返回属性时未设置错误对象变量或块变量

Posted 2023-03-29

【中文标题】返回属性时未设置错误对象变量或块变量

【英文标题】：Error Object variable or with block variable not set while returning property

【发布时间】：2021-01-16 10:59:13

【问题描述】：

我正在尝试在 VB6 应用程序中使用我的 COM 类。我做了某种包装。当我创建对象时，我看到消息Is Nothing 1，因此它表明已设置成员变量并且它不为空，但是当我尝试使用属性返回此成员时，然后在返回行中我看到异常Object variable or with block variable not set。我不知道如何解决它。

// MyComClass
This is a COM class with method Operation

// clsMyCom.cls
Private WithEvents m_myComClass As MyComClass

Private Sub Class_Initialize()
        
    If m_myComClass Is Nothing Then
        MsgBox "Is Nothing 1"
    End If
    
    Set m_myComClass = New MyComClass
    
    If m_myComClass Is Nothing Then
        MsgBox "Is Nothing 2"
    End If

End Sub

Public Property Get MyImplementation() As MyComClass

    If m_myComClass Is Nothing Then
        MsgBox "Is Nothing 3"
    End If
    
    // in this line I see exception:
    // object variable or with block variable not set
    MyImplementation = m_myComClass

End  Property

// usage
Dim variable As clsMyCom
Set variable = New clsMyCom
Call variable.MyImplementation.Operation(...)

【参考方案1】：

把方法改成这样：

Public Property Get MyImplementation() As MyComClass

    If m_myComClass Is Nothing Then
        MsgBox "Is Nothing 3"
    End If
    
    // in this line I see exception:
    // object variable or with block variable not set
    Set MyImplementation = m_myComClass

End  Property

需要明确的是，您错过了Set

【讨论】：

我不知道返回对象时Property中需要Set。

MyImplementation = <<expr>> 分配给对象的默认属性（如果有），例如MyImplementation.Text = "some string" 的简写。错误“需要对象...”意味着 MyImplementation 在尝试分配给其默认属性时是 Nothing。