CODEWITHSUNDEEP
androidmultithreadinguser-interface
user2651167
user2651167

Reputation: 93

Generate android buttons with while loop in separate thread

I'm lost here. I need to read the files in a directory and make buttons from them when an app starts. I have to use a while loop, and I have to update the UI. I've tried for quite a while to run a runnable and have only the code inside the loop run in the UI thread. I'm relatively new to android, but this seemed simple enough.

This code is what I have right now. It throws no errors or warnings, but it doesn't do anything. I know the button making code works because the "add button" button makes buttons correctly. I have no idea why it isn't working. (This runs in OnCreate)

Runnable aRunnable = new Runnable() {

    public void run() {
        Looper.prepare();
        File f = new File(Environment.getExternalStorageDirectory() + "/myapp/");
        File[] filearray = f.listFiles();
        int amount = filearray.length;
        final String[] files = new String[amount];
        int count = 0;
        while (count != amount) {
            files[count] = filearray[count].toString();
            count += 1;
        }
        int times = files.length;
        int counter = 0;
        while (counter != times) {
            Handler handler = new Handler();
            handler.post(new Runnable() {
                public void run() {
                    // Button making code
                }
            });
        }
        Looper.loop();
    }
};
Thread thread = new Thread(aRunnable);
thread.start();

Upvotes: 1

Views: 244

Answers (2)

Nate
Nate

Reputation: 31045

One problem with your existing code is that everything in the run() method gets run on a background thread, not the main (sometimes called the UI) thread.

This is where you're creating your handler object:

        Handler handler = new Handler();

This is not correct. You need to create (instantiate) the Handler on the main thread, if using the default constructor. From the Handler docs:

public Handler () Added in API level 1

Default constructor associates this handler with the Looper for the current thread. If this thread does not have a looper, this handler won't be able to receive messages so an exception is thrown.

So, a simple fix is simply to move that line of code earlier, into a place that you know is run on the main thread. For example, in Activity#onCreate():

public void onCreate(Bundle b) {
   super.onCreate(b);

   handler = new Handler();
}

where handler is changed to be a member variable:

private Handler handler;

Also, just remove your Looper calls.

See this article for more on Handler.

Other Options

Another option would be to avoid using Handler at all, and get famliar with the AsyncTask class. I personally think that's easier for new developers to use. The vogella.com link I showed also has good information on AsyncTask.

Yet one more option would be to avoid Handler and use the runOnUiThread() method in your Activity to add your buttons.

Upvotes: 1

Budius
Budius

Reputation: 39846

it seems to me that you're trying to have a list of buttons based on some array. It seems that is a job for a ListView and a custom array adapter. I believe you should google some examples on it (there're billions around the internet, it's a fairly basic android pattern).

and while you're in the learning process, don't forget to check how to use for() in Java, all those while loops are just so ugly.

Upvotes: 0

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