I want to show some text (like "No items") when there are no items in QListView.
I tried to override paintEvent method of QListView, but it doesn't have any effect.
The code below shows a simple way of doing it by overloading the paintEvent method of the view. Painting of the text should probably use the style mechanism to obtain the font and pen/brush, but I'll leave that up for grabs by a keen editor.
It uses Qt 5 and its C++11 features, doing it the Qt 4 or pre-C++11 way would require a QObject-deriving class with a slot to connect to the spin box's valueChanged signal. The implementation of ListView doesn't need to change between Qt 4 and Qt 5.
#include <QtWidgets>
class ListView : public QListView {
void paintEvent(QPaintEvent *e) {
QListView::paintEvent(e);
if (model() && model()->rowCount(rootIndex()) > 0) return;
// The view is empty.
QPainter p(this->viewport());
p.drawText(rect(), Qt::AlignCenter, "No Items");
}
public:
ListView(QWidget* parent = 0) : QListView(parent) {}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget window;
QFormLayout layout(&window);
ListView view;
QSpinBox spin;
QStringListModel model;
layout.addRow(&view);
layout.addRow("Item Count", &spin);
QObject::connect(&spin, (void (QSpinBox::*)(int))&QSpinBox::valueChanged,
[&](int value){
QStringList list;
for (int i = 0; i < value; ++i) list << QString("Item %1").arg(i);
model.setStringList(list);
});
view.setModel(&model);
window.show();
return a.exec();
}
If you use a QListView, you probably have a custom model containing data you want to display. This is maybe the best place to returns "No items" when your model is empty.
Related
The question is pretty straight forward: is it possible to change the default behavior of a checkable QGroupBox object? I designed a user interface with many QLineEdit objects inside a checkable QGroupBox, the desired behavior is: when QGroupBox is not checked all of its children are enable and when it is checked all of its children are disable.
As you can see at the oficial QGroupBox documentation, it says:
If the check box is checked, the group box's children are enabled; otherwise, the children are disabled and are inaccessible to the user.
One trick is to modify the painting so that when it is checked the check is not shown and vice versa:
#include <QtWidgets>
class GroupBox: public QGroupBox{
public:
using QGroupBox::QGroupBox;
protected:
void paintEvent(QPaintEvent *){
QStylePainter paint(this);
QStyleOptionGroupBox option;
initStyleOption(&option);
if(isCheckable()){
option.state &= ~(isChecked() ? QStyle::State_On : QStyle::State_Off);
option.state |= (isChecked() ? QStyle::State_Off : QStyle::State_On);
}
paint.drawComplexControl(QStyle::CC_GroupBox, option);
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
GroupBox groupBox;
groupBox.setCheckable(true);
QVBoxLayout *vbox = new QVBoxLayout;
vbox->addWidget(new QLineEdit);
vbox->addWidget(new QLineEdit);
vbox->addWidget(new QLineEdit);
vbox->addStretch(1);
groupBox.setLayout(vbox);
groupBox.show();
return a.exec();
}
I'm struggling with an issue that QEvent::Drop event is never generated for my QQuickView window.
I need to implement a drag'n'drop functionality, to drop files from explorer to the QQuickView.
As described in this post, i've istalled an eventfilter for the QQuickView objet, and in eventFilter() method trying to catch required events. The QEvent::DragMove is being generated as expected, as i drag a file over the view. But when i drop the file on the view, the QEvent::Drop is not being generated. Instead, the QEvent::DragLeave is generated.
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
Filter f;
QQuickView *view = new QQuickView;
view->installEventFilter(&f);
view->show();
return a.exec();
}
And here is a (Event)Filter class code:
(header)
class Filter : public QObject
{
Q_OBJECT
public:
Filter(){};
virtual bool eventFilter(QObject *watched, QEvent *event) Q_DECL_OVERRIDE;
};
(source)
bool Filter::eventFilter(QObject *watched, QEvent *event)
{
if(event->type() == QEvent::DragMove)
qDebug() << "it's a drag";
if(event->type() == QEvent::Drop)
qDebug() << "it's a drop"; // <<-- Never reaches here
return QObject::eventFilter(watched, event);
}
My colleagues helped me out with this question.
