Question

I have a form with a ‘Clear’ button.

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.

All of my controls are contained on a Panel.

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.

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.

Edit: Thanks to your suggestions, the below code is greatly simplified.

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: 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) 

Then this line gives me ‘Unable to cast object of type ‘ControlCollection’ to type ‘ControlCollection’.’:

  ClearAllControls(panMid.Controls) 

Answer 1

You can skip the GetType and CType dance with TryCast:

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

That’ll save you about 10 lines.

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 

Edit: 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()