Need help with checkbox in tableview

[vieraci]

I'm trying to get my table to display a QCheckBox for a column that is boolean (actually int) from a QSqlQueryModel.

I've implemented a delegate so when the field is clicked a check box appears and this works fine, but I can't work out what code to implement to get the column to display a check box instead of a 0 or 1.

I've read in another post:

You can reimplement QAbstractItemModel::flags() to return Qt::ItemIsUserCheckable together with other flags for the checkable column. But notice that you must also handle Qt::CheckStateRole in data() and setData().

With this in mind, I reimplemented flags() which seems to work

Qt::ItemFlags PurchaseOrdersRequests::flags(
        const QModelIndex &index) const
{
    Qt::ItemFlags flags = QSqlQueryModel::flags(index);
    flags |= Qt::ItemIsEditable;
    if (index.column() == 6)
    {
        flags |= Qt::ItemIsUserCheckable;
    }
    return flags;
}

Qt::ItemFlags PurchaseOrdersRequests::flags(
        const QModelIndex &index) const
{
    Qt::ItemFlags flags = QSqlQueryModel::flags(index);
    flags |= Qt::ItemIsEditable;
    if (index.column() == 6)
    {
        flags |= Qt::ItemIsUserCheckable;
    }
    return flags;
}

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...but data() is totally wrong.

QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
        return QVariant();
 
//    if (role == Qt::ItemIsUserCheckable) // NEVER happens !
//        qDebug() << "  ItemIsUserCheckable";
 
     if (role == Qt::DisplayRole)
    {
        QSqlRecord rec = record(index.row());
        QString val = rec.value(index.column()).toString();
        return val; // ALWAYS returns an empty string :-(
    }
     else
         return QVariant();
 }

QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
        return QVariant();

//    if (role == Qt::ItemIsUserCheckable) // NEVER happens !
//        qDebug() << "  ItemIsUserCheckable";
        
     if (role == Qt::DisplayRole)
    {
        QSqlRecord rec = record(index.row());
        QString val = rec.value(index.column()).toString();
        return val; // ALWAYS returns an empty string :-(
    }
     else
         return QVariant();
 }

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Problems are:
1) record() is returning empty values.
2) ItemIsUserCheckable returns false, I thought flags() would be called here where I set it (?)
3) I don't know what to do with CheckStateRole so there's nothing in my code to return a checkbox for display.

[shentian]

The role you need to use in QAbstractItemModel::data is Qt::CheckStateRole. I think the method should look like this:

QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
    {
        return QVariant();
    }
    QSqlRecord rec = record(index.row());
    QVariant val = rec.value(index.column());
 
    switch (role)
    {
    case Qt::CheckStateRole:
        if (index.column() != 6)
            return QVariant();
        else if (val.toInt() == 0) // or whatever
            return Qt::Unchecked;
        else
            return Qt::Checked;
    case Qt::DisplayRole:
        return val;
    default:
        return QVariant();
    }
}

QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
    {
        return QVariant();
    }
    QSqlRecord rec = record(index.row());
    QVariant val = rec.value(index.column());

    switch (role)
    {
    case Qt::CheckStateRole:
        if (index.column() != 6)
            return QVariant();
        else if (val.toInt() == 0) // or whatever
            return Qt::Unchecked;
        else
            return Qt::Checked;
    case Qt::DisplayRole:
        return val;
    default:
        return QVariant();
    }
}

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Depending on the type stored in val, QVariant::toString() may well return an empty string. Use QVariant::typeName() to check what type it is. I think it's best to just pass on the QVariant value.

No guarantees, I did not check the code above, but I hope it gives you an idea.

[vieraci]

Thanks, case Qt::CheckStateRole is what I was missing.

Now the program crashes at
QSqlRecord rec = this->record(index.row());
It appears to continually recurse the function.

If I change the line to:
QSqlRecord rec = this->record();
it doesn't crash, but I get no data. typeName() is blank (one space).

This function is re-entering like over 100 times and I only have 9 columns and one row of data. that's strange ?

[vieraci]

It turns out the required code is:

QVariant value = QSqlQueryModel::data(index, role);

QVariant value = QSqlQueryModel::data(index, role);

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Now data() seems to be called once for DisplayRole and again for CheckStateRole.
What I end up with is a unchecked checkbox and in the same column, 0 or 1.

switch (role)
    {
    case Qt::CheckStateRole:
        if (index.column() != 6)
            return value;
        else if (value.toInt() == 0) // or whatever
            return Qt::Unchecked;
        else
            return Qt::Checked;
    case Qt::DisplayRole:
        return value;
    default:
        return QVariant();
    }

switch (role)
    {
    case Qt::CheckStateRole:
        if (index.column() != 6)
            return value;
        else if (value.toInt() == 0) // or whatever
            return Qt::Unchecked;
        else
            return Qt::Checked;
    case Qt::DisplayRole:
        return value;
    default:
        return QVariant();
    }

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[vieraci]

Can anyone help me out here ? This is acting strange.

When role is Qt::CheckStateRole the data returned from the model seems to be empty, in contrast to when role is DisplayRole, data is valid.

Still, I don't know why the column shows a checkbox (ALWAYS not checked because of what I just stated) and 0 or 1 next to it in the same column which seems to be getting into the column during role == DisplayRole.

This is the whole code:

QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
        return QVariant();
    QVariant value = QSqlQueryModel::data(index, role);
 
    if (role == Qt::CheckStateRole && index.column() == 6)
        return (value.toInt() != 0) ? Qt::Checked : Qt::Unchecked;
    else if (role ==  Qt::DisplayRole)
        return value;
    return QVariant();
}

QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
{
    if (!index.isValid())
        return QVariant();
    QVariant value = QSqlQueryModel::data(index, role);

    if (role == Qt::CheckStateRole && index.column() == 6)
        return (value.toInt() != 0) ? Qt::Checked : Qt::Unchecked;
    else if (role ==  Qt::DisplayRole)
        return value;
    return QVariant();
}

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This code I'm sure is correct, if not, can someone correct me or suggest what else could be the problem ?

[vieraci]

OK I worked out what was happening.
data() was returning a checkbox AND a value. To stop it, I had to modify it:

QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
{
    QVariant value = QStandardItemModel::data(index, role);
    if (index.column() == 6)
    {
        if (role == Qt::CheckStateRole)
            return (QStandardItemModel::data(index).toInt() != 0) ? Qt::Checked : Qt::Unchecked;
        else if (role == Qt::DisplayRole)
            return QVariant(); // Don't show value !!
    }
    return value;
}

QVariant PurchaseOrdersRequests::data ( const QModelIndex & index, int role ) const
{
    QVariant value = QStandardItemModel::data(index, role);
    if (index.column() == 6)
    {
        if (role == Qt::CheckStateRole)
            return (QStandardItemModel::data(index).toInt() != 0) ? Qt::Checked : Qt::Unchecked;
        else if (role == Qt::DisplayRole)
            return QVariant(); // Don't show value !!
    }
    return value;
}

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