IOS learning: KVO

 

1 # import <Foundation/Foundation. h> 2 3 // The twfxstudata class is used as the class in the model layer to manage data 4 @ interface twfxstudata: nsobject 5 {6 nsstring * Name; 7 nsinteger age; 8} 9 10 @ property (retain, nonatomic) nsstring * schoolname; 11 12 @ end13 14 15 16 17 # import "twfxstudata. H "18 19 @ implementation twfxstudata20 21 @ end

 

1 // 2 // http://www.189works.com/article-103444-1.html 3 // KVO (key value coding) is a cocoa protocol used to set values or values (nskeyvaluecoding), a bit similar to Java EJB. 4 // both variables and function names are standardized to facilitate the setting of class member values. it is an important mechanism of cocoa, 5 // It is a bit similar to notification, but it provides a way to observe the changes of a certain attribute, and notification requires an object to send notification, in this way, KVO greatly simplifies the code than notification. 6 // This kind of observation-the observed model applies to such situations. For example, according to a property value change in a (data class), a property in B (View class) changes accordingly. For cocoa, which advocates MVC, KVO has a high application value. 7 // 8 9 # import "twfxviewcontroller. H "10 11 @ interface twfxviewcontroller () 12 13 @ end 14 15 @ implementation twfxviewcontroller 16 17-(void) viewdidload 18 {19 [Super viewdidload]; 20 // do any additional setup after loading the view, typically from a nib. 21 22 // twfxstudata is a data storage class used to simulate model data 23 studata = [[twfxstudata alloc] init]; 24 testcount = 1; 25 26 27 // Step 1: register the observer 28 // For the observer studata, it does not know who is observing it 29 // parameter description: the first parameter observer indicates who the observer is 30 // The second parameter keypath specifies the attribute to be observed 31 // The third parameter option can choose to observe the key value changes, for example, the value before and after the change 32 // The fourth parameter context needs to transmit data 33 34 [studata addobserver: Self 35 forkeypath: @ "name" 36 options: nskeyvalueobservingoptionnew | nskeyvalueobservingoptionold 37 context: nil]; 38 39 [studata addobserver: Self 40 forkeypath: @ "Age" 41 options: Unknown | nskeyvalueobservingoptionold 42 context: Nil]; 43 44 [studata addobserver: Self forkeypath: @ "schoolname" Options: nskeyvalueobservingoptionnew | nskeyvalueobservingoptionold context: Nil]; 45} 46 48 // Step 2: The Observer implements the change method. When the registered attribute changes, this method will be called 49 // parameter ofobject: the object will be observed. change: Changes to the observed attributes, which are specified during registration. context: 50-(void) observevalueforkeypath :( nsstring *) keypath 51 ofobject :( ID) object 52 change :( nsdictionary *) Change 53 context :( void *) context 54 {55 if ([keypath isinclutostring: @ "name"]) 56 {57 self. outlet_name.text = [studata valueforkey: @ "name"]; 58} 59 else if ([keypath ispath tostring: @ "Age"]) 60 {61 // the property value obtained through valueforkey is also 62 self of the object type. outlet_age.text = [nsstring stringwithformat: @ "% @", [studata valueforkey: @ "Age"]; 63} 64 else if ([keypath isw.tostring: @ "schoolname"]) 65 {66 self. outlet_schoolname.text = [studata valueforkey: @ "schoolname"]; 67} 68} 69 70 71 // Step 3: simulate a change in the value of the observed attribute 72-(ibaction) btnclick_changename :( uibutton *) sender {73 74 [studata setvalue: [nsstring stringwithformat: @ "liming % d", testcount] forkey: @ "name"]; 75 testcount ++; 76 77 // change the property value: method 1 78 [studata setvalue: @ "" forkey: @ "schoolname"]; 79} 80 81-(ibaction) btnclick_changeage :( uibutton *) sender {82 83 // when setting the attribute value through setvalue, the value must be of the object type, and the system should convert the value type 84 [studata setvalue: [nsnumber numberwithinteger: testcount] forkey: @ "Age"]; 85 testcount ++; 86 87 // change the attribute value: method 2 (valid for property) 88 [studata setschoolname: @ ""]; 89} 90 91-(ibaction) btnclick_test :( uibutton *) sender {92 93 // change the attribute value: method 3 (valid for property) 94 studata. schoolname = @ "d "; 95} 96 97 98 99 // Step 4: Disable observation 100-(void) dealloc {101 102 103 // disable Observation [studata removeobserver: self forkeypath: @ "name" context: Nil]; 104 [studata removeobserver: Self forkeypath: @ "Age" context: Nil]; 105 [studata removeobserver: Self forkeypath: @ "schoolname" context: Nil]; 106 107 // release 108 [studata release]; 109 110 [_ outlet_temp release]; 111 [_ outlet_name release]; 112 [_ outlet_age release]; 113 114 [_ outlet_schoolname release]; 115 [Super dealloc]; 116} 117 118} 119 @ end