LINQ之OfType

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OfType()

OfType()可以用於篩選指定類型（及其子類）。
MSDN

下面代碼示例中使用的類結構如下圖所示。

代碼示例：

public static class Program
{
    private class BaseClass
    {
        public virtual string   Type    { get { return "-"; } }
        public string           Name    { get; set; }

        public override string ToString()
        {
            return string.Format( "Type:{0}, Name:{1}", Type, Name );
        }
    }
    private class ClassA : BaseClass
    {
        public override string  Type    { get { return "A"; } }
    }
    private class ClassB : BaseClass
    {
        public override string  Type    { get { return "B"; } }
    }
    private class ClassC : ClassB
    {
        public override string  Type    { get { return "C"; } }
    }

    static void Main( string[] args )
    {
        BaseClass[] parameters  = new BaseClass[]
        {
            new ClassA() { Name = "正一郎" },
            new ClassB() { Name = "清次郎" },
            new ClassB() { Name = "誠三郎" },
            new ClassC() { Name = "徵史郎" },
        };

        // 轉換
        IEnumerable<BaseClass>  reaultBase  = parameters.OfType<BaseClass>();
        IEnumerable<ClassA>     reaultA     = parameters.OfType<ClassA>();
        IEnumerable<ClassB>     reaultB     = parameters.OfType<ClassB>();
        IEnumerable<ClassC>     reaultC     = parameters.OfType<ClassC>();

        // 輸出
        System.Console.WriteLine( "parameters:{0}", parameters.Text() );
        System.Console.WriteLine( "BaseClass:{0}", reaultBase.Text() );
        System.Console.WriteLine( "ClassA:{0}", reaultA.Text() );
        System.Console.WriteLine( "ClassB:{0}", reaultB.Text() );
        System.Console.WriteLine( "ClassC:{0}", reaultC.Text() );

        System.Console.ReadKey();
    }

    public static string Text<TSource>( this IEnumerable<TSource> i_source )
    {
        string text = string.Empty;
        foreach( var value in i_source )
        {
            text += string.Format( "[{0}], ", value );
        }
        return text;
    }
}
parameters:[Type:A, Name:正一郎], [Type:B, Name:清次郎], [Type:B, Name:誠三郎],
[Type:C, Name:徵史郎],
BaseClass:[Type:A, Name:正一郎], [Type:B, Name:清次郎], [Type:B,
Name:誠三郎], [Type:C, Name:徵史郎],
ClassA:[Type:A, Name:正一郎],
ClassB:[Type:B, Name:清次郎], [Type:B, Name:誠三郎], [Type:C,
Name:徵史郎],
ClassC:[Type:C, Name:徵史郎],

下面使用ArrayList進行試驗。

代碼示例：

public static class Program
{
    static void Main( string[] args )
    {
        ArrayList list = new ArrayList() { 1, 3, "2", 5.5f };

        // 轉換
        IEnumerable<int>    reaultInt       = list.OfType<int>();
        IEnumerable<string> reaultString    = list.OfType<string>();
        IEnumerable<float>  reaultFloat     = list.OfType<float>();
        IEnumerable<long>   reaultLong      = list.OfType<long>();

        System.Console.WriteLine( "list:{0}", list.Text() );
        System.Console.WriteLine( "int:{0}", reaultInt.Text() );
        System.Console.WriteLine( "string:{0}", reaultString.Text() );
        System.Console.WriteLine( "float:{0}", reaultFloat.Text() );
        System.Console.WriteLine( "long:{0}", reaultLong.Text() );

        System.Console.ReadKey();
    }

    public static string Text( this IEnumerable i_source )
    {
        string text = string.Empty;
        foreach( var value in i_source )
        {
            text += string.Format( "[{0}], ", value );
        }
        return text;
    }
} 
list:[1], [3], [2], [5.5],
int:[1], [3],
string:[2],
float:[5.5],
long: