Handler用来发消息和处理消息.典型的用法是更新界面.android不允许在子线程里面更新界面,通常是把Handler传到子线程中,在子线程里通过sendEmptyMessage函数发消息.Handler的handleMessage函数响应消息,实现更新界面.
下面看一个例子.Handler的定义如下:
public class PlayHandler extends Handler {
private ImageView imageView;
int currentImageId = 0;
private int[] imageIds = new int[] {
R.drawable.java,
R.drawable.ee,
R.drawable.ajax,
R.drawable.xml,
R.drawable.classic
};
public PlayHandler(ImageView imageView) {
this.imageView = imageView;
}
@Override
public void handleMessage(android.os.Message msg) {
if (msg.what == Message.PLAY) {
imageView.setImageResource(imageIds[currentImageId++
% imageIds.length]);
}
}
}
函数handleMessage用于处理消息,改变ImageView的内容.需要更新的时候只用拿到Handler的实例,调用sendEmptyMessage之类的函数即可.代码如下所示.
public class PlayTimerTask extends TimerTask {
private Handler handler;
public PlayTimerTask(Handler handler) {
this.handler = handler;
}
@Override
public void run() {
handler.sendEmptyMessage(Message.PLAY);
}
}
源代码地址:https://github.com/zhouyang209117/AndroidTutorial/tree/master/Crazy/ch3/HandlerMsg