ARC中的object_getInstanceVariable/object_setInstanceVariable [英] object_getInstanceVariable/object_setInstanceVariable in ARC

问题描述

为什么Objective-C运行时方法object_getInstanceVariable和object_setInstanceVariable在自动引用计数下不可用，我该怎么办?

Why are the Objective-C runtime methods object_getInstanceVariable and object_setInstanceVariable are not available under Automatic Reference Counting and what can I do about it?

object_getInstanceVariable有问题.我该如何解决?

object_getInstanceVariable is buggy when the instance variable's size is larger than the development target's pointer size. How can I get around this?

推荐答案

请改用valueForKey:和setValue:forKey:方法.这些允许您读取/写入对象的任何实例变量.对于原始类型的实例变量，这些方法返回/获取包装为NSNumber或NSValue对象的值.

Use the valueForKey: and setValue:forKey: methods instead. These allow you to read/write any instance variable of an object. For primitive-typed instance variables these methods return/take values wrapped as NSNumber or NSValue objects.

您拥有的实例变量大于指针大小，也许是struct的大小?这是一些显示与struct一起使用的代码片段，首先让我们定义一个struct:

You have instance variables larger than the pointer size, maybe struct's? Here are some code fragments showing use with a struct, first let's define a struct:

typedef struct
{
   int i;
   float f;
   char c;
} ThreePrimitives;

和带有(私有)实例变量的类:

and a class with a (private) instance variable:

@interface StructClass : NSObject
...
@end

@implementation StructClass
{
   ThreePrimitives myStruct;
}
...
@end

设置实例变量:

ThreePrimitives a = { 42, 3.14, 'x' };
NSValue *wrapA = [NSValue value:&a withObjCType:@encode(ThreePrimitives)];
[sc setValue:wrapA forKey:@"myStruct"];

要读取实例变量，请执行以下操作:

To read the instance variable:

ThreePrimitives b;
NSValue *extracted = [sc valueForKey:@"myStruct"];   
[extracted getValue:&b];

HTH

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