无法在未调用Looper.prepare（）的线程内创建处理程序

Question

I tried to show an alert dialog after some delay:

Thread thread = new Thread() {
                    @Override
                    public void run() {
                        try {
                            synchronized (this) {
                                wait(3000);
                            }
                        } catch (InterruptedException ex) {
                        }

                        final AlertDialog.Builder builder = new AlertDialog.Builder(stop_watch.fa);
                        builder.setMessage("Want to exit?");
                        builder.setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(DialogInterface dialog, int which) {
                                locator_activity.fa.finish();
                            }
                        });
                        AlertDialog alertDialog = builder.create();
                        alertDialog.show();
                    }
                };
                thread.start();

After launching app. When it's time to show alertdialog the app stopped working. And it shows problem:-

java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()

Answer 1

AlertDialogs are UI elements and so the work needs to be executed on the UI Thread:

new Thread() {
    public void run() {
        activity.this.runOnUiThread(new Runnable() {
            public void run() {
                // Show dialog..
            }
        });
    }
}.start();