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 {  //圓的初始位置  private int x = 100;  private int y = 100;  Context context;    /**   * 有style資源文件時調用   * @param context   * @param attrs   * @param defStyle   */  public DrawCircle(Context context, AttributeSet attrs, int defStyle) {    super(context, attrs, defStyle);    this.context = context;  }  /**   * xml創建時調用   * @param context   * @param attrs   */  public DrawCircle(Context context, AttributeSet attrs) {    super(context, attrs);    this.context = context;  }  /**   * java代碼創建時調用   * @param context   */  public DrawCircle(Context context) {    super(context);    this.context = context;  }    @Override  protected void onDraw(Canvas canvas) {    super.onDraw(canvas);    // 畫筆    Paint paint = new Paint();    paint.setColor(Color.RED);    //繪制圓      //cx :圓心的x坐標    //cy :圓心的y坐標      //radius ：圓的半徑    //paint ：畫筆    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:        // 獲取當前觸摸點的x,y坐標                    x = (int) event.getX();          y = (int) event.getY();                break;    }    //獲取屏幕寬高    WindowManager manager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);    int width = manager.getDefaultDisplay().getWidth();    int heigh = manager.getDefaultDisplay().getHeight();        //重新繪制圓 ,控制小球不會被移出屏幕    if(x>=20 && y>=20 && x<=width-20 && y<=heigh-90){      invalidate();    }      // 自己處理觸摸事件      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">    <!-- 自定義控件的全類名 -->  <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);        //獲取容器    RelativeLayout container = (RelativeLayout) findViewById(R.id.rl);        //創建自定義控件    DrawCircle circle = new DrawCircle(this);        //添加到容器    container.addView(circle);  }}