[Problems RESOLVED]
Hi Kulrom, thanks for your reply. It did help, but in the perspective manner. So, finally I have resolved it. Now I want to contribute it as well:
I am making a simple tutorial in creating MDI for my conclusion, and will to share with others my experience.
Let's get started !
The CASE:
You are trying to make an MDI Application, which has:
1. A parent form --> as the name for example: frmParentForm.
2. Children forms --> one of them is the command panel which has buttons to navigate users to access / open other child forms. In this example, the Command Panel form has the name frmCommandPanel.
3. In the frmCommandPanel you have a button or maybe more buttons to open one or more children forms. But in this example we'll use only one button and it's named as: btnOpenChildForm. btnOpenChildForms opens a child form when it's clicked.
The PROBLEM:
1. Everytime you click the button which opens the Child Form, it will always create a new instance, which you don't want those. But you only one instance, and if the Child Form has been opened, you want just to activate it to note the user that it has been opened, and if it has been opened but it is minimized, and the user clicks again the button, you want the child from to be maximized or normaled.
2. After you close the frmChildForm, then you try to click the button which opens the child form again and you get an error of OBJECTDISPOSEDEXCEPTION.
If that the cases and your problems. Then this simple tutorial is for you.
Let's go solve your problem !
The STEPS:
1. Create the frmParentForm, and set its IsMDIContainer property to TRUE.
2. Create the frmCommandPanel. Add a button on it, and name it : btnOpenChildForm.
3. Next, you'll want that the frmCommandPanel is showed automatically as the child form of frmParentForm, when the application is first to start.
4. So, at Design Mode of the frmParentForm, right click over it and select VIEW CODE, let's dive into coding:
Option Strict On
Public Class frmParentForm
Inherits System.Windows.Forms.Form
'We're not going to talk about Windows Form Generated Code, so let's skip it....
+ Windows Form Generated Code
'Define the Variables here at first as a FRIEND variable, so that it could be accessed later by other Children Forms. Don't define
'the variable as a local variable for the form, if you want it to be able to call the variable in other class.
'(This was where my mistake, I defined the variable as the local variable...)
Friend CommandPanel as frmCommandPanel
'Then at the LOAD EVENT....You Type:
Private Sub frmParentForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Try
If CommandPanel Is Nothing Then
CommandPanel = New frmCommandPanel
With CommandPanel
.MdiParent = frmParentForm.ActiveForm
.StartPosition = FormStartPosition.CenterScreen
.Show()
End With
End If
Catch ex As Exception
MsgBox(ex.ToString)
Application.Exit()
End Try
End Sub
5. Create another Form and name it: frmChildForm. Add a button on the frmChildForm and name it : btnCloseChildForm.
6. At the frmCommandPanel's code....let's dive into the code:
Option Strict On
Public Class frmCommandPanel
Inherits System.Windows.Forms.Form
'Define the variable here...
Friend ChildForm as frmChildForm
'Just skip this part....
+ Windows Form Designer Generated Code
'Then....at the btnOpenChildForm:
Private Sub btnOpenChildForm_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOpenChildForm.Click
'See if an instance of the ChildForm has been created, if not then create one
If ChildForm is Nothing Then
ChildForm = New frmChildForm
'Then set its MDIParent to frmParentForm,
'and its startposition to CenterScreen or anywhere you like
'finally show the form
With ChildForm
.MDIParent = frmParentForm.ActiveForm
.StartPosition = FormStartPosition.CenterScreen
.Show()
End With
'And if an instance of the ChildForm has been created, but it's on minimize state then,
'bring it to NORMAL State or any state you like...
ElseIf Not (ChildForm is Nothing) Then
If ChildForm.WindowState = FormWindowState.Minimized Then
ChildForm.WindowState = FormWindowState.Normal
End If
'If it's already created and the user tries to click the btnOpenChildForm again,
'do not create another instance, instead just ACTIVATE it.
ChildForm.Activate()
End IF
End Sub
7. This step is to prevent the OBJECTDISPOSEDEXCEPTION comes up to surface after you close the child form. To do that you'll have to write codes at the frmChildForm:
Option Strict On
Public Class frmEnterNewFoodReciepe
Inherits System.Windows.Forms.Form
'Skip this part, since we're not going to talk about it....
+ Windows Form Designer Generated Code
'At the btnCloseChildForm Click Event, and Closed Event, type:...
Private Sub btnCloseChildForm_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCloseChildForm.Click
'Close the frmChildForm
Me.Close()
'This line is very important to prevent OBJECTDISPOSEDEXCEPTION occurs.....which got me for days before finally realized
' it...
ChildForm = Nothing
End Sub
Private Sub btnCloseChildForm_Closed(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Closed
'After the frmChildForm is Closed, then Dispose it...
Me.Dispose()
'And set the ChildForm to Nothing again....
ChildForm = Nothing
End Sub
8. Congratulations, you finally made a simple MDI Application Interface...It's time to test your code !
Hope that would help to explain and to help you to understand better about Multiple Document Interfaces.
Best regards,
Chris
Note, you can find this code in eXtremeVisualBasicTalk(http:\\
www.visualbasicforum.com\). My NickName there is Kampfcoder.
