views:

1740

answers:

6

Hi all,

I am working on the listview with the custom adapter. I want to load the images and text view on it. The images are load from the internet urls. I just want to show the images which are visible list item to hte user. I refered the Shelves opensource project example from romainguy, but its to complicated to understand the code. For a beginner level, I just want to know how to handle the tag between the adapter and activity. From the commonsware example I can set the tag on adapter, but can't show the corresponding image at the idle state of the listview. Please help me with your ideas. Sample codes are more understandable.

Thanks.

EDIT:

The combination of Efficient and Slow Adapter in ApiDemos is more helpful to understand.

changes done on efficient adapter example like this:

public class List14 extends ListActivity implements ListView.OnScrollListener {
// private TextView mStatus;

private static boolean mBusy = false;
static ViewHolder holder;

public static class EfficientAdapter extends BaseAdapter {
    private LayoutInflater mInflater;
    private Bitmap mIcon1;
    private Bitmap mIcon2;

    public EfficientAdapter(Context context) {
        // Cache the LayoutInflate to avoid asking for a new one each time.
        mInflater = LayoutInflater.from(context);

        // Icons bound to the rows.
        mIcon1 = BitmapFactory.decodeResource(context.getResources(),
                R.drawable.icon48x48_1);
        mIcon2 = BitmapFactory.decodeResource(context.getResources(),
                R.drawable.icon48x48_2);
    }

    /**
     * The number of items in the list is determined by the number of
     * speeches in our array.
     * 
     * @see android.widget.ListAdapter#getCount()
     */
    public int getCount() {
        return DATA.length;
    }

    /**
     * Since the data comes from an array, just returning the index is
     * sufficent to get at the data. If we were using a more complex data
     * structure, we would return whatever object represents one row in the
     * list.
     * 
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem(int position) {
        return position;
    }

    /**
     * Use the array index as a unique id.
     * 
     * @see android.widget.ListAdapter#getItemId(int)
     */
    public long getItemId(int position) {
        return position;
    }

    /**
     * Make a view to hold each row.
     * 
     * @see android.widget.ListAdapter#getView(int, android.view.View,
     *      android.view.ViewGroup)
     */
    public View getView(int position, View convertView, ViewGroup parent) {
        // A ViewHolder keeps references to children views to avoid
        // unneccessary calls
        // to findViewById() on each row.

        // When convertView is not null, we can reuse it directly, there is
        // no need
        // to reinflate it. We only inflate a new View when the convertView
        // supplied
        // by ListView is null.
        if (convertView == null) {
            convertView = mInflater.inflate(R.layout.list_item_icon_text,
                    null);

            // Creates a ViewHolder and store references to the two children
            // views
            // we want to bind data to.
            holder = new ViewHolder();
            holder.text = (TextView) convertView.findViewById(R.id.text);
            holder.icon = (ImageView) convertView.findViewById(R.id.icon);

            convertView.setTag(holder);
        } else {
            // Get the ViewHolder back to get fast access to the TextView
            // and the ImageView.
            holder = (ViewHolder) convertView.getTag();
        }
        if (!mBusy) {
            holder.icon.setImageBitmap(mIcon1);

            // Null tag means the view has the correct data
            holder.icon.setTag(null);
        } else {
            holder.icon.setImageBitmap(mIcon2);

            // Non-null tag means the view still needs to load it's data
            holder.icon.setTag(this);
        }
        holder.text.setText(DATA[position]);

        // Bind the data efficiently with the holder.
        // holder.text.setText(DATA[position]);

        return convertView;
    }

    static class ViewHolder {
        TextView text;
        ImageView icon;
    }
}

private Bitmap mIcon1;
private Bitmap mIcon2;
@Override
public void onCreate(Bundle savedInstanceState) {
    mIcon1 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_1);
    mIcon2 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_2);
    super.onCreate(savedInstanceState);
    setListAdapter(new EfficientAdapter(this));
    getListView().setOnScrollListener(this);
}

public void onScroll(AbsListView view, int firstVisibleItem,
        int visibleItemCount, int totalItemCount) {
}

public void onScrollStateChanged(AbsListView view, int scrollState) {
    switch (scrollState) {
    case OnScrollListener.SCROLL_STATE_IDLE:
        mBusy = false;

        int first = view.getFirstVisiblePosition();
        int count = view.getChildCount();
        for (int i = 0; i < count; i++) {

            holder.icon = (ImageView) view.getChildAt(i).findViewById(
                    R.id.icon);
            if (holder.icon.getTag() != null) {
                holder.icon.setImageBitmap(mIcon1);
                holder.icon.setTag(null);
            } 
        }

