objective-c - 宏编译器错误：当参数名称出现在别处时出现“解析问题”

Question

我尝试制作一个简单的宏来在 iOS 中创建和显示一个简单的“ok”对话框：

#define ALERT_DIALOG(title,message) \
do\
{\
    UIAlertView *alert_Dialog = [[UIAlertView alloc] initWithTitle:(title) message:(message) delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];\
    [alert_Dialog show];\
} while ( 0 )

如果我尝试在我的代码中使用它：

ALERT_DIALOG(@"Warning", @"Message");

我得到错误：

解析问题。预期的 ']'

并且错误似乎指向第二个@之前"Message"。

但是，如果我只是复制粘贴宏，我不会收到此错误：

NSString *title = @"Warning";
NSString *message = @"Message";
do
{
    UIAlertView *alert_Dialog = [[UIAlertView alloc] initWithTitle:(title) message:(message) delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [alert_Dialog show];
} while ( 0 );

是否反对在宏中使用 Objective-c 结构？或者那是别的什么？

Answer 1

你的宏的问题是两个出现的messagein

... [[UIAlertView alloc] initWithTitle:(title) message:(message) ...

替换为@"Message"，导致

.... [[UIAlertView alloc] initWithTitle:(@"Warning") @"Message":(@"Message") ...

这会导致语法错误。

I don't think that it is really worth defining this as a macro, but if you do, you have to use macro arguments which do not occur at places where they should not be expanded, e.g.

#define ALERT_DIALOG(__title__,__message__) \
do\
{\
    UIAlertView *alert_Dialog = [[UIAlertView alloc] initWithTitle:(__title__) message:(__message__) delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];\
    [alert_Dialog show];\
} while ( 0 )

or similar.

Answer 2

您可以将其声明为 C 函数，而不是将其声明为宏：

void ALERT_DIALOG(NSString *title, NSString *message) {
    UIAlertView *alert_Dialog = [[UIAlertView alloc] initWithTitle:(title) message:(message) delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];\
    [alert_Dialog show];
}