在运行时加载图像，具体取决于ImageView的大小

Question

I need to load a scaled down version of an image programmatically at runtime depending on the size of ImageView .

For this I intend to use BitmapFactory as described in http://developer.android.com/training/displaying-bitmaps/load-bitmap.html .

Also I need to load it again if the size has changed, so that if the view would get bigger, image would still remain high quality, and of course if it would get smaller, I would free up some memory.

I could override one of onSizeChanged , onMeasure , onLayout , but I don't know which way would be the most appropriate way, maybe even none of these :).

So what I am asking is for advice when and where should I load my image?

Note: Just a bit of information what I am going to do next, just in case if it affects where and when the image should be loaded. After this I will work on loading image in chunks if it is still to big to load in one shot.

Answer 1

我想你对位图有想法，所以可以使用位图在后台加载图像和线程以供执行，然后在位图中传递图像值。

Answer 2

It looks like incorporating image loading into layout mechanism was not a good idea, because most of the time this results in unnecessary work during layout.

Since I am developing a framework, my subclass of ImageView can be re-sized in various cases, for example:

If orientation change has occurred and ImageView dimensions are relative to device dimensions - it will get re-sized (if I am handling orientation change myself, since by default android recreates whole view hierarchy), but using inSampleSize option when loading with BitmapFactory - usually bitmap size will still be a bit larger, inSampleSize works with powers of two only. So this does not necessarily mean that I will have to reload the bitmap.

If I am setting ImageView dimensions explicitly - I know if I have to reload bitmap or not and I can do both things in one shot.

There are more ifs and each case can have it's own optimizations that will save both - processing power and memory.

Since no correct answer was provided, I hope my solution will by useful to someone else as well.

If You have a better idea how this kind of issue should be handled - please share it here with everyone, so that I and everyone else could improve their knowledge a bit :).