"Daniel Manes" <danth***@cox.net> wrote in message
news:1163377882.104364.321610@i42g2000cwa.googlegroups.com...
>I need a strategy to debug this situation...
>
> I can't put all the code involved, but here are some of the critical
> lines with comments:
>
> -------------------------
> Private _parentDataCell As DataGridViewCell 'declare private field
> _parentDataCell = _parentDataGrid.Rows(rowIndex).Cells(columnIndex)
> 'set to a specific cell
> Debug.Print(_parentDataCell.DataGridView.ToString) 'prints:
> System.Windows.Forms.DataGridView
> _childDialogResult = _childDialog.ShowDialog() 'show a dialog, user
> does certain stuff with dialog
> Debug.Print(_parentTableName & " " &
> _parentDataCell.DataGridView.ToString) 'throws NullReferenceException
> -------------------------
>
> So, the problem is that, somehow, while the user is doing stuff with
> the dialog that gets opened, _parentDataCell gets "disembodied"--it's
> no longer pointing to a DataGridView. If I do "? _parentDataCell" in
> the Immediate window, I get the following:
>
> -------------------------
> ? _parentDataCell
> {System.Windows.Forms.DataGridViewButtonCell}
>    System.Windows.Forms.DataGridViewButtonCell:
> {System.Windows.Forms.DataGridViewButtonCell}
>    AccessibilityObject:
> {System.Windows.Forms.DataGridViewButtonCell.DataGridViewButtonCellAccessibleObject}
>    ColumnIndex: 2
>    ContentBounds: {X = 0 Y = 0 Width = 0 Height = 0}
>    ContextMenuStrip: Nothing
>    DataGridView: Nothing
>    DefaultNewRowValue: Nothing
>    Displayed: False
>    EditedFormattedValue: Nothing
>    EditType: Nothing
>    ErrorIconBounds: {"Cell is not in a DataGridView. The cell cannot
> retrieve the inherited cell style."}
>    ErrorText: ""
>    FormattedValue: Nothing
>    FormattedValueType: {Name = "String" FullName = "System.String"}
>    Frozen: False
>    HasStyle: False
>    InheritedState: 80
>    InheritedStyle: {"Cell is not in a DataGridView. The cell cannot
> retrieve the inherited cell style."}
>    IsInEditMode: False
>    OwningColumn: {System.Windows.Forms.DataGridViewButtonColumn}
>    OwningRow: {System.Windows.Forms.DataGridViewRow}
>    PreferredSize: {Width = -1 Height = -1}
>    ReadOnly: False
>    Resizable: False
>    RowIndex: -1
>    Selected: False
>    Size: {Width = -1 Height = -1}
>    State: None {0}
>    Style: {System.Windows.Forms.DataGridViewCellStyle}
>    Tag: Nothing
>    ToolTipText: ""
>    Value: Nothing
>    ValueType: {Name = "String" FullName = "System.String"}
>    Visible: True
> -------------------------
>
> Notice that _parentDataCell is not "Nothing", but it no longer has a
> DataGridView, it's dimensions are zero, it's not displayed, etc..
> Interestingly, it still has a ColumnIndex of 2, but it's RowIndex is
> now -1.
>
> I can't find anything in my code that would be causing this, but
> obviously something is. What I need is some way to track or trace
> _parentDataCell over time so I can see exactly when it "loses its
> identity." Then maybe I'll have some hope of figuring out what's going
> on.
>
> How do I do this in Visual Studio 2005?
>
> Any other tips/advice?
>
> Thanks in advance,
>
> -Dan
>
>

> The easiest thing to do is add the line where you
> set _parentDataCell right before you use it again.
> But I understand why you would want to know where
> it's getting changed.
>
> I thought there was a way to break in debug mode
> when the value of a variable changed, but I can't
> find it.
>
> So I'd put a breakpoint where you first set
> _parentDataCell. When you get there and it stops,
> right-click on it and add a Watch on it. Then step
> through your code, and watch it in the Watch
> window and see when it changes.
>
> It could be that if you are changing rowIndex
> and/or columnIndex somewhere, it is redefining
> parentDataCell to point at that new location,
> although I think that would be unexpected.
>
> Robin S.
> ------------------
> "Daniel Manes" <danth***@cox.net> wrote in message
> news:1163377882.104364.321610@i42g2000cwa.googlegroups.com...
> >I need a strategy to debug this situation...
