我在我的web项目中使用这些，主要是MVC。我为ViewData和TempData写了一些这样的代码

/// <summary>
/// Checks the Request.QueryString for the specified value and returns it, if none 
/// is found then the default value is returned instead
/// </summary>
public static T QueryValue<T>(this HtmlHelper helper, string param, T defaultValue) {
    object value = HttpContext.Current.Request.QueryString[param] as object;
    if (value == null) { return defaultValue; }
    try {
        return (T)Convert.ChangeType(value, typeof(T));
    } catch (Exception) {
        return defaultValue;
    }
}

这样我就可以写……

<% if (Html.QueryValue("login", false)) { %>
    <div>Welcome Back!</div>

<% } else { %>
    <%-- Render the control or something --%>

<% } %>

ASP。NET中，我使用这些扩展httpessionstate来加载会话中的对象。 它允许您以干净的方式加载会话对象，如果它们不存在，则将创建和初始化它们。 我使用两个扩展方法，如下所示:

private bool CreateMode;
private MyClass SomeClass;

protected override void OnInit (EventArgs e)
{
    CreateMode = Session.GetSessionValue<bool> ("someKey1", () => true);
    SomeClass = Session.GetSessionClass<MyClass> ("someKey2", () => new MyClass () 
    { 
       MyProperty = 123 
    });
}

下面是扩展类:

public static class SessionExtensions    
{
    public delegate object UponCreate ();
    public static T GetSessionClass<T> (this HttpSessionState session, 
       string key, UponCreate uponCreate) where T : class
    {
        if (null == session[key])
        {
            var item = uponCreate () as T;
            session[key] = item;
            return item;
        }
        return session[key] as T;
    }
    public static T GetSessionValue<T> (this HttpSessionState session, 
       string key, UponCreate uponCreate) where T : struct
    {
        if (null == session[key])
        {
            var item = uponCreate();
            session[key] = item;
            return (T)item;
        }
        return (T)session[key];
    }
}

// Values ordered true/false
// True/false values separated by a capital letter
// Only two values allowed
// ---------------------------
// Limited, but could be useful
public enum BooleanFormat
{
    OneZero,
    YN,
    YesNo,
    TF,
    TrueFalse,
    PassFail,
    YepNope
}

public static class BooleanExtension
{
    /// <summary>
    /// Converts the boolean value of this instance to the specified string value. 
    /// </summary>
    private static string ToString(this bool value, string passValue, string failValue)
    {
        return value ? passValue : failValue;
    }

    /// <summary>
    /// Converts the boolean value of this instance to a string. 
    /// </summary>
    /// <param name="booleanFormat">A BooleanFormat value. 
    /// Example: BooleanFormat.PassFail would return "Pass" if true and "Fail" if false.</param>
    /// <returns>Boolean formatted string</returns>
    public static string ToString(this bool value, BooleanFormat booleanFormat)
    {
        string booleanFormatString = Enum.GetName(booleanFormat.GetType(), booleanFormat);
        return ParseBooleanString(value, booleanFormatString);      
    }

    // Parses boolean format strings, not optimized
    private static string ParseBooleanString(bool value, string booleanFormatString)
    {
        StringBuilder trueString = new StringBuilder();
        StringBuilder falseString = new StringBuilder();

        int charCount = booleanFormatString.Length;

        bool isTrueString = true;

        for (int i = 0; i != charCount; i++)
        {
            if (char.IsUpper(booleanFormatString[i]) && i != 0)
                isTrueString = false;

            if (isTrueString)
                trueString.Append(booleanFormatString[i]);
            else
                falseString.Append(booleanFormatString[i]);
        }

        return (value == true ? trueString.ToString() : falseString.ToString());
    }

我总是使用格式，希望与StringBuilder的新行，所以下面这个非常简单的扩展节省了几行代码:

public static class Extensions
{
    public static void AppendLine(this StringBuilder builder,string format, params object[] args)
    {
        builder.AppendLine(string.Format(format, args));
    }
}

替代方案是StringBuilder中带\n或Environment.NewLine的AppendFormat。

在ASP。我总是厌倦了使用FindControl，然后必须强制转换并检查引用之前的值是否为空。所以，我添加了一个TryParse()方法来控制，它反映了框架中类似的Int32等。

public static bool TryParse<T>(this Control control, string id, out T result) 
    where T : Control
{
    result = control.FindControl(id) as T;
    return result != null;
}

现在你可以在ASP中做这个。NET网页表单页面:

Label lbl;
if (Page.TryParse("Label1", out lbl))
{
    lbl.Text = "Safely set text";
}

将任何字符串转换为类型Int32

// Calls the underlying int.TryParse method to convert a string
// representation of a number to its 32-bit signed integer equivalent.
// Returns Zero if conversion fails. 
public static int ToInt32(this string s)
{
    int retInt;
    int.TryParse(s, out retInt);
    return retInt;
}

示例使用: 字符串s = "999"; int i = s.ToInt32();