如何通过变量访问窗体控件？VB.NET窗体控件引用问题

你的核心问题是：targetForm被声明为Form基类类型，编译器无法识别具体窗体上的DeptCombox控件，而且你传入的myControl参数也没被用到。下面给你两种直接可用的解决方案：

方案1：用控件集合查找（推荐） #

WinForms的控件集合自带按名称查找的方法，支持递归查找子控件（比如放在Panel、GroupBox里的控件也能找到），代码修改如下：

Public Function DeptList(ByVal myForm As String, ByVal myControl As String)
    Dim asm As System.Reflection.Assembly = System.Reflection.Assembly.GetExecutingAssembly()
    Dim targetForm As Form = CType(asm.CreateInstance("Jigsaw2." & myForm), Form)
    SqlTxt = "SELECT * FROM Department WHERE Dept_Status = 'Active';"
    sql.ExecQuery(SqlTxt)
    
    ' 按控件名称查找，True表示递归查找所有子控件
    Dim foundControls() As Control = targetForm.Controls.Find(myControl, True)
    
    If foundControls.Length > 0 Then
        ' 将找到的控件转换为ComboBox类型
        Dim targetCombo As ComboBox = CType(foundControls(0), ComboBox)
        Try
            For Each r As DataRow In sql.DBDT.Rows
                targetCombo.Items.Add(r("Dept_Name"))
            Next
        Catch ex As Exception
            ' 可选：添加异常提示，方便调试
            MessageBox.Show("填充失败：" & ex.Message)
        End Try
    Else
        MessageBox.Show("未找到名为 " & myControl & " 的控件")
    End If
End Function

方案2：用反射获取控件属性 #

如果你的控件是直接拖到窗体上的（成为窗体的成员属性），可以用反射直接获取这个属性：

Public Function DeptList(ByVal myForm As String, ByVal myControl As String)
    Dim asm As System.Reflection.Assembly = System.Reflection.Assembly.GetExecutingAssembly()
    ' 用Object类型存储窗体实例，避免基类的类型限制
    Dim targetForm As Object = asm.CreateInstance("Jigsaw2." & myForm)
    SqlTxt = "SELECT * FROM Department WHERE Dept_Status = 'Active';"
    sql.ExecQuery(SqlTxt)
    
    Try
        ' 通过反射获取控件属性
        Dim comboProp As System.Reflection.PropertyInfo = targetForm.GetType().GetProperty(myControl)
        If comboProp IsNot Nothing Then
            Dim targetCombo As ComboBox = CType(comboProp.GetValue(targetForm), ComboBox)
            For Each r As DataRow In sql.DBDT.Rows
                targetCombo.Items.Add(r("Dept_Name"))
            Next
        Else
            MessageBox.Show("窗体上不存在名为 " & myControl & " 的控件属性")
        End If
    Catch ex As Exception
        MessageBox.Show("填充失败：" & ex.Message)
    End Try
End Function

额外提醒：窗体实例的问题 #

你当前代码是用CreateInstance创建了一个新的窗体实例，如果你的需求是给已经打开的窗体填充控件，那应该替换创建实例的代码，改为查找已打开的窗体：

' 替换原来的CreateInstance代码
Dim targetForm As Form = Application.OpenForms.OfType(Of Form).FirstOrDefault(Function(f) f.Name = myForm)
If targetForm Is Nothing Then
    MessageBox.Show("未找到已打开的 " & myForm & " 窗体")
    Return
End If

内容的提问来源于stack exchange，提问作者Clamont