C#用反射判斷一個類型是否是Nullable同時擷取它的根類型

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在我們的應用程式中我們使用類描述我們的業務對象，為我們產生一些報表之類的，那就依賴大量不同的對象，我們建立一個協助方法來轉換我們的業務對象，或是一個List的業務對象到DataTables.

由於資料庫表中欄位可為null,對應.net 2.0以後我們可用Nullable類型來實現，那當我們業務對象類中欄位有null時，並需要轉換為DataTable時，這個情境產生，你可能用到以下方法：

下面的代碼是一個list對象(不支援處理複雜類型)返回一個描述對象的DataTable

/// <summary> /// Converts a Generic List into a DataTable /// </summary> /// <param name="list"></param> /// <param name="typ"></param> /// <returns></returns> private DataTable GetDataTable(IList list, Type typ) {     DataTable dt = new DataTable();     // Get a list of all the properties on the object     PropertyInfo[] pi = typ.GetProperties();     // Loop through each property, and add it as a column to the datatable     foreach (PropertyInfo p in pi)     {         // The the type of the property         Type columnType = p.PropertyType;         // We need to check whether the property is NULLABLE         if (p.PropertyType.IsGenericType && p.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>))         {             // If it is NULLABLE, then get the underlying type. eg if "Nullable<int>" then this will return just "int"             columnType = p.PropertyType.GetGenericArguments()[0];         }         // Add the column definition to the datatable.         dt.Columns.Add(new DataColumn(p.Name, columnType));     }     // For each object in the list, loop through and add the data to the datatable.     foreach (object obj in list)     {         object[] row = new object[pi.Length];         int i = 0;         foreach (PropertyInfo p in pi)         {             row[i++] = p.GetValue(obj, null);         }         dt.Rows.Add(row);     }     return dt; }

 

上面的代碼的關鍵點：

• 用 PropertyType.IsGenericType 決定property是否是generic類型
• 用 ProprtyType.GetGenericTypeDefinition() == typeof(Nullable<>) 檢測它是否是一個nullable類型
• 用 PropertyType.GetGenericArguments() 擷取基底類型。

下面讓我們來應用一下：

public class Person{    public string Name { get; set; }    public DateTime DateOfBirth { get; set; }    public DateTime? DateOfDeath { get; set; }}public class Example{    public static DataTable RunExample()    {        Person edward = new Person() { Name = "Edward", DateOfBirth = new DateTime(1900, 1, 1), DateOfDeath = new DateTime(1990, 10, 15) };        Person margaret = new Person() { Name = "Margaret", DateOfBirth = new DateTime(1950, 2, 9), DateOfDeath = null };        Person grant = new Person() { Name = "Grant", DateOfBirth = new DateTime(1975, 6, 13), DateOfDeath = null };        List<Person> people = new List<Person>();        people.Add(edward);        people.Add(margaret);        people.Add(grant);        DataTable dt = GetDataTable(people, typeof(Person));        return dt;    }}

 

將返回的DataTable像下面的內容:

Name (string)	DateOfBirth (DateTime)	DateOfDeath (DateTime)
Edward	1/1/1900	15/10/1990
Margaret	9/2/1950	[NULL]
Grant	13/6/1975	[NULL]

 

 

 

 

實際開發中應用

    /// <summary>         /// 集合裝換DataSet         /// </summary>         /// <param name="list">集合</param>         /// <returns></returns>         /// 2008-08-01 22:08 HPDV2806         public static DataSet ToDataSet<T>(IList<T> p_List)        {            DataSet result = new DataSet();            DataTable _DataTable = new DataTable();            if (p_List.Count > 0)            {                PropertyInfo[] propertys = p_List[0].GetType().GetProperties();                foreach (PropertyInfo pi in propertys)                {                    if (pi.PropertyType.IsGenericType && pi.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>))                    {                            _DataTable.Columns.Add(pi.Name, pi.PropertyType.GetGenericArguments()[0]);                    }                    else                    {                        _DataTable.Columns.Add(pi.Name, pi.PropertyType);                    }                 }                for (int i = 0; i < p_List.Count; i++)                {                    ArrayList tempList = new ArrayList();                    foreach (PropertyInfo pi in propertys)                    {                        object obj = pi.GetValue(p_List[i], null);                        tempList.Add(obj);                    }                    object[] array = tempList.ToArray();                    _DataTable.LoadDataRow(array, true);                }            }            result.Tables.Add(_DataTable);            return result;        }

 

 

 

參考：76708225

 

C#用反射判斷一個類型是否是Nullable同時擷取它的根類型