Catch Exception Missing the Ball?

General
1

I sometimes get bug reports from my users that my app crashed on a specific method with a nil object exception. However that method has a exception catcher that reports it and deals with it. But the pitched exception sometimes seems to not be getting caught?

Is this a known issue? I assume that if this method calls another method that raises an exception, the exception handler in this method should catch it.

I think I’m going to get a t=shirt that says

“Nil objects happen.”

Exception err As RuntimeException If err IsA EndException Or err IsA ThreadEndException Then Raise err End If // Do reporting/cleanup

2

Can you post the entire method?

3

Sure. All these are controls or subclassed controls. It’s unlikely but not impossible for something to be nil. However it’s odd that the exception doesn’t catch it.

[code]If app.IsQuiting Then Return

Dim currentView As ViewData = uistate.GetCurrentState.ViewData

lbheader.Visible = False

// Move Sessionbox
If currentView.ShowFilters Then
// Move down to make way for filters
TheReportsContainer.Visible = True
theGraphAndLegend.Top = SegmentedChooser.top + SegmentedChooser.Height + 92 // Move graph out of the way of report controls
SessionBox.top = SegmentedChooser.top + SegmentedChooser.Height + 92
SessionBox.AdjustHeight

Else
// Listbox top aligns with graph top

theGraphAndLegend.Top = SegmentedChooser.top + SegmentedChooser.Height + 20
SessionBox.top = theGraphandLegend.top -3
SessionBox.AdjustHeight
TheReportsContainer.Visible = False
End If

// Set bottom of graph
theGraphAndLegend.Height = Self.TrueWindow.Height - TheGraphAndLegend.top

// Sessionbox wide and showing details? Hide graph
If currentView.ShowDetails = True Then
TheGraphAndLegend.Visible = False
Else
TheGraphAndLegend.Visible = True
End If

If currentView.ShowDetails = True Then
// Show wide over top of invisible graph
SessionBox.width = theGraphandLegend.Left + theGraphandLegend.Width - SessionBox.Left
Else
// Summary with graph
SessionBox.width = theGraphandLegend.Left - 20 - SessionBox.Left
End If

lbheader.MoveHeader
lbheader.Visible = True

Exception err As RuntimeException
If err IsA EndException Or err IsA ThreadEndException Then
Raise err
End If

debug.Warning CurrentMethodName, 3, err

[/code]

And FYI, here’s the stack being called

[code]Full stack trace:
RuntimeRaiseException
RaiseNilObjectException
MainWindow.MainWindow.MoveControls%%o<MainWindow.MainWindow>
Delegate.IM_Invoke%%
Xojo.Core._CallLaterTimer.Event_Action%%o<Xojo.Core._CallLaterTimer>
_ZN10TimerImpCF15FireTimerActionEv
_ZN10TimerImpCF13TimerCallbackEv
CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION
__CFRunLoopDoTimer
__CFRunLoopDoTimers
__CFRunLoopRun
CFRunLoopRunSpecific
RunCurrentEventLoopInMode
ReceiveNextEventCommon
_BlockUntilNextEventMatchingListInModeWithFilter
_DPSNextEvent
-[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:]
XojoFramework$4551
XojoFramework$4552
Application._CallFunctionWithExceptionHandling%%op
_Z33CallFunctionWithExceptionHandlingPFvvE
XojoFramework$4551
-[NSApplication run]
RuntimeRun
REALbasic._RuntimeRun
_Main
main

Verbose stack trace:
2 OfficeTime 0x0000000103011614 App.Event_UnhandledException%b%oo + 4100
3 OfficeTime 0x0000000102bbc40b Application._CallFunctionWithExceptionHandling%%op + 475
4 XojoFramework 0x00000001049764bb _Z33CallFunctionWithExceptionHandlingPFvvE + 262
5 XojoFramework 0x00000001047f12a2 _Z29CocoaFinishApplicationStartupv + 2076
6 AppKit 0x00007fff3519175d -[NSApplication run] + 699
7 XojoFramework 0x000000010497482d RuntimeRun + 42
8 OfficeTime 0x0000000102cc8a23 REALbasic._RuntimeRun + 19
9 OfficeTime 0x0000000103fb1cd8 _Main + 536
10 OfficeTime 0x0000000103f9be03 main + 19
11 libdyld.dylib 0x00007fff64d80085 start + 1
[/code]

4

When are you executing your code? Do your controls already exist? Have you tried to do your code in a timer a couple of ms later?

5

When the interface receives a signal to change state, it does a Xojo.core.timer.callLater(0) to this method. (Mostly to stop flicker on Windows.)

It might be trying to call after the window has been closed despite me cancelling the call on CancelClose. I’ll be a bit more aggressive in my nil checking.

6

If there’s a calllater that refers to a control that has now been closed then you can get this effect

7

@Stephen Dodd — Does the exception appears on quitting the app? Because you use “if app.IsQuitting” at the beginning and I have seen many cases where the App object would become nil while the app is quitting and so, “if app.IsQuitting” would raise a NilObjectException (possibly in a non-catchable way, I don’t remember if it was the case for me).

As a workaround, I usually use:

If App=nil OR App.IsQuitting then....