[Swift]ViewController中xib控件为空

在ViewController的xib中定义了一些控件，而后在使用的时候会由于这个控件为空而崩溃，报错为：

Swift Error fatal error: unexpectedly found nil while unwrapping an Optional value

　　

 What?

解决办法以下：

 

1.首先要保证正确初始化了ViewController，使用初始化方法 init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?)  初始化视图控制器（OC中对应 -(instancetype)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil），OC中直接使用init也是能够的，这时系统会自动调用initWithNibName 方法。

/*
  The designated initializer. If you subclass UIViewController, you must call the super implementation of this
  method, even if you aren't using a NIB.  (As a convenience, the default init method will do this for you,
  and specify nil for both of this methods arguments.) In the specified NIB, the File's Owner proxy should
  have its class set to your view controller subclass, with the view outlet connected to the main view. If you
  invoke this method with a nil nib name, then this class' -loadView method will attempt to load a NIB whose
  name is the same as your view controller's class. If no such NIB in fact exists then you must either call
  -setView: before -view is invoked, or override the -loadView method to set up your views programatically.
*/
- (instancetype)initWithNibName:(nullable NSString *)nibNameOrNil bundle:(nullable NSBundle *)nibBundleOrNil

　　

2.在viewDidLoad方法加载以前，这些xib的控件是可能为空的，因此在变量的属性观察器中使用xib控件时要注意。如：

   var naviTitle :String?{
        didSet{
            naviView.title = naviTitle
        }
    }

　　应当在viewDidLoad以后使用这些控件。