Question

I am creating an application in which i need to start camera and scan QR code. I am using a class in through which scanner starts. it is fine in iPhone but crashes in iPad.
i am using the code

if(![[appDelegate.tabbarcontroller.viewControllers objectAtIndex:1] isMovingFromParentViewController]) { 
    [[appDelegate.tabbarcontroller.viewControllers objectAtIndex:1] popToRootViewControllerAnimated:NO];
}

Answer 1

Using defensive programming in iOS is a very good strategy to prevent crashes.

About your question, from Apple doc:

To use an image picker controller containing its default controls,
perform these steps:

Verify that the device is capable of picking content from the desired
source. Do this calling the isSourceTypeAvailable: class method,
providing a constant from the “UIImagePickerControllerSourceType”
enum.

Check which media types are available, for the source type
you’re using, by calling the availableMediaTypesForSourceType: class
method. This lets you distinguish between a camera that can be used
for video recording and one that can be used only for still images.

The link iphone-tutorial-better-way-to-check-capabilities-of-ios-devices by Mugunth Kumar provides the info you need to checke against device capabilities.

Hope it helps.