.NET开发中经常用到的扩展方法
整理一下自己经常用到的几个扩展方法，在实际项目中确实好用，节省了不少的工作量。
1 匿名对象转化
在WinForm中，如果涉及较长时间的操作，我们一般会用一个BackgroundWorker来做封装长时间的操作，给它传递一个类型参数。
var parm = new { UserId = txtUserId.Text, UserText = txtText.Text, TabIndex = tabControl.SelectedIndex, CheckUrl = urls, SupportFormat = supportFormat, DeleteMHT = chkDelete.Checked, FileFormat=supportFileFormat }; backgroundWorker.RunWorkerAsync(parm);
注意到一点，我这里没有用一个类型，而是用一个匿名类型，以节省类型的定义。这种场景经常遇到，比如这个后台方法需要传三个参数，那个后台方法需要五个参数，如果不用我这个方法，那你需要额外的定义二个类型，分别包含三个参数或是五个参数。
再来看DoWork时，如何使用这个匿名方法
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});
与RunWorkerAsnyc中传递的参数一样，定义一个匿名类型，各属性放默认值，然后调用TolerantCast方法，即可得到前面传入的值。
这个方法很大的方便了这种使用情景：方法与方法之间需要传递不固定的参数，但是又不愿意重新定义一个新的类型。这个方法不来自于CodeProject，我把它的代码转在下面，供您参考
/// <summary> /// 转换匿名类型 /// </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 集合对象上的扩展方法
先看例子，下面的测试方法
var @enum = new[] {1, 2, 3, 4}.AsEnumerable(); var sum = 0; @enum.ForEach(n => sum += n);
这个扩展方法，可以直接在一个集合上执行一个Lambda表达式，返回结果，相当于有二个参数的Fun<T,T>，来看它的源代码定义
public static void ForEach<T>(this IEnumerable<T> @enum, Action<T> mapFunction) { foreach (var item in @enum) mapFunction(item); }
3 字符串类型上的扩展方法
这里可以做的扩展方法比较多，一个明显的例子就是，依据String类型写的Helper类型方法最多。
来看一个字符串拼凑的例子，平时我们用string.Format这样的写法，如果用下面的扩展方法，看起来更直观一些。
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),
这个扩展方法的定义也简单，只有一行代码
/// <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); }
可以考虑把参数延长到任意个，改写这个扩展方法，也只需要一行代码皆可
/// <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); }
另一个有用的扩展方法是字符串与枚举类型之间的转化，扩展方法定义如下
/// <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); }
参考下面的例子，使用这个实用的扩展方法
enum ProductVersion { Standard, Enteprise, Ultimate } [TestMethod] public void StringToEnumTest() { Assert.AreEqual(ProductVersion.Standard, "Standard".ToEnum<ProductVersion>()); }
4 数字类型上的扩展方法
我这里有一个明显的例子是显示容量的扩展方法，请看下面的方法组：
/// <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; }
用起来就很轻松了，简单的一行代码，获取容量的数字值
var kb = 1.KB(); var mb = 1.MB(); var gb = 1.GB(); var tb = 1.TB();
最后一组扩展方法在计算百分比中经常遇到，比如统计计算，任务完成百分比计算：
#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
来看几个测试用例，增强对它的直观感受，因为涉及到的数值类型多一些，所以扩展方法的数量也多。
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));
