Question

I’m very new to programming, and I jumped right into a project (I know thats not the smartest thing to do, but I’m learning as I go). The app that I’m writing has 10 UIImageViews that display a picture from the users camera roll. The code I’m using needs each of the UIImageViews to have tags. I’m currently using NSData to save the array images, and it works great, but I can’t use this method anymore because NSData doesn’t support the use of tags. I also can’t use NSUserDefaults, because I can’t save images to a plist. Here is how I’m attempting to do this (using the NSData method, which works but I have to edit this so that my tags work.)

This is my current code:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)img editingInfo:(NSDictionary *)editInfo {
    if (imageView.image == nil) {
        imageView.image = img;

        [self.array addObject:imageView.image];

        [picker dismissModalViewControllerAnimated:YES];
        [self.popover dismissPopoverAnimated:YES];
        return;

    }

    if (imageView2.image == nil) {
        imageView2.image = img;
        NSLog(@"The image is a %@", imageView);
        [self.array addObject:imageView2.image];

        [picker dismissModalViewControllerAnimated:YES];
        [self.popover dismissPopoverAnimated:YES];
        return;
    }
    ...


- (void)applicationDidEnterBackground:(UIApplication*)application {
    NSLog(@"Image on didenterbackground: %@", imageView);

    [self.array addObject:imageView.image];
    [self.array addObject:imageView2.image];

    [self.user setObject:self.array forKey:@"images"];
    [user synchronize];

}

- (void)viewDidLoad
{
    self.user = [NSUserDefaults standardUserDefaults];
    NSLog(@"It is %@", self.user);
    self.array = [[self.user objectForKey:@"images"]mutableCopy];
    imageView.image = [[self.array objectAtIndex:0] copy];
    imageView2.image = [[self.array objectAtIndex:1] copy];    

    UIApplication *app = [UIApplication sharedApplication];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationDidEnterBackground:)
                                                 name:UIApplicationDidEnterBackgroundNotification
                                               object:app];

    [super viewDidLoad];

}

Any help or suggestions on how to edit this code so that I can save the images, while using tags is much appreciated, thanks!

EDIT: Here is my updated code:

       -(IBAction)saveButtonPressed:(id)sender {
    NSString *docsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask,YES) objectAtIndex:0];

    for (UIImageView *imageView in self.array) {

        NSInteger tag = self.imageView.tag;
        UIImage *image = self.imageView.image;
        NSString *imageName = [NSString stringWithFormat:@"Image%i.png",tag];

        NSString *imagePath = [docsDir stringByAppendingPathComponent:imageName];
        [UIImagePNGRepresentation(image) writeToFile:imagePath atomically:YES];
    }
NSLog(@"Saved Button Pressed");
}



- (void)applicationDidEnterBackground:(UIApplication*)application {

}


-(void)viewDidLoad {

    NSString *docsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES) objectAtIndex:0];

    NSArray *docFiles = [[NSFileManager defaultManager]contentsOfDirectoryAtPath:docsDir error:NULL];

    for (NSString *fileName in docFiles) {

        if ([fileName hasSuffix:@".png"]) {
            NSString *fullPath = [docsDir stringByAppendingPathComponent:fileName];
            UIImage *loadedImage = [UIImage imageWithContentsOfFile:fullPath];

            if (!imageView.image) {
                imageView.image = loadedImage;
            } else {
                imageView2.image = loadedImage;
            }
        }
    }
}

Answer 1

You need to use “Fast Enumeration” to parse the array’s objects, and write each object to disk sequentially. First, you’re going to need to add the UIImageView objects to the array instead of the UIImage property of the UIImageView, so you can recover the tag. So instead of writing

[self.array addObject:imageView.image];

It will be

[self.array addObject:imageView];

Try to follow along with my code. I inserted comments on each line to help.

-(void)applicationDidEnterBackground:(UIApplication *)application {
    //Obtain the documents directory
    NSString *docsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainmask,YES) objectAtIndex:0];
    //begin fast enumeration
    //this is special to ObjC: it will iterate over any array one object at a time
    //it's easier than using for (i=0;i<array.count;i++)
    for (UIImageView *imageView in self.array) {
        //get the imageView's tag to append to the filename
        NSInteger tag = imageView.tag;
        //get the image from the imageView;
        UIImage *image = imageView.image;
        //create a filename, in this case "ImageTAGNUM.png"
        NSString *imageName = [NSString stringWithFormat:@"Image%i.png",tag];
        //concatenate the docsDirectory and the filename
        NSString *imagePath = [docsDir stringByAppendingPathComponent:imageName];
        [UIImagePNGRepresentation(image) writeToFile:imagePath atomically:YES];
    }
}

To load the images from disk, you’ll have to look at your viewDidLoad method

-(void)viewDidLoad {
    //get the contents of the docs directory
    NSString *docsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainmask,YES) objectAtIndex:0];
    //Get the list of files from the file manager
    NSArray *docFiles = [[NSFileManager defaultManager]contentsOfDirectoryAtPath:docsDir error:NULL]);
    //use fast enumeration to iterate the list of files searching for .png extensions and load those
    for (NSString *fileName in docFiles) {
        //check to see if the file is a .png file
        if ([fileName hasSuffix:@".png"]) {
            NSString *fullPath = [docsDir stringByAppendingPathComponent:fileName];
            UIImage *loadedImage = [UIImage imageWithContentsOfFile:fullPath];
            //you'll have to sort out how to put these images in their proper place
            if (!imageView1.image) {
                imageView1.image = loadedImage;
            } else {
                imageView2.image = loadedImage;
            }
        }
    }
}

Hope this helps

One thing you need to be aware of is that when an app enters the background it has about 5 seconds to clean up its act before it’s suspended. The UIPNGRepresentation() function takes a significant amount of time and is not instantaneous. You should be aware of this. It would probably be better to write some of this code in other places and do it earlier than at app backgrounding. FWIW