LVN_ITEMCHANGED event triggered multiple times on single click

[Dan English]

Would anyone know why a listview might trigger the LVN_ITEMCHANGED event 3 times on a single click?

I'm not doing any FF_ListView_SetSelectedItem calls on the listview, and I don't have any code in place to mess with my mouse clicks...

[Dan English]

Here's a bit more detail...

I have a listview where there's several rows populated.  Each represents a single record in a database.  The form for the record appears to the right of the listview.  If any of the form fields are updated, the program knows there's pending changes to be saved.

If the user clicks another listview row while changes are pending, the user needs to be prompted to save the changes first.  Here's the pseudo code to demonstrate what I'm doing:

Code Select Expand


Function FORM1_LISTVIEW1_LVN_ITEMCHANGING ( ... ) As Long

    ' show "do you want to save your changes?" messagebox:
    ' - if YES, save record and return %FALSE
    ' - if NO, don't save record and return %FALSE
    ' - if CANCEL, don't save record and return %TRUE (which cancels LVN_ITEMCHANGED)

End Function

Function FORM1_LISTVIEW1_LVN_ITEMCHANGED ( ... ) As Long

    If IsTrue (@lpNMV.uNewState And %LVIS_SELECTED) Then
        ' load record for selected row...
    End If

End Function


Is this the right way to handle this sort of situation?

[Dan English]

A further observation:  LVN_ITEMCHANGING is also triggered 3 times on clicking a listview row...

[Paul Squires]

Chris posted this several years ago to show what messages get posted when the mouse button is clicked:

Mouse Button Down:

NM_RELEASEDCAPTURE
LVN_ITEMCHANGING           (state changes for item unselected)
LVN_ITEMCHANGED
LVN_ITEMCHANGING
LVN_ITEMCHANGED
LVN_ITEMCHANGING          (state changes for item selected)
LVN_ITEMCHANGED
NM_CUSTOMDRAW

Mouse Up:

I guess that's why you need to check the new state flag.

[Dan English]

Thanks, I guess that confirms what I've been seeing.

Is there an alternative way to deal with prompting the user to save changes when they change the listview row?

[Paul Squires]

This is a question which I thought would have an easy answer but I am having a hard time trying to figure out the answer. It seems like it should be easy....

I tried a few combinations of canceling the change while using PostMessage with a user defined message to pop up a message box confirmation and then manually set the row if the user decides to continue. No success. I googled this problem and it seems other are having similar problems. Not sure what the answer is at this point. Maybe I am missing something obvious.

[Paul Squires]

hmmm... this post response by Dominic may hold some promise:
http://www.powerbasic.com/support/pbforums/showthread.php?t=19344

[Christian Weilguny]

Hi

I had the same problem.

My solution is this:

Code Select Expand

   Case %WM_Notify               
                   NMList = lParam
                   Select Case @NMList.Hdr.Code
                     Case %LVN_ITEMCHANGING                                             
                        If (@NMList.uChanged And %LVIF_STATE) = %LVIF_STATE Then
                           If (@NMList.uOldState And 1) = 1 Then                             
                              If IsTrue(VerifyChange(hWnd)) Then Function = %True: Exit Function
                           End If
                        End If
                   End Select                 


When the change is stopped with function = %True: Exit Function then the message comes a second time. I have catched this in the VerifyChange -Routine with a static variable:

Code Select Expand

Function VerifyChange(hWnd As Long) As Long
   Static bChg As Long
   
   If IsTrue(IsDirty(hWnd)) Then
      If IsTrue(bChg) Then
         bChg = %False: Function = %True: Exit Function
      End If
      Select Case MsgBox("Ã,,nderungen übernehmen?", %MB_ICONWARNING Or %MB_YESNOCANCEL Or %MB_DEFBUTTON1 Or %MB_APPLMODAL, "Datensatz geändert")
         Case %IDYES   : SyncToBrowser hWnd
         Case %IDCANCEL: bChg = %True: Function = %True: Exit Function       
      End Select                         
   End If                           

End Function


Maybe this is helpful.

Christian

[Paul Squires]

Thanks Christian! Appreciate your code. Hope it works to fix Dan's problem.

[Christian Weilguny]

Hi Paul,

thanks for the honor,

something new about my option-button problem?

Christian

[Dan English]

Thanks guys...  I've since moved on to a different form design to avoid this situation, but I'm quite sure I'll run into this again.  I'll give it a shot when that time comes!