Check if form is Opened - vb.net

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