So I have a QMainWindow and in its constructor I do the following stuff:
QStringList stringList;
stringList << "aaa" << "bbb" << "ccc";
QStringListModel *list = new QStringListModel(stringList);
ui->listView->setModel(list);
stringList.append("ddd");
list->setStringList(stringList);
QObject::connect(ui->listView->selectionModel(), &QItemSelectionModel::currentChanged, [&]() {
//do stuff
});
Why is the currentchanged emitted when the application starts and how can I avoid emitting the currentChanged until I actually click on the ListView?
[What's wrong?]
Since the listView is the only widget in your QMainWindow, it will be automatically focused as the application starts. Once the listView gets focused, the first item automatically becomes the current item if there wasn't already a current item. Hence the signal emitted.
[Solution]
Option 1
Add other widgets into your application and call QWidget::setFocus on one of them to make it the default focused widget as app starts.
Option 2
Call QListView::setFocusPolicy and make it Qt::ClickFocus, so the listView will only be focused if one of the items is clicked.
Option 3
The signal QItemSelectionModel::currentChanged has actually two arguments: QModelIndex ¤t and QModelIndex &privious. Use them by conventional signal/slot connection. For example
connect(ui->listView->selectionModel(), SIGNAL(currentChanged(QModelIndex,QModelIndex)), this, SLOT(yourSlot(QModelIndex, QModelIndex)));
In the slots :
void MainWindow::yourSlot(QModelIndex cur, QModelIndex pre)
{
if(pre.isValid()) {
// do stuff
}
}
P.S. pre being invalid signifies that there was no current item previously. This bypasses the signal emit by auto-selected for the first time the listView is focused.
Related
I want to make each item listed in QTableview, when clicked, emit a signal that opens up a dialog for instance. I need help on this
QFileSystemModel *listModel = new QFileSystemModel(this);
QString directory = "/home/uboho/monitor_test_module/logs/tmp/etc/nodes";
ui->clusterList->setModel(listModel);
ui->clusterList->setRootIndex(listModel->setRootPath(directory));
ui->clusterList->
setEditTriggers(QAbstractItemView::AnyKeyPressed |
QAbstractItemView::DoubleClicked);
}
bool displayTable::DoubleClicked (const QModelIndex index )
{
QDialog * test = new QDialog();
test->show();
}
QTableView inherits QAbstractItemView that emits the signal clicked. You can register a slot/callback that creates a popup with the QTableView object for the clicked signal.
// Qt 5
connect(theQTableView, &QAbstractItemView::clicked,
theCallbackReceiver, &CallbackReceiver::clickedCallback);
// Qt 4
connect(theQTableView, SIGNAL(clicked(QModelIndex)),
theCallbackReceiver, SLOT(clickedCallback(QModelIndex)));
Via the index parameter of the clicked signal you can find out which item was clicked.
I have a Qt Desktop aplication which has several top-level widgets. Subwidgets of top-level widgets can be moved between top-level widgets by using drag-and-drop mechanism.
The problem i have now is to drop a sub-widget outside any of existing top-level widgets and create a new top-level widget to contain this one. Lets call this separation.
Can this be done using drag-and-drop? I could not find a way where my dropEvent goes?
Can i want to handle the drop event in my application even if the drop place is not allowed? Maybe a mouse release or something?
I cannot change everything now but also a question for the future. Is docking/undocking a better way to do this?
Regards
Mihai
I found a way to do this. When drag moves outside of the application widgets QDrag object emits a targetChanged signal with 0 parameter.
So i inherited from QDrag and then emit a custom signal in destructor if the target() is null.
The only problem is that the cursor looks like interdiction of drop and this i could not fix because QDrag can only set cursor pixmap for valid actions like Move or Copy or Link
Update:
Here is the inherited class.
class TabDrag: public QDrag
{
Q_OBJECT
public:
explicit TabDrag(QWidget *dragSource);
~TabDrag();
signals:
void tearOff(); /// emit tearOff signal if the QDrag object is destroyed and target was null
};
TabDrag::TabDrag(QWidget *dragSource):QDrag(dragSource)
{
}
TabDrag::~TabDrag()
{
// check if we need to detach this tab
if(!target())
{
emit tearOff();
}
}
The tearOff signal should be connected to whatever you want to happen. In my case i pull out the widget from the tab and change parent to a new window.
Example of usage
void MyTabBar::mouseMoveEvent(QMouseEvent* event)
{
..................
TabDrag * drag = new TabDrag(this);
drag->setMimeData(mimeData);
drag->setPixmap(*m_tabPixmap.data());
drag->setHotSpot(QPoint(m_dragStartPos.x() - tabAtRect.x(), m_dragStartPos.y() - tabAtRect.y()));
drag->exec();
connect(drag, SIGNAL(tearOff()), this, SLOT(onTearOff()));
}
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.
I am adding custom widget to QListWidget.
My Custom Widget contains 2 Labels, 1 Button
/* My Custom Widget
UserDetails *myItem = new UserDetails(0," ALOA, Jeon");
UserDetails *myItem1 = new UserDetails(0," LOUIS, Stacy");
QListWidgetItem *item = new QListWidgetItem();
QListWidgetItem *item1 = new QListWidgetItem();
item->setSizeHint(QSize(0,45));
item1->setSizeHint(QSize(0,45));
ui->listWidget->addItem(item);
ui->listWidget->addItem(item1);
ui->listWidget->setItemWidget(item,myItem);
ui->listWidget->setItemWidget(item1,myItem1);
Using above Code I am adding mu Custom Widget item to QListWidget.
