android try/catch execute sequence

what I want to achieve is Upon click, app shows toasts message "TEXT1", and keeps showing TEXT1 until finish other function call 20 times at a random interval/delay. After calling function,shows toast message "TEXT2". My problem: TEXT1 does not show until app finishes function call. and TEXT1 keeps up for the time it takes to execute 20 times function call,then TEXT2 shows up.My code:

public void onClick(View v) {
    switch (v.getId()) {
        case R.id.example:
                Toast.makeText(getBaseContext(),"Please wait until finish",Toast.LENGTH_SHORT).show();
                int i = 0;
                while (i <= 19 ){

                    int delay = new Random().nextInt(5000);
                    try {
                            Thread.sleep(delay);
                        } catch(InterruptedException ex) {
                            Thread.currentThread().interrupt();
                        }
                    //some function here
                    i++;
                }
                Toast.makeText(getBaseContext(),"Finished",Toast.LENGTH_SHORT).show();
                break;
        }
    }
}

Solution

Never block the UI thread!

All user interface operations are handled in the UI thread. If you block the UI thread with a Thread.sleep call, an ANR (Application Not Responding) will occur. Moreover, Thread.sleep is never the right way to create timers, unless you are writing the core heartbeat of a worker thread.

Instead, you should use Handler.postDelayed:

public void onClick(View v) {
    final Handler handler = new Handler();
    final Random random = new Random();

    Runnable runnable = new Runnable() {
        private int count = 0;

        @Override
        public void run() {
            count++;
            if(count > 20) { // 20 times passed
                Toast.makeText(getBaseContext(), "Finished", LENGTH_SHORT).show();
                return;
            }

            Toast.makeText(getBaseContext(), "Please wait until finish", LENGTH_SHORT).show();
            handler.postDelayed(this, random.nextInt(5000));
        }
    };
    runnable.run();
}

Edit: the OP wanted to use something like this. https://gist.github.com/SOF3/07c3c110aa214fcdd752e95573b7076f