objective-c - UIImage 和 NSCoding iOS 5.1

Question

在 iOS 5.1 之前，如果你想将 NSCoding 协议(protocol)与 UIImage 一起使用，你必须这样做。

@interface UIImage (NSCoding)

-(id)initWithCoder:(NSCoder *)deocder;
-(void)encodeWithCoder:(NSCoder *)encoder;

@end

然后自己实现。然而，对于 iOS 5.1，这会在该协议(protocol)的 .M 文件中生成警告“Category is implementing a method which will also be implemented by its primary class”。现在，如果我删除这个扩展类，iOS5.1 会很高兴，但是这应该会在 iOS4.0 上崩溃并烧毁。那么最好的行动方案是什么？

Answer 1

我有同样的问题，因为现在使用子类而不是类别为时已晚，我听从了 zoul 的建议使用 class_addMethod，下面是我的实现:

#import "UIImage-NSCoding.h"
#include <objc/runtime.h>
#define kEncodingKey        @"UIImage"

static void __attribute__((constructor)) initialize() {
    @autoreleasepool {

        if (![[UIImage class] conformsToProtocol:@protocol(NSCoding)]) {
            Class class = [UIImage class];

            if (!class_addMethod(
                                 class,
                                 @selector(initWithCoder:), 
                                 class_getMethodImplementation(class, @selector(initWithCoderForArchiver:)),
                                 protocol_getMethodDescription(@protocol(NSCoding), @selector(initWithCoder:), YES, YES).types
                                )) {
                                    NSLog(@"Critical Error - [UIImage initWithCoder:] not defined.");
                                }

            if (!class_addMethod(
                                 class,
                                 @selector(encodeWithCoder:),
                                 class_getMethodImplementation(class, @selector(encodeWithCoderForArchiver:)),
                                 protocol_getMethodDescription(@protocol(NSCoding), @selector(encodeWithCoder:), YES, YES).types
                                )) {
                                    NSLog(@"Critical Error - [UIImage encodeWithCoder:] not defined.");
                                }

        } 
    }
}

@implementation UIImage(NSCoding)

- (id) initWithCoderForArchiver:(NSCoder *)decoder {

    if ((self = [super init]))
    {
        NSData *data = [decoder decodeObjectForKey:kEncodingKey];
        self = [self initWithData:data];
    }

    return self;

}

- (void) encodeWithCoderForArchiver:(NSCoder *)encoder {

    NSData *data = UIImagePNGRepresentation(self);
    [encoder encodeObject:data forKey:kEncodingKey];

}

@end

到目前为止，我还没有发现任何进一步的问题。希望对您有所帮助!

[注意]

如果您使用此 UIImage 类别来归档 UIImageViewer 对象，请注意 iOS 5 中 UIImageViewer 的 NSCoding 实现似乎已损坏。当在 XIB 中指定时，UIImageViewer 的图像属性在保存和加载后丢失(我没有尝试查看在代码中创建 UIImageViewer 对象时是否存在相同的问题)。这已在 iOS 6 中修复。

[更新]

我更改了我的代码以在 +load 中添加方法而不是 initialize()，它仍然只执行一次，但更早。我当前的实现:

#import "UIImage+NSCoding.h"
#import <objc/runtime.h>
#define kEncodingKey        @"UIImage"

@implementation UIImage (NSCoding)

+ (void) load
{

    @autoreleasepool {
        if (![UIImage conformsToProtocol:@protocol(NSCoding)]) {
            Class class = [UIImage class];
            if (!class_addMethod(
                                 class,
                                 @selector(initWithCoder:), 
                                 class_getMethodImplementation(class, @selector(initWithCoderForArchiver:)),
                                 protocol_getMethodDescription(@protocol(NSCoding), @selector(initWithCoder:), YES, YES).types
                                 )) {
                NSLog(@"Critical Error - [UIImage initWithCoder:] not defined.");
            }

            if (!class_addMethod(
                                 class,
                                 @selector(encodeWithCoder:),
                                 class_getMethodImplementation(class, @selector(encodeWithCoderForArchiver:)),
                                 protocol_getMethodDescription(@protocol(NSCoding), @selector(encodeWithCoder:), YES, YES).types
                                 )) {
                NSLog(@"Critical Error - [UIImage encodeWithCoder:] not defined.");
            }

        } 
    }
}

- (id) initWithCoderForArchiver:(NSCoder *)decoder {
    if (self = [super init]) {
        NSData *data = [decoder decodeObjectForKey:kEncodingKey];
        self = [self initWithData:data];
    }

    return self;

}

- (void) encodeWithCoderForArchiver:(NSCoder *)encoder {

    NSData *data = UIImagePNGRepresentation(self);
    [encoder encodeObject:data forKey:kEncodingKey];

}

@end