问题描述
我在某种情况下，我想在运行时为一个类动态生成getter和setter（以类似于NSManagedObject在后台的方式）。从我的理解，这是可能使用resolveInstanceMethod：在一个特定的类。此时，您必须使用class_addMethod动态添加基于选择器的方法。我理解这在理论层面，但我没有深入到obj-c运行时，所以我很好奇，如果有任何伟大的例子如何做到这一点。我的大部分知识来自这篇文章：
I am in a situation where I want to dynamically generate getters and setters for a class at runtime (in a similar manner to what NSManagedObject does behind the scenes). From my understanding, this is possible using resolveInstanceMethod: on a specific class. At this point, you would have to use class_addMethod to dynamically add the method based on the selector. I understand this at a theoretical level, but I haven't delved much into the obj-c runtime, so I was curious if there were any great examples of how to do this. Most of my knowledge comes from this article:
任何想法/示例？
推荐答案
Ash的。这不是那么难，实际上。
The only nice discussion I know is at Mike Ash's blog post. It's not that hard, actually.
我曾经需要将一个大的 NSManagedObject 子类拆分为两个，但决定保留实现细节我不必重写我的应用程序的其他部分。所以，我需要合成getter和setter，发送 [self foo] 到 [self.data foo] 。
I once needed to split a big NSManagedObject subclass into two, but decided to keep the fact an implementation detail so that I don't have to rewrite other parts of my app. So, I needed to synthesize getter and setter which sends [self foo] to [self.data foo], automatically.
为此，我做了以下工作：
To achieve that, I did the following:
-
新的方法，已经在我的类。
Prepare the new method, already in my class.
- (id)_getter_
{
return objc_msgSend(self.data, _cmd);
}
- (void)_setter_:(id)value
{
objc_msgSend(self.data, _cmd,value);
}
注意 _cmd 有选择器。因此，通常， _cmd 是 @selector（_getter _）或 @selector（_setter_） 在这些方法中，但我要插入 _getter _ 的实现作为 foo 。然后， _cmd 包含 @selector（foo），因此调用 self.data '
Note that _cmd has the selector in it. So, usually, _cmd is either @selector(_getter_) or @selector(_setter_) in these methods, but I'm going to plug the implementation of _getter_ as the implementation of foo. Then, _cmd contains @selector(foo), and thus calls self.data's foo.
写一个通用合成方法：
+(void)synthesizeForwarder:(NSString*)getterName
{
NSString*setterName=[NSString stringWithFormat:@"set%@%@:",
[[getterName substringToIndex:1] uppercaseString],[getterName substringFromIndex:1]];
Method getter=class_getInstanceMethod(self, @selector(_getter_));
class_addMethod(self, NSSelectorFromString(getterName),
method_getImplementation(getter), method_getTypeEncoding(getter));
Method setter=class_getInstanceMethod(self, @selector(_setter_:));
class_addMethod(self, NSSelectorFromString(setterName),
method_getImplementation(setter), method_getTypeEncoding(setter));
}
注意这是一个类方法。因此 self 代表类。还要注意，我没有硬编码类型编码（这告诉Objective-C运行时特定方法的参数）。类型编码的语法是文档化的，但手工构建非常容易出错;我浪费了几天，直到迈克·艾姆告诉我停止它。
Note that this is a class method. So self stands for the class. Note also that I didn't hardcode type encodings (which tells Objective-C runtime what the arguments of the particular method are). The syntax of type encodings is documented, but constructing by hand is very error-prone; I wasted a few days that way until Mike Ash told me to stop it. Generate it using an existing method.
尽早生成转发器：
+(void)load
{
for(NSString*selectorName in [NSArray arrayWithObjects:@"foo", @"bar", @"baz",nil]){
[self synthesizeForwarder:selectorName];
}
}
这会生成 foo ， setFoo：， bar ， setBar：和 baz ， setBaz：。
希望这有助于！
这篇关于动态Getters和Setter与Objective C的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！