I have a custom QGraphicsItem implementation. I need to be able to limit where the item can be moved - i,e. restrict it to a certain area. When I checked the Qt documentation this is what it suggested:
QVariant Component::itemChange(GraphicsItemChange change, const QVariant &value)
{
if (change == ItemPositionChange && scene()) {
// value is the new position.
QPointF newPos = value.toPointF();
QRectF rect = scene()->sceneRect();
if (!rect.contains(newPos)) {
// Keep the item inside the scene rect.
newPos.setX(qMin(rect.right(), qMax(newPos.x(), rect.left())));
newPos.setY(qMin(rect.bottom(), qMax(newPos.y(), rect.top())));
return newPos;
}
}
return QGraphicsItem::itemChange(change, value);
}
So basically, check the position passed to itemChange, and if you don't like it, change it and return the new value.
Seems simple enough, except it doesn't actually work. When I checked the call stack I see that itemChange is being called from QGraphicsItem::setPos, but it doesn't even look at the return value. So there is no purpose to me returning a changed position, no one is looking at it. See code from QGraphicsItem.cpp
// Notify the item that the position is changing.
const QVariant newPosVariant(itemChange(ItemPositionChange, qVariantFromValue<QPointF>(pos)));
QPointF newPos = newPosVariant.toPointF();
if (newPos == d_ptr->pos)
return;
// Update and repositition.
d_ptr->setPosHelper(newPos);
// Send post-notification.
itemChange(QGraphicsItem::ItemPositionHasChanged, newPosVariant);
d_ptr->sendScenePosChange();
Any suggestions? I was hoping to avoid re-implementing the whole click and drag behavior myself using mouse-down mouse-move etc..., but I suppose I will have to if I can't find a better idea.
I didn't actually try it but it looks to me it is checking the return position. The returned restricted position is used in the constructor of newPosVariant to converted to newPos. It's then used to set the position of the item if it's different from the current one.
Related
I have created by myself model (MyListModel) that store list of my objects MyObj. MyObj stores some text information. Then I created class ItemDelegate, in order to manage view of every item and also to add QProgressBar to each item. The problem is that I need busy progressbar, but when I execute app, QProgressBar doesn't do any action.
I'm guessing, it's because QListView only show static data. Is there any way to make it work properly?
My realisation of paint method for Delegate:
void StatusItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
{
StatusItem my_item = index.data().value<StatusItem>();
wdg->name->setText(my_item.m_name);
switch (my_item.m_state)
{
case 0: wdg->progress->setMaximum(0); wdg->progress->setMinimum(0); break;
case 1: wdg->progress->setRange(0, 0); wdg->progress->setValue(100); break;
case 2: wdg->progress->setHidden(true); break;
}
QPalette pal;
QLinearGradient gradient(0, 0, 0, 100);
if ((option.state & QStyle::State_Selected) == QStyle::State_Selected)
{
pal.setBrush(QPalette::Window, QBrush(QColor(0, 255, 200)));
}
else
{
gradient.setColorAt(0.0, QColor(255,250,0));
gradient.setColorAt(1.0, QColor(255,255,255));
pal.setBrush(QPalette::Window, QBrush(QColor(Qt::transparent)));
pal.setBrush(QPalette::Window, QBrush(gradient));
}
wdg->setPalette(pal);
wdg->resize(option.rect.size());
painter->save();
painter->setRenderHint(QPainter::Antialiasing, true);
painter->translate(option.rect.topLeft());
wdg->render(painter);
painter->restore();
}
I think the problem exists because the view repaints items only when something is changed. While model data remains unchanged, according cells are not repainted.
In this situation you should cause additional repaints from the delegate. Unfortunately there is no convenient way to do it, but there are longer ways. You need to do the following action in the paint method:
view->update(index);
There are two issues:
You don't have view pointer in the paint method. You can either try to use painter->device() and assume that this is the view's viewport (but it's not guaranteed) or store view in the delegate's class member variable.
Calling update inside paint can cause infinite recursion (I'm not sure about this one). If that's the case, you can delay update using QTimer::singleShot(0, ...). But you will need to create a slot for that somewhere an pass view and index somehow so that they will be accessible in the slot.
Is there any way to get a list of currently visible items in QAbstractItemView? And, if it possible, to receive any notifications about changing of this list.
Upd:
I'm asking exactly about QAbstractItemView or QTreeView with non-plain structure, not QTableView.
Upd2:
I'm implementing tree view model with checkboxes. I want next behavior (same for checking/uncheking):
If one of checkbox is checked - then all childs must be checked
If all child checkboxes are checked - then parent check box should be checked too. And same for parent of parent, and so on...
