Android，弹出异常提示信息

Question

I have an android app connected to a servlet. If the servlet is down (happened to me yesterday) the app crashes. I need to pop up a message to the user informing about some connection issues and then terminate the application.

on onCreate() method, i call an AsyncTask class, in which is done the first connection to the server. I have a try/catch(UnknownHostException e) block, which is activated if the sevlet is down. The problem is that i cant create a pop up message there. I tried toast and AllertDialogs, but both return an exception

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

Is there some other way i can do this? Thanks in advance, ilias

Answer 1

You could set a boolean and read it after the function call, at which point you should be able to show a toast/dialog. But that's hard to say without the rest of the code.

Answer 2

Your AsyncTask is running in a background thread. Calls to show a Toast or a Dialog must be made on the main (UI) thread. To do this from within an AsyncTask you can do this:

You'll need an activity context in your AsyncTask , so have your activity create your AsyncTask like this:

MyAsyncTask task = new MyAsyncTask(this, ...); // pass "this" so AsyncTask has an activity context

In your AsyncTask constructor, save the activity context so you can use it later:

private Activity activity;

// Constructor
MyAsyncTask(Activity activity, ...) {
    this.activity = activity;
    ...
}

When you want to show a Dialog or a Toast, make sure the code runs on the main (UI) thread:

// Here we want to Toast
activity.runOnUiThread(new Runnable() {
        @Override
        public void run() {
            // Do your Toast or Dialog stuff in here
            ...        
        }
 });