我有一个价格字段显示,有时可以是100或100.99或100.9,我想要的是显示价格在小数点后2位,只有小数输入的价格,例如,如果它的100,它应该只显示100而不是100.00,如果价格是100.2,它应该显示100.20类似的100.22应该是一样的。 我谷歌了一下,找到了一些例子,但它们并不完全符合我想要的:

// just two decimal places
String.Format("{0:0.00}", 123.4567);      // "123.46"
String.Format("{0:0.00}", 123.4);         // "123.40"
String.Format("{0:0.00}", 123.0);         // "123.00"

当前回答

如果你的程序需要快速运行,调用value. tostring (formatString)可以获得比$"{value:formatString}"和string快35%的字符串格式化性能。格式(formatString值)。

Data

Code

using System;
using System.Diagnostics;

public static class StringFormattingPerformance
{
   public static void Main()
   {
      Console.WriteLine("C# String Formatting Performance");
      Console.WriteLine("Milliseconds Per 1 Million Iterations - Best Of 5");
      long stringInterpolationBestOf5 = Measure1MillionIterationsBestOf5(
          (double randomDouble) =>
          {
             return $"{randomDouble:0.##}";
          });
      long stringDotFormatBestOf5 = Measure1MillionIterationsBestOf5(
          (double randomDouble) =>
          {
             return string.Format("{0:0.##}", randomDouble);
          });
      long valueDotToStringBestOf5 = Measure1MillionIterationsBestOf5(
          (double randomDouble) =>
          {
             return randomDouble.ToString("0.##");
          });
      Console.WriteLine(
$@"            $""{{value:formatString}}"": {stringInterpolationBestOf5} ms
 string.Format(formatString, value): {stringDotFormatBestOf5} ms
       value.ToString(formatString): {valueDotToStringBestOf5} ms");
   }

   private static long Measure1MillionIterationsBestOf5(
       Func<double, string> formatDoubleUpToTwoDecimalPlaces)
   {
      long elapsedMillisecondsBestOf5 = long.MaxValue;
      for (int perfRunIndex = 0; perfRunIndex < 5; ++perfRunIndex)
      {
         var random = new Random();
         var stopwatch = Stopwatch.StartNew();
         for (int i = 0; i < 1000000; ++i)
         {
            double randomDouble = random.NextDouble();
            formatDoubleUpToTwoDecimalPlaces(randomDouble);
         }
         stopwatch.Stop();
         elapsedMillisecondsBestOf5 = Math.Min(
            elapsedMillisecondsBestOf5, stopwatch.ElapsedMilliseconds);
      }
      return elapsedMillisecondsBestOf5;
   }
}

代码的输出

C# String Formatting Performance
Milliseconds Per 1 Million Iterations - Best Of 5
            $"{value:formatString}": 419 ms
 string.Format(formatString, value): 419 ms
       value.ToString(formatString): 264 ms

参考文献

自定义数字格式字符串[learn.microsoft.com]

Qt图表BarChart示例[doc.qt.io]

其他回答

为了让Kahia写的代码更清晰(它是清晰的,但当你想要添加更多文本时就会变得棘手)…试试这个简单的解决方法。

if (Math.Round((decimal)user.CurrentPoints) == user.CurrentPoints)
     ViewBag.MyCurrentPoints = String.Format("Your current Points: {0:0}",user.CurrentPoints);
else
     ViewBag.MyCurrentPoints = String.Format("Your current Points: {0:0.0}",user.CurrentPoints);

我必须添加额外的转换(小数)来拥有Math。对两个十进制变量进行四舍五入比较。

恐怕没有内置格式可以做到这一点。您必须使用不同的格式,这取决于该值是否为整数。或者始终格式化到小数点后2位,然后操作字符串以删除任何尾随的“.00”。

当处理来自(T-)SQL数据库的小数时,您希望能够将可为空的小数和不可为空的小数转换为x位小数,并且能够根据表定义轻松地检查代码——当然,还要向用户显示正确的小数数量。

