Invoke or BeginInvoke cannot be called on a control until the window handle has been created

Question

I have a SafeInvoke Control extension method similar to the one Greg D discusses here  minus the IsHandleCreated check       I am calling it from a System Windows Forms Form as follows   public void Show string text        label SafeInvoke     gt label Text   text       this Show        this Refresh        Sometimes  this call can come from a variety of threads  this results in the following error       System InvalidOperationException occurred      Message   Invoke or BeginInvoke cannot be called on a control until the window handle has been created        Source   System Windows Forms   StackTrace  at System Windows Forms Control MarshaledInvoke Control caller  Delegate method  Object   args  Boolean synchronous  at System Windows Forms Control Invoke Delegate method  Object   args  at System Windows Forms Control Invoke Delegate method  at DriverInterface2 UI WinForms Dialogs FormExtensions SafeInvoke T  T control  Action 1 action   in C  code DriverInterface2 DriverInterface2 UI WinForms Dialogs FormExtensions cs line 16    What is going on and how do I fix it   I know as much as it is not a problem of form creation  since sometimes it will work once and fail the next time so what could the problem be   PS  I really really am awful at WinForms  does anyone know a good series of articles that explains the whole model and how to work with it

User · Answer

The method in the post you link to calls Invoke/BeginInvoke before checking if the control's handle has been created in the case where it's being called from a thread that didn't create the control.

So you'll get the exception when your method is called from a thread other than the one that created the control. This can happen from remoting events or queued work user items...

EDIT

If you check InvokeRequired and HandleCreated before calling invoke you shouldn't get that exception.

User · Answer

What about this         public static bool SafeInvoke  this Control control  MethodInvoker method                 if  control    null      control IsDisposed    control IsHandleCreated    control FindForm   IsHandleCreated                         if  control InvokeRequired                                 control Invoke  method                              else                               method                              return true                    else return false

User · Answer

Here is my answer to a similar question      I think  not yet entirely sure  that   this is because InvokeRequired will   always return false if the control has   not yet been loaded shown  I have done   a workaround which seems to work for   the moment  which is to simple   reference the handle of the associated   control in its creator  like so   var x   this Handle          See   http   ikriv com en prog info dotnet MysteriousHang html

User · Answer

I had this problem with this kind of simple form   public partial class MyForm   Form       public MyForm                 Load    new EventHandler Form1 Load              private void Form1 Load Object sender  EventArgs e                InitializeComponent               internal void UpdateLabel string s                Invoke new Action      gt    label1 Text   s                 Then for n other async threads I was using new MyForm   UpdateLabel text  to try and call the UI thread  but the constructor gives no handle to the UI thread instance  so other threads get other instance handles  which are either Object reference not set to an instance of an object or Invoke or BeginInvoke cannot be called on a control until the window handle has been created  To solve this I used a static object to hold the UI handle   public partial class MyForm   Form       private static MyForm  mf               public MyForm                 Load    new EventHandler Form1 Load              private void Form1 Load Object sender  EventArgs e                InitializeComponent             mf   this             internal void UpdateLabel string s                 mf Invoke  MethodInvoker  delegate    mf label1 Text   s                I guess it s working fine  so far

User · Answer

var that   this     this is a form  new Thread     gt         var action  new Action      gt           something               if  that IsDisposed                if that IsHandleCreated                          if  that InvokeRequired                  that BeginInvoke action                 else                action Invoke                      else             that HandleCreated   sender event    gt                    action Invoke                               Start

User · Answer

If you re going to use a Control from another thread before showing or doing other things with the Control  consider forcing the creation of its handle within the constructor   This is done using the CreateHandle function   In a multi-threaded project  where the  controller  logic isn t in a WinForm  this function is instrumental in Control constructors for avoiding this error

User · Answer

Reference the handle of the associated control in its creator  like so   Note  Be wary of this solution If a control has a handle it is much slower to do things like set the size and location of it  This makes InitializeComponent much slower  A better solution is to not background anything before the control has a handle

User · Answer

It s possible that you re creating your controls on the wrong thread   Consider the following documentation from MSDN      This means that InvokeRequired can   return false if Invoke is not required    the call occurs on the same thread     or if the control was created on a   different thread but the control s   handle has not yet been created       In the case where the control s handle   has not yet been created  you should   not simply call properties  methods    or events on the control  This might   cause the control s handle to be   created on the background thread    isolating the control on a thread   without a message pump and making the   application unstable       You can protect against this case by   also checking the value of   IsHandleCreated when InvokeRequired   returns false on a background thread    If the control handle has not yet been   created  you must wait until it has   been created before calling Invoke or   BeginInvoke  Typically  this happens   only if a background thread is created   in the constructor of the primary form   for the application  as in   Application Run new MainForm       before the form has been shown or   Application Run has been called    Let s see what this means for you    This would be easier to reason about if we saw your implementation of SafeInvoke also   Assuming your implementation is identical to the referenced one with the exception of the check against IsHandleCreated  let s follow the logic   public static void SafeInvoke this Control uiElement  Action updater  bool forceSynchronous        if  uiElement    null                throw new ArgumentNullException  uiElement               if  uiElement InvokeRequired                if  forceSynchronous                        uiElement Invoke  Action delegate   SafeInvoke uiElement  updater  forceSynchronous                         else                       uiElement BeginInvoke  Action delegate   SafeInvoke uiElement  updater  forceSynchronous                           else                   if  uiElement IsDisposed                        throw new ObjectDisposedException  Control is already disposed                        updater              Consider the case where we re calling SafeInvoke from the non-gui thread for a control whose handle has not been created   uiElement is not null  so we check uiElement InvokeRequired   Per the MSDN docs  bolded  InvokeRequired will return false because  even though it was created on a different thread  the handle hasn t been created   This sends us to the else condition where we check IsDisposed or immediately proceed to call the submitted action    from the background thread   At this point  all bets are off re  that control because its handle has been created on a thread that doesn t have a message pump for it  as mentioned in the second paragraph   Perhaps this is the case you re encountering

User · Answer

Add this before you call method invoke   while   this IsHandleCreated      System Threading Thread Sleep 100

User · Answer

I found the InvokeRequired not reliable  so I simply use  if   this IsHandleCreated        this CreateHandle

[winforms] Invoke or BeginInvoke cannot be called on a control until the window handle has been created

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