动态绘制图形的基本思路

动态图形绘制的基本思路是，创建一个类继承View类（或者继承SurfaceView类）。覆盖onCreate()方法，使用Canvas对象在界面上绘制不同的图形，使用invalidate()方法刷新界面。下面通过一个弹球实例来讲述动态图形绘制的基本思路。该实例是在界面上动态绘制一个小球，当小球触顶或者触底时自动改变方向继续运行。实例步骤说明如下：

public class MainActivity extends Activity{ImageView img;@Overrideprotected void onCreate(Bundle savedInstanceState){super.onCreate(savedInstanceState);MyView v = new MyView(this, null);setContentView(v);}class MyView extends View implements Runnable{private int x = 20, y = 20;public MyView(Context context, AttributeSet attrs){super(context, attrs);setFocusable(true);new Thread(this).start();// TODO Auto-generated constructor stub}@Overridepublic void run(){// TODO Auto-generated method stub// Looper.prepare();while (!Thread.currentThread().isInterrupted()){Message m = new Message();m.what = 0x101;Log.e("Thread", "running---");refreshHandler.sendMessage(m);try{Thread.sleep(100);} catch (Exception e){e.printStackTrace();}// Looper.loop();}}@Overrideprotected void onDraw(Canvas canvas){// TODO Auto-generated method stubsuper.onDraw(canvas);Paint paint = new Paint();paint.setColor(Color.RED);canvas.drawCircle(x, y, 10, paint);}RefreshHandler refreshHandler = new RefreshHandler(){@Overridepublic void handleMessage(Message msg){// TODO Auto-generated method stubsuper.handleMessage(msg);if(msg.what==0x101){MyView.this.update();MyView.this.invalidate();}}};class RefreshHandler extends Handler{}private void update(){int h = getHeight();y += 5;if (y >= h)y = 20;}}}

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