在Objective-C中将对象转换(或复制)到子类实例 [英] Transform (or copy) an object to a subclass instance in Objective-C

问题描述

我想将一个对象的实例转换为该对象类的子类的实例，以便可以在Objective-C中使用该子类的其他方法和属性.

I want to transform an instance of an object into an instance of a subclass of that object class, so that I can use the additional methods and properties of that subclass, in Objective-C.

如何以不需要我在复制方法中硬编码该对象类的属性的方式来做到这一点?

How can I do this in a way that does not require me to hardcode the properties of that object class in a copy method?

推荐答案

在Objective-C中无法将对象转换为子类的实例.但是，通过下面的类，您可以提供对象和子类的实例，并将所有属性的值复制到子类实例.此实现适用于 Objective-C 对象类型和 C 原语.只要知道重要变量是可见的并且可以设置的(即，没有显示为只读"的属性)，就不必指定(甚至确定)需要复制的属性.完全不公开，其值无法由该类重新计算).因此，此方法对于已知类相对健壮，并且不需要更新以支持您在适合这些参数的对象类中所做的未来更改.它与iOS 8兼容.

It is not possible to transform an object into an instance of a subclass in Objective-C. However, with the class below you can supply an instance of both the object and the subclass and have the values of all properties copied to the subclass instance. This implementation works with both Objective-C object types and C primitives. You do not have to specify (or indeed even determine) the properties that need to be copied, providing you know that the important variables are visible and can be set (i.e., there are no properties that are exposed as "read only" or not exposed at all, whose values cannot be recalculated by the class). This method is thus relatively robust for known classes and will not require updating to support future changes you make in your object class that fit these parameters. It is iOS 8 compatible.

此类提供了四个类方法:

This class provides four class methods:

+ (id) copyObject:(id)object toSubclassObject:(id)subclassObject

将对象的所有属性复制到subclassObject.如果subclassObject不是对象的子类，则返回nil.

Copies all properties of object to subclassObject. If the subclassObject is not a subclass of object, nil is returned.

+ (NSDictionary *) propertiesOfObject:(id)object;

返回一个对象的所有可见属性的字典，包括其所有超类(NSObject除外)的那些属性.

Returns a dictionary of all visible properties of an object, including those from all its superclasses (other than NSObject).

+ (NSDictionary *) propertiesOfClass:(Class)class;

返回一个类的所有可见属性的字典，包括来自其所有超类(NSObject除外)的那些属性.

Returns a dictionary of all visible properties of a class, including those from all its superclasses (other than NSObject).

+ (NSDictionary *) propertiesOfSubclass:(Class)class;

将所有特定于 的可见属性的字典返回给子类.它的超类的属性不包含在 中.

Returns a dictionary of all visible properties that are specific to a subclass. Properties for its superclasses are not included.

标题:

//  SYNUtilities.h

#import <Foundation/Foundation.h>

@interface SYNUtilities : NSObject
+ (id) copyObject:(id)object toSubclassObject:(id)subclassObject;
+ (NSDictionary *) propertiesOfObject:(id)object;
+ (NSDictionary *) propertiesOfClass:(Class)class;
+ (NSDictionary *) propertiesOfSubclass:(Class)class;
@end

实施:

#import "SYNUtilities.h"
#import <objc/runtime.h>
#import <objc/message.h>

@implementation SYNUtilities
+ (id) copyObject:(id)object toSubclassObject:(id)subclassObject
{
    if (![[subclassObject class] isSubclassOfClass:[object class]]) {
        return nil;
    }

    NSDictionary * properties = [self propertiesOfObject:object];
    NSLog(@"Properties of %@:\n%@", [object class], properties);

    for (NSString * property in properties) {
        SEL selector = NSSelectorFromString(property);
        if (selector) {
            id value = [object valueForKey:property];
            [subclassObject setValue:value forKey:property];
        }
    }
    return subclassObject;
}

+ (NSDictionary *) propertiesOfObject:(id)object
{
    Class class = [object class];
    return [self propertiesOfClass:class];
}

+ (NSDictionary *) propertiesOfClass:(Class)class
{
     if (class == NULL) {
        return nil;
    }

   NSMutableDictionary * properties = [NSMutableDictionary dictionary];
    [self propertiesForHierarchyOfClass:class onDictionary:properties];
    return [NSDictionary dictionaryWithDictionary:properties];
}

+ (NSDictionary *) propertiesOfSubclass:(Class)class
{
    if (class == NULL) {
        return nil;
    }

    NSMutableDictionary *properties = [NSMutableDictionary dictionary];
    return [self propertiesForSubclass:class onDictionary:properties];
}

+ (NSMutableDictionary *)propertiesForHierarchyOfClass:(Class)class onDictionary:(NSMutableDictionary *)properties
{
    if (class == NULL) {
        return nil;
    }

    if (class == [NSObject class]) {
        // On reaching the NSObject base class, return all properties collected.
        return properties;
    }

    // Collect properties from the current class.
    [self propertiesForSubclass:class onDictionary:properties];

    // Collect properties from the superclass.
    return [self propertiesForHierarchyOfClass:[class superclass] onDictionary:properties];
}

+ (NSMutableDictionary *) propertiesForSubclass:(Class)class onDictionary:(NSMutableDictionary *)properties
{
    unsigned int outCount, i;
    objc_property_t *objcProperties = class_copyPropertyList(class, &outCount);
    for (i = 0; i < outCount; i++) {
        objc_property_t property = objcProperties[i];
        const char *propName = property_getName(property);
        if(propName) {
            const char *propType = getPropertyType(property);
            NSString *propertyName = [NSString stringWithUTF8String:propName];
            NSString *propertyType = [NSString stringWithUTF8String:propType];
            [properties setObject:propertyType forKey:propertyName];
        }
    }
    free(objcProperties);

    return properties;
}

static const char *getPropertyType(objc_property_t property) {
    const char *attributes = property_getAttributes(property);
    char buffer[1 + strlen(attributes)];
    strcpy(buffer, attributes);
    char *state = buffer, *attribute;
    while ((attribute = strsep(&state, ",")) != NULL) {
        if (attribute[0] == 'T' && attribute[1] != '@') {
            // A C primitive type:
            /*
             For example, int "i", long "l", unsigned "I", struct.
             Apple docs list plenty of examples of values returned. For a list
             of what will be returned for these primitives, search online for
             "Objective-c" "Property Attribute Description Examples"
             */
            NSString *name = [[NSString alloc] initWithBytes:attribute + 1 length:strlen(attribute) - 1 encoding:NSASCIIStringEncoding];
            return (const char *)[name cStringUsingEncoding:NSASCIIStringEncoding];
        }
        else if (attribute[0] == 'T' && attribute[1] == '@' && strlen(attribute) == 2) {
            // An Objective C id type:
            return "id";
        }
        else if (attribute[0] == 'T' && attribute[1] == '@') {
            // Another Objective C id type:
            NSString *name = [[NSString alloc] initWithBytes:attribute + 3 length:strlen(attribute) - 4 encoding:NSASCIIStringEncoding];
            return (const char *)[name cStringUsingEncoding:NSASCIIStringEncoding];
        }
    }
    return "";
}

@end

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