xcode setString NSMutableString
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setString NSMutableString
提问by Jonathan Goyens
I am new to programming in XCode, and as a first familiarisation exercise, I would like to make a small Calculator app. So obviously I came upon a few problems: I try to have the user use buttons to type the digits and operators into a string, which he then sees. When I use
我是 XCode 编程的新手，作为第一个熟悉练习，我想制作一个小型计算器应用程序。很明显，我遇到了一些问题：我尝试让用户使用按钮将数字和运算符键入一个字符串，然后他会看到。当我使用
displayString = [NSString stringWithFormat:@"%@%@", displayString, operatorString];
everything works fine. Then I decided to work with NSMutableStrings in order to get deletebuttons. I changed the headerfile appropriately, after which I still the earlier NSString functionality (? because NSMutableString inherits from NSString?) And then I got the following problem:
一切正常。然后我决定使用 NSMutableStrings 来获取删除按钮。我适当地更改了头文件，之后我仍然使用较早的 NSString 功能（？因为 NSMutableString 继承自 NSString？）然后我遇到了以下问题：
[displayString setString:@"test"];
NSLog(@"%@", displayString);
Even when this is the first method I call, I still get nul. I What am I doing wrong?
即使这是我调用的第一个方法，我仍然得到空值。我做错了什么？
Unrelated, is there a way to have this string write to a sort of function: I would like to be able to do
不相关，有没有办法让这个字符串写入某种函数：我希望能够做到
result = contentof:displayString
or something a like. Any ideas in how I could do this?
或类似的东西。关于我如何做到这一点的任何想法？
回答by esqew
NSStringdoesn't have a setString:method. (Documentation)
NSString没有setString:方法。（文档）
For this case, you'd need an NSMutableString. Here's how you'd implement it:
对于这种情况，您需要一个NSMutableString. 下面是你如何实现它：
NSMutableString *mutableString = [[NSMutableString alloc] initWithFormat:"%@%@", displayString, operatorString];
... and then to change it:
...然后改变它：
[mutableString setString:@"test"];
