Question

我想知道是否存在使用Type作为表达式的技巧，例如在此代码中：

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    Dim ControlType = CheckBox ' CheckBox is a type and cannot be used as an expression

    Dim ControlArray(5) As ControlType ' (5) The number of controls to create.

    For num As Int64 = 0 To ControlArray.LongLength - 1
        ControlArray(num) = New ControlType ' Expected: New CheckBox
        ControlArray(num).Text = (ControlType.ToString & num.ToString) ' Expected string: "CheckBox 0"
        Me.Controls.Add(ControlArray(num))
    Next

End Sub

我不知道我怎么能做一个控制数组，我问我是否可以做一个通用的控制数组，例如在var（ControlType）中指定Type并在代码中使用它上面的例子。

更新

这是我尝试使用

的代码

我无法识别＆＃34; CheckedChanged＆＃34;尝试附加处理程序时CheckBox的事件

也无法识别＆＃34; .Checked＆＃34;尝试检查它的值时的属性。

Public Class Form1

    Dim ControlType As Type = GetType(CheckBox) ' The type of Control to create.
    Dim ControlArray(5) As Control              ' (5) The number of controls to create.

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        For num As Int64 = 0 To ControlArray.LongLength - 1
            ControlArray(num) = Activator.CreateInstance(ControlType) ' Create the control instance (New CheckBox)
            ControlArray(num).Name = ControlType.Name & num.ToString ' Name example  : CheckBox 0
            ControlArray(num).Text = ControlType.Name & num.ToString ' String example: CheckBox 0
            ControlArray(num).Top = 20 * num ' Adjust the location of each control.
            Me.Controls.Add(ControlArray(num)) ' Add the control to a container.

            ' This does not work:
            AddHandler ControlArray(num).CheckedChanged, AddressOf CheckBoxSub ' Add a event handler to a procedure.

        Next

    End Sub

    Public Sub CheckBoxSub(ByVal sender As Object, ByVal e As System.EventArgs) ' Sub which is handling the controls.

        If sender.Checked = True Then MsgBox(sender.name & " is checked") Else MsgBox(sender.name & " is unchecked")

        ' Just an example of how to use the controls,
        ' This does not work:
        ControlArray(2).checked = True ' CheckBox 2.Checked = True

    End Sub

End Class

Answer 1

您可以使用System.Type来保存对象的类型。

您还可以使用Activator.CreateInstance（MyType）创建MyType类型对象的实例。

e.g。

Dim ControlType As System.Type = GetType(CheckBox)
Dim ControlArray(5) As Control

For num As Int64 = 0 To 5
    ControlArray(num) = Activator.CreateInstance(ControlType)
    ControlArray(num).Left = num * 100
    ControlArray(num).Name = "CheckBox " & num
    ControlArray(num).Text = ControlArray(num).Name
    Me.Controls.Add(ControlArray(num))
Next

编辑：

要添加事件处理程序，您需要DirectCast（）将Control转换为对象类型，例如：

AddHandler DirectCast(ControlArray(Num), CheckBox).CheckedChanged, AddressOf MyHandler

Answer 2

关于您更新的问题：您需要将对象强制转换为正确的类型，以便能够使用特定于CheckBox的属性或事件。例如。而不是

AddHandler ControlArray(num).CheckedChanged, AddressOf CheckBoxSub

你写了

Dim cbx As CheckBox = TryCast(ControlArray(num), CheckBox)
If cbx IsNot Nothing Then
    AddHandler cbx.CheckedChanged, AddressOf CheckBoxSub
End If

第二个例子相同：

Dim cbx As CheckBox = TryCast(ControlArray(2), CheckBox)
If cbx IsNot Nothing Then         ' If the second control is a check box 
   cbx.Checked = True 
End If

TryCast将给定对象强制转换为给定类型，如果对象具有不同类型，则返回Nothing。

如何使用Type作为表达式？

2 个答案: