如何使用NSUserDefaults正确保存字段？

I'm creating a program that saves a String from one text field and an integer from a second text field. I am trying to use NSUserDefaults, but I can't seem to get either of them to save correctly when I run the program. It crashes when I press the save button with the breakpoint while handling the NSUserDefaults. Am I doing something wrong? I skimmed through the documentation, but it didn't help. Can I even use 2 different instances of NSUserDefaults?I'm creating a program that saves a String from