不幸的是,实体框架不能自动将SQL小数(18,2)转换为具有相同位数的。net等价小数(因为只有具有完全精度的小数可用)。您必须手动截断小数点数位。

所以,我是这样做的:

public static class Extensions
{
    public static string ToStringDecimal(this decimal d, byte decimals)
    {
        var fmt = (decimals>0) ? "0." + new string('0', decimals) : "0";
        return d.ToString(fmt);
    }

    public static string ToStringDecimal(this decimal? d, byte decimals)
    {
        if (!d.HasValue) return "";
        return ToStringDecimal(d.Value, decimals);
    }
}

使用示例:

void Main()
{
    decimal d = (decimal)1.2345;
    decimal? d2 = null; 

    Console.WriteLine(d.ToStringDecinal(2)); // prints: "1.23" (2 decimal places)
    Console.WriteLine(d.ToStringDecinal(0)); // prints: "1" (show integer number)
    Console.WriteLine(d2.ToStringDecimal(2)); // prints: "" (show null as empty string)
}

如果你的程序需要快速运行,调用value. tostring (formatString)可以获得比$"{value:formatString}"和string快35%的字符串格式化性能。格式(formatString值)。

Data

Code

using System;
using System.Diagnostics;

public static class StringFormattingPerformance
{
   public static void Main()
   {
      Console.WriteLine("C# String Formatting Performance");
      Console.WriteLine("Milliseconds Per 1 Million Iterations - Best Of 5");
      long stringInterpolationBestOf5 = Measure1MillionIterationsBestOf5(
          (double randomDouble) =>
          {
             return $"{randomDouble:0.##}";
          });
      long stringDotFormatBestOf5 = Measure1MillionIterationsBestOf5(
          (double randomDouble) =>
          {
             return string.Format("{0:0.##}", randomDouble);
          });
      long valueDotToStringBestOf5 = Measure1MillionIterationsBestOf5(
          (double randomDouble) =>
          {
             return randomDouble.ToString("0.##");
          });
      Console.WriteLine(
$@"            $""{{value:formatString}}"": {stringInterpolationBestOf5} ms
 string.Format(formatString, value): {stringDotFormatBestOf5} ms
       value.ToString(formatString): {valueDotToStringBestOf5} ms");
   }

   private static long Measure1MillionIterationsBestOf5(
       Func<double, string> formatDoubleUpToTwoDecimalPlaces)
   {
      long elapsedMillisecondsBestOf5 = long.MaxValue;
      for (int perfRunIndex = 0; perfRunIndex < 5; ++perfRunIndex)
      {
         var random = new Random();
         var stopwatch = Stopwatch.StartNew();
         for (int i = 0; i < 1000000; ++i)
         {
            double randomDouble = random.NextDouble();
            formatDoubleUpToTwoDecimalPlaces(randomDouble);
         }
         stopwatch.Stop();
         elapsedMillisecondsBestOf5 = Math.Min(
            elapsedMillisecondsBestOf5, stopwatch.ElapsedMilliseconds);
      }
      return elapsedMillisecondsBestOf5;
   }
}

代码的输出

C# String Formatting Performance
Milliseconds Per 1 Million Iterations - Best Of 5
            $"{value:formatString}": 419 ms
 string.Format(formatString, value): 419 ms
       value.ToString(formatString): 264 ms

参考文献

自定义数字格式字符串[learn.microsoft.com]

Qt图表BarChart示例[doc.qt.io]

如果其他答案都不适合你,这可能是因为你在OnLoad函数中绑定了控件的ContentProperty,这意味着这将不起作用:

private void UserControl_Load(object sender, RoutedEventArgs e)
{
  Bind.SetBindingElement(labelName, String.Format("{0:0.00}", PropertyName), Label.ContentProperty) 
}

解决方案很简单:在xaml中有一个ContentStringFormat属性。所以当你创建标签时,这样做:

//if you want the decimal places definite
<Label Content="0" Name="labelName" ContentStringFormat="0.00"/>

Or

//if you want the decimal places to be optional
<Label Content="0" Name="labelName" ContentStringFormat="0.##"/>