Simple use of KVO and KVC modes for IOS development

-(void) Viewdidload {

[Super Viewdidload];

Additional setup after loading the view, typically from a nib.

Use of 1.KVC

The abbreviation for key value coding, which indicates the code

Function: Accesses the property and instance variables of an object in a string-coded manner

Used in projects: using KVC to implement dictionary-to-model conversions in JSON

Car *car = [[Car alloc] init];

Car.type = @ "BMW";

Car.speed = 250;

NSLog (@ "type =%@,speed=%f", car.type,car.speed);

KVC Access Property One way (special use string to do key)

Key: Attribute name can do key, instance variable name can also do key

[Car setvalue:@ "Mini" forkey:@ "type"];

NSLog (@ "type=%@", [Car valueforkey:@ "type"]);

Modify the base type and pass in the NSNumber

[Car setvalue:@ (+) forkey:@ "Speed"];

NSLog (@ "speed =%f", [[Car valueforkey:@ ' speed '] doublevalue]);

[Car setvalue:@ (3.14) forkey:@ "_num"];

[Car show];

Note: If key does not exist, an exception is thrown

Workaround: Re-implement Setvalue:forundefinedkey:

Use of 1.2 keypath

Engine *engine = [[Engine alloc] init];

Car.engine = engine;

Set the power properties of car engine

[Car setvalue:@ (+) forkeypath:@ "Engine.power"];

NSLog (@ "power =%f", [[Car valueforkeypath:@ "Engine.power"] doublevalue]);

1.3 Dictionary and Object conversions

Nsdictionary *cardict = @{@ "type": @ "QQ",

@ "Speed": @ "180"};

[Car setvaluesforkeyswithdictionary:cardict];

NSLog (@ "type =%@,speed=%f", car.type,car.speed);

Use of 2.KVO

Key value Observer key monitor

Function: Monitor the change of an attribute of an object

Example: Car object, its speed property has changed, the instrument panel shows the velocity

Newcar = [[Car alloc] init];

newcar.speed = 0;

Monitoring

Function: Once the speed has changed, execute the specified method in self

[Newcar addobserver:self forkeypath:@ "Speed" options:nskeyvalueobservingoptionold| Nskeyvalueobservingoptionnew Context:nil];

Analog start

Newcar.speed = 50;

Newcar.speed = 100;

Newcar.speed = 120;

Newcar.speed = 120;

Newcar.speed = 120;

}

-(void) Observevalueforkeypath: (NSString *) KeyPath Ofobject: (ID) object change: (nsdictionary *) Change context: (void *) Context

{

static double prespeed = 0;

Show the new speed

Double speed = [[Object Valueforkeypath:keypath] doublevalue];

if (prespeed! = speed)

{

NSLog (@ "speed =%f", speed);

}

Prespeed = speed;

}

-(void) dealloc

{

[Newcar removeobserver:self forkeypath:@ "Speed"];

}

Simple use of KVO and KVC modes for IOS development