KVO && KVC

KVO:

• Key-value Observing
  • When the properties of the specified object are modified, the object receives a notification.
  • Simply put, the KVO will automatically notify the appropriate observer when the property of the observed object has been modified each time it is specified.
  • Steps to use:
    • 1. Register, specify the attributes of the person being observed (observers who are actively added by the observer to observe their own)
    • 2. Implementing a callback method
    • 3. Removal of observations
    • Examples of Use:
      • @interface Stockdata:nsobject {
      • NSString * STOCKNAME;
      • float price;
      • }
      • @end
      • @implementation StockData
      • @end
    • 
      
      • -(void) Viewdidload {
      • [Super Viewdidload];
    • 
      
      • STOCKFORKVO = [[StockData alloc] init];
      • [Stockforkvo setvalue:@ "Searph" forkey:@ "StockName"];
      • [Stockforkvo setvalue:@ "10.0" forkey:@ "Price"];
      • To add an observer to the Stockdat object
      • [Stockforkvo addobserver:self forkeypath:@ "Price" options:nskeyvalueobservingoptionnew| Nskeyvalueobservingoptionold Context:null];
    • 
      
      • MyLabel = [[UILabel alloc]initwithframe:cgrectmake (100, 100, 100, 30)];
      • Mylabel.textcolor = [Uicolor Redcolor];
      • MyLabel.Text = [Stockforkvo valueforkey:@ "Price"];
      • [Self.view Addsubview:mylabel];
    • 
      
      • UIButton * b = [UIButton buttonwithtype:uibuttontyperoundedrect];
      • B.frame = CGRectMake (0, 0, 100, 30);
      • [B addtarget:self Action: @selector (Buttonaction) forcontrolevents:uicontroleventtouchupinside];
      • [Self.view addsubview:b];
      • }
      • -(void) Buttonaction {
      • [Stockforkvo setvalue:@ "20.0" forkey:@ "price"];
      • }
      • As a KVO observer needs to implement callbacks
      • -(void) Observevalueforkeypath: (NSString *) KeyPath Ofobject: (ID) object change: (nsdictionary *) Change context: (void *) Context {
      • if ([KeyPath isequaltostring:@ "Price"]) {
      • MyLabel.Text = [Stockforkvo valueforkey:@ "Price"];
      • }
      • }
      • Finally we need to move the viewer
      • -(void) Dealloc {
      • [Stockforkvo removeobserver:self forkeypath:@ "Price"];
      • }

KVC:

• Abbreviation of keyvaluecoding
  • A mechanism for indirectly accessing an object's properties using a string identifier, rather than being accessed by invoking a setter, getter method.
  • You can read and write member variable values by KVC even if the member variable in the object is not a property
  • How to use:
  • Key methods:
    • Nskeyvaluecodingprotocol
    • Get Value:
      • Valueforkey: The name of the (NSString *) attribute
      • Valueforkeypath: (NSString *) The path of the passed-in property, xx.xx form.
      • Valueforundefinedkey
      • The default implementation is to throw an exception, and you can override this function to do error handling.
    • modifying values
      • Setvalue:forkey:
      • Setvalue:forkeypath:
      • Setvalue:forundefinedkey:
      • Setnilvalueforkey:
      • Called when Nil is set on a non-class object property, and the exception is thrown by default.
    • Case of a one-to-many relationship member
      • Mutablearrayvalueforkey:
      • Ordered one-to-many relationship member Nsarray
      • Mutablesetvalueforkey:
      • Unordered one-to-many relationship member Nsset
      • Demonstration examples:
        • Person class
        • @implementation person
        • @synthesize name,age;//property name will be monitored
        • -(void) changename{
        • [Email protected] "changename directly";
        • }
        • @end
        • The Personmonitor class monitors the Name property
        • @implementation Personmonitor
        • -(void) Observevalueforkeypath: (NSString *) KeyPath Ofobject: (ID) object change: (nsdictionary *) Change context: (void *) Context {
        • if ([KeyPath isequal:@ "name"]) {
        • NSLog (@ "Change happen, old:%@ new:%@", [Change Objectforkey:nskeyvaluechangeoldkey],[change Objectforkey: Nskeyvaluechangenewkey]);
        • }
        • }
        • @end
        • Test code
        • Initializing monitored objects
        • Person *p =[[person alloc] init];
        • Monitoring objects
        • Personmonitor *pm= [[Personmonitor alloc]init];
        • KVO
        • [P addobserver:pm forkeypath:@ "name" Options: (Nskeyvalueobservingoptionnew | Nskeyvalueobservingoptionold) Context:nil];
        • Pre-test data
        • NSLog (@ "P.name is%@", p.name);
        • KVC
        • By means of SetValue, the monitoring of personmonitor will be called
        • [P setvalue:@ "name KVC" forkey:@ "name"];
        • View the value after setting
        • NSLog (@ "p name Get by KVC is%@", [P valueforkey:@ "name"]);
        • The effect is consistent through SetValue
        • [Email protected] "name change by. Name=";
        • Change name by person's own function
        • [P changename];
        • /*
        • Result output
        • 2011-07-03 16:35:57.406 cocoa[13970:903] P.name is name
        • 2011-07-03 16:35:57.418 cocoa[13970:903] change happen, Old:name New:name KVC
        • 2011-07-03 16:35:57.420 cocoa[13970:903] p name Get by KVC is name KVC
        • 2011-07-03 16:35:57.421 cocoa[13970:903] change happen, Old:name KVC new:name change by. name=
        • The last modification is a direct modification, so no notification is generated.
        • */

KVO && KVC