Develop Reference

How to check if a Bitmap is empty (blank) on Android

How can I check if a Bitmap object is completely blank, i.e. all its pixels are transparent, without a x-y loop on every pixel?

You can check your Bitmap instance (in the example myBitmap) against an empty one with:
Bitmap emptyBitmap = Bitmap.createBitmap(myBitmap.getWidth(), myBitmap.getHeight(), myBitmap.getConfig());
if (myBitmap.sameAs(emptyBitmap)) {
// myBitmap is empty/blank
}

You can do this very easy but it depends on the application.
If you have an application that prompts the user for a drawing input, like signature or anything similar, you will usually have an ArrayList of Paths which are drawn to the Canvas of that View. You can do a check when you want to return the BitMap look to see if the ArrayList of Paths is bigger than 0 and return the BitMap if so, or else return null.

Decoding Bitmap to ImageView without caching, preventing memory leaks

So I've read all tutorials about Bitmap on http://developer.android.com/training/displaying-bitmaps/index.html and it seems they manage them caching with classes at a very specific level. I also know there are libraries like Universal Image Loader that takes care of that for you.
But let's go simple, what if I just want to decode a single Bitmap from a file and place it on an ImageView. As far as I know, to prevent memory leaks you're not supposed to keep a reference to a Bitmap so how can this be achieved. Suppose the bitmap's file path is stored in the following string: imagePath.

Its ok to hold a reference to the Bitmap object provided that you clean up once the Bitmap is no longer needed (e.g. when the activity is destroyed).
To ensure that you do not have any Bitmap-related leaks leaks:
imageView.setImageBitmap(null);
bitmap.recycle(); // frees the Bitmap instance
bitmap = null;

Bitmap bitmap = BitmapFactory.decodeFile(file.getAbsolutePath()); //File file
iv.setImageBitmap(bitmap); // ImageView iv

Android. OutOfMemory problems

I require displaying many images in my application. These being jpgs and pngs and i'm loading them inside ImageViews like so:
tile.setImageResource(R.drawable.tile_highlight);
I am currently having OutOfMemory problems (java.lang.OutOfMemoryError: bitmap size exceeds VM budget)
I've searched and found some other posts, they all suggest that you should recycle the bitmap of an ImageView manually, like so: ((BitmapDrawable)imageView.getDrawable()).getBitmap().recycle(); which will dump it from memory.
BUT in my case, being that i'm not using setBitmap() to load the images onto the ImageView objects, when i try and run the above code, it returns NullPointerException, more precisely, the method getBitmap() returns null, there is no bitmap ?!?!
Do i need to go back in my code and change the way i load all the images in the ImageViews, and then try with the recycle() method? Or how can i free up the memory so it doesn't crash anymore?
EDIT
I've tried something like so: imageView.setImageResource(-1); in hopes it will remove the image from memory and replace it with ... null or something, but it seems it doesn't help the cause.

It would be helpful if you could post some of your code. Specifically, how you're setting the images of the ImageView objects. If you're not using bitmaps, I would expect that getBitmap() will return null. However, if you're using another sort of Drawable or otherwise to set the image, there's likely a similar route to take that doesn't involve bitmaps.
EDIT:
Alright, give this a shot. You can create a Bitmap from a resource like this:
Bitmap bm = BitmapFactory.decodeResource(getResources(), R.drawable.image);
Then, use the bitmap like this, considering img is your ImageView:
img.setImageBitmap(bm);
//Do some stuff with it, then when memory gets low:
((BitmapDrawable)img.getDrawable()).getBitmap().recycle();
Of course, this is considering that you're in an activity. If not, you'll have to get a handle on the context and replace getResources() with context.getResources().

If you want to set an image from drawable to ImageView, Do not use ImageView.setImageResource(int resId) directly with drawable id. Instead get Scaled down bitmap(if applicable) and set it to imageView. like this:
this works for me.
iv.setImageBitmap(decodeResource(getResources(), R.drawable.big_image));
private static Bitmap decodeResource(Resources res, int id) {
Bitmap bitmap = null;
BitmapFactory.Options options = new BitmapFactory.Options();
for (options.inSampleSize = 1; options.inSampleSize <= 32; options.inSampleSize++) {
try {
bitmap = BitmapFactory.decodeResource(res, id, options);
Log.d(TAG_LOG, "Decoded successfully for sampleSize " + options.inSampleSize);
break;
} catch (OutOfMemoryError outOfMemoryError) {
// If an OutOfMemoryError occurred, we continue with for loop and next inSampleSize value
Log.e(TAG_LOG, "outOfMemoryError while reading file for sampleSize " + options.inSampleSize
+ " retrying with higher value");
}
}
return bitmap;
}
source: https://codingjunkiesforum.wordpress.com/2014/06/12/outofmemory-due-to-large-bitmap-handling-in-android/

try
((BitmapDrawable)im.getBackground()).getBitmap().recycle();

