What is the use of Main Interface option in the build settings for iOS application?

Question

When I start a single view application and instead of assigning the rootViewController programmatically from AppDelelgate, try to use the 'Main Interface' option to assign a xib as my main interface file, a SIGABRT signal is sent to the program when I run it. Why does this happen? What is the purpose of the 'Main Interface' option?

Answer 1

I found out how to do this. It was very obvious after I understood the whole process of how the application is loaded. So I thought I'll answer my own question.

The key is to initialize the window and set up the UIApplication and its delegate from the xib itself.

• Step 1: Create an xib with a UIWindow object in it. Make the file's owner of the xib as UIApplication.
• Step 2: Create an AppDelegate object in the xib and connect the file's owner's delegate outlet to this object.
• Step 3: Create an outlet for the window in the AppDelegate class.
• Step 4: Select the MainInterface option in build settings as the xib you created.
• Step 5: Comment out the code in applicationDidFinishLaunchingWithOptions: method.

If you run the program it will show the window in the simulator, but you'll get a warning that application is supposed to have a rootViewController at the end of application launch.

• Step 6: So inside applicationDidFinishLaunchingWithOptions: we can instantiate a UIViewController and assign the window outlets rootViewController as this view controller.