I have problems migrating from QTreeWidget to QtreeView. Things that were obvious and trivial with QTreeWidget seem to be impossible with view. Specifically: I have a main window with a treeview in it. TreeView uses the model I've implemented, but not directly – through QSortFilterProxyModel that is set as a tree's model. Now, the user activates an item in the tree and main windows receives a signal itemActivated(QModelIndex item). How can I tell which item of the underlying data was activated? Data is a vector, so with TreeWidget I could just store an item's vector index in the QTreeWidgetItem, but QModelIndex doesn’t even have setData API.
How can I tell which item of the underlying data was activated?
By inverting the proxy model:
// supposing to connect this to your itemActivated signal
void onItemActivated(const QModelIndex &index)
{
QModelIndex originalIndex = proxyModel->mapToSource(index);
originalModel->doSomething(originalIndex);
}
You can define custom roles in your source model, returning the underlying data or an identifier (if there's one) as variant. This has the advantage it works with any number of proxy models in between, as the data will be passed through the models unaltered and now mapping of indexes is required.
Assuming a model listing contacts, with a value struct/class Contact holding the data.
This requires Contact to be registered via Q_DECLARE_METATYPE.
class ContactModel ... {
...
enum Role {
ContactRole=Qt::UserRole,
ContactIdRole
};
QVariant data(...) const {
...
const Contact& contact = ...get from datastructure...
...
switch (role) {
...
case ContactRole:
return QVariant::fromValue( contact );
case ContactIdRole:
return contact.id;
}
}
...
And in the code receiving the index:
void SomeWidget::indexSelected(const QModelIndex& index)
{
const int id = index.data(ContactModel::ContactIdRole).toInt();
// look up Contact, do something with it
//or:
const Contact contact = index.data(ContactModel::ContactRole).value<Contact>();
// do something with the contact
...
}
The index can be from the contact model itself, or any proxy on top of it - the code here doesn't have to care.
The model to stores your data. The data is no longer owned by items/QModelIndex in the view. QModelIndex is only a unique identifier passed between the view and the model (in this case via QSortFilterProxyModel). The model should inherit QAbstractItemModel which has some pure virtual functions that need to be defined (you can copy boilerplate from http://qt-project.org/doc/qt-4.8/itemviews-simpletreemodel.html). You will e.g. have to define QAbstractItemModel::data( const QModelIndex & index, int role = Qt::DisplayRole) which defines which data that corresponds to a particular QModelIndex.
The QSortFilterProxyModel sits between the view and the model, but does not change the principles for the model. See the other answer on this question for how to deal with the QModelIndex conversion.
To conclude: QAbstractItemModel::data( const QModelIndex & index) will give you the data for a particular QModelIndex once you have defined it.
Related
I change the text of a column of QTableView by using displaytext function in QStyledItemDelegate class.
QString Msg_NameGIdDelegate::displayText(const QVariant &value, const QLocale &locale) const
{
return Diag_Utility::getMsgNameStr(value.toInt());
}
How I can get the text of each cell in this column after delegate. If I use the following code I get the text before delegation.
for(int i=0; i<ui->msgCount_tableView->model()->rowCount();i++)
qDebug()<<ui->msgCount_tableView->model()->index(i,6).data().toString();
Looks like you change delegate text but not change model data and you are fetching model data and you want delegate data.
QAbstractItemDelegate *QAbstractItemView::itemDelegate(const QModelIndex &index) function will return your delegate so you can get displayText.
If this solution doesn't work you change model's data by model()->setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole)function instead of delegate's displayText and you can fetch model->data()
I have a list of application specific items uniquely identified by an id. Their names are displayed in a QTreeWidget (one item corresponds to a single QTreeWidgetItem). I would like to somehow attach the corresponding ids to these QTreeWidgetItems so that upon selection changed I can access the id of the corresponding item and do some processing.
QTreeWidgetItem does not inherit from QObject so I cannot use its setProperty function. How could I do this?
Just create some user defined roles for the properties...
typedef enum {
id_1_role = Qt::UserRole,
id_2_role,
id_N_role,
} property_id_role;
Then you can use the normal means of getting/setting the data associated with a QTreeWidgetItem.
QTreeWidgetItem *item = ...
/*
* Set the property value.
*/
item->setData(column, property_id_role::id_2_role, id_2_value);
/*
* Get the property value.
*/
auto id_2_value = item->data(column, property_id_role::id_2_role).value<id_2_type>();
Do you know that QTreeWidgetItem has a setData method?
setData(int column, int role, const QVariant &value)
You can use it with your roles. For example:
int your_id = 123;
ui->treeWidget->currentItem()->setData(0,Qt::UserRole,your_id);
qDebug() << ui->treeWidget->currentItem()->data(0,Qt::UserRole);
I'm a looking for a way how to pass larger amount of QObjects to QML as Model and than use Repeater {} to draw them. This solution have to meet following criteria:
when new object is added to list, only this item will be refreshed
when any of passed object is changed, Qml content have to be automatically refreshed
list have to be universal, no hard-coded property names
Solution 1.
