观察 Objective-C 中任何类属性的变化

Question

简而言之，当 Objective-C 类中的任何属性发生更改时，有没有办法接收一般通知？我知道我可以使用 KVO 来监视特定的属性更改，但每当任何 setProperty: 消息发送到我的类时，我都需要调用特定的方法。我希望能够收到通用通知，而不用担心具体修改了哪个属性。

如果这有助于澄清我为什么要这样做，我将使用此处找到的一些快速表格滚动代码： http://blog.atebits.com/2008/12/fast-scrolling-in-tweetie-with-uitableview/

完成此操作的部分过程是每当修改表视图单元格中的属性时，都需要调用 [ self setNeedsDisplay ] 。我不想只是为了进行此调用而重写类中每个属性的 setter 方法。

Answer 1

正如 Chuck 所指出的，您可以创建一个依赖键，或者当然您可以直接观察所有属性（这比重载设置器要少一些工作）。

使用 Objective-C 运行时，如果您专门使用属性，则可以使用 class_copyPropertyList()。但我可能只会在您遇到这个问题时才这样做。如果您只有一个此问题的实例，那么直接观察属性列表可能会更容易、更安全且更易于维护，除非您想在 ObjC 运行时中工作。

Answer 2

下面是根据 Chuck 和 Rob 的建议构建的示例：

DrakeObject.h

@interface DrakeObject : NSObject

@property (nonatomic, strong) NSNumber *age;
@property (nonatomic, strong) NSNumber *money;
@property (nonatomic, strong) NSString *startPosition;
@property (nonatomic, strong) NSString *currentPosition;
@property (nonatomic, strong, readonly) id propertiesChanged;

@end

DrakeObject.m

@implementation DrakeObject

- (instancetype)init {
    self = [super init];
    if (self) {
        self.age = @25;
        self.money = @25000000;
        self.startPosition = @"bottom";
        self.currentPosition = @"here";
    }
    return self;
}

- (id)propertiesChanged {
    return nil;
}

+(NSSet *)keyPathsForValuesAffectingPropertiesChanged {
    return [NSSet setWithObjects:@"age", @"money", @"startPosition", @"currentPosition", nil];
}

观察propertiesChanged 将让我们知道属性何时发生更改。

[self.drakeObject addObserver:self
                   forKeyPath:@"propertiesChanged"
                      options:NSKeyValueObservingOptionNew
                      context:nil];

Answer 3

不完全是。您可以创建依赖键这取决于您希望公开然后观察的每个属性。我想这就是你能得到的最接近的结果了。

Answer 4

这是代码示例。我有一个一般对象和另一个对象。 Dother 对象必须在更改每个属性时保存其状态。

#import <Foundation/Foundation.h>

@interface GeneralObject : NSObject

+ (instancetype)instanceWithDictionary:(NSDictionary *)aDictionary;
- (instancetype)initWithDictionary:(NSDictionary *)aDictionary;
- (NSDictionary *)dictionaryValue;
- (NSArray *)allPropertyNames;

@end

实现

#import "GeneralObject.h"
#import <objc/runtime.h>

@implementation GeneralObject

#pragma mark - Public

+ (instancetype)instanceWithDictionary:(NSDictionary *)aDictionary {
    return [[self alloc] initWithDictionary:aDictionary];
}

- (instancetype)initWithDictionary:(NSDictionary *)aDictionary {
    aDictionary = [aDictionary clean];

    for (NSString* propName in [self allPropertyNames]) {
        [self setValue:aDictionary[propName] forKey:propName];
    }

    return self;
}

- (NSDictionary *)dictionaryValue {
    NSMutableDictionary *result = [NSMutableDictionary dictionary];
    NSArray *propertyNames = [self allPropertyNames];

    id object;
    for (NSString *key in propertyNames) {
        object = [self valueForKey:key];
        if (object) {
            [result setObject:object forKey:key];
        }
    }

    return result;
}

- (NSArray *)allPropertyNames {
    unsigned count;
    objc_property_t *properties = class_copyPropertyList([self class], &count);

    NSMutableArray *array = [NSMutableArray array];

    unsigned i;
    for (i = 0; i < count; i++) {
        objc_property_t property = properties[i];
        NSString *name = [NSString stringWithUTF8String:property_getName(property)];
        [array addObject:name];
    }

    free(properties);

    return array;
}

@end

，毕竟我们有 dother 类，它应该在任何属性的每次更改

#import "GeneralObject.h"

extern NSString *const kUserDefaultsUserKey;

@interface DotherObject : GeneralObject

@property (strong, nonatomic) NSString *firstName;
@property (strong, nonatomic) NSString *lastName;
@property (strong, nonatomic) NSString *email;

@end

和实现上

#import "DotherObject.h"

NSString *const kUserDefaultsUserKey = @"CurrentUserKey";

@implementation DotherObject

- (instancetype)initWithDictionary:(NSDictionary *)dictionary {
    if (self = [super initWithDictionary:dictionary]) {
        for (NSString *key in [self allPropertyNames]) {
            [self addObserver:self forKeyPath:key options:NSKeyValueObservingOptionNew context:nil];
        }
    }

    return self;
}

- (void)observeValueForKeyPath:(nullable NSString *)keyPath ofObject:(nullable id)object change:(nullable NSDictionary<NSKeyValueChangeKey, id> *)change context:(nullable void *)context {
    NSDictionary *dict = [self dictionaryValue];
    [[NSUserDefaults standardUserDefaults] setObject:dict forKey:kUserDefaultsUserKey];
    [[NSUserDefaults standardUserDefaults] synchronize];
}

- (NSString *)description {
    return [NSString stringWithFormat:@"%@; dict:\n%@", [super     description], [self dictionaryValue]];
}

@end

保存他的状态快乐编码！