如何将Userform对象作为参数传递给子过程？解决运行时错误438

问题背景 #

原本在窗体Initialize事件中使用私有子过程可以正常设置窗体位置：

Private Sub subSetFormPosition()
    Dim Top As Double, Left As Double

    Me.StartUpPosition = 0
    Top = Abs(Application.Top) + (Application.Height) - (Me.Height + 20)
    Left = Abs(Application.Left) + (Application.Width) - (Me.Width + 100)
    Me.Top = Top
    Me.Left = Left
End Sub

但改造为可跨窗体调用的公共子过程后，运行触发运行时错误438：对象不支持该属性或方法，错误指向frm.StartUpPosition = 0语句：

Public Sub subSetFormPosition(frm As MSForms.UserForm, ivHOffset As Integer, ivVOffset As Integer)
    Dim Top As Double, Left As Double
    
    frm.StartUpPosition = 0
    Top = Abs(Application.Top) + (Application.Height) - (frm.Height + ivVOffset)
    Left = Abs(Application.Left) + (Application.Width) - (frm.Width + ivHOffset)
    frm.Top = Top
    frm.Left = Left
End Sub

调用代码：

subSetFormPosition frmTimes, 200, 20

错误原因 #

1. 对象传递错误：如果直接传递窗体类名（如frmTimes）而非实例对象，操作的是窗体类而非具体实例，类对象不支持StartUpPosition属性。
2. 属性访问限制：通过MSForms.UserForm基类引用访问StartUpPosition时，VBA运行时对象模型不允许外部修改该属性（但窗体自身代码中用Me访问是允许的）。

解决方案 #

修改通用子过程 #

移除运行时设置StartUpPosition的语句，直接设置Top和Left即可——手动设置位置会自动覆盖默认的启动定位规则：

Public Sub subSetFormPosition(frm As MSForms.UserForm, ivHOffset As Integer, ivVOffset As Integer)
    Dim Top As Double, Left As Double
    
    Top = Abs(Application.Top) + Application.Height - (frm.Height + ivVOffset)
    Left = Abs(Application.Left) + Application.Width - (frm.Width + ivHOffset)
    frm.Top = Top
    frm.Left = Left
End Sub

正确调用方式 #

方式1：在窗体自身的Initialize事件中调用

传递Me作为窗体实例：

Private Sub UserForm_Initialize()
    subSetFormPosition Me, 200, 20
End Sub

方式2：在模块中创建实例后调用

先实例化窗体，再传递实例对象：

Sub ShowPositionedForm()
    Dim targetForm As New frmTimes
    subSetFormPosition targetForm, 200, 20
    targetForm.Show
End Sub

内容的提问来源于stack exchange，提问作者Tonynh