Best practis for handling bitmaps in android with mono droid / xamarin.android

问题

I am having some memory issues with our android app when handling bitmaps (duh!).

We are having multiple activities loading images from a server, this could be a background image for the activity. This background image could be the same for multiple activities, and right now each activity is loading its own background image. This means if the flow is ac1->ac2->ac3->ac4 the same image will be loaded 4 times and using 4x memory.

How do I optimize imagehandling for this scenario? Do I create an image cache where the image is stored and then each activity ask the cache first for images. If this is the case, how do I know when to garbage collect the image from the cache?

Any suggestions, link to good tutorials or similar is highly appreciated.

Regards

EDIT: When downloading images for the device the exact sizes is used, meaning that if the ui element needs an 100x100 pixel image it gets that size and therefore no need for scaling. So i am not sure about downscaling the image when loading it into the memory. Maybe it is needed to unload images in the activity when moving on the the next and then reload when going back.

回答1:

One thing you might want to try is scaling down your bitmaps (make a thumbnail) to a size that is more appropriate to your device. It's pretty easy to quickly use up all the RAM on an Android device with a bitmap if you don't scale it down. This recipe shows how to do so on the fly. You could adapt this to save the images to disk.

You could also create your own implementation of the LRUCache to cache the images for your app.

回答2:

After ready your update I will give you an other tip then. I can still post the patch too if people want that..

What you need to do with those bitmaps is call them with a using block. That way Android will unload the bitmap as soon as that block is executed.

Example:

using(Bitmap usedBitmap = new Bitmap()){
     //Do stuff with the Bitmap here
     //You can call usedBitmap.Dispose() but it's not really needed
}

With this code your app shouldn't keep all the used bitmaps in memory.

来源：https://stackoverflow.com/questions/17319361/best-practis-for-handling-bitmaps-in-android-with-mono-droid-xamarin-android