Android实现拖动小球跟随手指移动效果

public class DrawView extends View {
  public float currentX = 50;
  public float currentY = 50;

  public DrawView(Context context) {
    super(context);
  }
  public void onDraw(Canvas canvas){
    super.onDraw(canvas);
    Paint paint = new Paint();
    paint.setColor(Color.RED);
    canvas.drawCircle(currentX,currentY,10,paint);
  }
}

public class MainActivity extends Activity {

  public LinearLayout linearLayout;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    linearLayout = (LinearLayout) findViewById(R.id.root);

    final DrawView drawView = new DrawView(this);
    drawView.setOnTouchListener(new View.OnTouchListener() {
      @Override
      public boolean onTouch(View v, MotionEvent event) {
        drawView.currentX = event.getX();
        drawView.currentY = event.getY();
        //通过draw组件重绘
        drawView.invalidate();

        return true;
      }
    });
    linearLayout.addView(drawView);
  }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:paddingBottom="@dimen/activity_vertical_margin"
  android:paddingLeft="@dimen/activity_horizontal_margin"
  android:paddingRight="@dimen/activity_horizontal_margin"
  android:paddingTop="@dimen/activity_vertical_margin"
  android:id="@+id/root"
  tools:context="com.syt.androidtest.androidtest1.MainActivity">


</LinearLayout>