QSignalMapper and original Sender()

I have a bunch of QComboBoxes in a table. So that I know which one was triggered I remap the signal to encode the table cell location (as described in Selecting QComboBox in QTableWidget)

(Why Qt doesn't just send the cell activated signal fi开发者_StackOverflow中文版rst so you can use the same current row/column mechanism as any other cell edit I don't know.)

But this removes all knowledge of the original sender widget. Calling QComboBox* combo = (QComboBox* )sender() in the slot fails, presumably because sender() is now the QSignalMapper.

I can use the encoded row/column to lookup the QComboBox in the table widget but that seems wrong. Is there a more correct way to do it?

e.g.:

// in table creator
_signalMapper = new QSignalMapper(this);

 // for each cell
    QComboBox* combo = new QComboBox();
    connect(combo, SIGNAL(currentIndexChanged(int)), _signalMapper, SLOT(map()));
    _signalMapper->setMapping(combo, row);

   // and finally       
   connect(_signalMapper, SIGNAL(mapped(int)),this, SLOT(changedType(int)));

 // slot
 void myDlg::changedType(int row)
 {      
        QComboBox* combo = (QComboBox* )sender(); // this doesn't work !!
 }

EDIT: Added for future search: there is a new book "Advanced Qt Programming" by Mark Summerfield that explains how to do this sort of thing.

Why not connect the QComboBox's signal straight to your slot?

QComboBox *combo = ...
connect(combo, SIGNAL(currentIndexChanged(int)), this, SLOT(changedType(int)));

And then in your slot you can use the sender() method to retrieve the QComboBox that was changed.

void myDlg::changedType(int row)
{
    QComboBox *combo = qobject_cast<QComboBox *> sender();

    if(combo != 0){
        // rest of code
    }
}

Alternatively, to use the QSignalMapper method you would just need to change your slot to use the mapping you set up:

void myDlg::changedType(int row)
{
    QComboBox *combo = qobject_cast<QComboBox *>(_signalMapper->mapping(row));

    if(combo != 0){
        // rest of code
    }
}        

I don't know exact answer, but maybe you should use: QComboBox* combo = qobject_cast(sender()) instead of QComboBox* combo = (QComboBox* )sender(). Someting like this:

 QObject* obj = sender();
 QComboBox* combo = qobject_cast<QComboBox*>(obj);
 if(combo)
 {
  doSomethingWithCombo(combo);
 }
 else
 {
  // obj is not QComboBox instance
 }

But maybe QSignalMapper really substitutes itself instead of real sender...