Android自定义控件实现随手指移动的小球

package com.dc.customview.view;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;import android.view.WindowManager;public class DrawCircle extends View {  //圆的初始位置  private int x = 100;  private int y = 100;  Context context;    /**   * 有style资源文件时调用   * @param context   * @param attrs   * @param defStyle   */  public DrawCircle(Context context, AttributeSet attrs, int defStyle) {    super(context, attrs, defStyle);    this.context = context;  }  /**   * xml创建时调用   * @param context   * @param attrs   */  public DrawCircle(Context context, AttributeSet attrs) {    super(context, attrs);    this.context = context;  }  /**   * java代码创建时调用   * @param context   */  public DrawCircle(Context context) {    super(context);    this.context = context;  }    @Override  protected void onDraw(Canvas canvas) {    super.onDraw(canvas);    // 画笔    Paint paint = new Paint();    paint.setColor(Color.RED);    //绘制圆      //cx :圆心的x坐标    //cy :圆心的y坐标      //radius ：圆的半径    //paint ：画笔    canvas.drawCircle(x, y, 20, paint);  }  @Override  public boolean onTouchEvent(MotionEvent event) {    switch (event.getAction()) {      case MotionEvent.ACTION_DOWN:      case MotionEvent.ACTION_MOVE:      case MotionEvent.ACTION_UP:        // 获取当前触摸点的x,y坐标                    x = (int) event.getX();          y = (int) event.getY();                break;    }    //获取屏幕宽高    WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);    int width = manager.getDefaultDisplay().getWidth();    int heigh = manager.getDefaultDisplay().getHeight();        //重新绘制圆 ,控制小球不会被移出屏幕    if(x>=20 && y>=20 && x<=width-20 && y<=heigh-90){      invalidate();    }      // 自己处理触摸事件      return true;    }  }

<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"   android:id="@+id/rl">    <!-- 自定义控件的全类名 -->  <com.dc.customview.view.DrawCircle    android:id="@+id/circle"    android:layout_width="wrap_content"    android:layout_height="wrap_content" >  </com.dc.customview.view.DrawCircle></RelativeLayout>

package com.dc.customview;import com.dc.customview.view.DrawCircle;import android.os.Bundle;import android.app.Activity;import android.view.Menu;import android.view.View;import android.widget.RelativeLayout;public class MainActivity extends Activity {  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);        //获取容器    RelativeLayout container = (RelativeLayout) findViewById(R.id.rl);        //创建自定义控件    DrawCircle circle = new DrawCircle(this);        //添加到容器    container.addView(circle);  }}