Custom QAbstractProxyModel

[alizadeh91]

Hello
I have a question about QAbstractProxyModel. Suppose there is model and view.
I want to use a proxy between model and view which multiplies a column of data in model by a value. Is it possible?
Thanks

[wysota]

Yes, of course.

[alizadeh91]

Should i re-implement specific methods for that?

[wysota]

Should i re-implement specific methods for that?

Yes, you need to implement all pure virtual methods and reimplement those virtual methods that govern the behaviour you want to change. Note that if you're not used to proxy models and you only wish to change data returned by the base model, consider subclassing QSortFilterProxyModel instead of QAbstractProxyModel.

[alizadeh91]

Thanks for useful hints,
That's true, i can use QSortFilterProxyModel. But in this case what methods should i re-implement?

[wysota]

But in this case what methods should i re-implement?

If you wish to modify values returned by the model, reimplement data().

[anda_skoa]

Since you don't want to change the structure of the data, I'd suggest to have a look at QIdentityProxyModel.

So you'll only have to reimplement data and can forward any call that is not the display role and for the column which you want to change.

Cheers,
_

[alizadeh91]

Here is what i want to do, see if can suggest me best way:
I have a view and a custom header with comboBox for every column.
In the comboBox there are some units(e.g kilogram,gram, pound, ...). if user change the unit, the content of that column have to be changed according to unit.
Since just the unit of data is changed i don't want to change the model. I just want to display its equivalent in desired unit.
So i thought best way to implement this is proxy. may be if i use a proxy in model i can fix the model but just change the displaying data in proxy.
Is that true?
Is there better solutions?

[wysota]

So i thought best way to implement this is proxy. may be if i use a proxy in model i can fix the model but just change the displaying data in proxy.
Is that true?
Is there better solutions?

Hmmm... are you even reading what we have been writing here? Posts #6 and #7 already contain all the answers you need.

[alizadeh91]

Thanks wysota, Yes i'm reading! i just want to clear the problem!

[alizadeh91]

If you wish to modify values returned by the model, reimplement data().

Thanks again wysota, I've implemented the data() and it's ok except that the table doesn't update itself when i modify values returned by the model. I've even
try emit dataChanged() signal but i'm getting a weird error:

error: C2662: 'QAbstractItemModel::dataChanged' : cannot convert 'this' pointer from 'const TCustomProxyModel' to 'QAbstractItemModel &'
Conversion loses qualifiers

error: C2662: 'QAbstractItemModel::dataChanged' : cannot convert 'this' pointer from 'const TCustomProxyModel' to 'QAbstractItemModel &'
Conversion loses qualifiers

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(TCustomProxyModel: my custom proxy model)

Just another thing: when i click on table the table update itself!!!