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>