android substuting the click with a timer

Question

I found this example and i have a small question: How can I remove the on click to a timer or a delay where it displays the first image and waits a couple of seconds then moves to the next image?

http://mobile.dzone.com/news/displaying-images-sd-card?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+javalobby%2Ffrontpage+%28Javalobby+%2F+Java+Zone%29

Thank you.

package blog.android.sdcard;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.AdapterView.OnItemClickListener;

/**
 * Displays images from an SD card.
 */
public class SDCardImagesActivity extends Activity {

    /**
     * Cursor used to access the results from querying for images on the SD
     * card.
     */
    private Cursor cursor;
    /*
     * Column index for the Thumbnails Image IDs.
     */
    private int columnIndex;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.sdcard);

        // Set up an array of the Thumbnail Image ID column we want
        String[] projection = { MediaStore.Images.Thumbnails._ID };
        // Create the cursor pointing to the SDCard
        cursor = managedQuery(
                MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, projection, // Which
                                                                                // columns
                                                                                // to
                                                                                // return
                null, // Return all rows
                null, MediaStore.Images.Thumbnails.IMAGE_ID);
        // Get the column index of the Thumbnails Image ID
        columnIndex = cursor
                .getColumnIndexOrThrow(MediaStore.Images.Thumbnails._ID);

        GridView sdcardImages = (GridView) findViewById(R.id.sdcard);
        sdcardImages.setAdapter(new ImageAdapter(this));

        // Set up a click listener
        sdcardImages.setOnItemClickListener(new OnItemClickListener() {
            public void onItemClick(AdapterView parent, View v, int position,
                    long id) {
                // Get the data location of the image
                String[] projection = { MediaStore.Images.Media.DATA };
                cursor = managedQuery(
                        MediaStore.Images.Media.EXTERNAL_CONTENT_URI,
                        projection, // Which columns to return
                        null, // Return all rows
                        null, null);
                columnIndex = cursor
                        .getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
                cursor.moveToPosition(position);
                // Get image filename
                String imagePath = cursor.getString(columnIndex);
                // Use this path to do further processing, i.e. full screen
                // display
            }
        });
    }

    /**
     * Adapter for our image files.
     */
    private class ImageAdapter extends BaseAdapter {

        private Context context;

        public ImageAdapter(Context localContext) {
            context = localContext;
        }

        public int getCount() {
            return cursor.getCount();
        }

        public Object getItem(int position) {
            return position;
        }

        public long getItemId(int position) {
            return position;
        }

        public View getView(int position, View convertView, ViewGroup parent) {
            ImageView picturesView;
            if (convertView == null) {
                picturesView = new ImageView(context);
                // Move cursor to current position
                cursor.moveToPosition(position);
                // Get the current value for the requested column
                int imageID = cursor.getInt(columnIndex);
                // Set the content of the image based on the provided URI
                picturesView.setImageURI(Uri.withAppendedPath(
                        MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, ""
                                + imageID));
                picturesView.setScaleType(ImageView.ScaleType.FIT_CENTER);
                picturesView.setPadding(8, 8, 8, 8);
                picturesView
                        .setLayoutParams(new GridView.LayoutParams(100, 100));
            } else {
                picturesView = (ImageView) convertView;
            }
            return picturesView;
        }
    }
}

Answer 1

No need for threads. Just use a Handler with postDelayed messages...

public class HelloHandler extends Activity {

protected Handler handler = new Handler();

@Override
    public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       // blah blah blah

       handler.postDelayed(new UpdateTask(),500);
   }


   protected class UpdateTask implements Runnable {
   public void run() {
      // Do stuff.  This is UI thread.
      handler.postDelayed(this, 500);
   }
}
}

Answer 2

Since blocking the UI thread is fundamentally against the Android framework, what you'd probably have to do is set up a Thread and Handler to sleep on another thread in a loop and use the Handler to pass messages back to the UI Thread and change the image. I know I had a good Thread/Handler example around here somewhere...

Ah yes... have a look at the example on how to update a ProgressDialog through a Thread and Handler. It should give you some ideas.

http://developer.android.com/guide/topics/ui/dialogs.html#ProgressDialog

(see the expandable section "Example ProgressDialog with a second thread."