Now the problem is I am using One QPushButton in my CustomWidget now when i click on ListWidgetItem in ListWidget that button i want to change pressed state to some background-image and on release it should come back to normal state.For that I using stylesheet to do so but when i click on button it does not get click event of the List Widget (itemclicked SLOT of List) on double click it gets.
How to get on single click ?
This is not that simple, however it is doable. The problem is that when you click on the button the press event is not propagated to the list widget. So you have to find a way to propagate the signal back to the list widget.
When the button is pressed the pressed signal is emitted. When it is released the released signal is emitted. I will show you how to do it for one of them, you should do the same for the other.
The most straight forward way to do what you want is to add a connection between the pressed signal of the button and the slot which will modify the background of your list. What you have is a QListWidget in which there are some UserDetails widgets each of which has a QPushButton. So we have to go all the way up from the QPushButton to the QListWidget.
In your UserDetails class create a new signal, eg buttonPressed() and connect your button's pressed() signal with it. This way every time the button is clicked in your widget the widget itself will notify the world that its button has been clicked.
connect(ui->button, SIGNAL(pressed()), this, SIGNAL(buttonPressed())
Now we want to notify the QListWidget that the button has been pressed. In order to achieve this we have to connect the buttonPressed signal from the UserDetails with a slot, let's call the slot buttonPressedSlot()
connect(myItem, SIGNAL(pressed()), this, SLOT(buttonPressedSlot())
Now the slot should detect which is the sender (since all UserDetails objects will get connected to the same slot, find the corresponding QListWidgetItem and call the slot that will update the background of this item.
void LiwstWidgetClick::buttonPressedSlot()
{
QObject* signalSender = QObject::sender();
UserDetails* p = qobject_cast<UserDetails *>(signalSender);
if (p == NULL)
return;
// Get Position in list widget
for (unsigned i=0; i<ui->listWidget->count(); i++)
{
QListWidgetItem* item = ui->listWidget->item(i);
if (ui->listWidget->itemWidget(item) == p)
cellClicked(item); // THIS IS YOUR FUNCTION THAT CHANGES THE
// BACKGROUND OF THE GIVEN ITEM
}
}
You should do the same for the released() signal.
EDIT
If the button was public you could avoid the extra signal, eg if you had a function (getButton()) in your UserDetails that returned the ui->button you could have just one connection
connect(myItem->button(), SIGNAL(pressed()), this, SLOT(buttonPressedSlot()));
EDIT 2
If you just want to change the background of you button when it is pressed then you can achieve it using stylesheets. You need to entries in your stylesheet one for the normal button state and one for the pressed state. For a list of available states have a look here. Sample code follows
QListView QPushButton {
color: grey;
border-image: url(/path/to/image1) 3 10 3 10;
}
QListView QPushButton:pressed {
color: red;
border-image: url(/path/to/image2) 3 10 3 10;
}
Notice that I use the QListView Descendant Selector in order to get only these QPushButtons that are children of a QListView
In Qt, when a widget receives focus, how can get a notification about it, so I can execute some custom code? Is there a signal or an event for that?
You can add en event filter.
This is an example of an application written with QtCreator. This form has a QComboBox named combobox.
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),ui(new Ui::MainWindow)
{
ui->setupUi(this);
ui->comboBox->installEventFilter(this);
.
.
.
}
bool MainWindow::eventFilter(QObject *object, QEvent *event)
{
if (event->type() == QEvent::FocusOut)
{
if (object == ui->comboBox)
{
qWarning(object->objectName().toLatin1().data());
}
}
return false;
}
There is a "focusChanged" signal sent when the focus changes, introduced in Qt 4.1.
It has two arguments, he widget losing focus and the one gaining focus:
void QApplication::focusChanged(QWidget * old, QWidget * now)
Qt Designer isn't designed for this level of WYSIWYG programming.
Do it in C++:
class LineEdit : public QLineEdit
{
virtual void focusInEvent( QFocusEvent* )
{}
};
The simplest way is to connect a slot to the QApplication::focusChanged signal.
I'd have to play with it, but just looking at the QT Documentation, there is a "focusInEvent". This is an event handler.
Here's how you find information about.... Open up "QT Assistant". Go to the Index. Put in a "QLineEdit". There is a really useful link called "List of all members, including inherited members" on all the Widget pages. This list is great, because it even has the inherited stuff.
I did a quick search for "Focus" and found all the stuff related to focus for this Widget.
You have hit on of the weird splits in QT, if you look at the documentation focusInEvent is not a slot it is a protected function, you can override it if you are implementing a subclass of your widget. If you you just want to catch the event coming into your widget you can use QObject::installEventFilter it let's you catch any kind of events.
For some odd reason the developers of Trolltech decided to propagate UI events via two avenues, signals/slots and QEvent
Just in case anybody looking for two QMainWindow focus change .
You can use
if(e->type() == QEvent::WindowActivate)
{
//qDebug() << "Focus IN " << obj << e ;
}
QWidget::setFocus() is slot, not signal. You can check if QLineEdit is in focus with focus property. QLineEdit emits signals when text is changed or edited, see documentation.