Re: Doc/View question
I consider using data variables to be a serious design error. I avoid them entirely. You
should think about whether or not their existence makes sense. I consider the whole
UpdateData mechanism to be a seriously deep design failure. I have yet to find a reason
that it could ever make sense within the context of a dialog or CFormView-derived class.
Their only value, which is marginal at best, is for a very limited subset of control types
(edit controls, static controls, and check boxes; they are completely useless for any
other kind of control)
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Well, Joe first I must thank you for giving me what I asked for (as usual ) but the
context of the above pretty much flys right over my head. When you read this you
probably are either laughing or sighing. But without burdening your super helpful
energetic input methods, could you briefly elaborate on specifically you mean by
not using data variables ? Are you referrering to data variables for the controls ?
And I am correct in surmizing that you directing me further as to how to implement
this in the rest of your reply below ?
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Probably the wrong decision. What I do is keep the values in variables in the
CDocument-derived class. In the serialize routine I simply call UpdateAllViews()
using a > specific lHint and pHint value which are not (0,NULL), and when this particular
combination is detected in my OnUpdate handler, I simply use operations like
GetWindowText, GetCurSel, and similar operations to copy the values out of the controls
and place them in variables in the CDocument-derived classs. In this way, onlly the
document understands how to read and write the data, and there is never any use of streams
in the view. Data transfer to and from the document are managed by the document class,
which is where it should be handled.
When the CFormView starts up, the OnInitialUpdate loads the controls from the variables in
the CDocument-derived class.
I do not believe in the DDX and DDV mechanisms at all, except for the DDX_Control calls to
bind the controls to control variables.
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Ok.... I will have to dwell on this awhile.
At first I thought I could just make the view class a friend of the document,
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NO!!!! This would require the CDocument-derived class know about the views, and this is
COMPLETELY WRONG!. Use UpdateAllViews to handle the transfer, as described.
NEVER include a view header file in the document class; if you think you have to, your
design is wrong!
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Ok, I had a feeling as such
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I consider writing UpdateData to be a fundamental design error. It is based on a set of
myths that I simply do not believe; that it makes sense to EVER transfer *every* data
value either to the controls, or from the controls. This has nasty implications when the
values interact. Read my essay on Dialog Control Management on my MVP Tips site.
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Ok I will check Tips site out
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DocPtr->InletA->dInvert_In_1 = m_Invert_In_1;
DocPtr->InletA->dInvert_Out_1 = m_Invert_Out_1;
DocPtr->InletA->uiInletNum = m_InletNum;
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THis is incosnsitent with your declaration; it should be
DocPtr->InLetA.dInvert_In_1 = m_Invert_In_1;
because InLetA is not a pointer
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Yes that is correct, your eagle eye caught it. While we are here
would you be so kind as to tell me how I might write this if I changed
InletA to an array of structs as in
Inlet InletA[10];
In other words how would I first even declare properly the StructArrayPtr?
Inlet* InletA[10]; I sense this would only be an array of pts and not
what I want.
And then how would I properly write the update code ?
DocPtr->InletA[2] ?? dInvert_In_1 = m_Invert_In_1;
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And finally to this last input (below) from you. I am saving this and will study
over it. But I have the following questions:
1. If I implement the below then I surmise I should call the OnUpDate from
my OnEnter handler ? (from a control button click)
2. Notwithstanding the previous input you have given me, is there an
additional key directional thought focus item that you could give me as
why this method is better than, or safer than, or logistically better than
using DDX
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I would do it using approximately the same idea, but do it in the OnUpdate handler:
void CMyView::OnUpdate(CView * view, LPARAM lHint, CObject * pHint)
{
if(lHint == 0 && pHint == NULL)
{
CView::OnUpdate(view, lHint, pHint);
return;
}
switch(lHint)
{ /* lHint */
case VALUES_TO_DOCUMENT:
{
CMyDoc * DocPtr = ...etc.
DocPtr->SetInvertIn(...);
DocPtr->SetInvertOut(...);
DocPtr->SetInletNum(...);
// I prefer to use set/get methods rather than directly access variables
// I might also do this as
// DocPtr->SetInLetValues(..., ..., ....);
// and not worry about the specification of the structure at all!
}
break;
case ...
break;
default:
...maybe ASSERT(FALSE) here....your choice
break;
} /* lHint */
} // CMyView::OnUpdate
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