"Cannot access a disposed object"

Question

0.00/5 (No votes)

See more:

Hi everyone,

Can anybody tell me why i get "Cannot access a disposed object" error when i am migrating from 1 form to another without closing the previous form. To be precise i am using windows form as modal forms, and i have started the timer when i am in the 1st form & when i switch to 2nd form i am stopping the timer. Also i have used delegates to process data from a library & this library is accessed from both the forms. So i get this error in the delegate event in the 2nd form when trying to open 2nd form. So how to handle this type of error? The error what i get is "Cannot access a disposed object." "Object name: 'Form2'".

So can anybody tell me how to safely switch between forms without affecting any of the stuffs like those...?

Posted 21-Mar-13 20:44pm

Jagadisha_Ingenious

Add a Solution

Comments

Rohit Kumar Mumbai 22-Mar-13 2:53am

Can you please paste exact code where you are getting the exception?

Jagadisha_Ingenious 22-Mar-13 3:20am

I have added the piece of code here..

_Maxxx_ 22-Mar-13 2:55am

I don't understand how you are swapping between modal forms - only one form can be modal at a time...

I suggest you post some code so we can see where you are going wrong.

Jagadisha_Ingenious 22-Mar-13 3:21am

I have added the piece of code here..

Jagadisha_Ingenious 22-Mar-13 3:03am

#region Delegate Functions
public void DoGUIClear()
{
if (this.InvokeRequired)
{
GUIClear delegateMethod = new GUIClear(this.DoGUIClear);
this.Invoke(delegateMethod);
}

// this.lstRegisterValues.Items.Clear();
}
public void DoGUIStatus(string paramString)
{
if (this.InvokeRequired)
{
GUIStatus delegateMethod = new GUIStatus(this.DoGUIStatus);
this.Invoke(delegateMethod, new object[] { paramString });
//this.lblStatus.Text = paramString;
}
/* else
this.lblStatus.Text = paramString;*/
}
public void DoGUIUpdate(string paramString)
{
if (this.InvokeRequired)
{
GUIDelegate delegateMethod = new GUIDelegate(this.DoGUIUpdate);
this.Invoke(delegateMethod, new object[] { paramString });
}
/* else
this.lstRegisterValues.Items.Add(paramString);*/
}
#endregion
This is the delegate function which i am using.

The following to switch.
private void btnOk_Click(object sender, EventArgs e)
{
if (form2 == null || form2.IsDisposed)
{
form2 = new Annunciator_Window(descriptionName, btnName.Text, Port, devicescount, SlvID);
form2.MdiParent = MdiParent;
form2.WindowState = FormWindowState.Maximized;
// myPictureForm.FormClosing += form2_Closing;
this.FormClosing += new System.Windows.Forms.FormClosingEventHandler(this.MainForm_FormClosing);
}
this.Hide();
form2.Show();
}

toATwork 22-Mar-13 3:43am

How do you switch back from Form2 to Form1?

Jagadisha_Ingenious 22-Mar-13 4:30am

I will close form2 & open form1. But the problem what i am facing is initially when i switch from form1 to form2 i get this error.

toATwork 22-Mar-13 4:40am

You mean that the code you posted above still causes the problem?
private void btnOk_Click(object sender, EventArgs e)
{
if (form2 == null || form2.IsDisposed)
{
form2 = new Annunciator_Window(descriptionName, btnName.Text, Port, devicescount, SlvID);
form2.MdiParent = MdiParent;
form2.WindowState = FormWindowState.Maximized;
// myPictureForm.FormClosing += form2_Closing;
this.FormClosing += new System.Windows.Forms.FormClosingEventHandler(this.MainForm_FormClosing);
}
this.Hide();
form2.Show();
}

Jagadisha_Ingenious 22-Mar-13 4:50am

Yes exactly i still get this problem...

toATwork 22-Mar-13 4:51am

And line "form2.Show();" causes the exception?

Jagadisha_Ingenious 22-Mar-13 4:53am

It shows error sometimes @ this point of the code...

public void DoGUIClear()
{
if (this.InvokeRequired)
{
GUIClear delegateMethod = new GUIClear(this.DoGUIClear);
this.Invoke(delegateMethod);
}

// this.lstRegisterValues.Items.Clear();
}

And sometimes @ this point of code...

public void DoGUIStatus(string paramString)
{
if (this.InvokeRequired)
{
GUIStatus delegateMethod = new GUIStatus(this.DoGUIStatus);
this.Invoke(delegateMethod, new object[] { paramString });
//stswarning.Text = "How did he do that?";
//this.lblStatus.Text = paramString;
}
/* else
this.lblStatus.Text = paramString;*/
}

toATwork 22-Mar-13 5:06am

Somewehere you are disposing your Form along the way. The code you have posted is not sufficient.

