在我的MiscUtil项目中有各种扩展方法(完整的源代码在那里可用-我不打算在这里重复它)。我最喜欢的，其中一些涉及其他类(如范围):

日期和时间——主要用于单元测试。我不确定我会在生产中使用它们:)

var birthday = 19.June(1976);
var workingDay = 7.Hours() + 30.Minutes();

范围和步进——非常感谢Marc Gravell的运算符使这成为可能:

var evenNaturals = 2.To(int.MaxValue).Step(2);
var daysSinceBirth = birthday.To(DateTime.Today).Step(1.Days());

比较:

var myComparer = ProjectionComparer.Create(Person p => p.Name);
var next = myComparer.ThenBy(p => p.Age);
var reversed = myComparer.Reverse();

参数检查:

x.ThrowIfNull("x");

LINQ to XML应用于匿名类型(或其他具有适当属性的类型):

// <Name>Jon</Name><Age>32</Age>
new { Name="Jon", Age=32}.ToXElements();
// Name="Jon" Age="32" (as XAttributes, obviously)
new { Name="Jon", Age=32}.ToXAttributes()

Push LINQ -在这里解释太长了，但是可以搜索一下。

对于Winform控件:

/// <summary>
/// Returns whether the function is being executed during design time in Visual Studio.
/// </summary>
public static bool IsDesignTime(this Control control)
{
    if (LicenseManager.UsageMode == LicenseUsageMode.Designtime)
    {
        return true;
    }

    if (control.Site != null && control.Site.DesignMode)
    {
        return true;
    }

    var parent = control.Parent;
    while (parent != null)
    {
        if (parent.Site != null && parent.Site.DesignMode)
        {
            return true;
        }
        parent = parent.Parent;
    }
    return false;
}

/// <summary>
/// Sets the DropDownWidth to ensure that no item's text is cut off.
/// </summary>
public static void SetDropDownWidth(this ComboBox comboBox)
{
    var g = comboBox.CreateGraphics();
    var font = comboBox.Font;
    float maxWidth = 0;

    foreach (var item in comboBox.Items)
    {
        maxWidth = Math.Max(maxWidth, g.MeasureString(item.ToString(), font).Width);
    }

    if (comboBox.Items.Count > comboBox.MaxDropDownItems)
    {
        maxWidth += SystemInformation.VerticalScrollBarWidth;
    }

    comboBox.DropDownWidth = Math.Max(comboBox.Width, Convert.ToInt32(maxWidth));
}

IsDesignTime用法:

public class SomeForm : Form
{
    public SomeForm()
    {
        InitializeComponent();

        if (this.IsDesignTime())
        {
            return;
        }

        // Do something that makes the visual studio crash or hang if we're in design time,
        // but any other time executes just fine
    }
}

SetDropdownWidth用法:

ComboBox cbo = new ComboBox { Width = 50 };
cbo.Items.Add("Short");
cbo.Items.Add("A little longer");
cbo.Items.Add("Holy cow, this is a really, really long item. How in the world will it fit?");
cbo.SetDropDownWidth();

我忘了说，请随意在Codeplex上使用这些…

我在所有项目中用到的两个小技巧(有些人会觉得很傻)是:

public static bool IsNull(this object o){
  return o == null;
}

and

public static bool IsNullOrEmpty(this string s){
  return string.IsNullOrEmpty(s);
}

它使我的代码更流畅。

if (myClassInstance.IsNull()) //... do something

if (myString.IsNullOrEmpty()) //... do something

我认为这些是很好的扩展属性;如果我们能得到这些。

获取一个camelCaseWord或PascalCaseWord并将其“Word化”，即camelCaseWord => camelCaseWord

public static string Wordify( this string camelCaseWord )
{
    // if the word is all upper, just return it
    if( !Regex.IsMatch( camelCaseWord, "[a-z]" ) )
        return camelCaseWord;

    return string.Join( " ", Regex.Split( camelCaseWord, @"(?<!^)(?=[A-Z])" ) );
}

我经常将它与大写字母结合使用

public static string Capitalize( this string word )
{
    return word[0].ToString( ).ToUpper( ) + word.Substring( 1 );
}

示例使用

SomeEntityObject entity = DataAccessObject.GetSomeEntityObject( id );
List<PropertyInfo> properties = entity.GetType().GetPublicNonCollectionProperties( );

// wordify the property names to act as column headers for an html table or something
List<string> columns = properties.Select( p => p.Name.Capitalize( ).Wordify( ) ).ToList( );

在codeplex项目中免费使用

在单元测试中很有用:

public static IList<T> Clone<T>(this IList<T> list) where T : ICloneable
{
    var ret = new List<T>(list.Count);
    foreach (var item in list)
        ret.Add((T)item.Clone());

    // done
    return ret;
}

像TWith2Sugars这样的一系列，交替缩短语法:

public static long? ToNullableInt64(this string val)
{
    long ret;
    return Int64.TryParse(val, out ret) ? ret : new long?();
}

最后，在BCL中是否已经有一些东西做了下面的事情?

public static void Split<T>(this T[] array, 
    Func<T,bool> determinator, 
    IList<T> onTrue, 
    IList<T> onFalse)
{
    if (onTrue == null)
        onTrue = new List<T>();
    else
        onTrue.Clear();

    if (onFalse == null)
        onFalse = new List<T>();
    else
        onFalse.Clear();

    if (determinator == null)
        return;

    foreach (var item in array)
    {
        if (determinator(item))
            onTrue.Add(item);
        else
            onFalse.Add(item);
    }
}

我相信以前有人这样做过，但我发现自己经常使用这种方法(和更简单的导数):

public static bool CompareEx(this string strA, string strB, CultureInfo culture, bool ignoreCase)
{
    return string.Compare(strA, strB, ignoreCase, culture) == 0;
}

您可以以多种方式编写它，但我喜欢它，因为它非常快速地统一了比较字符串的方法，同时节省了代码行数(或代码字符)。