I think you should display images with lower resolution. This would resolve the OOM problem. You can also read Android Developer Guideline link

OutOfMemory error comes when you dont free bitmap once its being used(may be large size) so to prevent this we should keep in mind of re-sizing,taking weakreferences etc.
but there are good libraries available which is taking care all problem one of them is Picasso. please have a look at-
loading images using Picasso

Android: "trying to use a recycled bitmap" error with temporary Bitmaps

My app can load quite large images. In an effort to be memory-conservative, I'm attempting to use a temporary bitmap to load and another for the final image after transformation:
.....
finalBitmap.recycle();
finalBitmap = null;
Bitmap tempBitmap = BitmapFactory.decodeStream(fin, ...);
finalBitmap = Bitmap.createBitmap(tempBitmap, ....);
imgview.setImageBitmap(finalBitmap);
.....
Now, at this point we're done with tempBitmap, which was only needed to transport the decoded Bitmap to the transformation step in createBitmap. So:
.....
tempBitmap.recycle();
tempBitmap = null;
.....
And... it crashes with a "trying to use a recycled bitmap" error specifically because of the recycling of tempBitmap. tempBitmap wasn't displayed and is only used right there.
What's going wrong here? Should I just use "finalBitmap" throughout and rely on createBitmap to manage it (finalBitmap = Bitmap.createBitmap(finalBitmap , ....))? I fail to see what ongoing dependency on tempBitmap there would be that would cause such a failure.
Edit: Yes, the null assignment seems to result in the appropriate, eventual garbage collection, but I'm mystified as to why recycle() on a temp Bitmap is so problematic in this case. I get the impression that createBitmap() is holding a reference to it but why, and for how long?

Straight from the Android documentation:
Returns an immutable bitmap from the specified subset of the source
bitmap. The new bitmap may be the same object as source, or a copy may
have been made.
It seems that the createBitmap functions have the potential to re-use the bitmap that you provided. If that is the case, then you shouldn't recycle the temporary bitmap since your final bitmap is using it. One thing you can do is
if(tempBitmap != finalBitmap) {
tempBitmap.recycle();
}
That should only recycle the tempBitmap when it isn't the same as the finalBitmap. At least that seems to be what the documentation is implying.

IllegalStateException while adding bitmap to Canvas

I was trying to set a bitmap image to a canvas using setBitMap ,at that time I got an IllegalStateException.This canvas have some images on it currently, I am trying to replace it.
Any one have any idea why this happened?
Code Snippet
editBm = Bitmap.createBitmap(951, 552, Bitmap.Config.ARGB_8888);
Canvas mCanvas=new Canvas(editBm);
eBit=LoadBMPsdcard(filePath); ---->returns a bitmap when the file path to the file is provided
Log.i("BM size", editBm.getWidth()+"");
mCanvas.setBitmap(eBit);
I am not getting any NullPointer errors and the method LoadBMPsdcard() is working good.
Please let me know about any ideas you have ...
Thanks in advance
Happy Coding

IllegalStateException could be thrown because you're loading a Bitmap (eBit) and use mCanvas.setBitmap(eBit) without checking if the bitmap is mutable. This is requiered to draw on the Bitmap. To make sure your Bitmap is mutable use:
eBit=LoadBMPsdcard(filePath);
Bitmap bitmap = eBit.copy(Bitmap.Config.ARGB_8888, true);
canvas.setBitmap(bitmap);

Try to use drawBitmap instead of the setBitmap. It looks like you've already set a bitmap to draw into by passing it to the canvas constructor, so now you just need to draw everything onto it.

Canvas.setBitmap() throws IllegalStateException if and only if Bitmap.isMutable() returns true. Bitmap.createBitmap() builds an immutable Bitmap instance only, in all of its forms. To create a mutable bitmap you either use new Bitmap(), or Bitmap.copy(true), depending on whether you have a source bitmap that you want to start with. A typical block for me looks like:
Bitmap image = ...
Canvas c = new Canvas(image.isMutable()?image:image.copy(true));
...
This assumes, of course, that you don't mind clobbering the source Bitmap (which I generally don't but that's by no means universal).