Object becomes Nil when pushing controller

Question

I have a the first application controller, MAViewControllerMenu, and when that controller loads, I already allocate the next controller, imageControllerView.

- (void)viewDidAppear{
    [super viewDidAppear:(YES)];
    if (!imageControllerView)
        imageControllerView = [[self storyboard] instantiateViewControllerWithIdentifier:@"chosenImageController"];
}

Then, I select an image from the image picker, and want to move to the next controller,imageControllerView, where the image would be displayed. I set the next window's image property as follows:

imageControllerView.image = [[self.pageViews objectAtIndex:(centered_image_ind)] image];

This line works, I checked that there's a value in imageControllerView.image. However, when I move to the next controller,imageControllerView , I notice that the memory address of imageControllerView changes, or in other words, imageControllerView's properties that I change before moving to that controller, specifically image, reset when I move there.

Instead of throwing code here, I was hoping you could let me know what I should provide. I think it's a common problem people know of: Controller's objects re-init'ing when moving from one controller to another.

Here's a screen shot that might give a hint of what Im trying to do

Left most one is where I select pictures which in turn go into the slide show scrollview. Then I click next, and the image is supposed to appear in the centered ImageView

Thanks

Answer 1

OK...

You cannot "already allocate the next view controller" this won't work. There is no point in creating it like this at all. You can delete the imageViewController property (or iVar) completely.

The arrows that you have between the view controllers in your storyboard are segues. In Interface Builder you can select a segue and give it an identifier. For instance you would use something like @"ImageViewSegue".

I guess the segue is attached to the Next button. This is fine.

Now, in your MAViewControllerMenu you need to put this method...

- (void)prepareForSegue:(UIStoryBoardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"ImageViewSegue"]) {
        // the controller is CREATED by the segue.
        // the one you create in view did load is never used
        ImageViewController *controller = segue.destinationController;
        controller.image = [[self.pageViews objectAtIndex:(centered_image_ind)] image];
    }
}

Now for the segues in the other direction...

You appear to be using segues to dismiss the modal views. You can't do this. What it will do is create a new view controller and present that instead of dismissing the presented view.

i.e. you'll go...

A -> B -> C -> B -> A -> B
// you'll now have 6 view controllers in memory
// each segue will create a fresh view controller with no values set.

What you want is...

A -> B -> C
A -> B
A
// now you only have one view controller because the others were dismissed.
// when you dismiss a view controller it will go back to the original one.
// the original one will have all the values you set previously.

To do this you need to create a method something like...

- (IBAction)dismissView
{
    [self dismissViewControllerAnimated:YES completion:nil];
}

Then whatever the button is for your dismiss action attach it to this method.

Now delete all the backwards curly segues.

Passing info back

To pass info back to the original view controller you need a delegation pattern or something similar.

You can read more about creating a delegate at This random Google Search

Create a delegate method something like...

- (void)imageViewSelectedImage:(UIImage *)image;

or something like this.

Now when you do prepareForSegue you can do...

controller.delegate = self;

and have a method...

- (void)imageViewSelectedImage:(UIImage *)image
{
    // save the method that has been sent back into an array or something
}

Answer 2

I might be wrong, but seems you go to your second view controller using a segue, it is normal your controller instance isn't the same than the one retrieved by [[self storyboard] instantiateViewControllerWithIdentifier:@"chosenImageController"]

you should take a look at - (void) prepareForSegue:(UIStoryboardSegue *)segue

(UIViewController method)

inside this method set your image property to the segue destination controller (check the identifier of the segue)