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

定义

命名空间:

System.Dynamic

程序集:

netstandard.dll, System.Linq.Expressions.dll

Source:

DynamicObject.cs

为调用成员的操作提供实现。 派生自类的 DynamicObject 类可以重写此方法，以指定调用方法等操作的动态行为。

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。 该 binder.Name 属性提供执行动态操作的成员的名称。 例如，对于语句 sampleObject.SampleMethod(100)，其中 sampleObject 从类派生 DynamicObject 的类 binder.Name 的实例返回“SampleMethod”。 该 binder.IgnoreCase 属性指定成员名称是否区分大小写。

args

Object[]

在调用操作期间传递给对象成员的参数。 例如，对于从类sampleObject.SampleMethod(100)派生的sampleObject语句DynamicObjectargs[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，则语言的运行时绑定器将确定行为。 （在大多数情况下，将引发特定于语言的运行时异常。

示例

假设你想要提供用于访问字典中的值的替代语法，以便无需在 Visual Basic 中编写 sampleDictionary["Text"] = "Sample text" （sampleDictionary("Text") = "Sample text"），则可以编写 sampleDictionary.Text = "Sample text"。 此外，你希望能够在此字典上调用所有标准字典方法。

下面的代码示例演示 DynamicDictionary 了派生自该类的 DynamicObject 类。 DynamicDictionary 类包含用于存储键值对的 Dictionary<string, object> 类型（Visual Basic Dictionary(Of String, Object)）的对象。 它重写 TryInvokeMember 方法以支持类的方法 Dictionary<TKey,TValue> ，并重写 TrySetMember 支持新语法的方法和 TryGetMember 方法。 它还提供一种方法 Print ，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

派生自该类的 DynamicObject 类可以重写此方法，以指定应如何为动态对象执行调用对象成员的操作。 如果未重写该方法，则语言的运行时绑定器将确定行为。 （在大多数情况下，将引发特定于语言的运行时异常。

如果重写此方法，则执行类似于sampleObject.SampleMethod(100)sampleObject从类派生DynamicObject的操作时，会自动调用此方法。

还可以将自己的方法添加到派生自该类的 DynamicObject 类。 例如，如果重写 TryInvokeMember 该方法，动态调度系统会首先尝试确定类中是否存在指定的方法。 如果未找到该方法，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。