I get this strange behavior with a simple reimplementation of ResizeEvent from a standard Widget. After calling show, the resize event is called 2 times. I trace the behavior with breakpoint (see where below "<- - - -") and I got this :
first call :
event->oldSize = (-1, -1)
event->size = (5, 13)
second call :
event->oldSize = (640, 480)
event->size = (640, 480)
The first call seem coherent. But, is anyone can explain to me why I got a second call with inconsistant values and how to get rid of this second resize event?
class MyClass : public QLabel
{
Q_OBJECT
public:
MyClass(QWidget *parent = 0, Qt::WindowFlags f = 0);
~MyClass();
protected:
void resizeEvent(QResizeEvent *event);
};
MyClass::MyClass(QWidget *parent, Qt::WindowFlags f)
: QLabel(parent, f)
{
}
MyClass::~MyClass()
{
}
void MyClass::resizeEvent(QResizeEvent *event)
{
int a = 0; // <- - - - use break point here
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MyClass w;
w.show();
return a.exec();
}
Your last question make me do some tests and I found a solution.
I just add in the constructor :
this->setGeometry(...)
With that, I got only one resizeEvent call (the first one).
I do not know why Qt make this second call but I can guess is to set an initial geometry.
However, thank you for your time. It help me a lot! :-)
Related
In my application, I want to disable some items (i.e. not selectable, no highlights when mouse hovering above, and the texts are greyed out) in the QComboBox when certain conditions are met.
I indeed found someone did ask the same question here: Disable Item in Qt Combobox
But none of these solutions in the answers seem to actually work (including the trick).
Is there a decent and 'correct' way to implement this?
EDIT:
I found out why setting the flags wouldn't disable the items in my application: for some reasons, I had to set the style QStyle::SH_ComboBox_UseNativePopup(see https://codereview.qt-project.org/#/c/82718/). And this setting for some reasons blocked the flag setting. Does anyone have an idea why, and how to work around? A minimum test example is included (modified from the answer of #Mike):
#include <QApplication>
#include <QComboBox>
#include <QStandardItemModel>
#include <QProxyStyle>
class ComboBoxStyle : public QProxyStyle
{
public:
int styleHint ( StyleHint hint, const QStyleOption * option = 0, const QWidget * widget = 0, QStyleHintReturn * returnData = 0 ) const override
{
if ( hint == QStyle::SH_ComboBox_UseNativePopup )
{
return 1;
}
return QProxyStyle::styleHint( hint, option, widget, returnData );
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QComboBox comboBox;
// Setting this style would block the flag settings later on.
comboBox.setStyle( new ComboBoxStyle() );
comboBox.insertItem(0, QObject::tr("item1"));
comboBox.insertItem(1, QObject::tr("item2"));
QStandardItemModel* model = qobject_cast<QStandardItemModel*>(comboBox.model());
QStandardItem* item= model->item(1);
item->setFlags(item->flags() & ~Qt::ItemIsEnabled);
comboBox.show();
return a.exec();
}
The answer linked in my comment above seems to be talking about an old version of Qt. I have tested on Qt5.4 and Qt5.6 and there is no need set the color yourself here, you just need to set and/or clear the Qt::ItemIsEnabled flag, here is an example:
#include <QtWidgets>
int main(int argc, char *argv[]) {
QApplication a(argc, argv);
QComboBox comboBox;
comboBox.addItem(QObject::tr("item1"));
comboBox.addItem(QObject::tr("item2"));
comboBox.addItem(QObject::tr("item3"));
QStandardItemModel *model =
qobject_cast<QStandardItemModel *>(comboBox.model());
Q_ASSERT(model != nullptr);
bool disabled = true;
QStandardItem *item = model->item(2);
item->setFlags(disabled ? item->flags() & ~Qt::ItemIsEnabled
: item->flags() | Qt::ItemIsEnabled);
comboBox.show();
return a.exec();
}
Here is the technique #Mike describes, wrapped up in a convenient utility function:
void SetComboBoxItemEnabled(QComboBox * comboBox, int index, bool enabled)
{
auto * model = qobject_cast<QStandardItemModel*>(comboBox->model());
assert(model);
if(!model) return;
auto * item = model->item(index);
assert(item);
if(!item) return;
item->setEnabled(enabled);
}
I am developing calculator using Qt SDK I want to get values from the calculator buttons in to one Qlabel. I have designed GUI using design view I tried to get values using following code.
void MainWindow::on_three_button_clicked(){
ui->label->setText("3");
}
but then Only I can get one button value at a time
please help me on this...
You can have one QString variable to store current pressed value. Here I am considering your class variable defined as QString myEnteredNum. Then you can use it as below code:
void MainWindow::on_three_button_clicked(){
myEnteredNum.append("3"); // This method you can add in each number slot
ui->label->setText(myEnteredNum);
}
I hope this helps you.
There are two general approaches to this. You can append the digits directly to a number, and bind the label to the number. The m_first label below is updated that way. You can also append the digits directly to the label. The m_second label is updated so.
#include <QtWidgets>
class Window : public QWidget {
Q_OBJECT
Q_PROPERTY(double number MEMBER m_number WRITE setNumber NOTIFY numberChanged)
double m_number;
QGridLayout m_grid;
QLabel m_first, m_second;
QPushButton m_digits[10], m_clear;
public:
Window(QWidget * parent = 0) : QWidget(parent),
m_grid(this), m_clear("C") {
m_grid.addWidget(&m_first, 0, 0, 1, 3);
m_grid.addWidget(&m_second, 1, 0, 1, 3);
m_grid.addWidget(&m_clear, 5, 2);
for (int i = 0; i < 9; ++i) {
m_digits[i].setText(QString::number(i));
if (i > 0) m_grid.addWidget(m_digits + i, 2 + (i-1)/3, (i-1)%3);
else m_grid.addWidget(m_digits + i, 5, 1);
QObject::connect(m_digits + i, &QPushButton::clicked, [i, this]{
// Add the digit to the number
setNumber(m_number * 10.0 + i);
// Add the digit to the label
m_second.setText(m_second.text().append(QString::number(i)));
});
}
QObject::connect(&m_clear, &QPushButton::clicked, [this]{
setNumber(0);
m_second.setText("0");
});
QObject::connect(this, &Window::numberChanged,
&m_second, &QLabel::setNum);
emit m_clear.clicked(); // initialize everything
}
Q_SIGNAL void numberChanged(double);
void setNumber(double n) { m_number = n; emit numberChanged(n); }
};
int main(int argc, char ** argv) {
QApplication app(argc, argv);
Window window;
window.show();
return app.exec();
}
#include "main.moc"
Finally, a calculator is stateful and, to avoid common mistakes, you could use a QStateMachine to make this fact explicit, and to adjust the behavior of the calculator depending on which state it's in.
My application is designed in that way that different plugins can set the central widget of the main windows to show the desired content.
This works so far.
But if I set a QQuickView-WindowContainer as central widget, the app does not quit when I close the main window.
If I set a "normal" widget like QPushButton as central widget the appliation quits just fine. Why is that?
This is the code of a minimal example which shows this behaviour (MainWindow is a class created from the QtCreator wizard):
class AppCore : public QObject
{
Q_OBJECT
public:
explicit AppCore(QObject *parent = 0);
signals:
public slots:
void showMainWindow();
private:
MainWindow *m_mainWindow;
};
AppCore::AppCore(QObject *parent) :
QObject(parent)
{
}
void AppCore::showMainWindow()
{
QQuickView *view;
QWidget *container;
view = new QQuickView();
container = QWidget::createWindowContainer(view);
view->setSource(QUrl("qrc:/main.qml"));
m_mainWindow = new MainWindow();
//m_mainWindow->setCentralWidget(new QPushButton("Button"));
m_mainWindow->setCentralWidget(container);
m_mainWindow->show();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
AppCore appCore;
appCore.showMainWindow();;
return a.exec();
}
This looks like a bug. I see a dead lock in debugger: v8::internal::RuntimeProfiler::WaitForSomeIsolateToEnterJS and QQmlDataLoader::shutdownThread wait for each other. I can't find a good workaround for this issue.
