Displaying Images from SD Card In Android - Part 2

In one of my previous posts, I wrote about how to fetch and display images from the SD card. The problem with the previous post is that one would have to wait until the first couple of images are available and shown on the screen. This implies that when the user wants to see the images, he will wait a couple of seconds until the first screen of images is available. The code that I'm going to post here works more like the Gallery application, meaning that one image at a time will be displayed on the screen. To achieve this effect, I used an AsyncTask, which fetches one image at a time in the background, and adds that image to the grid view during the progress update.

package blog.android.sdcard2;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.drawable.BitmapDrawable;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.Display;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.view.WindowManager;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import android.widget.AdapterView.OnItemClickListener;

/**
 * Loads images from SD card. 
 * 
 * @author Mihai Fonoage
 *
 */
public class LoadImagesFromSDCardActivity extends Activity implements
OnItemClickListener {
    
    /**
     * Grid view holding the images.
     */
    private GridView sdcardImages;
    /**
     * Image adapter for the grid view.
     */
    private ImageAdapter imageAdapter;
    /**
     * Display used for getting the width of the screen. 
     */
    private Display display;

    /**
     * Creates the content view, sets up the grid, the adapter, and the click listener.
     * 
     * @see android.app.Activity#onCreate(android.os.Bundle)
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);        
        // Request progress bar
        requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
        setContentView(R.layout.sdcard);

        display = ((WindowManager) getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay();

        setupViews();
        setProgressBarIndeterminateVisibility(true); 
        loadImages();
    }

    /**
     * Free up bitmap related resources.
     */
    protected void onDestroy() {
        super.onDestroy();
        final GridView grid = sdcardImages;
        final int count = grid.getChildCount();
        ImageView v = null;
        for (int i = 0; i < count; i++) {
            v = (ImageView) grid.getChildAt(i);
            ((BitmapDrawable) v.getDrawable()).setCallback(null);
        }
    }
    /**
     * Setup the grid view.
     */
    private void setupViews() {
        sdcardImages = (GridView) findViewById(R.id.sdcard);
        sdcardImages.setNumColumns(display.getWidth()/95);
        sdcardImages.setClipToPadding(false);
        sdcardImages.setOnItemClickListener(LoadImagesFromSDCardActivity.this);
        imageAdapter = new ImageAdapter(getApplicationContext()); 
        sdcardImages.setAdapter(imageAdapter);
    }
    /**
     * Load images.
     */
    private void loadImages() {
        final Object data = getLastNonConfigurationInstance();
        if (data == null) {
            new LoadImagesFromSDCard().execute();
        } else {
            final LoadedImage[] photos = (LoadedImage[]) data;
            if (photos.length == 0) {
                new LoadImagesFromSDCard().execute();
            }
            for (LoadedImage photo : photos) {
                addImage(photo);
            }
        }
    }
    /**
     * Add image(s) to the grid view adapter.
     * 
     * @param value Array of LoadedImages references
     */
    private void addImage(LoadedImage... value) {
        for (LoadedImage image : value) {
            imageAdapter.addPhoto(image);
            imageAdapter.notifyDataSetChanged();
        }
    }
    
    /**
     * Save bitmap images into a list and return that list. 
     * 
     * @see android.app.Activity#onRetainNonConfigurationInstance()
     */
    @Override
    public Object onRetainNonConfigurationInstance() {
        final GridView grid = sdcardImages;
        final int count = grid.getChildCount();
        final LoadedImage[] list = new LoadedImage[count];

        for (int i = 0; i < count; i++) {
            final ImageView v = (ImageView) grid.getChildAt(i);
            list[i] = new LoadedImage(((BitmapDrawable) v.getDrawable()).getBitmap());
        }

        return list;
    }
    /**
     * Async task for loading the images from the SD card. 
     * 
     * @author Mihai Fonoage
     *
     */
    class LoadImagesFromSDCard extends AsyncTask<Object, LoadedImage, Object> {
        
        /**
         * Load images from SD Card in the background, and display each image on the screen. 
         *  
         * @see android.os.AsyncTask#doInBackground(Params[])
         */
        @Override
        protected Object doInBackground(Object... params) {
            //setProgressBarIndeterminateVisibility(true); 
            Bitmap bitmap = null;
            Bitmap newBitmap = null;
            Uri uri = null;            

