ProgressDialog - why runnable doesn't make appear ProgressDialog?

Question

When I try to update text in my progressDialog like someone suggests here or here.

In my case, I'm trying to update the text in a loop while the progressDialog is not dismissed (?) elsewhere... But my loop inside the runnable doesn't seems work, or better, the runnable doesn't make show the progressDialog.

So, in this way the code shows the progressDialog:

@Override
public void onDirectionFinderStart() {
    String title = "PriscaLobby";
    String msg  = "Loading...";
    progressDialog = ProgressDialog.show (MapsActivity.this,title,msg,true,false);

//--> runOnUiThread(changeMessage);

}

private Runnable changeMessage = new Runnable() {
    @Override
    public void run() {
        progressDialog.setMessage("bruka");
        while (progressDialog.isShowing()) {
            try {
                Thread.sleep(1500);
                if (progressDialog.isShowing())
                    progressDialog.setMessage("Can you wait, please?");
                Thread.sleep(1500);
                if (progressDialog.isShowing())
                    progressDialog.setMessage("Here we are..");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }           
    }
};

In this way NO:

@Override
public void onDirectionFinderStart() {
    String title = "PriscaLobby";
    String msg  = getString(R.string.calculate_directions);
    progressDialog = ProgressDialog.show (MapsActivity.this,title,msg,true,false);

    runOnUiThread(changeMessage);

}

private Runnable changeMessage = new Runnable() {
    @Override
    public void run() {
        progressDialog.setMessage("bruka");
        while (progressDialog.isShowing()) {
            try {
                Thread.sleep(1500);
                if (progressDialog.isShowing())
                    progressDialog.setMessage("Can you wait, please?");
                Thread.sleep(1500);
                if (progressDialog.isShowing())
                    progressDialog.setMessage("Here we are..");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }           //Log.v(TAG, strCharacters);
    }
};

Why?