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