IOS-KVC/KVO

IOS-KVC/KVO

KVC is a tool for setting values. For an object pointing to an id, such as its memory access value. This is a bit like java reflection;

If the next object is known as its property name, the value can be:

id p=[[Person alloc] init];NSString *name=[p valueForKey:@"name"];

Suppose there is an array with a series of objects in it. We want to retrieve a property and put it in a queue, as shown below:

Book *book1=[[Book alloc] init];        book1.name=@"effctive c++";                Book *book2=[[Book alloc] init];        book2.name=@" more effctive c++";                Book *book3=[[Book alloc] init];        book3.name=@" most effctive c++";                NSArray *arr=@[book1,book2,book3];                NSLog(@"%@",[arr valueForKey:@"name"]);

In our daily life, we do have the above requirements;

KVO refers to the process of monitoring a value during the process to verify the business logic.

// Create a Monitored object Book * book1 = [[Book alloc] init]; // set the listening object BookObserve * observe = [[BookObserve alloc] init]; // listen on the stored value-you do not need to remove the listener after this method is used up [observe observeValueForKeyPath: @ "name" ofObject: book1 change: nil context: @ "sadsada"]; // listen on the stored value-02 [book1 addObserver: observe forKeyPath: @ "name" options: NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld context: nil]; book1.name = @ "most effctive c ++"; NSLog (@ "% @", book1.name); // cancel listening to its stored value-02 [book1 removeObserver: observe forKeyPath: @ "name"];

No proxy is required for the listener object because it is a derived class of NSObject.

You only need to implement the following method in the. m file to listen:

# Pragma mark keyPath: object property object: object change: dictionary for storing access values-(void) observeValueForKeyPath :( NSString *) keyPath ofObject :( id) object change :( NSDictionary *) change context :( void *) context {}