使用object_setIvar时为EXC_BAD_ACCESS

Jonathan 发表于 Dev

乔纳森

我试图在使用以下代码分配的运行时类上添加和设置Ivar。我没有使用Objective-C运行时函数的经验，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，都会在行上收到EXC_BAD_ACCESS（code = 2，address = 0x10）错误object_setIvar(objectClass, ivar, [value copy]);。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，但是显然ivar为nil。我试过NSLog ivar，但是遇到了同样的错误。

我曾尝试在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 Simulator上运行该应用程序。

马丁·R

您不能在类上为实例变量设置值。创建并注册该类之后，您可以创建该类的实例：

id myInstance = [[objectClass alloc] init];

然后为此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]);
}

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