            // 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 cursor = managedQuery( MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI,
                    projection, // Which columns to return
                    null,       // Return all rows
                    null,       
                    null); 
            int columnIndex = cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails._ID);
            int size = cursor.getCount();
            // If size is 0, there are no images on the SD Card.
            if (size == 0) {
                //No Images available, post some message to the user
            }
            int imageID = 0;
            for (int i = 0; i < size; i++) {
                cursor.moveToPosition(i);
                imageID = cursor.getInt(columnIndex);
                uri = Uri.withAppendedPath(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, "" + imageID);
                try {
                    bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(uri));
                    if (bitmap != null) {
                        newBitmap = Bitmap.createScaledBitmap(bitmap, 70, 70, true);
                        bitmap.recycle();
                        if (newBitmap != null) {
                            publishProgress(new LoadedImage(newBitmap));
                        }
                    }
                } catch (IOException e) {
                    //Error fetching image, try to recover
                }
            }
            cursor.close();
            return null;
        }
        /**
         * Add a new LoadedImage in the images grid.
         *
         * @param value The image.
         */
        @Override
        public void onProgressUpdate(LoadedImage... value) {
            addImage(value);
        }
        /**
         * Set the visibility of the progress bar to false.
         * 
         * @see android.os.AsyncTask#onPostExecute(java.lang.Object)
         */
        @Override
        protected void onPostExecute(Object result) {
            setProgressBarIndeterminateVisibility(false);
        }
    }

    /**
     * Adapter for our image files. 
     * 
     * @author Mihai Fonoage
     *
     */
    class ImageAdapter extends BaseAdapter {

        private Context mContext; 
        private ArrayList<LoadedImage> photos = new ArrayList<LoadedImage>();

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

        public void addPhoto(LoadedImage photo) { 
            photos.add(photo); 
        } 

        public int getCount() { 
            return photos.size(); 
        } 

        public Object getItem(int position) { 
            return photos.get(position); 
        } 

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

        public View getView(int position, View convertView, ViewGroup parent) { 
            final ImageView imageView; 
            if (convertView == null) { 
                imageView = new ImageView(mContext); 
            } else { 
                imageView = (ImageView) convertView; 
            } 
            imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
            imageView.setPadding(8, 8, 8, 8);
            imageView.setImageBitmap(photos.get(position).getBitmap());
            return imageView; 
        } 
    }

    /**
     * A LoadedImage contains the Bitmap loaded for the image.
     */
    private static class LoadedImage {
        Bitmap mBitmap;

        LoadedImage(Bitmap bitmap) {
            mBitmap = bitmap;
        }

        public Bitmap getBitmap() {
            return mBitmap;
        }
    }
    /**
     * When an image is clicked, load that image as a puzzle. 
     */
    public void onItemClick(AdapterView<?> parent, View v, int position, long id) {        
        int columnIndex = 0;
        String[] projection = {MediaStore.Images.Media.DATA};
        Cursor cursor = managedQuery( MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI,
                projection,
                null, 
                null, 
                null);
        if (cursor != null) {
            columnIndex = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);
            cursor.moveToPosition(position);
            String imagePath = cursor.getString(columnIndex); 

            FileInputStream is = null;
            BufferedInputStream bis = null;
            try {
                is = new FileInputStream(new File(imagePath));
                bis = new BufferedInputStream(is);
                Bitmap bitmap = BitmapFactory.decodeStream(bis);
                Bitmap useThisBitmap = Bitmap.createScaledBitmap(bitmap, parent.getWidth(), parent.getHeight(), true);
                bitmap.recycle();
                //Display bitmap (useThisBitmap)
            } 
            catch (Exception e) {
                //Try to recover
            }
            finally {
                try {
                    if (bis != null) {
                        bis.close();
                    }
                    if (is != null) {
                        is.close();
                    }
                    cursor.close();
                    projection = null;
                } catch (Exception e) {
                }
            }
        }
    }

}

The sdcard.xml file:

<?xml version="1.0" encoding="utf-8"?>

<FrameLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" 
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    
    <GridView  
        android:id="@+id/sdcard"
        android:layout_width="fill_parent" 
        android:layout_height="fill_parent"
        android:verticalSpacing="10dp"
        android:horizontalSpacing="10dp" 
        android:stretchMode="columnWidth"
        android:gravity="center" />
        
</FrameLayout>    

That's it. Let me know if you have any questions.

Enjoy!