学步园

android中实现view的更新有两组方法，一组是invalidate，另一组是postInvalidate，其中前者是在UI线程自身中使用，而后者在非UI线程中使用。

public void invalidate()
Invalidate the whole view. If the view is visible, onDraw(Canvas) will be called at some point in the future. This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().

public void postInvalidate ()
Cause an invalidate to happen on a subsequent cycle through the event loop. Use this to invalidate the View from a non-UI thread.

google的文档的说明实在是简单，往往看了开发中都会遇到这两个问题:
1. 没有任何异常，view没能刷新。
2. android应用异常终止，打开logcat会看到这样的异常信息, Only the original thread that created a view hierarchy can touch its views。

最后，通过查文档，上网查询才知道，invalidate和postInvalidate方法需要使用android提供的handler,才能实现重绘，而在文档的说明中却只字不提，真是简单啊。具体是在需要重绘的地方调用handler的sendMessage方法发送消息，紧接着会os会触发handler中的handlerMessage方法，在handlerMessage方法中再调用view的invalidate或者postInvalidate方法就能实现重绘。

view重绘代码如下：

class CustomizeView extends WhichView { </p> <p> public CustomizeView(Context context) {<br /> super(context);<br /> final Handler handler = new Handler(); </p> <p> new Thread(new Runnable() {<br /> @Override<br /> public void run() {<br /> // delay some minutes you desire.<br /> /*try {<br /> Thread.sleep(3000);<br /> } catch (InterruptedException e) {<br /> }*/<br /> handler.post(new Runnable() {<br /> public void run() {<br /> concreteUpdateUI();<br /> invalidate();<br /> }<br /> });<br /> }<br /> }).start();<br /> } </p> <p> protected void concreteUpdateUI() {<br /> // Add concrete movement for UI updates.<br /> // ...<br /> }<br /> }<br />

或者：

class CustomizeView extends TextView { </p> <p> public CustomizeView(Context context) {<br /> super(context);<br /> new Thread(new UIUpdateThread()).start();<br /> } </p> <p> class UIUpdateThread implements Runnable {<br /> final Handler mHandler = new Handler(); </p> <p> final Runnable mUpdateResults = new Runnable() {<br /> public void run() {<br /> concreteUpdateUI();<br /> invalidate();<br /> }<br /> }; </p> <p> public void run() {<br /> // delay some minutes you desire.<br /> /*try {<br /> Thread.sleep(1000 * 5);<br /> } catch (InterruptedException e) {<br /> e.printStackTrace();<br /> }*/<br /> mHandler.post(mUpdateResults);<br /> } </p> <p> } </p> <p> protected void concreteUpdateUI() {<br /> // Add concrete movement for UI updates.<br /> // ...<br /> } </p> <p>}<br />