> >
> > I can't put all the code involved, but here are some of the critical
> > lines with comments:
> >
> > -------------------------
> > Private _parentDataCell As DataGridViewCell 'declare private field
> > _parentDataCell = _parentDataGrid.Rows(rowIndex).Cells(columnIndex)
> > 'set to a specific cell
> > Debug.Print(_parentDataCell.DataGridView.ToString) 'prints:
> > System.Windows.Forms.DataGridView
> > _childDialogResult = _childDialog.ShowDialog() 'show a dialog, user
> > does certain stuff with dialog
> > Debug.Print(_parentTableName & " " &
> > _parentDataCell.DataGridView.ToString) 'throws NullReferenceException
> > -------------------------
> >
> > So, the problem is that, somehow, while the user is doing stuff with
> > the dialog that gets opened, _parentDataCell gets "disembodied"--it's
> > no longer pointing to a DataGridView. If I do "? _parentDataCell" in
> > the Immediate window, I get the following:
> >
> > -------------------------
> > ? _parentDataCell
> > {System.Windows.Forms.DataGridViewButtonCell}
> >    System.Windows.Forms.DataGridViewButtonCell:
> > {System.Windows.Forms.DataGridViewButtonCell}
> >    AccessibilityObject:
> > {System.Windows.Forms.DataGridViewButtonCell.DataGridViewButtonCellAccessibleObject}
> >    ColumnIndex: 2
> >    ContentBounds: {X = 0 Y = 0 Width = 0 Height = 0}
> >    ContextMenuStrip: Nothing
> >    DataGridView: Nothing
> >    DefaultNewRowValue: Nothing
> >    Displayed: False
> >    EditedFormattedValue: Nothing
> >    EditType: Nothing
> >    ErrorIconBounds: {"Cell is not in a DataGridView. The cell cannot
> > retrieve the inherited cell style."}
> >    ErrorText: ""
> >    FormattedValue: Nothing
> >    FormattedValueType: {Name = "String" FullName = "System.String"}
> >    Frozen: False
> >    HasStyle: False
> >    InheritedState: 80
> >    InheritedStyle: {"Cell is not in a DataGridView. The cell cannot
> > retrieve the inherited cell style."}
> >    IsInEditMode: False
> >    OwningColumn: {System.Windows.Forms.DataGridViewButtonColumn}
> >    OwningRow: {System.Windows.Forms.DataGridViewRow}
> >    PreferredSize: {Width = -1 Height = -1}
> >    ReadOnly: False
> >    Resizable: False
> >    RowIndex: -1
> >    Selected: False
> >    Size: {Width = -1 Height = -1}
> >    State: None {0}
> >    Style: {System.Windows.Forms.DataGridViewCellStyle}
> >    Tag: Nothing
> >    ToolTipText: ""
> >    Value: Nothing
> >    ValueType: {Name = "String" FullName = "System.String"}
> >    Visible: True
> > -------------------------
> >
> > Notice that _parentDataCell is not "Nothing", but it no longer has a
> > DataGridView, it's dimensions are zero, it's not displayed, etc..
> > Interestingly, it still has a ColumnIndex of 2, but it's RowIndex is
> > now -1.
> >
> > I can't find anything in my code that would be causing this, but
> > obviously something is. What I need is some way to track or trace
> > _parentDataCell over time so I can see exactly when it "loses its
> > identity." Then maybe I'll have some hope of figuring out what's going
> > on.
> >
> > How do I do this in Visual Studio 2005?
> >
> > Any other tips/advice?
> >
> > Thanks in advance,
> >
> > -Dan
> >
> >

"Daniel Manes" <danth***@cox.net> wrote in message
news:1163539399.540860.10720@i42g2000cwa.googlegroups.com...
> Hey Robin,
>
> Thanks for the reply. I actually managed to solved the problem, but I
> still wonder if there would have been an easier way. Some comments
> below.
>
>> So I'd put a breakpoint where you first set
>> _parentDataCell. When you get there and it stops,
>> right-click on it and add a Watch on it. Then step
>> through your code, and watch it in the Watch
>> window and see when it changes.
>
> Good idea. Actually what I tried :) But here's the problem: You can
> only step through the debugger until all code associated with an event
> is run. Then the debugger just stops. It wasn't until several mouse
> clicks later that the link was getting lost.
>
> So, I thought: put a break point in click event and keep watching the
> value. But there was a problem with that too. The event handlers are in
> a different class than _parentDataCell, so _parentDataCell is out of
> scope (i.e., you can't see its value in the debugger/watcher).
>
> Also, new instances of the class containing _parentDataCell get created
> as the user clicks various buttons, so, how would the watcher know
> which _parentDataCell I was talking about anyway?
>
> The only solution I could think of was to create a shared (static)
> variable called _firstParentDataCell, and set it equal to
> _parentDataCell only if _parentDataCell had not yet been set. Then I
> wrote a little shared function that tests to see whether
> _firstParentDataCell is still "intact." Finally, I placed calls to the
> function strategically through the code to see when the data was
> getting lost.
>
> This worked but it sure seemed like a lot of hassle. Turned out, the
> bug was caused by one of those user clicks causing the filter on the
> original DataGridView to get reapplied. The cell in question was still
> there, but the act of refiltering caused all references to go blooey.
