How to update progressbar in a ListView item

Question

I have a ListView attached to an ArrayAdapter. When the user clicks a download button for an item in the ListView a download starts using the DownloadManager.

What I want to do is to track the download progress with a progress bar (placed in the item layout). How can this be achieved?

The way Pocket Cast does it is exacly what I'm after:

Pocket Cast exampel http://www.mrcrab.net/images/thumb_big/9982-Pocket_Casts_Apk_v4.3.2_Android-0.jpg

Note: I know how to work with the DownloadManager, it's the instant update of the progress bar that is tricky.

Answer 1

This is the way I finally solved it (after many iterations and different implementations). It's a bit tricky but basically you need three things:

1. An AsyncTask that gathers meta data
2. A scroll listener that tells us when the user has stopped scrolling/flinging
3. A clever algorithm that finds any visible row that needs updating and asks the adapter to only update that specific row

This is the way I designed and implemented it:

I wrote in more detail about it here, and please see the github code for the complete imlementation.

    private class UpdaterAsyncTask extends AsyncTask<Void, Void, Void> {

    boolean isRunning = true;

    public void stop() {
        isRunning = false;
    }

    @Override
    protected Void doInBackground(Void... params) {

        while (isRunning) {

            // Gather data about your adapter objects
            // If an object has changed, mark it as dirty                

            publishProgress();

            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        return null;
    }

    @Override
    protected void onProgressUpdate(Void... params) {
        super.onProgressUpdate();

        // Update only when we're not scrolling, and only for visible views
        if (mScrollState == OnScrollListener.SCROLL_STATE_IDLE) {
            int start = mListview.getFirstVisiblePosition();
            for(int i = start, j = mListview.getLastVisiblePosition(); i<=j; i++) {
                View view = mListview.getChildAt(i-start);
                if (((Content)mListview.getItemAtPosition(i)).dirty) {
                    mListview.getAdapter().getView(i, view, mListview); // Tell the adapter to update this view
                }

            }
        }

      }
    }

Answer 2

For a specific view item, you can retrieve it using getChildAt(int index) and update it.

And you can traverse through all visible items by the help of getFirstVisiblePosition() and getLastVisiblePosition()