分享.NET系统开发过程中积累的扩展方法

.NET 3.5提供的扩展方法特性，可以在不修改原类型代码的情况下扩展它的功能。下面分享的这些扩展方法大部分来自于Code Project或是*，.NET为此还有一个专门提供扩展方法的网站(extensionMethod)。

涵盖类型转换，字符串处理，时间转化，集合操作等多个方面的扩展。

1  TolerantCast 匿名类型转换

这个需求来源于界面中使用BackgroundWorker，为了给DoWork传递多个参数，又不想定义一个类型来完成，于是我会用到TolerantCast方法。参考如下的代码：

//创建匿名类型
var parm = new { Bucket = bucket, AuxiliaryAccIsCheck = chbAuxiliaryAcc.Checked, AllAccountIsCheck = chbAllAccount.Checked };
backgroundWorker.RunWorkerAsync(parm);

 private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
 {
//解析转换匿名类型
  var parm = e.Argument.TolerantCast(new { Bucket = new RelationPredicateBucket(), AuxiliaryAccIsCheck = false, AllAccountIsCheck = false });

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

2  ForEach 集合操作

这个方法的定义很简单但也很实用，它的使用方法如下：

var buttons = GetListOfButtons() as IEnumerable<Button>;
buttons.ForEach(b => b.Click());

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

扩展方法的源代码定义只有一行，源代码如下：

public static void ForEach<T>(this IEnumerable<T> @enum, Action<T> mapFunction)
{
    foreach (var item in @enum) mapFunction(item);
}

当我想对一个集合中的每个元素执行相同的操作时，常常会借助于此方法实现。

3 Capitalize 字符串首字母大写

直接对字符串操作，将字符串的首字母改成大写，源代码参考如下：

public static string Capitalize(this string word)
{
      if (word.Length <= 1)
          return word;

      return word[0].ToString().ToUpper() + word.Substring(1);
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

4  ToDataTable 强类型对象集合转化为DataTable

开发中经常会遇到将List<Entity>转化为DataTable，或是反之将DataTable转化为List<Entity>，*上有很多这个需求的代码，参考下面的程序代码：

 public static DataTable ToDataTable<T>(this IEnumerable<T> varlist)
        {
            DataTable dtReturn = new DataTable();

            // column names
            PropertyInfo[] oProps = null;

            if (varlist == null) return dtReturn;

            foreach (T rec in varlist)
            {
                // Use reflection to get property names, to create table, Only first time, others will follow
                if (oProps == null)
                {
                    oProps = ((Type) rec.GetType()).GetProperties();
                    foreach (PropertyInfo pi in oProps)
                    {
                        Type colType = pi.PropertyType;

                        if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition() == typeof (Nullable<>)))
                        {
                            colType = colType.GetGenericArguments()[0];
                        }

                        dtReturn.Columns.Add(new DataColumn(pi.Name, colType));
                    }
                }

                DataRow dr = dtReturn.NewRow();

                foreach (PropertyInfo pi in oProps)
                {
                    dr[pi.Name] = pi.GetValue(rec, null) == null ? DBNull.Value : pi.GetValue
                                                                                      (rec, null);
                }

                dtReturn.Rows.Add(dr);
            }
            return dtReturn;
        }

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

5  SetAllValues 给数组中的每个元素赋值

实现给数组中的每个元素赋相同的值。

public static T[] SetAllValues<T>(this T[] array, T value)
{
     for (int i = 0; i < array.Length; i++)
     {
           array[i] = value;
     }

     return array;
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

6 ToXml 序列化对象为Xml格式

可以将一个对象序列化为Xml格式的字符串，保存对象的状态。

public static string ToXml<T>(this T o) where T : new()
{
        string retVal;
        using (var ms = new MemoryStream())
        {
              var xs = new XmlSerializer(typeof (T));
               xs.Serialize(ms, o);
               ms.Flush();
               ms.Position = 0;
               var sr = new StreamReader(ms);
               retVal = sr.ReadToEnd();
        }
        return retVal;
}

7  Between 值范围比较

可以判断一个值是否落在区间范围值中。

public static bool Between<T>(this T me, T lower, T upper) where T : IComparable<T>
{
      return me.CompareTo(lower) >= 0 && me.CompareTo(upper) < 0;
}

类似这样的操作，下面的方法是取2个值的最大值。

public static T Max<T>(T value1, T value2) where T : IComparable
{
     return value1.CompareTo(value2) > 0 ? value1 : value2;
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

8  StartDate DueDate 开始值或末值

业务系统中常常会用到时间比较，如果系统是用DateTime.Now变量与DateTime.Today来作比较，前者总是大于后者的，为此需要做一个简单转化，根据需要将值转化为开始值或末值，也就是0点0分0秒，或是23时59分59秒。

public static DateTime ConverToStartDate(this DateTime dateTime)
{
     return new DateTime(dateTime.Year, dateTime.Month, dateTime.Day, 0, 0, 0);
}

public static DateTime ConverToDueDate(this DateTime dateTime)
{
      return new DateTime(dateTime.Year, dateTime.Month, dateTime.Day, 23, 59, 59);
}

9 First Day Last Day 月的第一天或是最后一天

public static DateTime First(this DateTime current)
{
       DateTime first = current.AddDays(1 - current.Day);
       return first;
}

public static DateTime Last(this DateTime current)
{
      int daysInMonth = DateTime.DaysInMonth(current.Year, current.Month);

       DateTime last = current.First().AddDays(daysInMonth - 1);
       return last;
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

10 Percent 百分比值

计算前一个数值占后一个数值的百分比，常用于统计方面。

public static decimal PercentOf(this double position, int total)
{
     decimal result = 0;
     if (position > 0 && total > 0)
         result=(decimal)((decimal)position / (decimal)total * 100);
     return result;
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }

扩展方法源代码下载：http://files.cnblogs.com/files/JamesLi2015/ExtensionMethod.zip