Swapping headers in QSqlQueryModel (transpose table)

问题

I am having a problem to properly transpose the table I recieve from db. I followed the path found here , and ended up in subclassing a QAbstractProxyModel - like described here . unfortunatelly, it doesn't fully work, here's where the problem is:

What I have:

X | A  | B
----------
1 | A1 | B1
2 | A2 | B2

What I want:

X | 1  | 2
----------
A | A1 | A2
B | B1 | B2

What I get:

X | 1  | 1
----------
A | A1 | A2
A | B1 | B2

So as you can see, the data is correctly transposed, but the headers get bad... And I really need them :(

I tried to manually set header data, but it also failed:

origModel = new QSqlQueryModel; // set query and so on
transposedModel = new TransposeProxyModel;
transposedModel->setSourceModel(origModel );
for (int i = 0; i < origModel->columnCount(); i++) {
    qDebug() << "origModel->Qt::Horizontal(" << i << ")" << origModel->headerData(i, Qt::Horizontal, Qt::DisplayRole);
    //transposedModel->setHeaderData(i, Qt::Vertical, origModel->headerData(i, Qt::Horizontal, Qt::DisplayRole), Qt::DisplayRole); //#try1
    transposedModel->setHeaderData(i, Qt::Vertical, QVariant( "abc" ), Qt::DisplayRole); // #try2
}

No matter if I try #1, or #2 - call to setHeaderData evaluates to false...

Any ideas?

fixed as @Vinícius Gobbo A. de Oliveira pointed

回答1:

Well, if you used the example code you linked you should override the default definition for the headerData method of the TransposeProxyModel class, just like this:

QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const {
    return sourceModel()->headerData(section, (orientation == Qt::Horizontal ? Qt::Vertical : Qt::Horizontal), role);
}

Forget about the setHeaderData and setData methods: you want a proxy model that rely on the original one!

Well, don't know exactly what's wrong, which Qt release are you using? Try this code, it works perfectly here:

#include <QtCore>
#include <QtWidgets>

class TransposeProxyModel: public QAbstractProxyModel {
public:
    TransposeProxyModel(QObject *p = 0):
        QAbstractProxyModel(p)
    {
    }
    QModelIndex mapFromSource ( const QModelIndex & sourceIndex ) const{
        return index(sourceIndex.column(), sourceIndex.row());
    }
    QModelIndex mapToSource ( const QModelIndex & proxyIndex ) const{
        return sourceModel()->index(proxyIndex.column(), proxyIndex.row());
    }
    QModelIndex index(int r, int c, const QModelIndex &ind=QModelIndex()) const{
        return createIndex(r,c);
    }
    QModelIndex parent(const QModelIndex&) const {
        return QModelIndex();
    }
    int rowCount(const QModelIndex &) const{
        return sourceModel()->columnCount();
    }
    int columnCount(const QModelIndex &) const{
        return sourceModel()->rowCount();
    }
    QVariant data(const QModelIndex &ind, int role) const {
        return sourceModel()->data(mapToSource(ind), role);
    }
    QVariant headerData(int section, Qt::Orientation orientation,
        int role = Qt::DisplayRole) const {
        return sourceModel()->headerData(section,
            (orientation == Qt::Horizontal ? Qt::Vertical : Qt::Horizontal),
            role);
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QStandardItemModel model(3,3);
    model.setData(model.index(0,0), "1");
    model.setData(model.index(0,1), "2");
    model.setData(model.index(0,2), "3");
    model.setData(model.index(1,0), "4");
    model.setData(model.index(1,1), "5");
    model.setData(model.index(1,2), "6");
    model.setData(model.index(2,0), "7");
    model.setData(model.index(2,1), "8");
    model.setData(model.index(2,2), "9");
    model.setHeaderData(0, Qt::Horizontal, "a");
    model.setHeaderData(1, Qt::Horizontal, "b");
    model.setHeaderData(2, Qt::Horizontal, "c");
    TransposeProxyModel trans;
    trans.setSourceModel(&model);
    QSplitter split;
    QTableView *t1 = new QTableView(&split);
    t1->setModel(&model);
    QTableView *t2 = new QTableView(&split);
    t2->setModel(&trans);
    split.show();
    return a.exec();
}

Most of the code came from the link you provided, I just wrote the headerData method.