Apparently you have to add a DropArea item to your QML root file, and after that the QQuickView will start receiving QEvent::Drop events.
I can not find any documentation on this case though, and i also wonder what would be more general solution for this, if you had a QWindow class instead.
Anyway, I'm closing this question.
I'm new in Qt and have a question.
I have QLabel and QLineEdit objects, and when QLabel text is clicked on, I want to set this text in QLineEdit.
Also I have read that QLabel has not clicked signal.
Can you explain how can I do this and write code for me ?!
Either style another type of QWidget such as a specific QPushButton to look like a QLabel and use its clicked() signal or inherit QLabel yourself and emit your own clicked() signal.
See this example:
https://wiki.qt.io/Clickable_QLabel
If you choose the latter option you can pass the text in the signal. Then connect the necessary signals/slots up between the QLabel and the QLineEdit like so:
QObject::connect(&label, SIGNAL(clicked(const QString& text)),
&lineEdit, SLOT(setText(const QString& text)));
A simple way to accomplish that, without a need for any subclassing, is a signal source that monitors the events on some object and emits relevant signals:
// main.cpp - this is a single-file example
#include <QtWidgets>
class MouseButtonSignaler : public QObject {
Q_OBJECT
bool eventFilter(QObject * obj, QEvent * ev) Q_DECL_OVERRIDE {
if ((ev->type() == QEvent::MouseButtonPress
|| ev->type() == QEvent::MouseButtonRelease
|| ev->type() == QEvent::MouseButtonDblClick)
&& obj->isWidgetType())
emit mouseButtonEvent(static_cast<QWidget*>(obj),
static_cast<QMouseEvent*>(ev));
return false;
}
public:
Q_SIGNAL void mouseButtonEvent(QWidget *, QMouseEvent *);
MouseButtonSignaler(QObject * parent = 0) : QObject(parent) {}
void installOn(QWidget * widget) {
widget->installEventFilter(this);
}
};
The emit keyword is an empty macro, Qt defines it as follows:
#define emit
It is for use by humans as a documentation aid prefix only, the compiler and moc ignore it. As a documentation aid, it means: the following method call is a signal emission. The signals are simply methods whose implementation is generated for you by moc - that's why we have to #include "main.moc" below to include all the implementations that moc has generated for the object class(es) in this file. There's otherwise nothing special or magical to a signal. In this example, you could look in the build folder for a file called main.moc and see the implementation (definition) of void MouseButtonSignaler::mouseButtonEvent( .. ).
You can then install such a signaler on any number of widgets, such as a QLabel:
int main(int argc, char ** argv) {
QApplication app(argc, argv);
MouseButtonSignaler signaler;
QWidget w;
QVBoxLayout layout(&w);
QLabel label("text");
QLineEdit edit;
layout.addWidget(&label);
layout.addWidget(&edit);
signaler.installOn(&label);
QObject::connect(&signaler, &MouseButtonSignaler::mouseButtonEvent,
[&label, &edit](QWidget*, QMouseEvent * event) {
if (event->type() == QEvent::MouseButtonPress)
edit.setText(label.text());
});
w.show();
return app.exec();
}
#include "main.moc"
You need to create one Custom Label class, which will inherit QLabel. Then you can use MouseButtonRelease event to check clicking of Label and emit your custom signal and catch in one SLOT.