Check state are monitored/modified by external data source, so I need a mechanism to update all changed children/parents. dataChanged signal is not enough for me because it is very expansive to build a list of all changed QModelIndex for updating. And it is not necessary at all, because all fresh data will be picked from QAbstractItemModel::data.
I found next dirty hack to update all items: emit dataChanged( QModelIndex(), QModelIndex() ); but it's undocumented for invalid indexes.
So, I need a way to force all visible items redraw they content with fresh data.
You can get the topleft and bottom right cell by calling:
tableview->indexAt(tableview->rect().topLeft())
tableview->indexAt(tableview->rect().bottomRight())
To get notification of change, reimplement the virtual function of qabstractscrollarea
scrollContentsBy
This function is called when the view port is scrolled.
call QTableView::scrollContentsBy and then do whatever you need to.
For QTreeView, the list of visible items can be traversed like this:
QTreeView& tv (yourTreeView);
// Get model index for first visible item
QModelIndex modelIndex = tv.indexAt(tv.rect().topLeft());
while (modelIndex.isValid())
{
// do something with the item indexed by modelIndex
...
// This navigates to the next visible item
modelIndex = tv.indexBelow(modelIndex);
}
I think that there are no cases where list of visible items is requred. In case of correct model implementation all items are updated automatically.
Hard part of implementation - force children and parents to update. I wrote following code:
bool TreeModel::setData( const QModelIndex &index, const QVariant &value, int role )
case Qt::CheckStateRole:
{
TreeItemList updateRangeList; // Filled with items, in which all childred must be updated
TreeItemList updateSingleList; // Filled with items, which must be updated
item->setCheckState( value.toBool(), updateRangeList, updateSingleList ); // All magic there
foreach ( TreeAbstractItem *i, updateRangeList )
{
const int nRows = i->rowCount();
QModelIndex topLeft = indexForItem( i->m_childs[0] );
QModelIndex bottomRight = indexForItem( i->m_childs[nRows - 1] );
emit dataChanged( topLeft, bottomRight );
}
foreach ( TreeAbstractItem *i, updateSingleList )
{
QModelIndex updateIndex = indexForItem( i );
emit dataChanged( updateIndex, updateIndex );
}
}
i always update whole QAbstractTableModel with:
emit dataChanged(index(0, 0), index(rowCount(), columnCount()-1)); // update whole view
Method 1
i, j = table.indexAt(table.rect().topLeft()).row(), table.indexAt(table.rect().bottomLeft()).row() - 1
Method 2
i, j = table.rowAt(0), table.rowAt(table.height()) - 1
I am trying to develop an image gallery application using Qt Framework. The application loads all the images from the selected folder and those images are displayed using QListView control.
But now i want to reduce the memory consumption by loading only the images that are visible to user. Since there is no direct function to get all the visible items in the view, i am not able to achieve this.
You can get the visible items of a list view using the indexAt function. For more details and an example you can check the following article:
http://qt-project.org/faq/answer/how_can_i_get_hold_of_all_of_the_visible_items_in_my_qlistview
I found it! You have to connect the vertical scrollbar of the listwidget to a signal:
connect(ui->listWidget->verticalScrollBar(), SIGNAL(valueChanged(int)), this, SLOT(launch_timer()));
Every time the user scrolls, the valuechanged(int) signal is being omitted! The thing is that you shouldn't run the code provided by webclectic in this question every time the value of the vertical scrollbar of the listwidget changes, because the program will be unresponsive with so much code to run in so little time.
So, you have to have a singleshot timer and point it to the function that webclectic posted above. When launch_timer() is called, you do something like this:
if(timer->isActive()){
timer->stop();
timer->start(300);
}
else
timer->start(300);
and the timeout() signal of timer will be connected to the slot webclectic talked about. This way, if the user scrolls quickly all the way down only the last items will be updated. Generally, it will be updated anything visible for more than 300 milliseconds!
I think what you need is to implement your own model (take a look to the QAbstractListModel documentation) so that way you could decide when you have to load more images to show and maybe free some of the images that became non-visible.
although this is not so simple in Qt 4 but
it is always simple to copy below:
#include <private/qlistview_p.h>
class QListViewHelper : public QListView
{
typedef QListView super;
inline QListViewHelper() {} //not intended to be constructed
public:
inline static QVector<QModelIndex> indexFromRect(const QListView *view,
const QRect &rect)
{
const QListViewPrivate *d = static_cast<const QListViewPrivate *>(QObjectPrivate::get(view)); //to access "QListViewPrivate::intersectingSet(...)"
