Android自定义view圆并随手指移动

public class MainActivity extends AppCompatActivity { private int screenW; //屏幕宽度 private int screenH; //屏幕高度 @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Display dis = this.getWindowManager().getDefaultDisplay(); // 设置全屏 requestWindowFeature(Window.FEATURE_NO_TITLE); this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,  WindowManager.LayoutParams.FLAG_FULLSCREEN); // 获取屏幕宽度 screenW = dis.getWidth(); // 获取屏幕高度 screenH = dis.getHeight(); setContentView(new MyView(this)); } //自定义绘图类 class MyView extends View { private Paint paint; //定义画笔 private float cx = 50; //圆点默认X坐标 private float cy = 50; //圆点默认Y坐标 private int radius = 20; //定义颜色数组 private int colorArray[] = {Color.BLACK,Color.BLACK,Color.GREEN,Color.YELLOW, Color.RED}; private int paintColor = colorArray[0]; //定义画笔默认颜色 public MyView(Context context) {  super(context);  //初始化画笔  initPaint(); } private void initPaint(){  paint = new Paint();  //设置消除锯齿  paint.setAntiAlias(true);  //设置画笔颜色  paint.setColor(paintColor); } //重写onDraw方法实现绘图操作 @Override protected void onDraw(Canvas canvas) {  super.onDraw(canvas);  //将屏幕设置为白色  canvas.drawColor(Color.WHITE);  //修正圆点坐标  revise();  //随机设置画笔颜色  setPaintRandomColor();  //绘制小圆作为小球  canvas.drawCircle(cx, cy, radius, paint); } //为画笔设置随机颜色 private void setPaintRandomColor(){  Random rand = new Random();  int randomIndex = rand.nextInt(colorArray.length);  paint.setColor(colorArray[randomIndex]); } //修正圆点坐标 private void revise(){  if(cx <= radius){  cx = radius;  }else if(cx >= (screenW-radius)){  cx = screenW-radius;  }  if(cy <= radius){  cy = radius;  }else if(cy >= (screenH-radius)){  cy = screenH-radius;  } } @Override public boolean onTouchEvent(MotionEvent event) {  switch (event.getAction()) {  case MotionEvent.ACTION_DOWN:   // 按下   cx = (int) event.getX();   cy = (int) event.getY();   // 通知重绘   postInvalidate(); //该方法会调用onDraw方法，重新绘图   break;  case MotionEvent.ACTION_MOVE:   // 移动   cx = (int) event.getX();   cy = (int) event.getY();   // 通知重绘   postInvalidate();   break;  case MotionEvent.ACTION_UP:   // 抬起   cx = (int) event.getX();   cy = (int) event.getY();   // 通知重绘   postInvalidate();   break;  }  /*  * 备注1：此处一定要将return super.onTouchEvent(event)修改为return true，原因是：  * 1）父类的onTouchEvent(event)方法可能没有做任何处理，但是返回了false。  * 2)一旦返回false，在该方法中再也不会收到MotionEvent.ACTION_MOVE及MotionEvent.ACTION_UP事件。  */  //return super.onTouchEvent(event);  return true; } }}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_main" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.example.sn.MainActivity"> <com.example.sn.MainActivity.MyView android:id="@+id/myview" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" /></RelativeLayout>