Chapter 10: UIImagePickerControl photolibrary crash

Tom Kamphuis · November 26th, 2010, 09:27 AM

Hi,

I'm new to iPhone development and the help I'm getting through this book helps me a lot. I'm trying to build an application similar to the photo picker/camera as explained in chapter 10 (example 10-5). In order to learn best practices I've used code from the examples to make it work, but the given example doesn't even work when I use the code from the download. When I run the demo application the first time, I get two warnings as soon as I press the "Select Image" button about "Using two-stage rotation animation".
These are warnings, the application just works and shows me the photo album library. But when I click one of these albums, I get a SIGSEGV error and the applications stops running. At the bottom of the console window I get the "Object reference not set to an instance of..." error, and the args array in the Main method is empty.

What's wrong with the example/code? Or is it some version issue? Thanks for the help!

Tom

chrisntr · November 26th, 2010, 10:47 PM

Quote:

Originally Posted by Tom Kamphuis

Hi,

I'm new to iPhone development and the help I'm getting through this book helps me a lot. I'm trying to build an application similar to the photo picker/camera as explained in chapter 10 (example 10-5). In order to learn best practices I've used code from the examples to make it work, but the given example doesn't even work when I use the code from the download. When I run the demo application the first time, I get two warnings as soon as I press the "Select Image" button about "Using two-stage rotation animation".
These are warnings, the application just works and shows me the photo album library. But when I click one of these albums, I get a SIGSEGV error and the applications stops running. At the bottom of the console window I get the "Object reference not set to an instance of..." error, and the args array in the Main method is empty.

What's wrong with the example/code? Or is it some version issue? Thanks for the help!

Tom

Hi Tom,

Since the publishing of the book, the garbage collection of MonoTouch has greatly improved. This unfortunately meant that some of the samples would throw issues like this. The problem is that the UIImagePickerController is getting GC'd whilst the picker is being displayed so when an image is selected, it will crash.

To sort this issue out, all you need to do is move the UIImagePickerController to the class level and use it from there, see the following gist... https://gist.github.com/717504
or the code example below.

Code:

 
                UIImagePickerController picker;
		
		public override void ViewDidLoad ()
		{
			base.ViewDidLoad ();
			
			UIButton button = UIButton.FromType(UIButtonType.RoundedRect);
			button.Frame = new RectangleF(0f, 30f, 320, 40f);
			button.SetTitle("Select Image", UIControlState.Normal);
			button.TouchUpInside += delegate(object sender, EventArgs e) {
			picker = new UIImagePickerController();
				picker.Delegate = new MyImagePickerDelegate(this);
				this.PresentModalViewController(picker, true);
			};
			this.View.AddSubview(button);

		}

Hope this helps,

ChrisNTR

Tom Kamphuis · November 29th, 2010, 03:09 AM

Thanks Chris, that helped a lot. One thing still raises a warning; the using of two-stage rotation animation. Are these warnings showstoppers in distributing an app or should it be resolved (and when it should be resolved: how?).

chrisntr · November 29th, 2010, 08:11 PM

Weird, I'm not seeing that warning on my side, try reading through here and see if that helps - http://stackoverflow.com/questions/2...ckercontroller

Cheers,

ChrisNTR