>
> So, yeah, programming is hard :)
>
> -Dan
>
> RobinS wrote:
>> The easiest thing to do is add the line where you
>> set _parentDataCell right before you use it again.
>> But I understand why you would want to know where
>> it's getting changed.
>>
>> I thought there was a way to break in debug mode
>> when the value of a variable changed, but I can't
>> find it.
>>
>> So I'd put a breakpoint where you first set
>> _parentDataCell. When you get there and it stops,
>> right-click on it and add a Watch on it. Then step
>> through your code, and watch it in the Watch
>> window and see when it changes.
>>
>> It could be that if you are changing rowIndex
>> and/or columnIndex somewhere, it is redefining
>> parentDataCell to point at that new location,
>> although I think that would be unexpected.
>>
>> Robin S.
>> ------------------
>> "Daniel Manes" <danth***@cox.net> wrote in message
>> news:1163377882.104364.321610@i42g2000cwa.googlegroups.com...
>> >I need a strategy to debug this situation...
>> >
>> > I can't put all the code involved, but here are some of the critical
>> > lines with comments:
>> >
>> > -------------------------
>> > Private _parentDataCell As DataGridViewCell 'declare private field
>> > _parentDataCell = _parentDataGrid.Rows(rowIndex).Cells(columnIndex)
>> > 'set to a specific cell
>> > Debug.Print(_parentDataCell.DataGridView.ToString) 'prints:
>> > System.Windows.Forms.DataGridView
>> > _childDialogResult = _childDialog.ShowDialog() 'show a dialog, user
>> > does certain stuff with dialog
>> > Debug.Print(_parentTableName & " " &
>> > _parentDataCell.DataGridView.ToString) 'throws NullReferenceException
>> > -------------------------
>> >
>> > So, the problem is that, somehow, while the user is doing stuff with
>> > the dialog that gets opened, _parentDataCell gets "disembodied"--it's
>> > no longer pointing to a DataGridView. If I do "? _parentDataCell" in
>> > the Immediate window, I get the following:
>> >
>> > -------------------------
>> > ? _parentDataCell
>> > {System.Windows.Forms.DataGridViewButtonCell}
>> >    System.Windows.Forms.DataGridViewButtonCell:
>> > {System.Windows.Forms.DataGridViewButtonCell}
>> >    AccessibilityObject:
>> > {System.Windows.Forms.DataGridViewButtonCell.DataGridViewButtonCellAccessibleObject}
>> >    ColumnIndex: 2
>> >    ContentBounds: {X = 0 Y = 0 Width = 0 Height = 0}
>> >    ContextMenuStrip: Nothing
>> >    DataGridView: Nothing
>> >    DefaultNewRowValue: Nothing
>> >    Displayed: False
>> >    EditedFormattedValue: Nothing
>> >    EditType: Nothing
>> >    ErrorIconBounds: {"Cell is not in a DataGridView. The cell cannot
>> > retrieve the inherited cell style."}
>> >    ErrorText: ""
>> >    FormattedValue: Nothing
>> >    FormattedValueType: {Name = "String" FullName = "System.String"}
>> >    Frozen: False
>> >    HasStyle: False
>> >    InheritedState: 80
>> >    InheritedStyle: {"Cell is not in a DataGridView. The cell cannot
>> > retrieve the inherited cell style."}
>> >    IsInEditMode: False
>> >    OwningColumn: {System.Windows.Forms.DataGridViewButtonColumn}
>> >    OwningRow: {System.Windows.Forms.DataGridViewRow}
>> >    PreferredSize: {Width = -1 Height = -1}
>> >    ReadOnly: False
>> >    Resizable: False
>> >    RowIndex: -1
>> >    Selected: False
>> >    Size: {Width = -1 Height = -1}
>> >    State: None {0}
>> >    Style: {System.Windows.Forms.DataGridViewCellStyle}
>> >    Tag: Nothing
>> >    ToolTipText: ""
>> >    Value: Nothing
>> >    ValueType: {Name = "String" FullName = "System.String"}
>> >    Visible: True
>> > -------------------------
>> >
>> > Notice that _parentDataCell is not "Nothing", but it no longer has a
>> > DataGridView, it's dimensions are zero, it's not displayed, etc..
>> > Interestingly, it still has a ColumnIndex of 2, but it's RowIndex is
>> > now -1.
>> >
>> > I can't find anything in my code that would be causing this, but
>> > obviously something is. What I need is some way to track or trace
>> > _parentDataCell over time so I can see exactly when it "loses its
>> > identity." Then maybe I'll have some hope of figuring out what's going
>> > on.
>> >
>> > How do I do this in Visual Studio 2005?
>> >
>> > Any other tips/advice?
>> >
>> > Thanks in advance,
>> >
>> > -Dan
>> >
>> >
>