NSInvocation帶有枚舉？

Question

------------編輯-------------

TL; DR：

看來我錯誤地使用了NSInvocation類（缺少指針知識）。

使用這些方法的方式如下所示（工作）：

NSString *str = @"string";
UIControlState state = UIControlStateNormal;
[invocation setArgument: &str atIndex: 2];
[invocation setArgument: &state atIndex: 3];

---------------原始問題---------

可以用枚舉參數設置setArgument:atIndex:嗎？

請參見以下示例（無效）：

UIButton *btn = ...;
SEL selector = @selector(setTitle:forState:);
NSInovcation *invocation = [NSInovcation invocationWithMethodSignature: [btn methodSignatureForSelector: selector]];
[invocation setSelector: selector];
[invocation setArgument: @"Test" atIndex: 2];

//Nothing happens
UIControlState state = UIControlStateNormal;
[invocation setArgument: &state atIndex: 3];

//Runtime error (the pointer is NULL)
UIControlState *state = UIControlStateNormal;
[invocation setArgument: state atIndex: 3];

//No errors but no effect
int state2 = 0;
[invocation setArgument: &state atIndex: 3];

//Compile error (casting)
[invocation setArgument: @(UIControlStateNormal) atIndex: 3];
//Runtime EXC_BAD_ACCESS
[invocation setArgument: (void *)@(UIControlStateNormal) atIndex: 3];

...
[invocation invokeWithTarget: btn];

奇怪的是（或不是），它與performSelector:...一起使用時效果很好：

[btn performSelector: selector withObject: @"Testing" withObject:@(UIControlStateNormal)];

我不確定我是否以正確的方式使用NSInovcation。 有人想詳細說明嗎？

Answer 1

嘗試這個：

NSString *test = @"Test";
[invocation setArgument: &test atIndex: 2];

UIControlState state = UIControlStateNormal;
[invocation setArgument: &state atIndex: 3];