Code and Compiler Warnings

If the app isn’t working as it should, first compare your code with the code in Code Listings.

The tutorial code should compile without any warnings. If Xcode reports a warning, it’s a good idea to treat the warning in the same way that you treat errors. Objective-C is a very flexible language, and sometimes a warning is the only indication you receive when there is an issue that might cause an error.

Storyboard Items and Connections

When you’re accustomed to fixing all of an app’s problems in code, it’s easy to forget to check the objects in the storyboard. A great advantage of a storyboard is that, because it captures both the appearance and some of the configuration of app objects, you have less coding to do. To benefit from this advantage, it’s important to examine the storyboard, as well as the code, when an app doesn’t behave as you expect. Here are some examples.

A scene does not seem to receive the data you send to it in the prepareForSegue method. Check the segue’s identifier in the Attributes inspector. If you forget to give the segue the same identifier that you use in the prepareForSegue method, you can still transition to the scene during testing, but the scene won’t display the data that you send to it.

The same result occurs when you misspell a segue’s identifier in the prepareForSegue method. Xcode does not warn you when a segue is missing its identifier, or when the prepareForSegue method uses an incorrect identifier, so it’s important to check these values for yourself.

None of your changes to a custom view controller class seem to affect its scene. Check the scene’s class in the Identity inspector. If the name of your custom view controller class is not displayed in the Class pop-up menu, Xcode does not apply your changes to the scene.

Nothing happens when you click the Cancel or Done buttons in the add scene’s navigation bar. Make sure each button is connected to its unwind action. Control-click the button on the canvas or in the document outline and confirm that the connection in the Triggered Segues section is active and correct.

the text fields appear to work, but the data you enter is not displayed in the master list. Make sure the view controller’s outlets are connected to the text fields.

Delegate Method Names

A common mistake related to using delegates is to misspell the delegate method name. Even if you’ve set the delegate object correctly, if the delegate doesn’t use the right name in its method implementation, the correct method won’t be invoked. It’s usually best to copy and paste delegate method declarations—such as textFieldShouldReturn:—from a reliable source (such as the documentation or the declaration in a header file).