vxh.viet
3/30/2016 - 4:41 AM

How do you have the code pause for a couple of seconds in android?

How do you have the code pause for a couple of seconds in android?

Source: StackOverflow

Question: How do you have the code pause for a couple of seconds in android?

Answer: Learning to think in terms of events is indeed the key here. You can do it. :)

The first rule is: never stall the UI thread. The UI thread is responsible for keeping your app feeling responsive. Any work you do there should not block; do what you need to do and return as quickly as possible. Definitely avoid doing I/O on the UI thread. (There are some places where you can't really help it due to lifecycle requirements, for example saving app state in onPause.) If you ever call Thread.sleep on the UI thread you are doing it wrong.

Android enforces this with the "Application not responding" (or "ANR") error that the user sees. Whenever you see this in an Android app it means the developer did something that caused the UI thread to stall for too long. If the device is really bogged down for some reason this error might not actually be the app developer's fault, but usually it means the app is doing something wrong.

You can use this model to your advantage by posting your own events. This gives you an easy way to tell your app, "do this later." In Android the key to posting your own events is in the Handler class. The method postDelayed lets you schedule a Runnable that will be executed after a certain number of milliseconds.

private void waitFor(long millis){
        Handler mHandler = new Handler();
        mHandler.postDelayed(new Runnable() {
            public void run() {
                //doStuff();
            }
        }, millis);
    }

If you're writing a custom View it's even easier. Views have their own postDelayed method that will get everything posted to the correct Handler and you don't need to create your own.

The second rule is: Views should only be modified on the UI thread. Those exceptions you're getting and ignoring mean something went wrong and if you ignore them your app will probably start misbehaving in interesting ways. If your app does most of its work in other threads you can post events directly to the view you want to modify so that the modifications will run correctly.

If you have a reference to your Activity from that part of your code you can also use Activity#runOnUIThread, which does exactly what the name implies. You might prefer this approach if posting to a single view doesn't really make sense in context.

As for updates to views not appearing until you hit a button, what kind of views are these? Are they custom views that are drawing these updates? If so, are you remembering to call invalidate after data changes to trigger the redraw? Views only redraw themselves after they have been invalidated.