Why doesn't UIImage get successfully decoded? - ios

Question

Why doesn't the UIImage in this code snippet get restored back to its original state when I try to encode and decode it using NSKeyedArchiver?
I expect "decodedImage" to contain the image after decoding, but instead it is just NULL.
// Any image here seems to repro the issue
UIImage *image = [UIImage imageNamed:#"soda.jpg"];
// This prints YES (1), just a sanity check.
NSLog(#"Confirms %d", [[UIImage class] conformsToProtocol:#protocol(NSCoding)]);
NSMutableData *data = [[NSMutableData alloc] init];
NSKeyedArchiver *coder = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
[coder encodeObject:image forKey:#"image"];
[coder finishEncoding];
// I would expect this to be large, instead it's < 1kb.
NSLog(#"Data length is: %zu", (unsigned long)data.length);
NSKeyedUnarchiver *decoder = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
// This prints YES (1)
NSLog(#"containsValueForKey returns %d", [decoder containsValueForKey:#"image"]);
// decodedImage is NULL here, even though containsValueForKey returned YES
UIImage *decodedImage = [decoder decodeObjectForKey:#"image"];
[decoder finishDecoding];
In this case, I'm not looking for a workaround like converting the UIImage to NSData first and encoding that. The reason is that I'm trying to reproduce an unrelated piece of code which uses something like this and I'm trying to understand it.
The code works as expected if I roundtrip the image first through nsdata and back to uiimage, why??
UIImage *originalImage = [UIImage imageNamed:#"soda.jpg"];
NSData *imageData = UIImagePNGRepresentation(originalImage);
UIImage *image = [UIImage imageWithData:imageData];

Answer 1

Check this
Decode Data to image:
+(NSData *)decodeBase64ToImage:(NSString *)strEncodeData
{
NSData *data = [[NSData alloc]initWithBase64EncodedString:strEncodeData options:NSDataBase64DecodingIgnoreUnknownCharacters];
return data;
}
self.btnLicenseFront.image=[UIImage imageWithData:[Themes decodeBase64ToImage:licenseFront]];

Answer 2

I used your code and tried with 2 images:
1. A correct image file
The output is
> [36133:5889153] Confirms 1
> [36133:5889153] Data length is: 68267
> [36133:5889153] containsValueForKey returns 1
> [36133:5889153] decodedImage is 1879681920
2. Incorrect/corrupt image file
The output is
> [36130:5888794] Confirms 1
> [36130:5888794] Data length is: 136
> [36130:5888794] containsValueForKey returns 1
> [36130:5888794] decodedImage is 0
So looks like your source JPG file is corrupt or invalid.

Answer 3

I have found a solution.
It turns out that this only happens the image is loaded through the [UIImage imageNamed:]. If the UIImage is created through[UIImage imageWithContentsOfFile:], the issue does not happen.
I believe this must be a bug on the ios side. The imageNamed: way of creating a UIImage is specifically for images inside the bundle. There must be some optimization they have which causes NSCoder to not function as intended since the UIImage seems to not actually contain the image data (since decoding seems to return nil instead of recreating the UIImage with the image from the bundle as expected).