DynamicObject.TrySetIndex(SetIndexBinder, Object[], Object) Metodo

public:
 virtual bool TrySetIndex(System::Dynamic::SetIndexBinder ^ binder, cli::array <System::Object ^> ^ indexes, System::Object ^ value);

public virtual bool TrySetIndex(System.Dynamic.SetIndexBinder binder, object[] indexes, object value);

abstract member TrySetIndex : System.Dynamic.SetIndexBinder * obj[] * obj -> bool
override this.TrySetIndex : System.Dynamic.SetIndexBinder * obj[] * obj -> bool

Public Overridable Function TrySetIndex (binder As SetIndexBinder, indexes As Object(), value As Object) As Boolean

Parametri

Valori restituiti

true se l'operazione riesce; in caso contrario, false. Se questo metodo restituisce false, il binder di runtime del linguaggio determina il comportamento. Nella maggior parte dei casi viene generata un'eccezione di runtime specifica del linguaggio.

Esempio

Si supponga di voler creare un oggetto in cui è possibile accedere alle proprietà in base a nomi quali Property0, Property1 e così via o per indice, in modo che, ad esempio, sampleObject.Property0 equivale a sampleObject[0] in C# o sampleObject(0) in Visual Basic.

Nell'esempio di codice seguente viene illustrata la SampleDynamicObject classe , derivata dalla DynamicObject classe . La classe contiene un oggetto del tipo /> /> in Visual Basic) per archiviare le coppie chiave-valore. SampleDynamicObject esegue l'override dei TrySetIndex metodi e TryGetIndex per abilitare l'accesso in base all'indice. Esegue l'override dei TrySetMember metodi e TryGetMember per abilitare l'accesso in base al nome della proprietà.

// The class derived from DynamicObject.
public class SampleDynamicObject : DynamicObject
{
    // The inner dictionary to store field names and values.
    Dictionary<string, object> dictionary
        = new Dictionary<string, object>();

    // Get the property value.
    public override bool TryGetMember(
        GetMemberBinder binder, out object result)
    {
        return dictionary.TryGetValue(binder.Name, out result);
    }

    // Set the property value.
    public override bool TrySetMember(
        SetMemberBinder binder, object value)
    {
        dictionary[binder.Name] = value;
        return true;
    }

    // Set the property value by index.
    public override bool TrySetIndex(
        SetIndexBinder binder, object[] indexes, object value)
    {
        int index = (int)indexes[0];

        // If a corresponding property already exists, set the value.
        if (dictionary.ContainsKey("Property" + index))
            dictionary["Property" + index] = value;
        else
            // If a corresponding property does not exist, create it.
            dictionary.Add("Property" + index, value);
        return true;
    }

    // Get the property value by index.
    public override bool TryGetIndex(
        GetIndexBinder binder, object[] indexes, out object result)
    {

        int index = (int)indexes[0];
        return dictionary.TryGetValue("Property" + index, out result);
    }
}

class Program
{
    static void Test(string[] args)
    {
        // Creating a dynamic object.
        dynamic sampleObject = new SampleDynamicObject();

        // Creating Property0.
        // The TrySetMember method is called.
        sampleObject.Property0 = "Zero";

        // Getting the value by index.
        // The TryGetIndex method is called.
        Console.WriteLine(sampleObject[0]);

        // Setting the property value by index.
        // The TrySetIndex method is called.
        // (This method also creates Property1.)
        sampleObject[1] = 1;

        // Getting the Property1 value.
        // The TryGetMember method is called.
        Console.WriteLine(sampleObject.Property1);

        // The following statement produces a run-time exception
        // because there is no corresponding property.
        //Console.WriteLine(sampleObject[2]);
    }
}

// This code example produces the following output:

// Zero
// 1

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

    ' The inner dictionary to store field names and values.
    Dim dictionary As New Dictionary(Of String, Object)

    ' Get the property value.
    Public Overrides Function TryGetMember(
        ByVal binder As System.Dynamic.GetMemberBinder,
        ByRef result As Object) As Boolean

        Return dictionary.TryGetValue(binder.Name, result)

    End Function

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

        dictionary(binder.Name) = value
        Return True

    End Function

    ' Set the property value by index.
    Public Overrides Function TrySetIndex(
        ByVal binder As System.Dynamic.SetIndexBinder,
        ByVal indexes() As Object, ByVal value As Object) As Boolean

        Dim index As Integer = CInt(indexes(0))
        ' If a corresponding property already exists, set the value.
        If (dictionary.ContainsKey("Property" & index)) Then
            dictionary("Property" & index) = value
        Else
            ' If a property does not exist, create it.
            dictionary.Add("Property" & index, value)
        End If
        Return True
    End Function

    ' Get the property value by index.
    Public Overrides Function TryGetIndex(
        ByVal binder As System.Dynamic.GetIndexBinder,
        ByVal indexes() As Object, ByRef result As Object) As Boolean

        Dim index = CInt(indexes(0))
        Return dictionary.TryGetValue("Property" & index, result)
    End Function
End Class

Sub Test()
    ' Creating a dynamic object.
    Dim sampleObject As Object = New SampleDynamicObject()

    ' Creating Property0.
    ' The TrySetMember method is called.
    sampleObject.Property0 = "Zero"

    ' Getting the value by index.
    ' The TryGetIndex method is called.
    Console.WriteLine(sampleObject(0))

    ' Setting the property value by index.
    ' The TrySetIndex method is called.
    ' (This method also creates Property1.)
    sampleObject(1) = 1

    ' Getting the Property1 value.
    ' The TryGetMember method is called.
    Console.WriteLine(sampleObject.Property1)

    ' The following statement produces a run-time exception
    ' because there is no corresponding property.
    ' Console.WriteLine(sampleObject(2))
End Sub

' This code example produces the following output:

' Zero
' 1

Commenti

Le classi derivate dalla classe possono eseguire l'override DynamicObject di questo metodo per specificare come devono essere eseguite le operazioni che accedono a un oggetto in base all'indice per un oggetto dinamico. Quando il metodo non viene sottoposto a override, il binder di runtime del linguaggio determina il comportamento. Nella maggior parte dei casi viene generata un'eccezione di runtime specifica del linguaggio.

Se questo metodo viene sottoposto a override, viene richiamato automaticamente quando si dispone di un'operazione come sampleObject[3] = 10 in C# o sampleObject(3) = 10 in Visual Basic, dove sampleObject deriva dalla classe DynamicObject.