I know I can use QQmlListProperty<QObject>. Unfortunately in case that object is added/removed all other objects are refreshed in Qml. In case of more complex/larger amount of objects this is very unwieldy.
This solution meets 2) and 3). When object is updated via setter and called notifyChange(), qml automatically update the content and it's possible to use it on any QObject
Solution 2.
QAbstractList with implemented roles as described in documentation (http://doc.qt.io/qt-5/qtquick-modelviewsdata-cppmodels.html#qabstractitemmodel).
This solution meets 1) but not 2) and 3). When new object is added and beginInsertRows/endInsertRows is called, only one item is correctly refreshed. But it's necessary to prepare Model object for each QObject and Model have to be manually updated when QObject changed
Solution 3.
I tried to implement QAbstractListModel which internally holds list of QObjects pointers: QList<boost::shared_ptr<AnimalObject>> m_animals;.
When roleNames() method isn't implemented Qml doesn't query for data via data() method at all. So it seems that it's not possible to use default Qt::DisplayRole role for returning QObject from QAbstractList
When roleNames() method is implemented with single role, for example "object" and data() returns inner QObject as QVariant, it's possible to access it from QML:
QVariant AnimalModel2::data(const QModelIndex & index, int role) const {
if ( index.row() < 0 || index.row() >= m_animals.count() )
return QVariant();
auto ptrAnimal = m_animals[index.row()];
if ( role == ObjectRole )
return qVariantFromValue(ptrAnimal.get());
}
QHash<int, QByteArray> AnimalModel2::roleNames() const {
QHash<int, QByteArray> roles;
roles[ObjectRole] = "object";
return roles;
}
and this is how to access QObject from QML
Repeater {
model: myModel
Text {
text: "[" + model.object.name + "]";
}
}
This solution meets all requirements. Unfortunately it's necessary to access this QObject with model.object.property instead of more straightforward model.property. Although it's not a big deal, would be great to have direct object access.
Question:
My Question is. Are these three methods the only possible solutions for this problem, or are there any other method I completely missed?
Is there any clean way how to create list of QObjects, pass it to QML with full support of adding/removing/updating objects from C++ and directly updating them in QML?
PS: I described all these methods here because I believe this can be useful for many others.It took me a few hours to figure out how to do all of this.
Edit
Suggested solution 1.
As suggested #Velkan, it's possible to use QMetaObject::property and QMetaObject::propertyCount to dynamically extend QAbstractListModel for object's properties. Unfortunately this means to implement also individual refresh for each object/property via QDynamicPropertyChangeEvent signals.
Unfortunately for large number of objects and properties this solution probably would be very inefficient. For anyone interested in this solution, here is a snippet with QMetaObject::property test:
QVariant AnimalModel4::data(const QModelIndex & index, int role) const {
if ( index.row() < 0 || index.row() >= m_animals.count() )
return QVariant();
auto ptrAnimal = m_animals[index.row()];
const QMetaObject * pMeta = ptrAnimal->metaObject();
int propertyNo= role - (Qt::UserRole + 1);
QMetaProperty propMeta = pMeta->property(propertyNo);
QVariant value = propMeta.read(ptrAnimal.get());
return value;
}
QHash<int, QByteArray> AnimalModel4::roleNames() const {
QHash<int, QByteArray> roles;
if ( m_animals.size() == 0 )
return roles;
int role= Qt::UserRole + 1;
const QMetaObject * pMeta = m_animals.front()->metaObject();
for ( int propertyNo= 0; propertyNo< pMeta->propertyCount(); propertyNo++ )
{
QMetaProperty propMeta = pMeta->property(propertyNo);
roles[role++] = propMeta.name();
}
return roles;
}
This solution meets all requirements. Unfortunately it's necessary to
access this QObject with model.object.property instead of more
straightforward model.property. Although it's not a big deal, would be
great to have direct object access.
If your problem is with model.object.property and your solution is a shorter model.property, then an equally good solution would be object.property which is entirely functional. You can directly use roleName from within the delegate object.
As for the generic list/model class, I already addressed that in that other question.
I have a standard treeview which is viewing a subclass of QStandardItemModel.
