[VS2008 - Compact Framework] How to prevent a closed form from been disposed

steve_9496613

Hello everybody. My application runs in Windows Embedded Compact 7,is written in C# and it uses .NET Compact Framework 3.5. In the application there is a form, I call it FormMain, two UserControlls, Page01_UC and SetupHome_UC, another form, FormDateTime. In FormMain i declared:

public static Page01_UC uc1 = new Page01_UC();
public static SetupHome_UC uc2 = new SetupHome_UC();
public static FormDateTime uc3 = new FormDateTime();

In the FormMain load event:

uc1.Parent = this;
uc1.Location = new Point(0, 0);
uc1.Page02_UC_Load(); //something to do at startup
uc1.Show();

In the uc1 UserControl there is a checkbox used to show SetupHome_UC:

private void SetupCB\_CheckStateChanged(object sender, EventArgs e)
{
  if (SetupCB.Checked)
  {
    FormMain.uc1.Hide();
    FormMain.uc2.Parent = FormMainRef; //reference to FormMain
    FormMain.uc2.Location = new Point(0, 0);
    FormMain.uc2.Page02\_UC\_Load(); //something to do at startup
    FormMain.uc2.Show();

    SetupCB.Checked = false;
  }
}

In uc2 UserControl ther is a button to show FormDateTime:

private void DateTimeBt\_Click(object sender, EventArgs e)
{
  FormMain.uc3.ShowDialog();
}

...at the end... in uc3 there is a button to close the form:

private void AbortBt\_Click(object sender, EventArgs e)
{
  Close();
}

I can show/close uc3 (FormDateTime) many times without problems but sometimes it happens that I get an ObjectDisposedException when I push the button to show uc3. I thought that uc3 should not be disposed but it seems that sometimes it happens. Have I made any mistakes that I don't see? There is a way to make uc3 UNdisposable until the application is closed? ...or any other way to avoid this problem... Thanks in advance.

realJSOP

Make it modeless. Instead of using form.ShowDialog(), use form.Show(). Whatever button you use to close the ford should hide it instead, using form.Hide().

".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013

steve_9496613

Thank you #realJSOP for your answer. I can't apply your solution because the form I show must stay over the others and must be closed to let user access to the window below, so I need a ShowModal().

realJSOP

ShowModal will ALWAYS dispose your form when you close it. If you need data shown in the window to be retained, you're going to have to store it in a static class so you can recall it whenever you need it.

".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013

dan sh

Can you post the complete error message? You say it works sometimes and sometimes does not, makes it tough to respond to.

"It is easy to decipher extraterrestrial signals after deciphering Javascript and VB6 themselves.", ISanti[^]

dan sh

MSDN states the opposite.

When a form is displayed as a modal dialog box, clicking the Close button (the button with an X at the upper-right corner of the form) causes the form to be hidden and the DialogResult property to be set to DialogResult.Cancel. Unlike non-modal forms, the Close method is not called by the .NET Framework when the user clicks the close form button of a dialog box or sets the value of the DialogResult property. Instead the form is hidden and can be shown again without creating a new instance of the dialog box. Because a form displayed as a dialog box is hidden instead of closed, you must call the Dispose method of the form when the form is no longer needed by your application.

Moreover, if the object is marked as static, I would expect them to be alive and healthy throughout the parent form's life.

"It is easy to decipher extraterrestrial signals after deciphering Javascript and VB6 themselves.", ISanti[^]

steve_9496613

Thank you lw@zi, here is the complete error message:

Error
sa7.exe
ObjectDisposedException
at Microsoft.AGL.Common.MISC.HandleAr(PAL_ERROR ar)
at System.Windows.Forms.Control.get_Visible()
at System.Windows.Forms.Form.ShowDialog()
at SA7.SetupHome_UC.DateTimeBt_Click(Object senter, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at BeeMobile.TransparentControls.TImageButton.OnClick(EventArgs e)
at System.Windows.Forms.Control.WnProc(WM wm, Int32 wParam, Int32 IParam)
at System.Windows.Forms.ContainerControl.WnProc(WM wm, Int32 wParam, Int32 IParam)
at System.Windows.Forms.Control._InternalWnProc(WM wm, Int32 wParam, Int32 IParam)
at Microsoft.AGL.Form.EVL.EnterMainLoop(IntPtr hwnMain)
at System.Windows.Forms.Application.Run(Form fm)
at SAT.Program.Main()

realJSOP

No, an EXTERNAL static class. I have such a class called Globals that I use for things that have to stick around for the life of the app.

".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013

steve_9496613

Hi #realJSOP, I have declared that object STATIC inside a form that is alive untill the app is closed, why it is not enough? Thanks

dan sh

What controls do you have on the form? Ones which are directly on the Form i.e controls whose parent is the form. And you are disposing anything on the form? Perhaps posting the code on the form may help.

"It is easy to decipher extraterrestrial signals after deciphering Javascript and VB6 themselves.", ISanti[^]

dan sh

I am not sure if I understand this. What I meant was that if I create a static object on the form, it has to be alive until that form (not application) is.

"It is easy to decipher extraterrestrial signals after deciphering Javascript and VB6 themselves.", ISanti[^]

realJSOP

When the modal form goes out of scope (closes), you can't access anything declared inside it because the form is no longer available/in scope.

".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013

steve_9496613

Sorry, I was not clear. I understood what you said, FormMain, in wich I declared a FormDateTime instance, is always in the background and is never closed.

steve_9496613

Clear. The form is used only to update date and time, it doesn't store any information.

realJSOP

Declare an EXTERNAL static class that the form can access

public static class Globals
{
public static MyDateTime { get; set; }
}

In your form, when you close it: Globals.MyDateTime = DateTime.Now; When your form closes, examine Globals.MyDateTime to ensure it's the expected value. The next time you open the form, the value will be the same as the last time you opened the form, and when you close it agaim, set Globals.MyDateTime again. The Globals.DateTime will be available everywhere else in the app as well.

".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013

realJSOP

I have no idea what you really want. I told you to make the form modelss so it never disposes, and you said it can't be modelss. Then I suggested that you make abn external statuic class because you wanted the form to be model. WTF do you actually want to do?

".45 ACP - because shooting twice is just silly" - JSOP, 2010
-----
You can never have too much ammo - unless you're swimming, or on fire. - JSOP, 2010
-----
When you pry the gun from my cold dead hands, be careful - the barrel will be very hot. - JSOP, 2013

dan sh

Yes, that is what I said as well.

"It is easy to decipher extraterrestrial signals after deciphering Javascript and VB6 themselves.", ISanti[^]

steve_9496613

In the form there are: 3 BeeMobile.TransparentControls.TImageButton 2 BeeMobile.TransparentControls.TLabel 2 BeeMobile.RoundTextBox.RoundTextBox 1 BeeMobile.MonthCalendar.MonthCalendar 1 BeeMobile.iWheel.iWheel 2 System.Windows.Forms.Timer For what I know, I do not dispose any control voluntarily... Here is the code on the form:

using System;
using System.Linq;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

//alias
using LangD = SA7.Cl_LangData;
using Gr = SA7.Cl_Graphics;
using Globals = SA7.Cl_Globals;

namespace SA7
{
public partial class FormDateTime : Form
{

private bool FormDateTime\_FirstShow = true;     // flag: first call to FormDateTime\_Load

Cl\_DateTime Tempo = new Cl\_DateTime();


public struct SYSTEMTIME
{
  public short wYear;
  public short wMonth;
  public short wDayOfWeek;
  public short wDay;
  public short wHour;
  public short wMinute;
  public short wSecond;
  public short wMilliseconds;
}

//functions to read and to set time
\[DllImport("coredll.dll")\]
private extern static void GetSystemTime(ref SYSTEMTIME lpSystemTime);

\[DllImport("coredll.dll")\]
private extern static uint SetSystemTime(ref SYSTEMTIME lpSystemTime);

//---------------------------------------------------------------------------------

public FormDateTime()
{
  InitializeComponent();
  this.Location = new Point((800 - this.Width) / 2, (480 - this.Height) / 2);
}
//---------------------------------------------------------------------------------.

private void FormDateTime\_Load(object sender, EventArgs e)
{
  if (FormDateTime\_FirstShow) {

    FormDateTime\_FirstShow = false;
  }

  CtrlsDesc();
  UpdateDateTime();
  ExitTr.Enabled = true;
}
//---------------------------------------------------------------------------------

private void FormDateTime\_Paint(object sender, PaintEventArgs e)
{
  //draw window border
  Gr.DrawFrContour(e, 0, 1, 1, this.Width - 1, this.Height - 1);
}
//---------------------------------------------------------------------------------

//update strings
public void CtrlsDesc()
{
  AbortBt.Text = FormMain.LF.GetStr(LangD.LANG\_Win, LangD.LANG\_WinExit);
  UpdateBt.Text = F

steve_9496613

I want to understand. I have made what you suggested and now my app is running with the form instance declared in a static class, sometime I push buttons to see if I get the exception. But I wanted to know why this is better considering that I had declared the form static instance inside a form that is never closed until the application is running. WTF...

steve_9496613

Thanks for the sample #realJSOP. Actually I don't need to save the exact moment the form is closed. This form is used to give the user the possibility to change the time and/or the date of the device (Windows CE based) on which the app is running and it is not used to change a variable used somewere else in the app. So I declared an external static class and in this class I declared my form instance:

public static class Cl_Forms
{
public static FormDateTime Suc3 = new FormDateTime();
}

As you suggest, in this way the form shown in a modal way should be static and should not be disposed until the app is running. Now I'm testing this solution. Unfortunately the exception occurred rarely and randomly and it was not easy to reproduce it.