4. KVO and KVO: Notification objective-C

KVC

[Object setvalue: avalue forkey: akey]; // assign a value to the akey variable of the object

Avalue = [object valueforkey: akey]; // obtain the value of the akey variable of the object

[Object setvalue: avalue forkeypath: akeypath]; // set the value

Id avalue = [object valueforkeypath: akeypath]; // Value

Note: variables in keypath! Akeypath, such as P. Name (many points can be entered)

Demo:

Student * Stu = [[STUDENT alloc] init];

[STU setvalue: @ "Zhang San" forkey: @ "name"]; // assign values to object variables

Nsstring S1 = [STU valueforkey: @ "name"]; // retrieve the variable value

[STU release];

KVO

1. register the listener

[Addobserver: Listener

Forkeypath: attributes of the Monitored object

Options: monitoring content (new value or old value)

Context: Additional information];

2. Listener implementation listening method (implemented in the listener class, will crash if not implemented)

-(Void) observervalueforkeypath :( nsstring *) keypath ofobject :( ID) object (Monitored object) Change :( nsdictionary *) Change (Monitored object attribute change) Context :( void *) Context

3. Listener trigger conditions

When the properties of the Monitored object change, // The following method is automatically called.

Demo:

-(Void) observervalueforkeypath :( nsstring *) keypath ofobject :( ID) object change :( nsdictionary *) Change
Context :( void *) Context

{

Nslog :( @ "keypath: % @ object: % @ change: % @ context: % @", keypath, object, change, context ); // You can implement what you want to do in this method, such as sending notifications.

}

Student * Stu = [[STUDENT alloc] init];

Stu. Name = @ "James ";

[STU addobserver self forkeypath: @ "name" Options: nskeyvalueobservingoptionnew context: Nil ];

Stu. Name = @ ""; // call Method for value change

Stu. Name = @ ""; // call Method for value change

[STU release ];

Notification

1. Get notification center objects

Nsicationicationcenter * center = [nsnotificationcenter defacenter center]; // the actual address of the single instance is the address of the notification center.

2. Listening for notifications

[Center addobserver: Listener selector: method to be executed name: name of notification to the listener object: Notification sender];

3. The notification center publishes messages.

[Center postnotificationname: @ "Long live the King" Object: Someone];

4. Remove the listener Center

[Center removeobserver: Self name: @ "Long live the King" Object: Someone];

Demo:

King * King = [[King alloc] init];

Farmer * farmer = [[Farmer alloc] init];

Nsicationicationcenter * center = [nsnotificationcenter defacenter center];

[Center addobserver: farmer selector: @ selector (test :) name: @ "Long live the King" Object: King];

[Center postnotificationname: @ "Long live the King" Object: King];

[Center removeobserver: Farmer];

[King release];

[Farmer release];

-(Void) test :( nsnotification *) N // The method must implement what you want to do in the listener notification class.

{

Nslog (@ "Name: % @ object: % @ userinfo: % @", [nname], [n object], [n userinfo]);

}