Question

I know this question has been asked multiple times, but I have an apparently clean code that just doesn’t work, giving me no Exceptions or anything.

I have a trivial one-button Activity (MainActivity). The button in it calls an AsyncTask in order to send an email in the background. I tried to do what I guess it’s a pretty common thing: show a ProgressDialog when the task starts and dismiss it when it ends. To do so I put the above-mentioned code into AsyncTask.onPreExecute() and AsyncTask.onPostExecute().
I thought the problem was in the Context provided to the dialog constructor, but I created a simple constructor for my AsyncTask to which I pass the application context. I added a simple Toast to debug, but it doesn’t show up neither…

Here’s the code for the button onClick method:

public void onClick(View v) {
    new Sender(this).execute("args");
}

And here’s the code for the task:

private class Sender extends AsyncTask<String, Void, Void> {
    private ProgressDialog progDialog;
    private Context context;

    public Sender(Context context) {
        this.context = context;
    }

    @SuppressWarnings("unused")
        protected void onPreExecute(Void... params) {
        Toast.makeText(this.context, "Sending...", Toast.LENGTH_SHORT).show();
        progDialog = ProgressDialog.show(this.context, "Sending", "Picture is being sent...", true);
    }

    protected Void doInBackground(String... mailSubj) {
        // some code that works
        return null;
    }

    @SuppressWarnings("unused")
    protected void onPostExecute(Void... v) {
        progDialog.dismiss();
        Toast.makeText(MainActivity.this, "Mail sent", Toast.LENGTH_SHORT).show();
    }
}

Where did I go wrong?

Answer 1

Your progress dialog not show up because you don’t override onPreExecute(). Add @Override annotation to your onPreExecute(), see what happens. onPreExecute takes no arguments.