        // mStatus.setText("Idle");
        break;
    case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
        mBusy = true;
        // mStatus.setText("Touch scroll");
        break;
    case OnScrollListener.SCROLL_STATE_FLING:
        mBusy = true;
        // mStatus.setText("Fling");
        break;
    }
}
private static final String[] DATA = { "Abbaye de Belloc",
        "Abbaye du Mont des Cats", "Abertam", "Abondance", "Ackawi",
        "Acorn", "Adelost", "Affidelice au Chablis", "Afuega'l Pitu"};
}

It Works fine now. But when the scrolling state its not reloading the image properly. some interval of items not shows the images2. that is the correct order of the images are loading. But not in all items of list. Mismatches happening between solid item intervals. how to correct it?

A: 

As far as I can see, the static ViewHolder isn't helping anything. Try putting the entire onScrollStateChanged function between /* and */, removing the static ViewHolder line, and changing holder = new ViewHolder(); to ViewHolder holder = new ViewHolder();.

Ben L.
"Try putting the entire onScrollStateChanged function between /* and */". its does not make a sense. then how can we trace the state of scroll to load the particular rows at visible.
Praveen Chandrasekaran
They get loaded in the adapter's getView function.
Ben L.
+2  A: 

Praveen -

As you already found my blog post on this, I just wanted to push it back to Stackoverflow so that others can use it.

Here's the basic discussion: http://ballardhack.wordpress.com/2010/04/05/loading-remote-images-in-a-listview-on-android/

And there's a class I documented later that uses a thread and a callback to load the images:

http://ballardhack.wordpress.com/2010/04/10/loading-images-over-http-on-a-separate-thread-on-android/

Update: To address your specific exception, I think that view returned in the list from getChildAt is not an ImageView -- it's whatever layout view you are using to hold the image and text.

jwadsack
Do you know how to get that image view object? I saw and used your code. But that not loading images properly. One or two images not completed to losd. And gets the Outofmemory exception too. why? May you?
Praveen Chandrasekaran
You'll need to trace through your view hierarchy. Calling getChildAt(index) on a ListView returns the list view item (a Layout view) for the index from the top of the visible list. On that view object you can call findViewById to get the image view.
jwadsack
Thanks it works. but not properly i edited my code in my question. if you find something wrong in it. please make a note.
Praveen Chandrasekaran
A: 

Ah, check your logcat to make sure your app isn't being killed and restarted. Most handsets limit your total application size to 16mb or 24mb. It's easy to load up a bunch of images, run over, get killed, restart, and have your onPause not load big data off screen. It's poor man's garabage collection.

Charles Merriam
i edited my question. please look on it.
Praveen Chandrasekaran
+1  A: 

As far as I understand you need to update your list after scrolling is finished. That's easy. Here's the fixed code for you:

EfficientAdapter adapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    mIcon1 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_1);
    mIcon2 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_2);
    super.onCreate(savedInstanceState);
    adapter=new EfficientAdapter(this);
    setListAdapter(adapter);
    getListView().setOnScrollListener(this);
}

public void onScroll(AbsListView view, int firstVisibleItem,
    int visibleItemCount, int totalItemCount) {
}

public void onScrollStateChanged(AbsListView view, int scrollState) {
    switch (scrollState) {
    case OnScrollListener.SCROLL_STATE_IDLE:
        mBusy = false;
        adapter.notifyDataSetChanged() 
        break;
    case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
        mBusy = true;
        // mStatus.setText("Touch scroll");
        break;
    case OnScrollListener.SCROLL_STATE_FLING:
        mBusy = true;
        // mStatus.setText("Fling");
        break;
    }
}

notifyDataSetChanged will tell the adapter to re-display all visible items, so they'll be displayed with image2.

Fedor
A: 

I got it. This is the Perfect code I Want. Lazy Loading works to custom adapter just visible list item's icons. Hope It helps to the beginners

public class List14 extends ListActivity implements ListView.OnScrollListener {
// private TextView mStatus;

private static boolean mBusy = false;
static ViewHolder holder;

public static class EfficientAdapter extends BaseAdapter {
    private LayoutInflater mInflater;
    private Bitmap mIcon1;
    private Bitmap mIcon2;
    private Context mContext;

    public EfficientAdapter(Context context) {
        // Cache the LayoutInflate to avoid asking for a new one each time.
        mInflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        mContext = context;
        // Icons bound to the rows.
        mIcon1 = BitmapFactory.decodeResource(context.getResources(),
                R.drawable.icon48x48_1);
        mIcon2 = BitmapFactory.decodeResource(context.getResources(),
                R.drawable.icon48x48_2);
    }

