Custom click listener

[rajohns08]

Allow someone to set their own custom click listener for media messages. Fall back to default full screen click listener if one isn't manually set.

MediaMessage message = new MediaMessage();
message.onClickListener = new OnClickListener() {
    @Override
    public void onClick(View view) {
        Log.d("TAG", "Do something custom");
    }
};

[luugiathuy]

I think Message, TextMessage or MediaMessage are our Models for messages. They should not contain View event attributes. Perhaps we can define in the MessageItem classes instead?