键/值观察不触发属性定义为：@property（readwrite，retain）__ attribute __（（NSObject））CGImageRef thumbnailImage

Question

我有一个具有如下属性定义的类：

// Interface
@property (retain) __attribute__((NSObject)) CGImageRef thumbnailImage;

// Implementation
@synthesize thumbnailImage;

问题是self.thumbnailImage = newCGImageRef;不会导致它触发键/值观察事件，并且永远不会调用observeValueForKeyPath:...。

我使用同一个类的另一个属性（BOOL）测试了代码，它对那个属性来说效果很好。这不也适用于上面的房产吗？

注意：我尝试手动设置属性（[self setValue:newValue forKey:@"thumbnailImage"]，导致以下错误：

setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key thumbnailImage.

Answer 1

__attribute__((NSObject))告诉编译器将结构指针视为对象，因此这允许您保留/释放对象（通常用于块）。此属性对CFImageRef是结构指针的事实没有影响，并且KVC不会自动换行结构指针，尽管它会包装结构。要解决您的问题，您需要在未定义的键上截取KVC以设置和返回正确的对象，或者只使用UIImage。

KVC Documentation:

  

自动包装和展开不仅限于NSPoint，NSRange，   NSRect和NSSize结构类型（即Objective-C的类型）   类型编码字符串以{）开头可以包装在NSValue中   对象

<强> TestCF_KVC.h

#import <Foundation/Foundation.h>

typedef struct
{
    int x, y, z;
} AStruct;

@interface TestCF_KVC : NSObject {}

@property (nonatomic, retain) NSString *text;
@property (nonatomic, assign) AStruct aStruct;
@property (nonatomic, retain) __attribute__((NSObject)) CFStringRef cftext;

-(void)test;

@end

<强> TestCF_KVC.m

#import "TestCF_KVC.h"

@implementation TestCF_KVC

@synthesize text, aStruct, cftext;

-(void)setValue:(id)value forUndefinedKey:(NSString *)key
{
    NSLog(@"undefined key set for %@", key);
    if([key isEqualToString:@"cftext"])
    {
        self.cftext = (CFStringRef)value;
    }
    else
    {
        [super setValue:value forUndefinedKey:key];
    }
}

-(id)valueForUndefinedKey:(NSString *)key
{
    NSLog(@"undefined key get for %@", key);
    if([key isEqualToString:@"cftext"])
    {
        return (NSString*)self.cftext;
    }

    return [super valueForUndefinedKey:key];
}

-(void)test
{
    NSString *txt = @"text worked";
    AStruct astr = { .x=1, .y=5, .z=10 };
    CFStringRef cftxt = (CFStringRef)@"cftext worked";

    //Test a normal NSString for KVC
    [self setValue:txt forKey:@"text"];
    txt = [self valueForKey:@"text"];
    NSLog(@"text[%s]: %@", @encode(NSString), [self valueForKey:@"text"]);

    //Test a struct for KVC
    NSValue *value = [NSValue value:&astr withObjCType:@encode(AStruct)];
    [self setValue:value forKey:@"aStruct"];
    [[self valueForKey:@"aStruct"] getValue:&astr];
    NSLog(@"aStruct[%s]: %d %d %d", @encode(AStruct), aStruct.x, aStruct.y, aStruct.z);

    //Test a Core Foundation type for KVC
    [self setValue:(NSString*)cftxt forKey:@"cftext"];
    cftxt = (CFStringRef)[self valueForKey:@"cftext"];
    NSLog(@"cftext[%s]: %@", @encode(CFStringRef), (NSString*)cftxt);
}

@end

来自呼叫测试的日志输出：

text[{NSString=#}]: text worked
aStruct[{?=iii}]: 1 5 10
undefined key set for cftext
undefined key get for cftext
cftext[^{__CFString=}]: cftext worked