.NET開發(fā)中經(jīng)常用到的擴展方法

小蟲子的館子 2013-07-03

展開全文

整理一下自己經(jīng)常用到的幾個擴展方法，在實際項目中確實好用，節(jié)省了不少的工作量。

1 匿名對象轉(zhuǎn)化

在WinForm中，如果涉及較長時間的操作，我們一般會用一個BackgroundWorker來做封裝長時間的操作，給它傳遞一個類型參數(shù)。

var parm = new { UserId = txtUserId.Text, UserText = txtText.Text, TabIndex = tabControl.SelectedIndex, CheckUrl = urls,

SupportFormat = supportFormat, DeleteMHT = chkDelete.Checked, FileFormat=supportFileFormat };
backgroundWorker.RunWorkerAsync(parm);

注意到一點，我這里沒有用一個類型，而是用一個匿名類型，以節(jié)省類型的定義。這種場景經(jīng)常遇到，比如這個后臺方法需要傳三個參數(shù)，那個后臺方法需要五個參數(shù)，如果不用我這個方法，那你需要額外的定義二個類型，分別包含三個參數(shù)或是五個參數(shù)。

再來看DoWork時，如何使用這個匿名方法

private void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
{
            #region Download 
     backgroundWorker.ReportProgress(10, string.Format("Analyst beginning......"));
     var parm = e.Argument.TolerantCast(new { UserId = string.Empty, UserText = string.Empty, TabIndex = 0,

CheckUrl = new List<string>(), SupportFormat = string.Empty, DeleteMHT = false, FileFormat=string.Empty});

與RunWorkerAsnyc中傳遞的參數(shù)一樣，定義一個匿名類型，各屬性放默認(rèn)值，然后調(diào)用TolerantCast方法，即可得到前面?zhèn)魅氲闹怠?/p>

這個方法很大的方便了這種使用情景：方法與方法之間需要傳遞不固定的參數(shù)，但是又不愿意重新定義一個新的類型。這個方法不來自于CodeProject，我把它的代碼轉(zhuǎn)在下面，供您參考

/// <summary>
/// 轉(zhuǎn)換匿名類型
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="o"></param>
/// <param name="example"></param>
/// <returns></returns>
public static T TolerantCast<T>(this object o, T example)
            where T : class
        {
            IComparer<string> comparer = StringComparer.CurrentCultureIgnoreCase;
            //Get constructor with lowest number of parameters and its parameters
            var constructor = typeof (T).GetConstructors(
                BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance
                ).OrderBy(c => c.GetParameters().Length).First();
            var parameters = constructor.GetParameters();

            //Get properties of input object
            var sourceProperties = new List<PropertyInfo>(o.GetType().GetProperties());

            if (parameters.Length > 0)
            {
                var values = new object[parameters.Length];
                for (int i = 0; i < values.Length; i  )
                {
                    Type t = parameters[i].ParameterType;
                    //See if the current parameter is found as a property in the input object
                    var source = sourceProperties.Find(delegate(PropertyInfo item)
                        {
                            return comparer.Compare(item.Name, parameters[i].Name) == 0;
                        });

                    //See if the property is found, is readable, and is not indexed
                    if (source != null && source.CanRead &&
                        source.GetIndexParameters().Length == 0)
                    {
                        //See if the types match.
                        if (source.PropertyType == t)
                        {
                            //Get the value from the property in the input object and save it for use
                            //in the constructor call.
                            values[i] = source.GetValue(o, null);
                            continue;
                        }
                        else
                        {
                            //See if the property value from the input object can be converted to
                            //the parameter type
                            try
                            {
                                values[i] = Convert.ChangeType(source.GetValue(o, null), t);
                                continue;
                            }
                            catch
                            {
                                //Impossible. Forget it then.
                            }
                        }
                    }
                    //If something went wrong (i.e. property not found, or property isn't
                    //converted/copied), get a default value.
                    values[i] = t.IsValueType ? Activator.CreateInstance(t) : null;
                }
                //Call the constructor with the collected values and return it.
                return (T) constructor.Invoke(values);
            }
            //Call the constructor without parameters and return the it.
            return (T) constructor.Invoke(null);
        }

