VB.NET - 遍历容器对象中的控件 [英] VB.NET - Iterating through controls in a container object

问题描述

我有一个带有清除"按钮的表单.

I have a form with a "Clear" button.

当用户单击清除"时，我想清除表单上所有可见元素的值.对于日期控件，我想将它们重置为当前日期.

When the user clicks "Clear", I want to clear the value of all the visible elements on the form. In the case of date controls, I want to reset them to the current date.

我的所有控件都包含在一个面板中.

All of my controls are contained on a Panel.

现在，我正在使用以下代码执行此操作.有没有比手动检查每种控件类型更简单的方法?这种方法似乎过于笨拙.

Right now, I'm doing this with the below code. Is there an easier way than manually checking for each control type? This method seems excessively unwieldy.

更糟糕的是，为了递归地清除子容器内的控件(即面板中的组框)，我必须使用重载的GroupBox"版本重复整个怪物.

To make matters worse, in order to recursively clear controls inside sub-containers (i.e., a group box within the panel) I have to repeat the whole monster with an overloaded "GroupBox" version.

感谢您的建议，大大简化了以下代码.

Private Sub btnClear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClear.Click
    'User clicks Clear, so clear all the controls within this panel
    ClearAllControls(panMid, True) 'True indicates that yes, i want to recurse through sub-containers
End Sub

ClearAllControls(ByRef container As Panel, Optional Recurse As Boolean = True)   
  'Clear all of the controls within the container object
  'If "Recurse" is true, then also clear controls within any sub-containers
  Dim ctrl As Control
  For Each ctrl In container.Controls
      If (ctrl.GetType() Is GetType(TextBox)) Then
          Dim txt As TextBox = CType(ctrl, TextBox)
          txt.Text = ""
      End If
      If (ctrl.GetType() Is GetType(CheckBox)) Then
          Dim chkbx As CheckBox = CType(ctrl, CheckBox)
          chkbx.Checked = False
      End If
      If (ctrl.GetType() Is GetType(ComboBox)) Then
          Dim cbobx As ComboBox = CType(ctrl, ComboBox)
          cbobx.SelectedIndex = -1
      End If
      If (ctrl.GetType() Is GetType(DateTimePicker)) Then
          Dim dtp As DateTimePicker = CType(ctrl, DateTimePicker)
          dtp.Value = Now()
      End If

      If Recurse Then
          If (ctrl.GetType() Is GetType(Panel)) Then
              Dim pnl As Panel = CType(ctrl, Panel)
              ClearAllControls(pnl, Recurse)
          End If
          If ctrl.GetType() Is GetType(GroupBox) Then
              Dim grbx As GroupBox = CType(ctrl, GroupBox)
              ClearAllControls(grbx, Recurse)
          End If
      End If
  Next
End Sub

@Theraccoonbear:我喜欢你的建议，但是当我把声明改成这样时:

@Theraccoonbear: I like your suggestion, but when I change the declaration to this:

Private Sub ClearAllControls(ByRef controls As ControlCollection, Optional ByVal Recurse As Boolean = True)

然后这一行给了我无法将'ControlCollection'类型的对象转换为'ControlCollection'类型.":

Then this line gives me "Unable to cast object of type 'ControlCollection' to type 'ControlCollection'.":

  ClearAllControls(panMid.Controls)

推荐答案

您可以使用 TryCast:

Dim dtp as DateTimePicker = TryCast(ctrl, DateTimePicker)
If dtp IsNot Nothing then dtp.Value = Now()

这将为您节省大约 10 行代码.

That'll save you about 10 lines.

Control 类中的扩展方法应该让它保持整洁:

An extension method off the Control class should keep it pretty tidy:

<Extension()> _
Public Shared Sub ClearValue(c as Control, recursive as Boolean)
   Dim dtp as DateTimePicker = TryCast(c, DateTimePicker)
   If dtp IsNot Nothing Then dtp.Value = Now()
   ' Blah, Blah, Blah
End Sub

如果想到忽略 NullReferenceExceptions 的 Evil 扩展方法不会让您感到畏缩:

If the thought of Evil extension methods that ignore NullReferenceExceptions don't make you cringe:

<Extension()> _
Public Shared Sub ClearValue(c as CheckBox)
   If c IsNot Nothing Then c.Checked = False
End Sub

TryCast(ctrl, CheckBox).ClearValue()

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