Your .h file will be as below:
class YourLabelClass : public QLabel{
signals:
void myLabelClicked(); // Signal to emit
public slots:
void slotLabelClicked(); // Slot which will consume signal
protected:
bool event(QEvent *myEvent); // This method will give all kind of events on Label Widget
};
In your .cpp file, your constructor will connect signal & slot as below :
YourLabelClass :: YourLabelClass(QWidget* parent) : QLabel(parent) {
connect(this, SIGNAL(myLabelClicked()), this, SLOT(slotLabelClicked()));
}
Remaining event method and SLOT method will be implemented as below:
bool YourLabelClass :: event(QEvent *myEvent)
{
switch(myEvent->type())
{
case(QEvent :: MouseButtonRelease): // Identify Mouse press Event
{
qDebug() << "Got Mouse Event";
emit myLabelClicked();
break;
}
}
return QWidget::event(myEvent);
}
void YourLabelClass :: slotLabelClicked() // Implementation of Slot which will consume signal
{
qDebug() << "Clicked Label";
}
For Changing a Text on QLineEdit, you need to create a Custom Class and share object pointer with custom QLabel Class. Please check test code at this link
In the above example the header needs Q_OBJECT:
class YourLabelClass : public QLabel{
Q_OBJECT
signals:
Item.h:
class Item:public QGraphicsRectItem
{
public:
Item(const QRectF & rect, QGraphicsItem * parent = 0);
void mousePressEvent(QGraphicsSceneMouseEvent * event);
void mouseMoveEvent(QGraphicsSceneMouseEvent * event);
~Item();
};
Item.cpp:
Item::Item(const QRectF & rect, QGraphicsItem * parent)
:QGraphicsRectItem(rect, parent)
{
}
void Item::mousePressEvent(QGraphicsSceneMouseEvent * event){
qDebug("press");
QGraphicsRectItem::mousePressEvent(event);
event->accept();
}
void Item::mouseMoveEvent(QGraphicsSceneMouseEvent * event){
qDebug("move");
}
Item::~Item()
{
}
main.cpp:
#include "mainwindow.h"
#include <QApplication>
#include "QGraphicsView"
#include "QGraphicsScene"
#include "item.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
// MainWindow w;
// w.show();
auto item = new Item(QRectF(QPointF(),QSize(100,150)));
auto scene = new QGraphicsScene;
scene->addItem(item);
auto view = new QGraphicsView(scene);
view->setMinimumSize(QSize(800,600));
view->scene()->setSceneRect(QRectF(QPointF(),view->size()));
view->show();
return a.exec();
}
I have read the doc about QGraphicsItem::mousePressEvent, which says "If you do reimplement this function, event will by default be accepted (see QEvent::accept()), and this item is then the mouse grabber. This allows the item to receive future move, release and doubleclick events." Now I have reimplemented it. Why doesn't it work?
When the mouse event is created it is set as accepted. Depending on the flags you have set to your item, the default mousePressEvent implementation might reject it.
In your case you are calling the default implementation which might reject the mouse press event. If that is the case, the mouseMoveEvent will never be called.
You should read this interesting article about events.
Enable flags to use the functionalities
item ->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable);
item ->setAcceptHoverEvents(true);
item ->setAcceptedMouseButtons(Qt::LeftButton);
I have two items of type QGraphicsRectItem. One over the other.
The first one is a custom class called Wall. Inside the wall there are windows and doors.
In fact, i have a list of Doors and Windows inside this custom Wall class.
The Doors are Items too, and are drawn inside the wall.
When i move the mouse over the door, the hover function of the wall is emited, but the hover of the door is not. Both of them correctly copied one from each other as virtual void protected.
Why is that happening? How can i make the door and window items realize about the hover?.
I have tried with a custom QGraphicsItem instead of a custom QGraphicsRectItem. It seems the hover event handler is successfully called for both Wall and Door. This is happening when explicitly setting QGraphicsItem with setAcceptHoverEvents(true). This is not tested with custom QGraphicsRectItem.
#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsItem>
#include <QPainter>
class Item : public QGraphicsItem
{
QBrush m_brush;
public:
explicit Item(bool nested = true, QGraphicsItem* parent = 0) : QGraphicsItem(parent), m_brush(Qt::white)
{
if (nested) {
Item* item = new Item(false, this);
item->setPos(10,10);
m_brush = Qt::red;
}
setAcceptHoverEvents(true);
}
QRectF boundingRect() const
{
return QRectF(0,0,100,100);
}
void hoverEnterEvent(QGraphicsSceneHoverEvent *)
{
m_brush = Qt::red;
update();
}
void hoverLeaveEvent(QGraphicsSceneHoverEvent *)
{
m_brush = Qt::white;
update();
}
void paint(QPainter *p, const QStyleOptionGraphicsItem *, QWidget *)
{
p->setBrush(m_brush);
p->drawRoundRect(boundingRect());
}
};
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QGraphicsScene scene;
scene.addItem(new Item);
QGraphicsView view;
view.setScene(&scene);
view.setMouseTracking(true);
view.show();
return app.exec();
}