So you'd only want to use WeakReference when you think your activity
might run out of memory?
But a list view already does efficient memory management for you
right?
You'd saying if I were create a large array or something like that
then it would be good to use WeakReference. right?
Thanks for the help guys,
David Shellabarger
www.nightshadelabs.com
On Jul 22, 2:26 pm, Romain Guy <romain...@android.com> wrote:
> You definitely do NOT want to use a WeakReference to cache object. If
> you do so, as soon as your data is put in the cache and not used
> outside of the cache, it gets garbage collected.
>
>
>
>
>
> On Thu, Jul 22, 2010 at 11:07 AM, Joseph Earl <joseph.w.e...@gmail.com> wrote:
> > Suppose you had a long list of images. As the user scrolled down you
> > load the images from the net, and then display them.
> > To avoid having to reload the images again if the user scrolls back
> > up, you put the images in a cache (probably something like a
> > Map<String, Drawable>)
>
> > However because it is a long list you don't want to run into an out of
> > memory situation if the user scrolls very far down and lots of images
> > are put in the cache.
> > So instead of storing the Drawables directly in the map, you create a
> > Map<String, WeakReference<Type>> (although I would use SoftReference
> > for the purpose described here).
> > This means that if Android is going to encounter an out of memory
> > situation it will clear all of the Soft/Weak references (and thus
> > hopefully avoid running out of memory). You will have to load the
> > images again since your cache has been cleared, but this is far better
> > than your application running out of memory and crashing.
>
> > So you do something like:
>
> > // caching an image
> > Map<String, SoftReference> cache = new HashMap<String,
> > SoftReference<Drawable>>();
> > cache.put("http://mysite.com/images/1.jpg";, new
> > SoftReference<Drawable>.put(myDrawable));
>
> > // retrieve an image
> > if (cache.containsKey(url)) {
> > // looks like we have this image cached
> > Drawable drawable = cache.get(url).get();
> > if (drawable == null) {
> > // the softreference has been cleared by the GC, reload the
> > image
> > } else {
> > // softreference is still valid, got our image
> > }
> > }
>
> > Essentially a weak reference is a weaker reference than a soft
> > reference - the GC should free weak references to regain memory before
> > soft references.
>
> > I think that's (mostly) correct, hope it helps.
>
> > On Jul 22, 6:48 pm, GodsMoon <godsm...@gmail.com> wrote:
> >> Google just posted a new blog post
> >> onhttp://android-developers.blogspot.com/2010/07/multithreading-for-per....
> >> I understand the AsyncTask and I'm even using one in a list with
> >> images already.
>
> >> But I don't understand what a WeakReference is. I gather is is a
> >> garbage collector directive, but I thought I didn't need to manage
> >> garbage collection on Android.
>
> >>http://developer.android.com/reference/java/lang/ref/WeakReference.html
> >> isn't as helpful as I was hoping it would be.
>
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> --
> Romain Guy
> Android framework engineer
> romain...@android.com
>
> Note: please don't send private questions to me, as I don't have time
> to provide private support. All such questions should be posted on
> public forums, where I and others can see and answer them
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![http://mysite.com/images/1.jpg"](http://mysite.com/images/1.jpg"){kind=link}