DownloadWithRunnables.java

package vandy.mooc.presenter.strategies;

import android.graphics.Bitmap;

/**
 * Use the Runnables and Handlers defined by the HaMeR framework to
 * implement an ImageStrategy interface that downloads a bitmap image
 * in a background thread and displays it on the UI thread.  This
 * class plays the role of the "Concrete Strategy" in the Strategy
 * pattern.
 */
public class DownloadWithRunnables
       implements ImageStrategy {
    /**
     * Thread object that's used for the download.
     */
    private Thread mThread = null;

    /**
     * Creates and starts a new Thread to download an image in the
     * background via a Runnable. The downloaded image is then
     * diplayed in the UI Thread by posting another Runnable via the
     * Activity's runOnUiThread() method, which uses an internal
     * Handler.
     */
    @Override
    public void downloadAndDisplay(final DownloadContext downloadContext) {
        final Runnable downloadRunnable = new Runnable() {
            /**
             * Download a bitmap image in a background Thread and then
             * post a Runnable to the UI Thread to set the image to
             * the ImageView.
             */
            @Override
            public void run() {
                // Download the image.
                final Bitmap image =
                    downloadContext.downloadBitmap(downloadContext.getUrl());

                // Display the downloaded image to the user.
                downloadContext.displayBitmap(image);
            }
        };

        // Inform the user that the download is starting with
        // this particular concurrency strategy.
        downloadContext.showToast("downloading via Handlers and Runnables");

        // Create and Start a new Thread to perform the download and
        // display the results to the user.
        mThread = new Thread(downloadRunnable);
        mThread.start();
    }

    /**
     * Cancel the download/display operation.
     */
    @Override
    public void cancel(DownloadContext downloadContext) {
        // Let the user know this download/display is being canceled.
        downloadContext.showToast("Canceling DownloadWithRunnable in progress");

        // Interrupt the Thread so it will stop the download/display.
        mThread.interrupt();
    }
}