How do I make a conditional statement with UIImagePicker for controlling a push segue occurrence?

Question

I'm trying to handle a case where if an image is successfully loaded from the photo library, then DO trigger push segue to another view controller, which is where the image will be displayed in an image view. If no image is loaded, say the cancel button is pressed, then DON'T trigger push segue, and stay on the current (root) view.

This is an app for iPhone.

What I have currently does not work, and sometimes I get this warning when I cycle through the process of accessing the photo library and selecting an image / canceling:

Warning: Attempt to present < selectDisplayViewController: 0x11d45360 > on < UINavigationController: 0x8f58ee0 > while a presentation is in progress!

My code is as follows:

ViewController.m

#import "ViewController.h"
#import "selectDisplayViewController.h"

@interface ViewController ()

@end

@implementation ViewController

- (IBAction)LibraryButton:(id)sender
{
    imagePicker.delegate = self;
    imagePicker.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
    [self presentViewController:imagePicker animated:YES completion:nil];
}
- (void) imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    /*UIImage *loadImage;
    loadImage = [info valueForKey:UIImagePickerControllerOriginalImage];
    buffer = loadImage;*/
    modBuffer = nil;
    modBuffer = [info valueForKey:UIImagePickerControllerOriginalImage];
    [picker dismissViewControllerAnimated:YES completion:nil];
}
- (BOOL)shouldPerformSegueWithIdentifier:(NSString *)identifier sender:(id)sender
{
    CGImageRef cgImRef = [modBuffer CGImage];
    CIImage *cIm = [modBuffer CIImage];
    if(cIm != nil && cgImRef != NULL)
    {
        return true;
        buffer = modBuffer;

    }
    return false;
}
- (void) imagePickerControllerDidCancel:(UIImagePickerController *)picker
{
    [picker dismissViewControllerAnimated:YES completion:nil];
    selectDisplayViewController *secondVC = [[selectDisplayViewController alloc]init];
    [self presentViewController:secondVC animated:YES completion:nil];
}
- (void)viewDidLoad
{
    imagePicker = [[UIImagePickerController alloc]init];

    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController
<UINavigationControllerDelegate,UIImagePickerControllerDelegate>
{
    UIImagePickerController *imagePicker;
    UIImage *modBuffer;
}

- (IBAction)LibraryButton:(id)sender;

@end

selectDisplayViewController.m

#import "selectDisplayViewController.h"

@interface selectDisplayViewController ()

@end

@implementation selectDisplayViewController
@synthesize selectDisplayView;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    selectDisplayView.image = buffer;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

selectDisplayViewController.h

#import <UIKit/UIKit.h>

@interface selectDisplayViewController : UIViewController

@property (strong, nonatomic) IBOutlet UIImageView *selectDisplayView;

@end

UIImage *buffer;

All I can get it to do is load the image. It doesn't go to the display view controller.

I greatly appreciate any help or suggestions.

Answer 1

The problem with your code is right here:

if(cIm != nil && cgImRef != NULL)
{
    return true;
    buffer = modBuffer;

} 

You return true and initiate your segue before you actually set your image. Your code should actually look like this:

   if(cIm != nil && cgImRef != NULL)
{
    buffer = modBuffer;
    return true;

}

Update: In order for your code to work the way you want it to, you are going to need to make make a updates to ViewController.m and SelectDisplayViewController. I will detail them below.

// Add to SelectDisplayViewController.m
// It is in this method that you should set UIImageViews, not viewDidLoad.

- (void)viewWillAppear:(BOOL)animated
{
    [selectDisplayView setImage:buffer];
}

// Add to ViewController.m
// This method is called right before segue, so values for next view should be set here.

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    buffer = modBuffer;
}  

- (void) imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
/*UIImage *loadImage;
 loadImage = [info valueForKey:UIImagePickerControllerOriginalImage];
 buffer = loadImage;*/
 modBuffer = nil;
 modBuffer = [info valueForKey:UIImagePickerControllerOriginalImage];

if (modBuffer) {
    [picker dismissViewControllerAnimated:YES completion:nil];

    // The value firstsegue is how your segue is recognized in code, 
    // it is set in storyboard. The following images attached illustrate this.
    [self performSegueWithIdentifier:@"firstsegue" sender:nil];

} else {
    // Figure out why modBuffer is not true
}

}