Blank QListView when using QSortFilterProxyModel

[jiveaxe]

Hi, I'm playing with QSortFilterProxyModel (never used before); so I created a sample application with a QListView whose items content is controlled by delegates. This is a piece of code without proxy:

model = new MyModel(this);
 
ItemDelegate *itemDelegate = new ItemDelegate(ui->listView);
ui->listView->setItemDelegate(itemDelegate);
 
ui->listView->setModel(model);
 
setModelData_1();

model = new MyModel(this);

ItemDelegate *itemDelegate = new ItemDelegate(ui->listView);
ui->listView->setItemDelegate(itemDelegate);

ui->listView->setModel(model);

setModelData_1();

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It works fine, but if I use MySortFilterProxyModel, like in this snippet:

model = new MyModel(this);
proxyModel = new MySortFilterProxyModel(this);
 
ItemDelegate *itemDelegate = new ItemDelegate(ui->listView);
ui->listView->setItemDelegate(itemDelegate);
 
ui->listView->setModel(proxyModel);
proxyModel->setSourceModel(model);
 
setModelData_1();

model = new MyModel(this);
proxyModel = new MySortFilterProxyModel(this);

ItemDelegate *itemDelegate = new ItemDelegate(ui->listView);
ui->listView->setItemDelegate(itemDelegate);

ui->listView->setModel(proxyModel);
proxyModel->setSourceModel(model);

setModelData_1();

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the view is empty.

MySortFilterProxyModel is very minimal; it contains only bool QSortFilterProxyModel::filterAcceptsRow(int sourceRow, const QModelIndex &sourceParent) const returning a true.

Where am I wrong?

Thanks for your help.

[Santosh Reddy]

set the source of proxy model first

proxyModel->setSourceModel(model);
ui->listView->setModel(proxyModel);

proxyModel->setSourceModel(model);
ui->listView->setModel(proxyModel);

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[jiveaxe]

set the source of proxy model first

proxyModel->setSourceModel(model);
ui->listView->setModel(proxyModel);

proxyModel->setSourceModel(model);
ui->listView->setModel(proxyModel);

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swapping lines does not help.

Perhaps I catched the problem; proxyModel->setSourceModel(...) must be called after feeding model with data. But now my program crashes at the following line:

void ItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    if (!index.isValid())
        return;
 
    const MyModel *model = qobject_cast<const MyModel*>(index.model());
 
    ...
    QString first = model->data(index, ItemRoles::First).toString(); // <-- debugger stops here
 
    ...
}

void ItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    if (!index.isValid())
        return;

    const MyModel *model = qobject_cast<const MyModel*>(index.model());

    ...
    QString first = model->data(index, ItemRoles::First).toString(); // <-- debugger stops here

    ...
}

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The debugger says that model's value is 0x0 and first's value is <not accessible>

[Santosh Reddy]

You should be doing this.

void ItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    if (!index.isValid())
        return;
 
    const MyModel *model = qobject_cast<const MyModel*>(index.model());
 
    ...
    if(model != 0)
        QString first = model->data(index, ItemRoles::First).toString(); // <-- debugger stops here
 
    ...
}

void ItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
    if (!index.isValid())
        return;

    const MyModel *model = qobject_cast<const MyModel*>(index.model());

    ...
    if(model != 0)
        QString first = model->data(index, ItemRoles::First).toString(); // <-- debugger stops here

    ...
}

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BTW, I don't see a need to get the model, if you need data of the index, you could use

QVariant QModelIndex::data ( int role = Qt::DisplayRole ) const

QVariant QModelIndex::data ( int role = Qt::DisplayRole ) const

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[lanz]

AFAIK, index.model () here returns proxy model and not underlying MyModel.
Anyway why do you need cast to MyModel if you're using model->data()?

[jiveaxe]

BTW, I don't see a need to get the model, if you need data of the index, you could use

QVariant QModelIndex::data ( int role = Qt::DisplayRole ) const

QVariant QModelIndex::data ( int role = Qt::DisplayRole ) const

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Very very thanks. Used your line and problem is fixed.