_ Cmd in IOS indicates the name of this method.

In Apple's official introduction, we can see an understatement: "The _ cmd variable is a hidden argument passed to every method that is the current selector ", in fact, _ cmd indicates the selector of the current method in the Objective-C method, just as self indicates the object instance called by the current method.

For example, to print the method to be called, you can write it as follows:

-(Void) viewDidLoad

{

[Super viewDidLoad];

NSLog (@ "Current method: % @", [self class], NSStringFromSelector (_ cmd ));

}

The output result is as follows:

TestingProject [570: 11303] Current method: FirstViewController viewDidLoad