Question

我对iOS很新,但我对一个简单任务的复杂性感到有点困惑。我试图将我定制的名为“车辆”的导航器类保存在NSUSER Defaults。显然,这无法完成,所以我需要先将其编码为NSDATA。好吧。

但这意味着我需要把每类财产都编码在代码里...

在我的车级...

- (void) encodeWithCoder: (NSCoder *) coder
{
    [coder encodeInt: x  forKey: @"x"];
    [coder encodeInt: y  forKey: @"y"];
    [coder encodeInt: direction  forKey: @"direction"];

} // encodeWithCoder

- (id) initWithCoder: (NSCoder *) coder
{
    if (self = [super init]) {
        x = [coder decodeIntForKey: @"x"];
        y = [coder decodeIntForKey: @"y"];
        direction = [coder decodeIntForKey: @"direction"];
    }

    return (self);

} // initWithCoder

如果我最后在车辆类中添加了一个新的属性, 我也必须添加编码和解码逻辑。这与使用 CopyWood Zone 创建一个类的副本是一样的。这就留下了3 或 4 个区域, 在类中添加新属性可能会出错。

我目前主要在LabVIEW做节目, 我们有能力上一个班, 并把它喂给编码器, 它将自动完成所有版本和产权操作。

所以我想我的问题是:

Is this not heard of in iOS?
If it s not possible, is there a way to enumerate through all properties in a class and write a function to do this automatically.

Answer 1

您可以使用目标- c 运行时间查找对象的所有属性并解码它们, 但我不推荐它。如果您没有解码, 我可以为您创建一个简单的示例。

举个例子:

#import <objc/runtime.h>

void decodePropertiesOfObjectFromCoder(id obj, NSCoder *coder)
{
    // copy the property list
    unsigned propertyCount;
    objc_property_t *properties = class_copyPropertyList([obj class], &propertyCount);

    for (int i = 0; i < propertyCount; i++) {
        objc_property_t property = properties[i];

        char *readonly = property_copyAttributeValue(property, "R");
        if (readonly)
        {
            free(readonly);
            continue;
        }

        NSString *propName = [NSString stringWithUTF8String:property_getName(property)];

        @try 
        {
            [obj setValue:[coder decodeObjectForKey:propName] forKey:propName];
        }
        @catch (NSException *exception) {
            if (![exception.name isEqualToString:@"NSUnknownKeyException"])
            {
                @throw exception;
            }

            NSLog(@"Couldn t decode value for key %@.", propName);
        }
    }

    free(properties);
}

void encodePropertiesOfObjectToCoder(id obj, NSCoder *coder)
{
    // copy the property list
    unsigned propertyCount;
    objc_property_t *properties = class_copyPropertyList([obj class], &propertyCount);

    for (int i = 0; i < propertyCount; i++) {
        objc_property_t property = properties[i];

        char *readonly = property_copyAttributeValue(property, "R");
        if (readonly)
        {
            free(readonly);
            continue;
        }

        NSString *propName = [NSString stringWithUTF8String:property_getName(property)];

        @try {
            [coder encodeObject:[obj valueForKey:propName] forKey:propName];
        }
        @catch (NSException *exception) {
            if (![exception.name isEqualToString:@"NSUnknownKeyException"])
            {
                @throw exception;
            }

            NSLog(@"Couldn t encode value for key %@.", propName);
        }
    }

    free(properties);
}

__attribute__((constructor))
static void setDefaultNSCodingHandler()
{
    class_addMethod([NSObject class], @selector(encodeWithCoder:), imp_implementationWithBlock((__bridge void *)[^(id self, NSCoder *coder) {
        encodePropertiesOfObjectToCoder(self, coder);
    } copy]), "v@:@");
    class_addMethod([NSObject class], @selector(initWithCoder:), imp_implementationWithBlock((__bridge void *)[^(id self, NSCoder *coder) {
        if ((self = [NSObject instanceMethodForSelector:@selector(init)](self, @selector(init))))
        {
            decodePropertiesOfObjectFromCoder(self, coder);
        }

        return self;
    } copy]), "v@:@");
}

这将允许您编码任何显示足够属性以进行自我重建的物体。

友情链接