回答2:

Funny thing though - the doc states that this is a virtual method:

virtual QVariant headerData(int section, Qt::Orientation orientation, int role) const

(...)

QVariant QAbstractProxyModel::headerData(int section, Qt::Orientation orientation, int role) const [virtual]

Reimplemented from QAbstractItemModel::headerData().

but in the actual headerthe virtual keyword is missing:

C:\Qt\Qt5.2.1\5.2.1\msvc2010\include\QtCore\qabstractproxymodel.h

(...)
QVariant data(const QModelIndex &proxyIndex, int role = Qt::DisplayRole) const; //line76
QVariant headerData(int section, Qt::Orientation orientation, int role) const; //line77

I checked in normal Qt dir and it is also missing:

C:\Qt\Qt5.2.1\5.2.1\Src\qtbase\src\corelib\itemmodels\qabstractproxymodel.h

(...)
QVariant data(const QModelIndex &proxyIndex, int role = Qt::DisplayRole) const;
QVariant headerData(int section, Qt::Orientation orientation, int role) const;

I have made a test:

sim = new QStandardItemModel (3,3);

for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++ ) {
        sim->setData(sim->index(i,j), QString("%1%2").arg(QChar(j+65), QString().setNum(i+1)));
        if (i==0)
            sim->setHeaderData(j, Qt::Horizontal, QChar(j+65));
    }
    sim->setHeaderData(i, Qt::Vertical, i+1);
}

transposedModel = new TransposeProxyModel;
transposedModel->setSourceModel(sim);

QAbstractItemModel * aim = transposedModel;
QAbstractProxyModel *apm = transposedModel;

for (int i = 0; i < apm->rowCount(); i++) {
    qDebug() << "aim->Qt::Vertical(" << i << ")" << aim->headerData(i, Qt::Vertical, Qt::DisplayRole);
    qDebug() << "apm->Qt::Vertical(" << i << ")" << apm->headerData(i, Qt::Vertical, Qt::DisplayRole);
    qDebug() << "transposedModel->Qt::Vertical(" << i << ")" << transposedModel->headerData(i, Qt::Vertical, Qt::DisplayRole);
}

And the debug is:

aim->Qt::Vertical( 0 ) QVariant(int, 1) 
apm->Qt::Vertical( 0 ) QVariant(int, 1) 
[ TransposeProxyModel::headerData ] //qDebug in TransposeProxyModel::headerData
transposedModel->Qt::Vertical( 0 ) QVariant(QChar, 'A') 
aim->Qt::Vertical( 1 ) QVariant(int, 1) 
apm->Qt::Vertical( 1 ) QVariant(int, 1) 
[ TransposeProxyModel::headerData ] //qDebug in TransposeProxyModel::headerData
transposedModel->Qt::Vertical( 1 ) QVariant(QChar, 'B') 
aim->Qt::Vertical( 2 ) QVariant(int, 1) 
apm->Qt::Vertical( 2 ) QVariant(int, 1) 
[ TransposeProxyModel::headerData ] //qDebug in TransposeProxyModel::headerData
transposedModel->Qt::Vertical( 2 ) QVariant(QChar, 'C')

So I guess that's the problem - the method isn't abstract, and that's why it doesn't call my overridden method. Qt bug ? or is that on purpose? I also took a peek into

C:\Qt\Qt5.2.1\5.2.1\Src\qtbase\src\corelib\itemmodels\qabstractproxymodel.cpp

/*!
    \reimp
 */
QVariant QAbstractProxyModel::headerData(int section, Qt::Orientation orientation, int role) const
{
    Q_D(const QAbstractProxyModel);
    int sourceSection;
    if (orientation == Qt::Horizontal) {
        const QModelIndex proxyIndex = index(0, section);
        sourceSection = mapToSource(proxyIndex).column();
    } else {
        const QModelIndex proxyIndex = index(section, 0);
        sourceSection = mapToSource(proxyIndex).row();
    }
    return d->model->headerData(sourceSection, orientation, role);
}

I guess it should get proper header anyway - it calls mapToSource, which is pure virtual, and this should obtain the correct index?

来源：https://stackoverflow.com/questions/26050030/swapping-headers-in-qsqlquerymodel-transpose-table

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