How can I tell if my context is still valid?

Question

I'm working with a fairly common situation right now - download some data over the web, then update a view to display it. Clearly, I want to do the web download in the background, and then update the view on the main UI thread. Now looking at my code, I'm a little worried about my Activity and its UI elements being killed off before I update them. Here's the essence of what I have in mind:

Click to copy

Thread update = new Thread() {
    public void run() {
        final Data newData = requestData();                     
        if (newData != null) {
            post(new Runnable() {
                public void run() {
                    Toast.makeText(MyClass.this, "I'll do things here that depend on my context and views being valid", Toast.LENGTH_SHORT).show();
                }
            });
        }
    }
};
update.start();

It seems possible that while I'm downloading data, the activity may be destroyed. What happens then? Will my thread continue to execute? Will I end up trying to access dead objects?

Usually I do this by AsycTask, but the work seemed simple enough this time to just inline the threads-launching-threads stuff. Will I make things any better by using an AsyncTask instead?

Answer 1

If your Context is an Activity, you can check if it is finishing or has finished with the isFinishing() method:

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if ( context instanceof Activity ) {
    Activity activity = (Activity)context;
    if ( activity.isFinishing() ) {
        return;
    }
}
Toast.makeText(context, "I'll do things here that depend on my context and views being valid", Toast.LENGTH_SHORT).show();

Answer 2

What you really want to use is an AsyncTaskLoader. These are my new favorite classes in the Android API. I use them all the time and they were made to solve problems just like this. You won't have to worry about when to stop your download or anything like that. All the threading logic is taken care of for you, including telling the thread to stop if the activity has been closed. Just say what it is you want to do in the loadInBackground() method. Note that if you are developing for an API lower than 3.0, you can still access all the loaders via the Android Support Package.