iOS can write or read from image data from disk - ios

Question

I'm trying to load images using the following method.
I first check if I already have the images on the disk, if I do then I will just get the image data from the disk and load it otherwise I will get the image from the server and write to disk so that the second time that I need the image I won't have to access the server.
The problem is it doesn't seem to write or read from the disk. Everytime that I want to load images for the second time it's still reads them from the server and the NSLog(#"disk"); never gets called.
I don't know what I'm doing wrong if anyone has any idea?
-(UIImage *)imageWith:(NSString *)imageName isPreview:(BOOL)preview
{
//imageName is something like "56.jpg"
NSString *mainOrPreview = #"Preview";
if (!preview) {
mainOrPreview = #"Main";
}
NSString *pathSuffix = [[#"Images" stringByAppendingPathComponent:mainOrPreview] stringByAppendingPathComponent:imageName];
NSString *path = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:pathSuffix];
NSData *imageData = [NSData dataWithContentsOfFile:path];
if (imageData) {
NSLog(#"disk");
}
if (!imageData && [self connected]) {
imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[serverURL stringByAppendingPathComponent: pathSuffix]]];
if (imageData) {
[imageData writeToFile:path atomically:YES];
}
NSLog(#"server");
}
return [UIImage imageWithData:imageData];
}

Answer 1

The problem is that the directories don't exist beyond Documents. Therefore the attempts to write the files are failing. It's always a good idea to use the file methods that have the NSError parameters so you can check the result.
You need to update only the code that actually writes the image from the server.
if (!imageData && [self connected]) {
// This needs to be done in on a background thread!
imageData = [NSData dataWithContentsOfURL:[NSURL URLWithString:[serverURL stringByAppendingPathComponent: pathSuffix]]];
if (imageData) {
[[NSFileManager defaultManager] createDirectoryAtPath:[path stringByDeletingLastPathComponent] withIntermediateDirectories:YES attributes:nil error:nil];
[imageData writeToFile:path atomically:YES];
}
NSLog(#"server");
}