如果我们想在子线程上创建Handler,通过直接new的出来是会报异常的比如:
- new Thread(new Runnable() {
- public void run() {
- Handler handler = new Handler(){
- @Override
- public void handleMessage(Message msg) {
- Toast.makeText(getApplicationContext(), "handler msg", Toast.LENGTH_LONG).show();
- }
- };
- handler.sendEmptyMessage(1);
- };
- }).start();
会报错:
01-12 02:49:31.814: E/AndroidRuntime(2226): Java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
1.方法1(直接获取当前子线程的looper)
既然它说要 Looper.prepare(),那我们就给他prepare()咯
- new Thread(new Runnable() {
- public void run() {
- Looper.prepare(); // 此处获取到当前线程的Looper,并且prepare()
- Handler handler = new Handler(){
- @Override
- public void handleMessage(Message msg) {
- Toast.makeText(getApplicationContext(), "handler msg", Toast.LENGTH_LONG).show();
- }
- };
- handler.sendEmptyMessage(1);
- };
- }).start();
然后我们再运行,发现不报错了,但是handleMessage内的代码没执行,因为还差重要的一步,Looper.loop();最终代码是
- new Thread(new Runnable() {
- public void run() {
- Looper.prepare();
- Handler handler = new Handler(){
- @Override
- public void handleMessage(Message msg) {
- Toast.makeText(getApplicationContext(), "handler msg", Toast.LENGTH_LONG).show();
- }
- };
- handler.sendEmptyMessage(1);
- Looper.loop();
- };
- }).start();
这样就OK了
2.方法2(获取主线程的looper,或者说是UI线程的looper)
这个方法简单粗暴,不过和上面的方法不一样的是,这个是通过主线程的looper来实现的
- new Thread(new Runnable() {
- public void run() {
- Handler handler = new Handler(Looper.getMainLooper()){ // 区别在这!!!!
- @Override
- public void handleMessage(Message msg) {
- Toast.makeText(getApplicationContext(), "handler msg", Toast.LENGTH_LONG).show();
- }
- };
- handler.sendEmptyMessage(1);
- };
- }).start();