const QListViewHelper *helper = static_cast<const QListViewHelper *>(view); //to access "QListView::horizontalOffset()"
return d->intersectingSet(rect.translated(helper->horizontalOffset(), helper->verticalOffset()), false);
}
inline static QVector<QModelIndex> visibleItems(const QListView *view)
{ return indexFromRect(view, view->rect()); }
inline static QModelIndex firstVisible(const QListView *view)
{ return visibleItems(view).value(0); }
inline static QModelIndex lastVisible(const QListView *view) {
const QVector<QModelIndex> &items = visibleItems(view);
return items.value(items.count() - 1);
}
};
void ourTest(const QListView *view) {
QModelIndex &index = QListViewHelper::firstVisible(view);
qDebug("QListViewHelper: first visible row is %d", index.row());
index = QListViewHelper::lastVisible(view);
qDebug("QListViewHelper: last visible row is %d", index.row());
}
usage:
QModelIndex &index =
QListViewHelper::firstVisible(listViewPointerHere)
note: since it does use Qt 4.8 private-headers it may no longer work in latter versions and will need some changes.
You can keep track of all the elements that are drawn per paint event. I used a delegate and overloaded the paint event.
I also overloaded the paint event in the view. During this call, all the visible delegates will get a paint event.
If you just need to know if an item is visible, you can increment a frame count in view->paintEvent and set that number in the delegate item. The item is visible of the item matches the current frame number.
If you need a list of all visible items, clear the visible item list in view->paintEvent and add each item in the int the delegate->paintEvent to the visible items list.
When I select several QGraphicsItem (with Ctrl key) I can move them together, but the mouseMoveEvent is triggered only for the item that actually receives the event. Is there a way to make every selected items receive the event ? I can't find it in Qt's doc.
Could I group selected items together and handle it within QGraphicsView's mouseMoveEvent ?
Thanks a lot for any help :)
No there is no default way to do what you want as far as I know. Something you could do is the following:
Subclass QGraphicsScene and implement the mouseMoveEvent
In the mouse move event check if there is an item at the event position using the itemAt function
If there is an item and it is selected (isSelected), get all selected items of the scene.
For all selected items call the same function you would call.
Sample code follows:
void mouseMoveEvent(QGraphicsSceneMouseEvent * mouseEvent)
{
QPointF mousePosition = mouseEvent->scenePos();
QGraphicsItem* pItem = itemAt(mousePosition.x(), mousePosition.y());
if (pItem == NULL)
{
QGraphicsScene::mouseMoveEvent(mouseEvent);
return;
}
if (pItem->isSelected() == false)
{
QGraphicsScene::mouseMoveEvent(mouseEvent);
return;
}
// Get all selected items
QList<QGraphicsItem *> items = selectedItems();
for (unsinged i=0; i<items.count(); i++)
// Do what you want to do when a mouse move over a selected item.
items[i]->doSomething();
QGraphicsScene::mouseMoveEvent(mouseEvent);
}
I'm reading between the lines of your question a little, but it sounds like you might be better served by implementing QGraphicsItem::itemChange on your QGraphicsItem class(es). This will get called whenever the position changes--whether by mouse, keyboard, programmatic, etc. You can even cancel the change if you want to.
http://doc.qt.io/qt-5/qgraphicsitem.html#itemChange
I have some problems with sizing row's height in QTreeWidget. I use QStyledItemDelegate with QPlainTextEdit. During editing text in QPlainTextEdit i check for changes with a help of:
rect = self.blockBoundingRect(self.firstVisibleBlock())
and if text's height changes i resize editor size and need row in QTreeWidget also resizing. But i don't know how to inform TreeWidget or a Delegate about changes. I tried to initialize editor with index, that i could use in a future, but Delegate creates new editor every time and i failed to use signals. Also I used following function to catch resize event, but it' doesn't:
bool QAbstractItemDelegate::editorEvent ( QEvent * event, QAbstractItemModel * model, const QStyleOptionViewItem & option, const QModelIndex & index )
How can i bound editor's size changes with TreeWidget?
And one more thing, by default all items (cells) in TreeWidget have -1 or some big value as default width. I need whole text in cell to be visible, so how can i limit cells width only by visible range and make it expand in height? I want for it the same behavior as in instance a table in MSWord.
Thank you in advance,
Serge
I believe you would have to notify model about the data change without closing editor, this should force treeview to recalculate its row height according to the new content of the field it's showing. What you could do is override eventFilter method in your delegate and try to emit commitData signal on key press; smth like this:
bool YourStyledItemDelegate::eventFilter(QObject* object, QEvent* event)
{
bool result = QStyledItemDelegate::eventFilter(object, event);
QWidget* editor = qobject_cast<QWidget*>(object);
if (editor)
{
if (event->type() == QEvent::KeyPress)
{
emit commitData(editor); //<- this should force row to recalculate its size
}
}
return result;
}
hope this would give you an idea on how to proceed, regars