Rohit Kumar Mumbai 22-Mar-13 4:54am

Where exactly you are getting error:-

this.Hide();
form2.Show();

Should work.

Try to debug and give exact exception.

Jagadisha_Ingenious 22-Mar-13 5:00am

public void DoGUIClear()
{
if (this.InvokeRequired)
{
GUIClear delegateMethod = new GUIClear(this.DoGUIClear);
this.Invoke(delegateMethod);................................... //@ this pont i get error.
}

And

public void DoGUIStatus(string paramString)
{
if (this.InvokeRequired)
{
GUIStatus delegateMethod = new GUIStatus(this.DoGUIStatus);
this.Invoke(delegateMethod, new object[] { paramString });.......@ here i get those errors.
//stswarning.Text = "How did he do that?";
//this.lblStatus.Text = paramString;
}
/* else
this.lblStatus.Text = paramString;*/
}

// this.lstRegisterValues.Items.Clear();
}

Once i might get in the 1st delegate function or i might get in the 2nd delegate function.

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

toATwork · Accepted Answer · 2013-03-21T23:21:00

Solution 1

From the comments it is clear that the Form is Disposed.
Add a breakpoint to the

C#

protected override void Dispose(bool disposing)

method of your form and check the call stack who caused the disposal of the Form.

Posted 21-Mar-13 23:21pm

toATwork

Comments

toATwork 22-Mar-13 5:31am

Is the issue resolved now? Which part exactly did the disposal?

Jagadisha_Ingenious 22-Mar-13 5:34am

I have put the breakpoint as u said but when i run it doesn't stop @ the breakpoint...

toATwork 22-Mar-13 5:38am

try to dump the StackTrace:
System.Console.WriteLine(Environment.StackTrace);

Jagadisha_Ingenious 22-Mar-13 6:03am

After stack trace i got this data in HTMl view.. by the way i have put that line of code in the button click event while migrating from 1 form to another.

" at System.Environment.GetStackTrace(Exception e, Boolean needFileInfo)
at System.Environment.get_StackTrace()
at AnnunciatorMonitoringTool.Annunciator_Devices.Annunciator_Devices_Click(Object sender, EventArgs e) in C:\AnnunciatorMonitoringTool\AnnunciatorMonitoringTool\Annunciator Devices.cs:line 462
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.Run(Form mainForm)
at AnnunciatorMonitoringTool.Program.Main() in C:\AnnunciatorMonitoringTool\AnnunciatorMonitoringTool\Program.cs:line 20
at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()".

toATwork 22-Mar-13 6:06am

This function is causing your Dispose:
Annunciator_Devices_Click(Object sender, EventArgs e)

Please provide the code of it.

Jagadisha_Ingenious 22-Mar-13 7:14am

Its is the same code from which i have started asking questions...

void Annunciator_Devices_Click(object sender, EventArgs e)
{
if (form2 == null || form2.IsDisposed)
{
form2 = new Annunciator_Window(descriptionName, btnName.Text, Port, devicescount, SlvID);
form2.MdiParent = MdiParent;
form2.WindowState = FormWindowState.Maximized;
// myPictureForm.FormClosing += form2_Closing;
this.FormClosing += new System.Windows.Forms.FormClosingEventHandler(this.MainForm_FormClosing);
}
this.Hide();
form2.Show();
}

toATwork 22-Mar-13 7:18am

Which one is the line 462 as mentioned in:
at AnnunciatorMonitoringTool.Annunciator_Devices.Annunciator_Devices_Click(Object sender, EventArgs e) in C:\AnnunciatorMonitoringTool\AnnunciatorMonitoringTool\Annunciator Devices.cs:line 462

Jagadisha_Ingenious 22-Mar-13 7:35am

Sir send me ur mail Id i will forward you the entire solution.. I dont have line 462 in my Annunciator devices form.

toATwork 22-Mar-13 7:43am

I am not confident in posting my mail addresse publicly. Is there any chance for private messages?

Jagadisha_Ingenious 25-Mar-13 2:53am

Sir so whats your suggestion on that issue..?

toATwork 27-Mar-13 3:41am

I sent you an email, please check your mailbox.

Jagadisha_Ingenious 27-Mar-13 3:48am

Yes sir i have received your mail n thanks for that. I was able to resolve the issue to some extent i guess. Like if i switch from 1 form to another 100 times i get only 5-6 times error mentioned earlier. I had to change few instructions in my code after which it is working fine.

toATwork 27-Mar-13 3:59am

In my opinion it should work always. My offer is still valid.

Jagadisha_Ingenious 27-Mar-13 4:06am

Yes sir i do agree..