C# 字符串格式标志或修饰符到小写参数 [英] C# string format flag or modifier to lowercase param

问题描述

是否可以在字符串格式参数上指定某种标志或修饰符以使其小写或大写?

Is it possible to specify some kind of flag or modifier on a string format param to make it lower case or upper case?

我想要的示例:

String.Format("Hi {0:touppercase}, you have {1} {2:tolowercase}.", "John", 6, "Apples");

想要的输出:

约翰，你有 6 个苹果.

Hi JOHN, you have 6 apples.

PS:是的，我知道我可以在以字符串格式使用参数之前更改参数的大小写，但我不想要这个.

PS: Yes I know that I can change the case of the param before using it in the string format, but I don't want this.

推荐答案

只有填充和对齐格式...所以简单的方法就像你说的那样，使用 "John".ToUpper()或 "John".ToLower().

There's only padding and allignment formating... So the easy way is like you said, use "John".ToUpper() or "John".ToLower().

另一种解决方案是创建自定义 IFormatProvider，以提供所需的字符串格式.

Another solution could be create a custom IFormatProvider, to provide the string format you want.

这就是 IFormatProvider 和 string.Format 调用的外观.

This is how will look the IFormatProvider and the string.Format call.

public class CustomStringFormat : IFormatProvider, ICustomFormatter
{
    public object GetFormat(Type formatType)
    {
        if (formatType == typeof(ICustomFormatter))
            return this;
        else
            return null;

    }

    public string Format(string format, object arg, IFormatProvider formatProvider)
    {
        string result = arg.ToString();

        switch (format.ToUpper())
        {
            case "U": return result.ToUpper();
            case "L": return result.ToLower();
            //more custom formats
            default: return result;
        }
    }
}

调用将如下所示:

String.Format(new CustomStringFormat(), "Hi {0:U}", "John");

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