iOS-設計一個在dealloc中自動移除KVO的分類

摘要： KVO在專案中使用很多，主要是兩種原因會使KVO崩潰 1、KVO沒有被移除 2、KVO移除的次數比新增的次數多 設計思路 1、利用runtime 交換了addObserver:for...

KVO在專案中使用很多，主要是兩種原因會使KVO崩潰

• 1、KVO沒有被移除
• 2、KVO移除的次數比新增的次數多

設計思路

• 1、利用runtime 交換了addObserver:forKeyPath:options:context:
• 2、在替換的addObserver:forKeyPath:options:context: 中
  • a、建立一個Map ，keyPath 作為key ，Value 是KVOItem 物件，而KVOItem 儲存是的被監聽的物件，監聽的屬性，這個Map 是儲存利用關聯屬性儲存的
  • b、呼叫原生的addObserver:forKeyPath:options:context: 方法，
  • c、最後利用method_setImplementation 修改了監聽者的dealloc 方法的實現，裡面先是判斷是否被當作監聽物件，如果有，遍歷並移除KVO，然後呼叫原有的dealloc 方法 。沒有使用交換方法的原因是，沒有被當作監聽的物件在dealloc方法中，也會判斷被當作監聽的物件。
• 3、但是在專案中，可能會有開發人員、系統自己在dealloc 中移除KVO ，這樣就會一個問題，因為在呼叫dealloc 之前，KVO 已經被移除了，這時候再次移除會崩潰，所以利用runtime 交換removeObserver:forKeyPath: 方法，由於removeObserver:forKeyPath:context 底層也是呼叫removeObserver:forKeyPath: , 所以這個方法不用替換。
• 4、在替換的removeObserver:forKeyPath: 中
  • a、利用observer 物件取出對應的Map ，判斷是否存在對應的keyPath , 如果存在，就移除KVO，並且從Map 移除對應的KeyPath

//
//NSObject+KVO.m
//CrashSafe
//
//Created by 無頭騎士 GJ on 2019/1/26.
//Copyright © 2019 無頭騎士 GJ. All rights reserved.
//

#import "NSObject+KVO.h"
#import <objc/message.h>

static const char KVOArrayKey;

@interface WTKVOItem: NSObject

@property (nonatomic, weak) id obj;

@property (nonatomic, strong) NSString *keyPath;


@end

@implementation WTKVOItem


@end

@implementation NSObject (KVO)

+ (void)load
{
Method addObserver = class_getInstanceMethod(self, @selector(addObserver:forKeyPath:options:context:));
Method wt_addObserver = class_getInstanceMethod(self, @selector(wt_addObserver:forKeyPath:options:context:));
method_exchangeImplementations(addObserver, wt_addObserver);

Method removeObserver = class_getInstanceMethod(self, @selector(removeObserver:forKeyPath:));
Method wt_removeObserver = class_getInstanceMethod(self, @selector(wt_removeObserver:forKeyPath:));
method_exchangeImplementations(removeObserver, wt_removeObserver);
}


- (void)wt_addObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context
{
if (observer == nil || keyPath == nil || keyPath.length == 0) return;

NSMutableDictionary *keyPathdict = objc_getAssociatedObject(observer, &KVOArrayKey);
if (keyPathdict == nil)
{
keyPathdict = [NSMutableDictionary dictionary];
objc_setAssociatedObject(observer, &KVOArrayKey, keyPathdict, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

WTKVOItem *item = [WTKVOItem new];
item.keyPath = keyPath;
item.obj = self;

keyPathdict[keyPath] = item;

[self wt_addObserver: observer forKeyPath: keyPath options: options context: context];


[self replaceImpl: observer.class];
}

- (void)wt_removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath
{
NSMutableDictionary *keyPaths = objc_getAssociatedObject(observer, &KVOArrayKey);
if (keyPaths == nil) return;

if ([keyPaths objectForKey: keyPath])
{
[self wt_removeObserver: observer forKeyPath: keyPath];

[keyPaths removeObjectForKey: keyPath];
}
}


- (void)wt_removeObserver:(NSObject *)observer forKeyPath:(NSString *)keyPath context:(void *)context
{
NSMutableDictionary *keyPaths = objc_getAssociatedObject(observer, &KVOArrayKey);
if (keyPaths == nil) return;

if ([keyPaths objectForKey: keyPath])
{
[self wt_removeObserver: observer forKeyPath: keyPath context: context];

[keyPaths removeObjectForKey: keyPath];
}
}

- (void)replaceImpl:(Class)cls
{
Method dealloc = class_getInstanceMethod([self class], NSSelectorFromString(@"dealloc"));

__block IMP deallocIMP = method_setImplementation(dealloc, imp_implementationWithBlock(^(__unsafe_unretained id self){

((void(*)(id, SEL))objc_msgSend)(self, @selector(cleanupSEL));

((void(*)(id, SEL))deallocIMP)(self, NSSelectorFromString(@"dealloc"));

}));
}

- (void)cleanupSEL
{
NSMutableDictionary *keyPaths = objc_getAssociatedObject(self, &KVOArrayKey);
if (keyPaths == nil) return;

[keyPaths enumerateKeysAndObjectsUsingBlock:^(NSString * _Nonnull key, WTKVOItem * _Nonnull obj, BOOL * _Nonnull stop) {

[obj.obj removeObserver: self forKeyPath: obj.keyPath];


}];

objc_setAssociatedObject(self, &KVOArrayKey, NULL, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}


@end