Re: Is this a good class hierarchy for my project

"crea" <>
Mon, 21 Mar 2011 20:28:26 -0000
Ok, good. I will try to clarify what I mean.
The point is anyway, that how the WeatherAnalysis -class can live
communicate with the Chart-drawing view. Thats the main point here. Also in
my opinion the point is not using MFC s doc/view system. I am thinking just
generally in c++... Although it might be the same thing isnt it - if we have
MFC or not there is still always doc/view communication?

The main problem I am facing is, that if in WeatherAnalysis I have a
for-loop and inside that I suddenly want to call view to draw something. And
vice verse: if in View i have a for loop and want to contact data for
certain item.

To comment your comments:

Joseph M. Newcomer wrote:

See below...
On Mon, 21 Mar 2011 17:25:28 -0000, "crea" <> wrote:

(this is also in comp.object group, but because it includes C++ and
MFC code also I put it here as well)

Lets say I have a weather data application to design. I have data
and then I will draw it on windows.
This is how I was thinking to implement it:

Base-Classes: Data, Chart (to draw data on window), DataAnalysis
(includes all functions to analyze the data and create corresponding
values to draw info on chart)

Then we can inherit different weathers from these, like "Finnish
weather" , "USA weather", "Moon weather", "globe weather" etc.

So the final result/class hierarchy would look like this (my
question below them) for USA Weather (for example):

// Data
class WeatherData
// classes for analysing data
class WeatherAnalysis
   WeatherData m_Data; // data to analyze
   void SetData(...);
   WeatherData& GetData();
   void DoSpecialAnalyze();
   virtual void DrawDifferentMark();
// class for USA weather
class USAWeatherAnalysis : public WeatherAnalysis
// data drawing
// CView is a windows class in Microsoft C++ MFC foundation classes
to draw to windows
class ChartView : public CView
   WeatherData* m_pData; // a pointer to data to draw

Now, this one bothers me. If you are using doc/view, then the data
displayed should be that of the document,

Yes it is. m_pData here at the end of the day will be pointing to current
document data. It will be set so later on ... see below.

 and that suggests that you

want documents with different WeatherData.

No, for USA for example there is only one WeatherData: the USA data. It will
be set in USAWeatherAnalysisView ::ReadUSAWeatherDataFromFile() below.

USAWeatherAnalysisView object contains basically only one document /data
and its address is copied to m_pData.

So making it part of the

view at this point looks suspect.

Is there another way to get hold of the WeatherData m_Data using this kind
of inheritance system than copying the address of it? How to go from
ChartView ->USAWeatherAnalysisView-> WeatherAnalysis ? I do not think its
possible...Going from one parent to another parent of
USAWeatherAnalysisView. If its possible, then its better obviously than
saving the pointer of it.

Making this member private means

you cannot derive subclasses of this view. Is that really what you
intended? ****

ok, my code is not perfect... and this is not really points here. So we can
forget this problem...

   virtual void DrawDifferentMark(int i);
   void SetWeatherData(WeatherData* pData) { m_pData=pData; }
// Then finally the class which hold everything together and links
data to windows view
class USAWeatherAnalysisView : public ChartView, public

Multiple inheritance is always a little suspect.

I know, but so far I did not find any other means to communicate between
those 2 classes: ChartView and WeatherAnalysis.

I used to use it a

lot, but eventually gave up on it as a model. Note that you are

deriving from a class which does not allow you to see the m_pData

but I see no corresponding GetWeatherData method either as

protected or public. ****

this is not a point really here, so we can change private to public...

I know the code might be a bit confusing.. :)

   void ReadUSAWeatherDataFromFile();

Why is the file format specific to the US? Why is not
ReadWeatherDataFromFile() not a method of the superclass?

   virtual void DrawDifferentMark();

Now we can read and set the data:
void USAWeatherAnalysisView ::ReadUSAWeatherDataFromFile()
// reading data from file to WeatherData object
WeatherData data;
// Then storing the data to WeatherData m_Data -member:

Pass-by-value is a bit suspect, since it is expensive, and except in
VS2010 will result in TWO copy operations, one to copy the parameter,
and one to do the assignment.

Sorry, I was meant to use references (or pointers) , so there is no copying
happening. But this is a side issue..

I would think it would make more sense to get a pointer to the
WeatherData object and read directly into it.

yes, it was meant to be that pointers/addresses of one data variable are
passed ... no copying.


//Then passing pointer of this data to the other parent class
ChartView: SetWeatherData(&GetData());

Why doesn't this set the WeatherData for the document and then the

view just uses the CWeatherDocument::GetData method?

Why is the data

stored in the view? ****

yes, I would do that (not to store the data address to view), but I do not
know how to contact from one parent class to another in my class hierarchy I
presented... Thats why I copy the addres of that data member to be able to
use the data. You know a way to contact directly without storing the


Now lets say we analyze data on WeatherAnalysis:
void WeatherAnalysis::DoSpecialAnalyze()
   for(eath data-item)
       if(data item is different than other items)

So we have a virtual function DrawDifferentMark in WeatherAnalysis:
class WeatherAnalysis
virtual void DrawDifferentMark(int item);.

When DrawDifferentMark is called it goes to USAWeatherAnalysisView
version, and from there we can call the corresponding drawing class
void USAWeatherAnalysisView ::DrawDifferentMark(int item)

So item pass route is: WeatherAnalysis -> USAWeatherAnalysisView ->

This all looks suspect, because if it is a virtual method, you should

ok, virtual or not virtual is not important really here... we can set it
non-virtual then..

just call it. It looks like you are not using virtual methods as
they are intended. ****

yes, maybe. But this is not the main point...

Is this a good way to implement the communication between data and
view/drawing windows? This way also if something happens in windows
and we want to communicate that to data classes (or analyzing
classes), then we can similarly create a virtual function in Chart
class and route it via USAWeatherAnalysisView to analysis/data
classes (ChartView ->USAWeatherAnalysisView-> WeatherAnalysis ).

You are using multiple inheritance to do what doc/view is supposed to
be doing. I am a bit suspect of this design.

I feel that you would totally have new class design. I am open to
suggestions. Lets see if it suits for what I need.


This is how I was thinking of doing it, but if anyone can tell if
this is the best way before I start would be nice :).

And if you give advices, can you please write corresponding code...
otherwise its difficult for me to understand it.

I have an appointment to rush off to, but I will think about this and
hopefully will be able to get back to you tonight.

ok. Hopefully I was able to clarify the situtuation. I ll wait for your

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