为什么我的比较if语句不工作？ [英] Why is my comparing if statement not working?

问题描述

为什么下面的代码（在可可中）不工作？

Why is the following code (in cocoa) not working?

NSString *extension = [fileName pathExtension];
NSString *wantedExtension = @"mp3";
if(extension == wantedExtension){
//work
}

在Xcode这只是运行没有警告或错误，但不做我认为它应该做的。

in Xcode this just runs without warnings or errors but doesn't do what I think it SHOULD do.

推荐答案

if ([extension isEqualToString:wantedExtension]) {
...
}

==比较指针。 isEqual：和isEqualToString：比较字符串，虽然isEqualToString是更好的，如果你知道extension和wantedExtension是NSString（在这种情况下你这样做）。

"==" compares the pointers. isEqual: and isEqualToString: compare the strings, although isEqualToString is better if you know both extension and wantedExtension are NSString (which you do in this case).

像我一样的旧的C ++和Java程序员，你可能会更快乐地把一个已知不是null，wantedextension，第一。在目标C中，由于发送消息（即调用方法）返回0或false，因此不必要。

Actually, if you're an old C++ and Java programmer like me, you might be happier putting the one that is known not to be null, "wantedextension", first. In Objective C that is not necessary because "sending a message" (ie calling a method) to a nil returns 0 or false.

if ([wantedExtension isEqualToString:extension]) {
   ...
}

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