2 集合對象上的擴展方法

先看例子，下面的測試方法

var @enum = new[] {1, 2, 3, 4}.AsEnumerable();
var sum = 0;
@enum.ForEach(n => sum  = n);

這個擴展方法，可以直接在一個集合上執(zhí)行一個Lambda表達式，返回結(jié)果，相當(dāng)于有二個參數(shù)的Fun<T,T>，來看它的源代碼定義

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

3 字符串類型上的擴展方法

這里可以做的擴展方法比較多，一個明顯的例子就是，依據(jù)String類型寫的Helper類型方法最多。

來看一個字符串拼湊的例子，平時我們用string.Format這樣的寫法，如果用下面的擴展方法，看起來更直觀一些。

string s = "{0} ought to be enough for {1}.";
string param0 = "64K";
string param1 = "everybody";

string expected = "64K ought to be enough for everybody.";
Assert.AreEqual(expected, s.FormatWith(param0, param1),

這個擴展方法的定義也簡單，只有一行代碼

/// <summary>
/// Formats a string with two literal placeholders.
/// </summary>
/// <param name="text">The extension text</param>
/// <param name="arg0">Argument 0</param>
/// <param name="arg1">Argument 1</param>
/// <returns>The formatted string</returns>
public static string FormatWith(this string text, object arg0, object arg1)
{
         return string.Format(text, arg0, arg1);
}

可以考慮把參數(shù)延長到任意個，改寫這個擴展方法，也只需要一行代碼皆可

/// <summary>
/// Formats a string with two literal placeholders.
/// </summary>
/// <param name="text">The extension text</param>
/// <param name="arg0">Argument 0</param>
/// <param name="arg1">Argument 1</param>
/// <returns>The formatted string</returns>
public static string FormatWith(this string text, params object[] args))
{
         return string.Format(text, args);
}

另一個有用的擴展方法是字符串與枚舉類型之間的轉(zhuǎn)化，擴展方法定義如下

/// <summary>
/// Parses a string into an Enum
/// </summary>
/// <typeparam name="T">The type of the Enum</typeparam>
/// <param name="value">String value to parse</param>
/// <returns>The Enum corresponding to the stringExtensions</returns>
public static T ToEnum<T>(this string value)
{
            return ToEnum<T>(value, false);
 }

參考下面的例子，使用這個實用的擴展方法

enum ProductVersion
{
    Standard,
    Enteprise,
    Ultimate
} 

[TestMethod]
public void StringToEnumTest()
{
      Assert.AreEqual(ProductVersion.Standard, "Standard".ToEnum<ProductVersion>());
}

4 數(shù)字類型上的擴展方法

我這里有一個明顯的例子是顯示容量的擴展方法，請看下面的方法組：

/// <summary> 
/// Kilobytes 
/// </summary> 
/// <param name="value"></param> 
/// <returns></returns> 
public static int KB(this int value)
        {
            return value * 1024;
        }

/// <summary> 
/// Megabytes 
/// </summary> 
/// <param name="value"></param> 
/// <returns></returns> 
public static int MB(this int value)
        {
            return value.KB() * 1024;
        }

/// <summary> 
/// Gigabytes 
/// </summary> 
/// <param name="value"></param> 
/// <returns></returns> 
public static int GB(this int value)
        {
            return value.MB() * 1024;
        }

/// <summary> 
/// Terabytes 
/// </summary> 
/// <param name="value"></param> 
/// <returns></returns> 
public static long TB(this int value)
        {
            return (long)value.GB() * (long)1024;
        }

用起來就很輕松了，簡單的一行代碼，獲取容量的數(shù)字值

var kb = 1.KB();
var mb = 1.MB();
var gb = 1.GB();
var tb = 1.TB();

最后一組擴展方法在計算百分比中經(jīng)常遇到，比如統(tǒng)計計算，任務(wù)完成百分比計算：

 #region PercentageOf calculations

        /// <summary>
        /// The numbers percentage
        /// </summary>
        /// <param name="number">The number.</param>
        /// <param name="percent">The percent.</param>
        /// <returns>The result</returns>
        public static decimal PercentageOf(this int number, int percent)
        {
            return (decimal)(number * percent / 100);
        }

