泛型約束的意思就是說:類的泛型,只能是where字句後面所寫的介面或類。
這麼說好像也有點不大明白,舉個例子。
我有一個介面,如下:
複製代碼 代碼如下: ///
/// 國籍的介面
///
public interface INationality
{
string Nationality
{
set;
get;
}
string GetNationality();
}
然後該介面有兩個實現,如下:複製代碼 代碼如下: ///
/// 中國人
///
public class Chinese : INationality
{
private string _Nationality;
public string Nationality
{
set
{
_Nationality = value;
}
}
public string GetNationality()
{
return string.IsNullOrEmpty(_Nationality) ? "Default." : _Nationality;
}
}
///
/// 美國人
///
public class American : INationality
{
private string _Nationality;
public string Nationality
{
set { _Nationality = value; }
}
public string GetNationality()
{
return string.IsNullOrEmpty(_Nationality) ? "Default." : _Nationality;
}
}
然後建立一個泛型類,帶有泛型約束的類,如下:複製代碼 代碼如下: ///
///
///
///
public class PrintNationality where T : INationality, new()
{
T item = new T();
public void Print()
{
Console.WriteLine(string.Format("Nationality:{0}", item.GetNationality()));
}
}
由於有where字句的泛型約束,所以,建立PrintNationality的對象時,T的類型只能是繼承子INationality介面的類。複製代碼 代碼如下: public class Program
{
static void Main(string[] args)
{
PrintNationality _c = new PrintNationality();
PrintNationality _a = new PrintNationality();
//PrintNationality _o = new PrintNationality(); 此句是錯誤的,因為泛型型別必須是繼承自INationality介面的類
_c.Print();
_a.Print();
Console.ReadKey();
}
}
以上的代碼運行結果: