使用任意字符串向左或向右填充 string.format(不是 padleft 或 padright)

问题描述

我可以使用 String.Format() 用任意字符填充某个字符串吗?

Can I use String.Format() to pad a certain string with arbitrary characters?

Console.WriteLine("->{0,18}<-", "hello");
Console.WriteLine("->{0,-18}<-", "hello");

returns 

->             hello<-
->hello             <-

我现在希望空格是任意字符.我无法使用 padLeft 或 padRight 执行此操作的原因是因为我希望能够在不同的位置/时间构造格式字符串，然后实际执行格式化.

I now want the spaces to be an arbitrary character. The reason I cannot do it with padLeft or padRight is because I want to be able to construct the format string at a different place/time then the formatting is actually executed.

--编辑--
看到我的问题似乎没有现有的解决方案，我想出了这个(在 三思而后行的建议)
--EDIT2--
我需要一些更复杂的场景，所以我选择了 Think Before Coding 的第二条建议

[TestMethod]
public void PaddedStringShouldPadLeft() {
    string result = string.Format(new PaddedStringFormatInfo(), "->{0:20:x} {1}<-", "Hello", "World");
    string expected = "->xxxxxxxxxxxxxxxHello World<-";
    Assert.AreEqual(result, expected);
}
[TestMethod]
public void PaddedStringShouldPadRight()
{
    string result = string.Format(new PaddedStringFormatInfo(), "->{0} {1:-20:x}<-", "Hello", "World");
    string expected = "->Hello Worldxxxxxxxxxxxxxxx<-";
    Assert.AreEqual(result, expected);
}
[TestMethod]
public void ShouldPadLeftThenRight()
{
    string result = string.Format(new PaddedStringFormatInfo(), "->{0:10:L} {1:-10:R}<-", "Hello", "World");
    string expected = "->LLLLLHello WorldRRRRR<-";
    Assert.AreEqual(result, expected);
}
[TestMethod]
public void ShouldFormatRegular()
{
    string result = string.Format(new PaddedStringFormatInfo(), "->{0} {1:-10}<-", "Hello", "World");
    string expected = string.Format("->{0} {1,-10}<-", "Hello", "World");
    Assert.AreEqual(expected, result);
}

因为代码有点多，不能发帖，我把它移到github上作为要点:
http://gist.github.com/533905#file_padded_string_format_info

Because the code was a bit too much to put in a post, I moved it to github as a gist:
http://gist.github.com/533905#file_padded_string_format_info

人们可以轻松地对其进行分支和任何事情:)

There people can easily branch it and whatever :)

推荐答案

还有另一种解决方案.

实现 IFormatProvider 以返回将传递给 string.Format 的 ICustomFormatter :

Implement IFormatProvider to return a ICustomFormatter that will be passed to string.Format :

public class StringPadder : ICustomFormatter
{
  public string Format(string format, object arg,
       IFormatProvider formatProvider)
  {
     // do padding for string arguments
     // use default for others
  }
}

public class StringPadderFormatProvider : IFormatProvider
{
  public object GetFormat(Type formatType)
  { 
     if (formatType == typeof(ICustomFormatter))
        return new StringPadder();

     return null;
  }
  public static readonly IFormatProvider Default =
     new StringPadderFormatProvider();
}

然后你可以这样使用它:

Then you can use it like this :

string.Format(StringPadderFormatProvider.Default, "->{0:x20}<-", "Hello");

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