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

Pad left or right with string.format (not padleft or padright) with arbitrary string

提问by Boris Callens

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

我可以使用 String.Format() 用任意字符填充某个字符串吗？

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

returns 

->             hello<-
->hello             <-

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.

我现在希望空格是任意字符。我不能用 padLeft 或 padRight 做到这一点的原因是因为我希望能够在不同的地点/时间构造格式字符串，然后实际执行格式。

--EDIT--
Seen that there doesn't seem to be an existing solution to my problem I came up with this (after Think Before Coding's suggestion)
--EDIT2--
I needed some more complex scenarios so I went for Think Before Coding's second suggestion

--EDIT--
看到我的问题似乎没有现有的解决方案，我想出了这个（在思考之前编码的建议之后）--
EDIT2--
我需要一些更复杂的场景，所以我选择了思考之前的编码第二个建议

[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);
}

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

因为代码有点多，放不下，我把它移到github上作为gist：http:
//gist.github.com/533905#file_padded_string_format_info

There people can easily branch it and whatever :)

在那里人们可以轻松地分支它等等:)

采纳答案by thinkbeforecoding

There is another solution.

还有另一种解决方案。

Implement IFormatProviderto return a ICustomFormatterthat will be passed to string.Format :

实现IFormatProvider返回一个ICustomFormatter将被传递给 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();
}

Then you can use it like this :

然后你可以像这样使用它：

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

回答by configurator

Edit: I misunderstood your question, I thought you were asking how to pad with spaces.

编辑：我误解了你的问题，我以为你在问如何填充空格。

What you are asking is not possible using the string.Formatalignment component; string.Formatalways pads with whitespace. See the Alignment Componentsection of MSDN: Composite Formatting.

使用string.Format对齐组件无法满足您的要求；string.Format总是用空格填充。请参阅MSDN: Composite Formatting的对齐组件部分。

According to Reflector, this is the code that runs inside StringBuilder.AppendFormat(IFormatProvider, string, object[])which is called by string.Format:

根据 Reflector，这是在内部运行的代码，StringBuilder.AppendFormat(IFormatProvider, string, object[])它被调用string.Format：

int repeatCount = num6 - str2.Length;
if (!flag && (repeatCount > 0))
{
    this.Append(' ', repeatCount);
}
this.Append(str2);
if (flag && (repeatCount > 0))
{
    this.Append(' ', repeatCount);
}

As you can see, blanks are hard coded to be filled with whitespace.

如您所见，空白被硬编码为用空白填充。

回答by thinkbeforecoding

You could encapsulate the string in a struct that implements IFormattable

您可以将字符串封装在实现 IFormattable 的结构中

public struct PaddedString : IFormattable
{
   private string value;
   public PaddedString(string value) { this.value = value; }

   public string ToString(string format, IFormatProvider formatProvider)
   { 
      //... use the format to pad value
   }

   public static explicit operator PaddedString(string value)
   {
     return new PaddedString(value);
   }
}

Then use this like that :

然后像这样使用：

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

result:

结果：

"->xxxxxxxxxxxxxxxHello<-"

回答by Emax83

Simple:

简单的：

    dim input as string = "SPQR"
    dim format as string =""
    dim result as string = ""

    'pad left:
    format = "{0,-8}"
    result = String.Format(format,input)
    'result = "SPQR    "

    'pad right
    format = "{0,8}"
    result = String.Format(format,input)
    'result = "    SPQR"