Cocoa - 从另一个可变参数调用可变参数方法（NSString stringWithFormat call） [英] Cocoa - Calling a variadic method from another variadic one (NSString stringWithFormat call)

问题描述

我有一个问题与 [NSString strigWithFormat：format] 因为它返回一个id，我有很多代码，我把NSString var更改为其他个人类型。但编译器不会阻止我有一个NSString将被设置为另一种类型的对象的地方。

I have a problem with [NSString strigWithFormat:format] because it returns an id, and I have a lot of code where I changed a NSString var to an other personal type. But the compiler does not prevent me that there are places where a NSString is going to be set into another type of object.

所以我写一个类NSString和我打算把 stringWithFormat 的所有调用替换为 myStringWithFormat 。

So I'm writing a category of NSString and I'm goind to replace all my calls to stringWithFormat to myStringWithFormat.

代码是：

@interface NSString (NSStringPerso)
+ (NSString*) myStringWithFormat:(NSString *)format;
@end



@implementation NSString (NSStringPerso)
+ (NSString*) myStringWithFormat:(NSString *)format {
    return (NSString*)[NSString stringWithFormat:format];
}
@end

编译器告诉我Format not a string没有格式参数。

The compiler tells me that "Format not a string literal and no format arguments".

你看到任何方法使这项工作吗？

Do you see any way to make this work ?

推荐答案

NSString 包括从变参函数接收参数列表的方法。看看这个示例函数：

NSString includes a method that takes in an argument list from a variadic function. Look at this sample function:

void print (NSString *format, ...) {
    va_list arguments;
    va_start(arguments, format);

    NSString *outout = [[NSString alloc] initWithFormat:format arguments:arguments];
    fputs([output UTF8String], stdout);
    [output release];

    va_end(arguments);
}

一些代码是不相关的，但关键是 NSString * output = [[NSString alloc] initWithformat：format arguments：arguments]; 。这是如何在一个可变函数/方法中构造一个 NSString 。

Some of that code is irrelevant, but the key line is NSString *output = [[NSString alloc] initWithformat:format arguments:arguments];. That's how you can construct an NSString in a variadic function/method.

在你的case，你的代码应该是这样：

In your case, your code should look something like this:

+ (NSString *)myStringWithFormat:(NSString *)format, ... {
    va_list arguments;
    va_start(arguments, format);

    NSString *formattedString = [[NSString alloc] initWithFormat:format arguments:arguments];
    va_end(arguments);

    // perform some modifications to formattedString

    return [formattedString autorelease];
}

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