DynamicObject.TrySetMember(SetMemberBinder, Object) 方法

public:
 virtual bool TrySetMember(System::Dynamic::SetMemberBinder ^ binder, System::Object ^ value);

public virtual bool TrySetMember (System.Dynamic.SetMemberBinder binder, object value);

public virtual bool TrySetMember (System.Dynamic.SetMemberBinder binder, object? value);

abstract member TrySetMember : System.Dynamic.SetMemberBinder * obj -> bool
override this.TrySetMember : System.Dynamic.SetMemberBinder * obj -> bool

Public Overridable Function TrySetMember (binder As SetMemberBinder, value As Object) As Boolean

參數

傳回

如果作業成功，則為 true，否則為 false。 如果這個方法傳回 false，語言的執行階段繫結器會決定行為。 (在大多數情況下，將會擲回特定語言的執行階段例外狀況)。

範例

假設您想要提供替代語法來存取字典中的值，因此您不需要在 Visual Basic) 中撰寫 sampleDictionary["Text"] = "Sample text" (sampleDictionary("Text") = "Sample text" ，而是可以撰寫 sampleDictionary.Text = "Sample text"。 此外，此語法必須不區分大小寫，因此相當於 sampleDictionary.TextsampleDictionary.text。

下列程式代碼範例示範 DynamicDictionary 衍生自 類別的 DynamicObject 類別。 類別 DynamicDictionary 包含 Visual Basic 中類型 (的物件 Dictionary<string, object>) ， Dictionary(Of String, Object) 用來儲存機碼/值組，並覆寫 TrySetMember 和 TryGetMember 方法來支援新的語法。 它也會提供 Count 屬性，其中顯示字典包含多少動態屬性。

// The class derived from DynamicObject.
public class DynamicDictionary : DynamicObject
{
    // The inner dictionary.
    Dictionary<string, object> dictionary
        = new Dictionary<string, object>();

    // This property returns the number of elements
    // in the inner dictionary.
    public int Count
    {
        get
        {
            return dictionary.Count;
        }
    }

    // If you try to get a value of a property
    // not defined in the class, this method is called.
    public override bool TryGetMember(
        GetMemberBinder binder, out object result)
    {
        // Converting the property name to lowercase
        // so that property names become case-insensitive.
        string name = binder.Name.ToLower();

        // If the property name is found in a dictionary,
        // set the result parameter to the property value and return true.
        // Otherwise, return false.
        return dictionary.TryGetValue(name, out result);
    }

    // If you try to set a value of a property that is
    // not defined in the class, this method is called.
    public override bool TrySetMember(
        SetMemberBinder binder, object value)
    {
        // Converting the property name to lowercase
        // so that property names become case-insensitive.
        dictionary[binder.Name.ToLower()] = value;

        // You can always add a value to a dictionary,
        // so this method always returns true.
        return true;
    }
}

class Program
{
    static void Main(string[] args)
    {
        // Creating a dynamic dictionary.
        dynamic person = new DynamicDictionary();

        // Adding new dynamic properties.
        // The TrySetMember method is called.
        person.FirstName = "Ellen";
        person.LastName = "Adams";

        // Getting values of the dynamic properties.
        // The TryGetMember method is called.
        // Note that property names are case-insensitive.
        Console.WriteLine(person.firstname + " " + person.lastname);

        // Getting the value of the Count property.
        // The TryGetMember is not called,
        // because the property is defined in the class.
        Console.WriteLine(
            "Number of dynamic properties:" + person.Count);

        // The following statement throws an exception at run time.
        // There is no "address" property,
        // so the TryGetMember method returns false and this causes a
        // RuntimeBinderException.
        // Console.WriteLine(person.address);
    }
}

// This example has the following output:
// Ellen Adams
// Number of dynamic properties: 2

' The class derived from DynamicObject.
Public Class DynamicDictionary
    Inherits DynamicObject

    ' The inner dictionary.
    Dim dictionary As New Dictionary(Of String, Object)

    ' This property returns the number of elements
    ' in the inner dictionary.
    ReadOnly Property Count As Integer
        Get
            Return dictionary.Count
        End Get
    End Property


    ' If you try to get a value of a property that is
    ' not defined in the class, this method is called.

    Public Overrides Function TryGetMember(
        ByVal binder As System.Dynamic.GetMemberBinder,
        ByRef result As Object) As Boolean

        ' Converting the property name to lowercase
        ' so that property names become case-insensitive.
        Dim name As String = binder.Name.ToLower()

        ' If the property name is found in a dictionary,
        ' set the result parameter to the property value and return true.
        ' Otherwise, return false.
        Return dictionary.TryGetValue(name, result)
    End Function

    Public Overrides Function TrySetMember(
        ByVal binder As System.Dynamic.SetMemberBinder,
        ByVal value As Object) As Boolean

        ' Converting the property name to lowercase
        ' so that property names become case-insensitive.
        dictionary(binder.Name.ToLower()) = value

        ' You can always add a value to a dictionary,
        ' so this method always returns true.
        Return True
    End Function
End Class

Sub Main()
    ' Creating a dynamic dictionary.
    Dim person As Object = New DynamicDictionary()

    ' Adding new dynamic properties.
    ' The TrySetMember method is called.
    person.FirstName = "Ellen"
    person.LastName = "Adams"

    ' Getting values of the dynamic properties.
    ' The TryGetMember method is called.
    ' Note that property names are now case-insensitive,
    ' although they are case-sensitive in C#.
    Console.WriteLine(person.firstname & " " & person.lastname)

    ' Getting the value of the Count property.
    ' The TryGetMember is not called, 
    ' because the property is defined in the class.
    Console.WriteLine("Number of dynamic properties:" & person.Count)

    ' The following statement throws an exception at run time.
    ' There is no "address" property,
    ' so the TryGetMember method returns false and this causes
    ' a MissingMemberException.
    ' Console.WriteLine(person.address)
End Sub
' This examples has the following output:
' Ellen Adams
' Number of dynamic properties: 2

備註

衍生自 類別的 DynamicObject 類別可以覆寫這個方法，以指定如何為動態物件執行將值設定為成員的作業。 未覆寫方法時，語言的運行時間系結器會決定行為。 (在大多數情況下，將會擲回特定語言的執行階段例外狀況)。

當您有 之類的 sampleObject.SampleProperty = "Test"語句時，會呼叫這個方法，其中 sampleObject 是衍生自 類別的 DynamicObject 類別實例。

您也可以將自己的成員新增至衍生自 類別的 DynamicObject 類別。 如果您的類別定義屬性並覆寫 TrySetMember 方法，動態語言執行平臺 (DLR) 會先使用語言系結器來尋找 類別中屬性的靜態定義。 如果沒有這類屬性，DLR 會呼叫 TrySetMember 方法。

適用於