" So you'd only want to use WeakReference when you think your activity
might run out of memory?"
Not exactly. If you use poor programming techniques just about any
long-running operation can run out of memory. WeakReference is an aid
to keep you from having to use much more complex techniques (like
reference chains) while still having "good" programming practices.
On Jul 22, 1:36 pm, GodsMoon <godsm...@gmail.com> wrote:
> 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 Shellabargerwww.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}