Question

Hi I am implementing a ‘save image to library’ feature as seen in the code snippet below. Basically, the photo saving is triggered when a user touches an image on the page.

TouchImageView *tiv = [[TouchImageView  alloc]initWithFrame:blockFrame];
        [tiv setCompletionHandler:^(NSString *imageUrl){
            //Spinner should start after user clicks on an image
            MBProgressHUD *hud = [MBProgressHUD showHUDAddedTo:self.navigationController.view animated:YES];
            hud.labelText = @"Saving photo to library";

            //trigger method to save image to library
            [self saveImageToLibrary];

        }];


-(void) saveImageToLibrary
{
    //convert url to uiimage
    UIImage *selectedImage = [UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:imageURL]]]; 

    //Save image to album
    ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];  
    // Request to save the image to camera roll  
    [library writeImageToSavedPhotosAlbum:[selectedImage CGImage] orientation:(ALAssetOrientation)[selectedImage imageOrientation] completionBlock:^(NSURL *assetURL, NSError *error){  

        [MBProgressHUD hideHUDForView:self.navigationController.view animated:YES];

        if (error) {  
            NSLog(@"error");  
        } else {  
            NSLog(@"url %@", assetURL);  
            //Trigger get photo from library function
            self.imgPicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
            [self presentModalViewController:self.imgPicker animated:YES];

        }  

    }];  
    [library release];     
}

The issue is that the HUD spinner does not appear (after a lag time of 3-4 seconds), my suspicion is that the ‘writeImageToSavedPhotosAlbum:’ is synchronous and locked the process from displaying the HUD spinner. Is this right? How do I resolve the lag in spinner display?

Answer 1

Yes, that is correct. Replace the call

 [self saveImageToLibrary];

by

[self performSelector:@selector(saveImageToLibrary) withObject:nil afterDelay:0];

so that the HUD gets a chance to show itself before you save.