Android: Caching images for imageView

Question

I'm writing an android app which calls codeline B many times.

Therefore I would like to cache the image 'image123' somewhere for performance reasons / making the app faster and only want to load it once and then just display it from the cache somehow.

Is there a way to achieve this without loading it again and again? Does anybody know ?

Is it important to call invalidate() (codeline C) just to be sure the image is always displayed immediately ? How can I find out when the image is displayed in the imageView exactly ?

Thanks for your help in advance.

// codeline A
ImageView imageView = (ImageView) this.findViewById(R.id.imageView);
// codeline B
imageView.setImageResource(R.mipmap.image123);
// codeline C
imageView.invalidate();

Answer 1

Is there a way to achieve this without loading it again and again?

There is an official tutorial for that: https://developer.android.com/training/displaying-bitmaps/cache-bitmap.html

Is it important to call invalidate() (codeline C) just to be sure the image is always displayed immediately ?

No, just setting a new image resource will automatically lead to a redraw.

How can I find out when the image is displayed in the imageView exactly ?

Use View.post to run code as soon as drawing is finished.