Check if form is Opened

Question

I give this question for more knowledge. How can I know if the form is Opened in my application or not, in order not to open it again I mean not to create an instance of the same form while it's running

   Dim frmCollection As New FormCollection()
    frmCollection = Application.OpenForms()
    If frmCollection.Item("Form2").IsHandleCreated Then
        MsgBox("Yes Opened")
    Else
        Dim f As New Form2()
        With f
            .Text = "form2"
            .Show()
        End With
    End If

if I executes this code many times it will create more instances of the form Form2 How can I check if this form is not already opened

Answer 1

You can try it like this:

 Imports System.Linq ' need to add 


If Application.OpenForms().OfType(Of Form2).Any Then
  MessageBox.Show("Opened")
Else
  Dim f2 As New Form2
  f2.Text = "form2"
  f2.Show()
End If

Answer 2

You can use the following code:

If myForm.IsHandleCreated then
   myForm is open
End If

Answer 3

As an extension of the answers given (thank you, all), here's a simple way to activate or show:

Dim frmCollection = System.Windows.Forms.Application.OpenForms
If frmCollection.OfType(Of Form2).Any Then
    frmCollection.Item("Form2").Activate()
Else
    Dim newForm2 = New Form2
    newForm2.Show()
End If

Answer 4

For more simplicity you may create a public static bool variable which will tell whether the form is opened or not. On form load event assign 'true' and on closed event assign 'false' value.

Answer 5

ANOTHER refactoring way from the one initiated by HumbleBeginnings:

    Dim xChildWindows = Application.OpenForms.OfType(Of frmForm2)
    If xChildWindows.Any Then
        xChildWindows.First().Focus() 'Focus if exists
    Else
        Dim xfrmNew As New frmForm2() 'Open window if doeasn't exists
        xfrmNew.MdiParent = Me
        xfrmNew.Show()
    End If

Answer 6

Hate to be a kill joy but some day some one is going to try and understand your code.

Dim frm as New frmDontknow
Dim frmCollection = System.Windows.Forms.Application.OpenForms
For i As Int16 = 0I To frmCollection.Count - 1I
  If frmCollection.Item(i).Name = frm.Name Then
      frmCollection.Item(i).Activate()
      Exit Sub
  End If
Next i

Then do the show etc as required?

Answer 7

Check if form is Opened, To validate if a form is open we use this method and function to be able to invoke from any form and use less code.

Example : This will use it in a form with mdiContainer and a panel object with 3 buttons that shows the 3 windows form.

Imports System Imports System.Reflection

Private Sub OpenWindowsForm(ByVal FormName As String)
    Dim instForm As Form = Application.OpenForms.OfType(Of Form)().Where(Function(frm) frm.Name = FormName).SingleOrDefault()
    If instForm Is Nothing Then
        Dim frm As New Form
        frm = DirectCast(CreateObjectInstance(FormName), Form)
        frm.MdiParent = Me
        Me.Panel1.Controls.Add(frm)
        Me.Panel1.Tag = frm
        frm.Show()
    Else
        instForm.Select()
        instForm.WindowState = FormWindowState.Maximized
        instForm.BringToFront()
    End If
End Sub

Public Function CreateObjectInstance(ByVal objectName As String) As Object
    Dim obj As Object
    Try
        If objectName.LastIndexOf(".") = -1 Then
            objectName = [Assembly].GetEntryAssembly.GetName.Name & "." & objectName
        End If

        obj = [Assembly].GetEntryAssembly.CreateInstance(objectName)

    Catch ex As Exception
        obj = Nothing
    End Try
    Return obj

End Function

How to use in click events Private Sub btnRegistro_Click(sender As Object, e As EventArgs) Handles btnRegistro.Click OpenWindowsForm("Registro") End Sub

Private Sub btnBusqueda_Click(sender As Object, e As EventArgs) Handles btnBusqueda.Click
    OpenWindowsForm("Busqueda")
End Sub

Private Sub btnCalendario_Click_1(sender As Object, e As EventArgs) Handles btnCalendario.Click
    OpenWindowsForm("Calendario")
End Sub

Here is an image of the Sample code

Answer 8

you can try this

Dim formText As String
Dim prevText As String

 Private Sub OpenForm(ByVal frm As Windows.Forms.Form)
        formText = frm.Text
        If formText = prevText Then Exit Sub
        CloseForms()
        ' Make it a child of this MDI form before showing it.
        frm.MdiParent = Me
        frm.Show()
        frm.Location = New Point(0, 0)
        prevText = formText
    End Sub

    Private Sub CloseForms()
        For Each ChildForm As Form In Me.MdiChildren
            ChildForm.Close()
        Next
    End Sub

    Private Sub NewToolStripButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PayablesToolStripMenuItem.Click
            OpenForm(frmPayables)
        End Sub

Answer 9

For Each frm As Form In Application.OpenForms
    If frm.Name = Form1.Name Then
       MessageBox.Show("Opened")
    End If
Next