一. 實現(xiàn)原理
- 動態(tài)生成子類 :
NSKVONotifying_xxx
1.1 中間生成的是一個動態(tài)類,但是修改的是 原對象的isa- 觀察的是
setter- 動態(tài)子類重寫了很多方法
setterclassdealloc_isKVOA- 移除觀察的時候 isa 指向回來
- 動態(tài)子類不會銷毀
@interface FXPerson : NSObject
@property (nonatomic, copy) NSString *name;
- (void)test001;
- (void)test002;
@end
@interface FXViewController ()
@property (nonatomic, strong)FXPerson *person;
@end
@implementation FXViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.person = [[FXPerson alloc] init];
[self printClasses:[FXPerson class]];
[self printClassAllMethod:[FXPerson class]];
[self.person addObserver:self forKeyPath:@"name" options:(NSKeyValueObservingOptionNew) context:NULL];
[self printClasses:[LGPerson class]];
[self printClassAllMethod:NSClassFromString(@"NSKVONotifying_FXPerson")];
}
#pragma mark - 遍歷類以及所有子類
- (void)printClasses:(Class)cls{
// 注冊類的總數(shù)
int count = objc_getClassList(NULL, 0);
// 創(chuàng)建一個數(shù)組砚亭， 其中包含給定對象
NSMutableArray *mArray = [NSMutableArray arrayWithObject:cls];
// 獲取所有已注冊的類
Class* classes = (Class*)malloc(sizeof(Class)*count);
objc_getClassList(classes, count);
for (int i = 0; i<count; i++) {
if (cls == class_getSuperclass(classes[i])) {
[mArray addObject:classes[i]];
}
}
free(classes);
NSLog(@"classes = %@", mArray);
}
#pragma mark - 遍歷cls所有的方法
- (void)printClassAllMethod:(Class)cls{
unsigned int count = 0;
Method *methodList = class_copyMethodList(cls, &count);
for (int i = 0; i<count; i++) {
Method method = methodList[i];
SEL sel = method_getName(method);
IMP imp = class_getMethodImplementation(cls, sel);
NSLog(@"%@-%p",NSStringFromSelector(sel),imp);
}
free(methodList);
}
@end
在添加
[self.person addObserver:self forKeyPath:@"name" options:(NSKeyValueObservingOptionNew) context:NULL]之前, 方法- (void)printClasses:(Class)cls只輸出一個FXPerson類, 而- (void)printClassAllMethod:(Class)cls輸出test001-0x10992c560test002-0x10992c570. 當(dāng)添加觀察者方法之后,
- (void)printClasses:(Class)cls輸出兩個類
FXPerson,NSKVONotifying_FXPerson
- (void)printClassAllMethod:(Class)cls輸出四個方法
setName:-0x7fff258e454b
class-0x7fff258e2fd5
dealloc-0x7fff258e2d3a
_isKVOA-0x7fff258e2d32
KVO 會為需要observed的對象動態(tài)創(chuàng)建一個子類NSKVONotifying_xxx宠蚂，然后將原對象的 isa指針指向新的子類魂奥，同時重寫class 方法，返回原先類對象戳表，這樣外部就無感知了；其次重寫所有要觀察屬性的setter方法昼伴，統(tǒng)一會走一個方法匾旭，然后內(nèi)部是會調(diào)用 willChangeValueForKey 和 didChangevlueForKey 方法，在一個被觀察屬性發(fā)生改變之前圃郊， willChangeValueForKey:一定會被調(diào)用价涝，這就 會記錄舊的值。而當(dāng)改變發(fā)生后持舆，didChangeValueForKey:會被調(diào)用色瘩，繼而 observeValueForKey:ofObject:change:context: 也會被調(diào)用。在移除觀察的時候又將isa指回原對象, 移除的時候這個中間動態(tài)子類不會銷毀.
