DynamicObject.TryInvokeMember(InvokeMemberBinder, Object[], Object) 方法

定义

命名空间:

System.Dynamic

程序集:

System.Linq.Expressions.dll

Source:

DynamicObject.cs

为调用成员的操作提供实现。 从 DynamicObject 类派生的类可以重写此方法，以便为诸如调用方法这样的操作指定动态行为。

public:
 virtual bool TryInvokeMember(System::Dynamic::InvokeMemberBinder ^ binder, cli::array <System::Object ^> ^ args, [Runtime::InteropServices::Out] System::Object ^ % result);

public virtual bool TryInvokeMember (System.Dynamic.InvokeMemberBinder binder, object?[]? args, out object? result);

abstract member TryInvokeMember : System.Dynamic.InvokeMemberBinder * obj[] * obj -> bool
override this.TryInvokeMember : System.Dynamic.InvokeMemberBinder * obj[] * obj -> bool

Public Overridable Function TryInvokeMember (binder As InvokeMemberBinder, args As Object(), ByRef result As Object) As Boolean

参数

binder

InvokeMemberBinder

提供有关动态操作的信息。 属性 binder.Name 提供对其执行动态操作的成员的名称。 例如，对于 语句 sampleObject.SampleMethod(100)，其中 sampleObject 是派生自 类的类的 DynamicObject 实例， binder.Name 返回“SampleMethod”。 属性 binder.IgnoreCase 指定成员名称是否区分大小写。

args

Object[]

调用操作期间传递给对象成员的参数。 例如，对于 从 类派生DynamicObject的 语句sampleObject.SampleMethod(100)sampleObject，args[0]等于 100。

result

Object

成员调用的结果。

返回

Boolean

如果操作成功，则为 true；否则为 false。 如果此方法返回 false，则该语言的运行时联编程序将决定行为。 （大多数情况下，将引发语言特定的运行时异常。）

示例

假设你想要提供替代语法来访问字典中的值，这样就可以编写 (，而不是sampleDictionary["Text"] = "Sample text"在 Visual Basic) 中编写 sampleDictionary.Text = "Sample text"。sampleDictionary("Text") = "Sample text" 此外，你希望能够调用此字典上的所有标准字典方法。

下面的代码示例演示 DynamicDictionary 派生自 类的 DynamicObject 类。 类DynamicDictionary包含 Visual Basic) 中 (Dictionary(Of String, Object) 类型的 对象Dictionary<string, object>，用于存储键值对。 它重写 TryInvokeMember 方法以支持 类的方法 Dictionary<TKey,TValue> ，并重写 TrySetMember 和 TryGetMember 方法以支持新语法。 它还提供了一个 Print 方法，该方法输出所有字典键和值。

// Add using System.Reflection;
// to the beginning of the file.

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

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

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

    // Calling a method.
    public override bool TryInvokeMember(
        InvokeMemberBinder binder, object[] args, out object result)
    {
        Type dictType = typeof(Dictionary<string, object>);
        try
        {
            result = dictType.InvokeMember(
                         binder.Name,
                         BindingFlags.InvokeMethod,
                         null, dictionary, args);
            return true;
        }
        catch
        {
            result = null;
            return false;
        }
    }

    // This methods prints out dictionary elements.
    public void Print()
    {
        foreach (var pair in dictionary)
            Console.WriteLine(pair.Key + " " + pair.Value);
        if (dictionary.Count == 0)
            Console.WriteLine("No elements in the dictionary.");
    }
}

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";

        // Calling a method defined in the DynmaicDictionary class.
        // The Print method is called.
        person.Print();

        Console.WriteLine(
            "Removing all the elements from the dictionary.");

        // Calling a method that is not defined in the DynamicDictionary class.
        // The TryInvokeMember method is called.
        person.Clear();

        // Calling the Print method again.
        person.Print();

        // The following statement throws an exception at run time.
        // There is no Sample method
        // in the dictionary or in the DynamicDictionary class.
        // person.Sample();
    }
}

// This example has the following output:

// FirstName Ellen
// LastName Adams
// Removing all the elements from the dictionary.
// No elements in the dictionary.

' Add Imports System.Reflection
' to the beginning of the file.

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

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

    ' Getting a 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

    ' Setting a 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


    ' Calling a method.
    Public Overrides Function TryInvokeMember(
        ByVal binder As System.Dynamic.InvokeMemberBinder,
        ByVal args() As Object, ByRef result As Object) As Boolean

        Dim dictType As Type = GetType(Dictionary(Of String, Object))
        Try
            result = dictType.InvokeMember(
                         binder.Name,
                         BindingFlags.InvokeMethod,
                         Nothing, dictionary, args)
            Return True
        Catch ex As Exception
            result = Nothing
            Return False
        End Try
    End Function

    ' This method prints out dictionary elements.
    Public Sub Print()
        For Each pair In dictionary
            Console.WriteLine(pair.Key & " " & pair.Value)
        Next
        If (dictionary.Count = 0) Then
            Console.WriteLine("No elements in the dictionary.")
        End If
    End Sub
End Class

Sub Test()
    ' 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"

    ' Calling a method defined in the DynmaicDictionary class.
    ' The Print method is called.
    person.Print()

    Console.WriteLine(
        "Removing all the elements from the dictionary.")

    ' Calling a method that is not defined in the DynamicDictionary class.
    ' The TryInvokeMember method is called.
    person.Clear()

    ' Calling the Print method again.
    person.Print()

    ' The following statement throws an exception at run time.
    ' There is no Sample method 
    ' in the dictionary or in the DynamicDictionary class.
    ' person.Sample()
End Sub


' This example has the following output:

' FirstName Ellen 
' LastName Adams
' Removing all the elements from the dictionary.
' No elements in the dictionary.

注解

派生自 类的 DynamicObject 类可以重写此方法，以指定应如何对动态对象执行调用对象成员的操作。 当方法未重写时，语言的运行时绑定器将确定行为。 （大多数情况下，将引发语言特定的运行时异常。）

如果此方法被重写，则执行等 sampleObject.SampleMethod(100)操作时会自动调用此方法，其中 sampleObject 派生自 DynamicObject 类。

还可以将自己的方法添加到派生自 类的 DynamicObject 类。 例如，如果重写 TryInvokeMember 方法，动态调度系统将首先尝试确定类中是否存在指定的方法。 如果找不到 方法，则使用 TryInvokeMember 实现。

此方法不支持 ref 和 out 参数。 数组中的所有 args 参数都按值传递。