java - 它说必须调用looper.prepare

Question

我正在 MainActivity 处理程序的帮助下更新进度条但它给出了错误:无法在未调用 Looper.prepare() 的线程内创建处理程序

Error

public class MainActivity extends AppCompatActivity {
ProgressBar progressBar;
Handler handler;
Thread thread;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    progressBar = (ProgressBar) findViewById(R.id.progressBar);
    thread = new Thread(new MyThread());
    thread.start();
    handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            progressBar.setProgress(msg.arg1);
        }
    };


}

class MyThread implements Runnable {

    @Override
    public void run() {
        Message message = Message.obtain();

        for (int i = 0; i < 100; i++) {
            message.arg1 = i;
            handler.sendMessage(message);
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

}

Answer 1

该错误是因为您正在从不同的线程更新 UI。所以你应该做的就是在主 ui 线程上调用 update 方法

handler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
          runOnUiThread(new Runnable() {
               @Override
               public void run() {
                   // Do something on UiThread
                   // update progress
               }
          });
 };