Android之view重绘

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。 
以下是我在android文档中找到的说明， 

引用

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。 

下面是我分别针对invalidate方法，给出view重绘代码，仅供参考： 

class CustomizeView extends WhichView {

    public CustomizeView(Context context) {
        super(context);
        final Handler handler = new Handler();

        new Thread(new Runnable() {
            @Override
            public void run() {
                // delay some minutes you desire.
                /*try {
                    Thread.sleep(3000);
                } catch (InterruptedException e) {
                }*/
                handler.post(new Runnable() {
                    public void run() {
                        concreteUpdateUI();
                        invalidate();
                    }
                });
            }
        }).start();
    }

    protected void concreteUpdateUI() {
        // Add concrete movement for UI updates.
        // ...
    }
}

或者这样实现也可以。 

class CustomizeView extends TextView {

    public CustomizeView(Context context) {
        super(context);
        new Thread(new UIUpdateThread()).start();
    }

    class UIUpdateThread implements Runnable {
        final Handler mHandler = new Handler();

        final Runnable mUpdateResults = new Runnable() {
            public void run() {
                concreteUpdateUI();
                invalidate();
            }
        };

        public void run() {
            // delay some minutes you desire.
            /*try {
                Thread.sleep(1000 * 5);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }*/
            mHandler.post(mUpdateResults);
        }

    }

    protected void concreteUpdateUI() {
        // Add concrete movement for UI updates.
        // ...
    }

}