ios开发学习之kvc的使用解析

ios开发学习之k的使用解析

整个过程：

证明第一步，走set和_set方法：

@interface person : nsobject

@end

#import "person.h"

@implementation person

- (void)setage:(nsstring *)age
{
 nslog(@"_setage");
}

//- (void)_setage:(nsstring *)age
//{
  //  nslog(@"_setage");
//}

@end

 self.person = [[person alloc] init];

 nskeyvalueobservingoptions optips = nskeyvalueobservingoptionnew | nskeyvalueobservingoptionold;
 [self.person addobserver:self forkeypath:@"age" options:optips context:@"sdf"];

 [self.person setvalue:@10 forkey:@"age"];


- (void)observevalueforkeypath:(nsstring *)keypath ofobject:(id)object change:(nsdictionary *)change context:(void *)context {
 nslog(@"监听到%@的%@属性发生了变化-%@ -%@",object, keypath, change, context);
}

结果：
当实现setage时 就会打印：
2018-07-18 23:18:23.984 newxc[5009:1640392] setage
当实现_setage时，就会打印
2018-07-18 23:18:23.984 newxc[5009:1640392] _setage

第二步：
不实现setage 和_setage


#import "person.h"

@implementation person

+ (bool)accessinstancevariablesdirectly
{
 return no;  // 不允许访问成员变量
}

结果：
会报错：
2018-07-18 23:20:35.584 newxc[5060:1644779] *** terminating app due to uncaught exception 'nsunknownkeyexception', reason: '[ valueforundefinedkey:]: this class is not key value coding-compliant for the key age.'
*** first throw call stack:
(
	0corefoundation 0x000000010aeceb0b __exceptionpreprocess + 171
	1libobjc.a.dylib0x000000010a933141 objc_exception_throw + 48
	2corefoundation 0x000000010aecea59 -[nsexception raise] + 9
	3foundation  0x000000010a511731 -[nsobject(nskeyvaluecoding) valueforundefinedkey:] + 226
	4foundation  0x000000010a440e1d -[nsobject(nskeyvaluecoding) valueforkey:] + 284
	5foundation  0x000000010a43bb44 nskeyvaluewillchangebysetting + 60
	6foundation  0x000000010a436057 nskeyvaluewillchange + 414
	7foundation  0x000000010a40c603 -[nsobject(nskeyvalueobservernotification) willchangevalueforkey:] + 477
	8foundation  0x000000010a51704b _nssetvalueandnotifyforundefinedkey + 45
	9foundation  0x000000010a448e8b -[nsobject(nskeyvaluecoding) setvalue:forkey:] + 292
	10  newxc 0x000000010a36316c -[viewcontroller viewdidload] + 476
	11  uikit 0x000000010b494cca -[uiviewcontroller loadviewifrequired] + 1235
	12  uikit 0x000000010b49510a -[uiviewcontroller view] + 27
	13  uikit 0x000000010b35d63a -[uiwindow addrootviewcontrollerviewifpossible] + 65
	14  uikit 0x000000010b35dd20 -[uiwindow _sethidden:forced:] + 294
	15  uikit 0x000000010b370b6e -[uiwindow makekeyandvisible] + 42
	16  uikit 0x000000010b2ea31f -[uiapplication _callinitializationdelegatesformainscene:transitioncontext:] + 4346
	17  uikit 0x000000010b2f0584 -[uiapplication _runwithmainscene:transitioncontext:completion:] + 1709
	18  uikit 0x000000010b2ed793 -[uiapplication workspacedidendtransaction:] + 182
	19  frontboardservices0x000000010e54b5f6 __fbsserialqueue_is_calling_out_to_a_block__ + 24
	20  frontboardservices0x000000010e54b46d -[fbsserialqueue _performnext] + 186
	21  frontboardservices0x000000010e54b7f6 -[fbsserialqueue _performnextfromrunloopsource] + 45
	22  corefoundation 0x000000010ae74c01 __cfrunloop_is_calling_out_to_a_source0_perform_function__ + 17
	23  corefoundation 0x000000010ae5a0cf __cfrunloopdosources0 + 527
	24  corefoundation 0x000000010ae595ff __cfrunlooprun + 911
	25  corefoundation 0x000000010ae59016 cfrunlooprunspecific + 406
	26  uikit 0x000000010b2ec02f -[uiapplication _run] + 468
	27  uikit 0x000000010b2f20d4 uiapplicationmain + 159
	28  newxc 0x000000010a36381f main + 111
	29  libdyld.dylib  0x000000010ddd665d start + 1
)
libc++abi.dylib: terminating with uncaught exception of type nsexception
(lldb) 

但是 如果返回的是yes

+ (bool)accessinstancevariablesdirectly
{
 return yes; // 允许访问成员变量。
}

这里需要注意一下，这里依然会监听，可能是内部实现了kvo必须实现的那两个方法。
2018-07-18 23:22:18.703 newxc[5079:1647618] 监听到的age属性发生了变化-{
 kind = 1;
 new = 10;
 old = 0;
} -sdf

这个赋值的属性请看下面

上面是kvo实现逻辑的验证过程。

这个是forkey和forkeypath的解释：

#import 

@interface cat : nsobject

@property (nonatomic, strong) nsstring *wight;


@end


@interface person : nsobject

@property (nonatomic, strong) nsstring *age;

@property (nonatomic, strong) cat *cat;


@end

 [self.person setvalue:@10 forkey:@"age"]; // key只能访问简单的属性
 [self.person setvalue:@10 forkeypath:@"cat.wight"]; // 这个可以一层一层访问

1：通过kvc修改属性会触发kvo么？

会触发

原理：

2：kvc的赋值和取值过程是怎样的？原理是什么？