Not loading an image from sd everytime (use WeakReference?)

问题

I have this list of people and each person has an avatar. There's a default avatar for everyone and later you can change it (the app saves the resized and circle-cropped image to the sd).

Here's my approach:

 <ImageView
        android:id="@+id/photo_list_item"
        android:layout_width="70dip"
        android:layout_height="70dip"
        android:layout_marginRight="16dip"
        android:contentDescription="@string/avatar_descp"
        android:src="@drawable/defavatar" >
    </ImageView>

This is part of the item that forms the list. defavataris the default avatar I already talked about. Then:

String m = person.getAvatar();
    if(!m.equals(""))
    {
        loadBitmap("file://"+m, avatar);
    }

getAvatar()gets the path of the avatar of the db. If not null:

public void loadBitmap(String resId, ImageView imageView)
{
    BitmapWorkerTask task = new BitmapWorkerTask(imageView);
    task.execute(resId);
}

class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap>
{
    private final WeakReference<ImageView> imageViewReference;

    public BitmapWorkerTask(ImageView imageView)
    {
        // Use a WeakReference to ensure the ImageView can be garbage collected
        imageViewReference = new WeakReference<ImageView>(imageView);
    }

    // Decode image in background.
    @Override
    protected Bitmap doInBackground(String... params)
    {
        return decodeSampledBitmapFromResource(getContext(), Uri.parse(params[0]), 320, 320);
    }

    // Once complete, see if ImageView is still around and set bitmap.
    @Override
    protected void onPostExecute(Bitmap bitmap)
    {
        if (imageViewReference != null && bitmap != null)
        {
            final ImageView imageView = imageViewReference.get();
            if (imageView != null)
            {
                imageView.setImageBitmap(bitmap);
            }
        }
    }
}

This code is copied mostly from the official Android Dev Guides.

My problem is this: Everytime the image is loaded, again and again (and also I see first the default avatar and some ms later the new avatar instead, and this is not very nice).

I'm guessing that I can use the WeakReference (which is a cache of the image, right?) that holds in the memory until a memory leak. Am I right? What can I do?

回答1:

Do not use WeakReference. Use an LruCache instead. Android's garbage collector is very aggressive and weak references to memory-intensive images would be cleared by the garbage collector very quickly. From Google:

In the past, a popular memory cache implementation was a SoftReference or WeakReference bitmap cache, however this is not recommended. Starting from Android 2.3 (API Level 9) the garbage collector is more aggressive with collecting soft/weak references which makes them fairly ineffective.

For help on using LruCache, see this link: Caching Bitmaps.

Also, as @Sainath suggested, use a third-party image loading library instead. There is a lot to consider when handling image loading in Android, so it's best to use a library that already takes all those factors into consideration.

回答2:

Ya this is good to see from android developer site, but you should use a third party library; image loading is very costly operation which will depend on many factors

I had used Picasso library in many applications, which is very good at performance as well as memory consumption.

You can find it from http://square.github.io/picasso/

来源：https://stackoverflow.com/questions/23522560/not-loading-an-image-from-sd-everytime-use-weakreference

标签

android

bitmap

weak-references