The items in the model are also subclassed form QStandardItem. The items have an additional object pointer which I use to store a pointer to an instance of my data class, a "stage" (itself a QObject). All items have either a pointer to a stage or subclass of it, or a NULL pointer in the _object.
class MyStandardItem : public QStandardItem
{
public:
MyStandardItem();
MyStandardItem(const QString &text);
MyStandardItem(const QIcon &icon, const QString &text);
~MyStandardItem();
void object(QObject *object) {_object = object;}
QObject *object(){return _object;}
private:
QObject *_object;
};
I want to move items around in the treeview, subject to some restrictions. I have given the treeview the correct policies:
view->setAcceptDrops(true);
view->setDragEnabled(true);
view->setDropIndicatorShown(true);
view->setDragDropMode(QAbstractItemView::InternalMove);
And in my model I provide the following:
Qt::DropActions MyStandardItemModel::supportedDropActions() const
{
return Qt::MoveAction;
}
Qt::ItemFlags MyStandardItemModel::flags(const QModelIndex &index) const
{
Qt::ItemFlags defaultFlags = Qt::ItemIsEnabled | Qt::ItemIsSelectable;
MyStandardItem *item = dynamic_cast<MyStandardItem*>(itemFromIndex(index));
if(!item || !item->object())
{
return defaultFlags;
}
Stage *stage = dynamic_cast<Stage*>(item->object());
switch (stage->type())
{
case Stage::STAGEA:
return Qt::ItemIsDropEnabled | defaultFlags;
break;
case Stage::STAGEB:
case Stage::STAGEC:
return Qt::ItemIsDragEnabled | defaultFlags;
break;
}
return defaultFlags;
}
The dragging behaviour looks ok. But when I then click on a dragged item in the treeview, the object pointer of the selected item is junk:
void Project::model_clicked(const QModelIndex& index)
{
MyStandardItem *item = static_cast<MyStandardItem*>(_tree_model->itemFromIndex(index));
if(!item || !item->isValid())
return;
QObject *object = item->object();
if(!object)
return;
// object is junk
Stage *stage = static_cast<Stage*>(object);
// and of course stage is junk
}
do I need to implement dropMimeData or something similarly special for the drop for my subclassed MyStandardItem? Since I'm only moving I expected the object pointers to be intact.
If I do need to implement dropMimeData, what is the mimetype of the dragged data? I know I can see it using the model selection, but logically I should be able to get the data from the mimedata.
Your help most appreciated!
Well I found the answer to my own question.
the data is "moved" by Qt inserting into the required position in the model and then deleting it.
This means it is necessary to implement a clone() member to be used by dropMimeData (which must be reimplemented too as far as I can see)
This means widgets must be stored as pointers within objects to allow easy movement within the tree (otherwise the data has to be manually copied between widgets as there's no default copy for QObjects (by design)
I've treeview in which I'd like to have displayed files selected by user via file_dialog.getOpenFileNames(); file_dialog is QFileDialog.
I did create model class:
class File_Display_Model : public QAbstractItemModel
{
Q_OBJECT
private:
QStringList* selected_files_;
public:
explicit File_Display_Model(QObject *parent = nullptr,QStringList* selected_files = nullptr);
int File_Display_Model::columnCount( const QModelIndex & parent ) const
{
selected_files_->count();
}
QVariant File_Display_Model::data(const QModelIndex & index, int role) const
{
if (!index.isValid())
{
return QVariant();
}
else
{
if (role == Qt::DisplayRole) {
if (index.row() == index.column())
{
return 0;
}
else
{
return selected_files_->at(role);
}
}
return QVariant();
}
}
QModelIndex File_Display_Model::index(int row, int column, const QModelIndex & parent ) const
{
/*DUMMY - HERE I JUST DON'T KNOW WHAT TO RETURN*/
return QModelIndex();
}
QModelIndex File_Display_Model::parent(const QModelIndex & index) const
{
return QModelIndex();
}
int File_Display_Model::rowCount( const QModelIndex & parent ) const
{
selected_files_->count();
}
};
And I also provided this class as a model to tree view. There is a problem with a index method in this class - I don't know what to return.
Could someone please help me and guide me how to make it work so files selected by an user are displayed in a treeview?
First of all there is no reason for using a QStringList*. Qt uses implicit sharing so it is efficient to pass it as an argument (dont forget that QStringList is nothing more than a QList<QString>).
Second you should review the excellent Qt Model/View Programming documentation.
Row and Column Count
You are trying to create a tree model so you should read carefully the tree model example. Notice that the rowCount and columnCount functions have as argument a model index.
The rowCount() function simply returns the number of child items for
the item that corresponds to a given model index, or the number of
top-level items if an invalid index is specified
and for the column count
Since each item manages its own column data, the columnCount()
function has to call the item's own columnCount() function to
determine how many columns are present for a given model index. As
with the rowCount() function, if an invalid model index is specified,
the number of columns returned is determined from the root item
So you have to think how your stringlist will be represented as a tree model. How columns will you have and what will be stored there for every level? How will be the rows hierarchy? Why are you using as column count the number of strings?
Model Index
When you reimplement the index() function you just have to check if the provided row and column are valid and if yes you should call the createIndex function. Again it all depends on what data your model contains and how you have structured them. Since you want to implement a tree model you have to take under consideration the parent item as well.
When reimplementing this function in a subclass, call createIndex() to
generate model indexes that other components can use to refer to items
in your model.