objective c - Ask permission to access Camera Roll

Question

I have a settings view where the user can choose switch on or off the feature 'Export to Camera Roll'

When the user switches it on for the first time (and not when he takes the first picture), I would like the app to ask him the permission to access the camera roll.

I've seen behavior in many app but can't find the way to do it.

Answer 1

I'm not sure if there is some build in method for this, but an easy way would be to use ALAssetsLibrary to pull some meaningless bit of information from the photo library when you turn the feature on. Then you can simply nullify what ever info you pulled, and you will have prompted the user for access to their photos.

The following code for example does nothing more than get the number of photos in the camera roll, but will be enough to trigger the permission prompt.

#import <AssetsLibrary/AssetsLibrary.h>

ALAssetsLibrary *lib = [[ALAssetsLibrary alloc] init];
[lib enumerateGroupsWithTypes:ALAssetsGroupSavedPhotos usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
    NSLog(@"%zd", [group numberOfAssets]);
} failureBlock:^(NSError *error) {
    if (error.code == ALAssetsLibraryAccessUserDeniedError) {
        NSLog(@"user denied access, code: %zd", error.code);
    } else {
        NSLog(@"Other error code: %zd", error.code);
    }
}];

EDIT: Just stumbled across this, below is how you can check the authorization status of your applications access to photo albums.

ALAuthorizationStatus status = [ALAssetsLibrary authorizationStatus];

if (status != ALAuthorizationStatusAuthorized) {
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Attention" message:@"Please give this app permission to access your photo library in your settings app!" delegate:nil cancelButtonTitle:@"Close" otherButtonTitles:nil, nil];
    [alert show];
}