private int widthImg; private int heightImg; @Override protected void onCreate(Bundle savedInstanceState) {  super.onCreate(savedInstanceState);  setContentView(R.layout.activity_main);  initView(); } //初始化视图 private void initView() {  imageView = (ImageView) findViewById(R.id.imageView);  relativeLayout = (RelativeLayout) findViewById(R.id.relativeLayout);  //获取滑动瞬间位置和点击瞬间位置，并移动imageview  relativeLayout.setOnTouchListener(new View.OnTouchListener() {   @Override   public boolean onTouch(View view, MotionEvent motionEvent) {    switch (motionEvent.getAction()) {     case MotionEvent.ACTION_MOVE:      moveView(imageView, motionEvent.getX(), motionEvent.getY());      break;     case MotionEvent.ACTION_DOWN:      getWidthAndHeight();      moveView(imageView, motionEvent.getX(), motionEvent.getY());      break;     default:      break;    }    return true;   }  }); } //因为不能在初始化视图时获得长宽，而每次计算一次长宽又影响性能 private void getWidthAndHeight(){  if(first){   widthRL=relativeLayout.getWidth();   heightRL=relativeLayout.getHeight();   widthImg=imageView.getWidth();   heightImg=imageView.getHeight();   halfWidth = imageView.getWidth() / 2;//imageView宽度的一半   halfHeight = imageView.getHeight() / 2;//imageView高度的一半   first=false;  } } //滑动瞬间，将x和y分别作imageView的中心点到relativeLayout最左和顶端距离 private void moveView(View view, float x, float y) {  RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) view.getLayoutParams();  //设置水平位置  if (x < halfWidth) {//左边缘   params.leftMargin = 0;//设置imageview到左端距离为0  } else if (x > widthRL- halfWidth) {   params.leftMargin = widthRL-widthImg;//设置imageview左端到左端端距离（params.rightMargin的性能非常糟糕）  } else {   params.leftMargin = (int) (x - halfWidth);//imageview左端到relativelayout左端距离  }  //设置竖直位置  if (y < halfHeight) {   params.topMargin = 0;  } else if (y > heightRL - halfHeight) {   params.topMargin = heightRL-widthImg;//params.bottomMargin的性能非常糟糕  } else {   params.topMargin = (int) (y - halfHeight);  }  view.setLayoutParams(params); }}