Question

I’m implementing a simple chatting application which has a TextView for text messages and a EditText for input.
I update my TextView by following method:

    private void addChatContent(String authorName, String content){
    final String newLine = authorName+" : "+content+"\n";
    chat_content.append(newLine);
    scroll.post(new Runnable(){
        @Override
        public void run() {
            scroll.smoothScrollTo(0, chat_content.getBottom()+5000);
        }
    });
}

A problem I’m facing is: when there are new incoming messages, UI thread will be busy for refreshing the TextView. It makes my EditText become lag, I can hardly edit my input.
I can not refresh the TextView with another thread, right?
So what should I do to overcome this limitation?
Could somebody give me some light? Thanks in advance.

Answer 1

Ultimately, and unfortunately, there is only one thread dedicated to the UI. If you are updating the TextView there is no way you can simultaneously have a lag-free experience with the EditText. You already know this, but I fear some people answering this question may not, so here’s a reference:

The system does not create a separate thread for each instance of a
component. All components that run in the same process are
instantiated in the UI thread, and system calls to each component are
dispatched from that thread. Consequently, methods that respond to
system callbacks (such as onKeyDown() to report user actions or a
lifecycle callback method) always run in the UI thread of the process

…

When your app performs intensive work in response to user interaction,
this single thread model can yield poor performance unless you
implement your application properly. Specifically, if everything is
happening in the UI thread, performing long operations such as network
access or database queries will block the whole UI. When the thread is
blocked, no events can be dispatched, including drawing events.

…

Additionally, the Andoid UI toolkit is not thread-safe. So, you must
not manipulate your UI from a worker thread—you must do all
manipulation to your user interface from the UI thread. Thus, there
are simply two rules to Android’s single thread model:

Do not block the UI thread
Do not access the Android UI toolkit from outside the UI thread

Hence, the answer is quite clear: don’t do this. Why does the Textview have to be absolutely, 100% up to date, as the user is updating the EditText field? Why are you scrolling all the way to the bottom; maybe you can get away with deleting most of the contents of the TextView and, when the user scrolls, dynamically re-adding content to it?

IMO you should focus on reducing the amount of work you need to do on the TextView.