        /// <summary>
        /// Percentage of the number.
        /// </summary>
        /// <param name="percent">The percent</param>
        /// <param name="number">The Number</param>
        /// <returns>The result</returns>
        public static decimal PercentOf(this int position, int total)
        {
            decimal result = 0;
            if (position > 0 && total > 0)
                result = (decimal)position / (decimal)total * 100;
            return result;
        }
        public static decimal PercentOf(this int? position, int total)
        {
            if (position == null) return 0;
            
            decimal result = 0;
            if (position > 0 && total > 0)
                result = (decimal)((decimal)position / (decimal)total * 100);
            return result;
        }

        /// <summary>
        /// The numbers percentage
        /// </summary>
        /// <param name="number">The number.</param>
        /// <param name="percent">The percent.</param>
        /// <returns>The result</returns>
        public static decimal PercentageOf(this int number, float percent)
        {
            return (decimal)(number * percent / 100);
        }

        /// <summary>
        /// Percentage of the number.
        /// </summary>
        /// <param name="percent">The percent</param>
        /// <param name="number">The Number</param>
        /// <returns>The result</returns>
        public static decimal PercentOf(this int position, float total)
        {
            decimal result = 0;
            if (position > 0 && total > 0)
                result = (decimal)((decimal)position / (decimal)total * 100);
            return result;
        }

        /// <summary>
        /// The numbers percentage
        /// </summary>
        /// <param name="number">The number.</param>
        /// <param name="percent">The percent.</param>
        /// <returns>The result</returns>
        public static decimal PercentageOf(this int number, double percent)
        {
            return (decimal)(number * percent / 100);
        }

        /// <summary>
        /// Percentage of the number.
        /// </summary>
        /// <param name="percent">The percent</param>
        /// <param name="number">The Number</param>
        /// <returns>The result</returns>
        public static decimal PercentOf(this int position, double total)
        {
            decimal result = 0;
            if (position > 0 && total > 0)
                result = (decimal)((decimal)position / (decimal)total * 100);
            return result;
        }

        /// <summary>
        /// The numbers percentage
        /// </summary>
        /// <param name="number">The number.</param>
        /// <param name="percent">The percent.</param>
        /// <returns>The result</returns>
        public static decimal PercentageOf(this int number, decimal percent)
        {
            return (decimal)(number * percent / 100);
        }

        /// <summary>
        /// Percentage of the number.
        /// </summary>
        /// <param name="percent">The percent</param>
        /// <param name="number">The Number</param>
        /// <returns>The result</returns>
        public static decimal PercentOf(this int position, decimal total)
        {
            decimal result = 0;
            if (position > 0 && total > 0)
                result = (decimal)position / (decimal)total * 100;
            return result;
        }

        /// <summary>
        /// The numbers percentage
        /// </summary>
        /// <param name="number">The number.</param>
        /// <param name="percent">The percent.</param>
        /// <returns>The result</returns>
        public static decimal PercentageOf(this int number, long percent)
        {
            return (decimal)(number * percent / 100);
        }

        /// <summary>
        /// Percentage of the number.
        /// </summary>
        /// <param name="percent">The percent</param>
        /// <param name="number">The Number</param>
        /// <returns>The result</returns>
        public static decimal PercentOf(this int position, long total)
        {
            decimal result = 0;
            if (position > 0 && total > 0)
                result = (decimal)position / (decimal)total * 100;
            return result;
        }

        #endregion

來看幾個測試用例，增強對它的直觀感受，因為涉及到的數(shù)值類型多一些，所以擴展方法的數(shù)量也多。

Assert.AreEqual(33.0M, 100.PercentageOf(33));
Assert.AreEqual(33.0M, 33.PercentOf(100));
Assert.AreEqual(33.0M, 100.PercentageOf((float)33.0F));
Assert.AreEqual(33.0M, 33.PercentOf((float)100.0F));
Assert.AreEqual(33.0M, 100.PercentageOf((double)33.0F));
Assert.AreEqual(33.0M, 33.PercentOf((double)100.0F));
Assert.AreEqual(33.0M, 100.PercentageOf((decimal)33.0M));
Assert.AreEqual(33.0M, 33.PercentOf((decimal)100.0M));
Assert.AreEqual(33.0M, 100.PercentageOf((long)33));
Assert.AreEqual(33.0M, 33.PercentOf((long)100));