Android跟随手指运动的小球 适合新手的很好的Demo

为了实现一个跟随手指的小球，我们运用自定义的View组件 ；这个UI组件将会在指定的位置绘制一个小球 ，这个位置可以动态改变 。当用户通过手指在屏幕上拖动时，程序监听这个手指动作，并把手指动作位置传给自定义UI组件，并通知组件重绘。

public class MainActivity extends Activity
{

	@Override
	protected void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		
	//	LinearLayout main = (LinearLayout)findViewById(R.id.root);
		final MyView draw = new MyView(this);
		draw.setMinimumWidth(300);
		draw.setMinimumHeight(500);
		setContentView(draw);
		draw.setOnTouchListener(new View.OnTouchListener()
		{
			
			@Override
			public boolean onTouch(View v, MotionEvent event)
			{
				// TODO Auto-generated method stub
				draw.currentx = event.getX();
				draw.currenty = event.getY();
				draw.invalidate();
				return true;
			}
		});

	}

	class MyView extends View implements Runnable
	{
		public float currentx=40;
		public float currenty=50;
		public MyView(Context context)
		{
			super(context);
			// TODO Auto-generated constructor stub
		}
		@Override
		public void run()
		{
			// TODO Auto-generated method stub
			
		}
		@Override
		protected void onDraw(Canvas canvas)
		{
			// TODO Auto-generated method stub
			super.onDraw(canvas);
			Paint p = new Paint();
			p.setColor(Color.GREEN);
			canvas.drawCircle(currentx, currenty, 15, p);
		}
		
	   
	}

}