ios - 使用 object_setIvar 时出现 EXC_BAD_ACCESS

Question

我正在尝试在我使用下面的代码分配的运行时类上添加和设置 Ivars。我对 Objective-C 运行时函数没有任何经验，这就是我尝试学习的原因。

    if ([object isKindOfClass:[NSDictionary class]])
    {
        const char *className = [aName cStringUsingEncoding:NSASCIIStringEncoding];

        // Allocate the class using the class name, NSObject metaclass, and a size of 0
        Class objectClass = objc_allocateClassPair([NSObject class], className, 0);

        // Get all of the keys in the dictionary to use as Ivars
        NSDictionary *dictionaryObject = (NSDictionary *)object;
        NSArray *dictionaryObjectKeys = [dictionaryObject allKeys];

        for (NSString *key in dictionaryObjectKeys)
        {
            // Convert the NSString to a C string
            const char *iVarName = [key cStringUsingEncoding:NSASCIIStringEncoding];

            // Add the Ivar to the class created above using the key as the name
            if (class_addIvar(objectClass, iVarName, sizeof(NSString*), log2(sizeof(NSString*)), @encode(NSString*)))
            {
                // Get the newly create Ivar from the class created above using the key as the name
                Ivar ivar = class_getInstanceVariable(objectClass, iVarName);

                // Set the newly created Ivar to the value of the key
                id value = dictionaryObject[key];
                object_setIvar(objectClass, ivar, [value copy]);
            }
        }

        objc_registerClassPair(objectClass);
    }

每次我运行上面的代码时，我都会在行 object_setIvar(objectClass, ivar, [value copy]); 上收到 EXC_BAD_ACCESS (code=2, address = 0x10) 错误。我不明白为什么会收到此错误。在尝试设置 Ivar 的值之前，我检查了 Ivar 是否已成功添加到类中，但显然 Ivar 为零。我试过对 ivar 进行 NSLog，但我得到了同样的错误。

我尝试在 Google 上搜索解决方案，但找不到关于 objective-c 运行时函数的太多信息。

我正在使用 ARC 并在 iOS 模拟器上运行该应用。

Answer 1

您不能为类 上的实例变量设置值。创建并注册类后，您可以创建该类的实例:

id myInstance = [[objectClass alloc] init];

然后为该对象的实例变量设置值:

for (NSString *key in dictionaryObjectKeys)
{
    const char *iVarName = [key cStringUsingEncoding:NSASCIIStringEncoding];

    id value = dictionaryObject[key];
    Ivar ivar = class_getInstanceVariable(objectClass, iVarName);

    object_setIvar(myInstance, ivar, [value copy]);
}