    /**
     * The number of items in the list is determined by the number of
     * speeches in our array.
     * 
     * @see android.widget.ListAdapter#getCount()
     */
    public int getCount() {
        return DATA.length;
    }

    /**
     * Since the data comes from an array, just returning the index is
     * sufficent to get at the data. If we were using a more complex data
     * structure, we would return whatever object represents one row in the
     * list.
     * 
     * @see android.widget.ListAdapter#getItem(int)
     */
    public Object getItem(int position) {
        return position;
    }

    /**
     * Use the array index as a unique id.
     * 
     * @see android.widget.ListAdapter#getItemId(int)
     */
    public long getItemId(int position) {
        return position;
    }

    /**
     * Make a view to hold each row.
     * 
     * @see android.widget.ListAdapter#getView(int, android.view.View,
     *      android.view.ViewGroup)
     */
    public View getView(int position, View convertView, ViewGroup parent) {
        // A ViewHolder keeps references to children views to avoid
        // unneccessary calls
        // to findViewById() on each row.

        // When convertView is not null, we can reuse it directly, there is
        // no need
        // to reinflate it. We only inflate a new View when the convertView
        // supplied
        // by ListView is null.
        if (convertView == null) {
            convertView = mInflater.inflate(R.layout.list_item_icon_text,
                    parent, false);

            // Creates a ViewHolder and store references to the two children
            // views
            // we want to bind data to.
            holder = new ViewHolder();
            holder.text = (TextView) convertView.findViewById(R.id.text);
            holder.icon = (ImageView) convertView.findViewById(R.id.icon);
            // holder.icon.setTag(holder);
            // convertView.setTag(holder.icon);
        } else {
            // Get the ViewHolder back to get fast access to the TextView
            // and the ImageView.
              holder.text = (TextView) convertView.findViewById(R.id.text);
             holder.icon = (ImageView)
             convertView.findViewById(R.id.icon);
            // holder = (ViewHolder) convertView.getTag();
        }

        if (!mBusy) {

            holder.icon.setImageBitmap(mIcon1);

            // Null tag means the view has the correct data
            holder.icon.setTag(null);

        } else {
            holder.icon.setImageBitmap(mIcon2);

            // Non-null tag means the view still needs to load it's data
            holder.icon.setTag(this);
        }
        holder.text.setText(DATA[position]);

        // Bind the data efficiently with the holder.
        // holder.text.setText(DATA[position]);

        return convertView;
    }

    static class ViewHolder {
        TextView text;
        ImageView icon;
    }
}

private Bitmap mIcon1;
private Bitmap mIcon2;

@Override
public void onCreate(Bundle savedInstanceState) {
    mIcon1 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_1);
    mIcon2 = BitmapFactory.decodeResource(this.getResources(),
            R.drawable.icon48x48_2);
    super.onCreate(savedInstanceState);
    setListAdapter(new EfficientAdapter(this));
    getListView().setOnScrollListener(this);
}

public void onScroll(AbsListView view, int firstVisibleItem,
        int visibleItemCount, int totalItemCount) {
}

public void onScrollStateChanged(AbsListView view, int scrollState) {
    switch (scrollState) {
    case OnScrollListener.SCROLL_STATE_IDLE:
        mBusy = false;

        int first = view.getFirstVisiblePosition();
        int count = view.getChildCount();

        for (int i = 0; i < count; i++) {

            holder.icon = (ImageView) view.getChildAt(i).findViewById(
                    R.id.icon);
            if (holder.icon.getTag() != null) {
                holder.icon.setImageBitmap(IMAGE[first+i]);// this is the image url array.
                holder.icon.setTag(null);
            }
        }

        // mStatus.setText("Idle");
        break;
    case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
        mBusy = true;
        // mStatus.setText("Touch scroll");
        break;
    case OnScrollListener.SCROLL_STATE_FLING:
        mBusy = true;
        // mStatus.setText("Fling");
        break;
    }
}

private static final String[] DATA = { "Abbaye de Belloc",
        "Abbaye du Mont des Cats", "Abertam", "Abondance", "Ackawi",
        "Acorn", "Adelost", "Affidelice au Chablis", "Afuega'l Pitu",
        "Yarra Valley Pyramid", "Yorkshire Blue", "Zamorano",
        "Zanetti Grana Padano", "Zanetti Parmigiano Reggiano" };

}

Praveen Chandrasekaran
A: 

i am pretty new to android can u plz upload the main.xml file code for the above java code

i don't know where i need to add the icon ids in main.xml file.....so plz help me in.....

bhavani