初始化 NSString 时将 alloc 和 init 分开

发布于 2024-11-28 12:17:30 字数 679 浏览 2 评论 0原文

我有一种情况，我想分配一个 NSString 对象，并在 if-else 块内为其分配文本。当我编写这样的代码时：

NSString *string = [NSString alloc];  
if (firstCase) 
    [string initWithString:@"firstCase"];  
else if(secondCase)
    [string initWithString:@"secondCase"];  
[self someFunction:string];

我在 someFunction 内部收到错误（当我尝试使用 string 时抛出 NSInvalidArgumentException）。另外，当我单步执行代码时，一旦输入 someFunction，控制台就会生成一行内容：

你忘记嵌套alloc和init了吗？

它指的是字符串。

我已经尝试使用 NSMutableString 进行同样的操作，只是执行 string = [[NSMutableString alloc] init] 并附加到每个 if-else 块中的字符串，但我想知道是否有人知道为什么以前的方法不会产生相同的结果。

原文

I have a situation where I want to allocate a single NSString object, and assign text to it inside of an if-else block. When I write the code like this:

NSString *string = [NSString alloc];  
if (firstCase) 
    [string initWithString:@"firstCase"];  
else if(secondCase)
    [string initWithString:@"secondCase"];  
[self someFunction:string];

I get an error inside of someFunction (throws an NSInvalidArgumentException when I try to use string).
Also, when I step through my code, once i enter someFunction, the console produces a line that says:

Did you forget to nest alloc and init?

which is referring to string.

I've tried the same thing using an NSMutableString and just doing string = [[NSMutableString alloc] init] and just appending to the string in each if-else block, but I was wondering if anyone knew why the previous way does not produce the same results.

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守护在此方 2024-12-05 12:17:30

您是否可能遇到不满足 if 和 else if 要求的情况？您可能需要仔细检查您的情况...或者您可能希望将字符串默认为“”。 编辑：在使用 stringByAppendingString 将字符串声明为某个值后，您可以将其追加到该字符串

NSString *string = [[NSString alloc] initWithString:@""];
if(case1)
   [string stringByAppendingString:@"desired string"];
elseif(case2)
   [string stringByAppendingString:@"other string"];

这里是苹果 NSString 类参考的链接：
http://开发人员。 apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html

Is it possible your running into a case where you are not meeting requirements for your if and else if?? you might want to double check what your cases are... or you might want to default your string to "". EDIT: you can then append to the string after you have declared it to some value using stringByAppendingString

NSString *string = [[NSString alloc] initWithString:@""];
if(case1)
   [string stringByAppendingString:@"desired string"];
elseif(case2)
   [string stringByAppendingString:@"other string"];

here is a link to apple's NSString class reference:
http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html

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