I found a dirty hack that solved the issue. If container is deleted a bit earlier, all works ok:
void MainWindow::closeEvent(QCloseEvent *e) {
QMainWindow::closeEvent(e);
if (e->isAccepted() && centralWidget()) {
delete centralWidget();
}
}
You probably should send a bug report. Note that m_mainWindow is not needed to reproduce the issue. Using container->show(); gives the same result.
I'm creating a simple virtual keyboard in a QDockWidget...
When the widget is docked into the QMainWindow, the selected widget (for example a qdoublespinbox) is highlighted and if I click on the virtual keyboard clearFocus() works...
When the QDockWidget is floating above the window and I click a button, clearFocus doesn't work and I can't see the focused widget in QMainWindow...
How can I force the QDockWidget to not have any focus at all?
Thanks :-)
This is the code:
// class MyVirtualKeyboard : public QDockWidget
void MyVirtualKeyboard::sendKey(Qt::Key key, Qt::KeyboardModifier mod)
{
this->clearFocus();
QMainWindow *w = dynamic_cast<QMainWindow *>(this->parent());
if(w == NULL) return;
QWidget *widget = w->focusWidget();
QString repr = QKeySequence(key).toString();
QKeyEvent *pressEvent = new QKeyEvent(QEvent::KeyPress, key, mod, repr);
QKeyEvent *releaseEvent = new QKeyEvent(QEvent::KeyRelease, key, mod, repr);
qDebug("%s", pressEvent->text().toAscii().data());
MyApplication *app = MyApplication::myInstance();
app->postEvent(widget, pressEvent);
app->postEvent(widget, releaseEvent);
}
void MyVirtualKeyboard::on_BTN_1_clicked()
{
sendKey(Qt::Key_1);
}
...
The clearFocus() call should be unnecessary. Your dock widget and all of its widgets must have the Qt::NoFocus policy.
The code below shows how you might do it.
// https://github.com/KubaO/stackoverflown/tree/master/questions/vkb-focus-18558664
#include <QtGui>
#if QT_VERSION >= QT_VERSION_CHECK(5,0,0)
#include <QtWidgets>
#endif
class Keyboard : public QDockWidget {
Q_OBJECT
QWidget m_widget;
QGridLayout m_layout{&m_widget};
QToolButton m_buttons[10];
void sendKey(Qt::Key key, Qt::KeyboardModifier mod)
{
if (! parentWidget()) return;
auto target = parentWidget()->focusWidget();
if (! target) return;
auto repr = QKeySequence(key).toString();
auto pressEvent = new QKeyEvent(QEvent::KeyPress, key, mod, repr);
auto releaseEvent = new QKeyEvent(QEvent::KeyRelease, key, mod, repr);
qApp->postEvent(target, pressEvent);
qApp->postEvent(target, releaseEvent);
qDebug() << repr;
}
Q_SLOT void clicked() {
auto key = sender()->property("key");
if (key.isValid()) sendKey((Qt::Key)key.toInt(), Qt::NoModifier);
}
public:
explicit Keyboard(const QString & title, QWidget *parent = nullptr) : Keyboard(parent) {
setWindowTitle(title);
}
explicit Keyboard(QWidget *parent = nullptr) : QDockWidget(parent) {
int i{};
for (auto & btn : m_buttons) {
btn.setText(QString::number(i));
btn.setProperty("key", Qt::Key_0 + i);
m_layout.addWidget(&btn, 0, i, 1, 1);
connect(&btn, SIGNAL(clicked()), SLOT(clicked()));
btn.setFocusPolicy(Qt::NoFocus);
++i;
}
setWidget(&m_widget);
setFeatures(QDockWidget::DockWidgetFloatable | QDockWidget::DockWidgetMovable);
}
};
int main(int argc, char ** argv)
{
QApplication a(argc, argv);
QMainWindow w;
w.setCentralWidget(new QLineEdit);
w.addDockWidget(Qt::TopDockWidgetArea, new Keyboard("Keyboard", &w));
w.show();
return a.exec();
}
#include "main.moc"
You can prevent a widget from taking focus by setting QWidget::focusPolicy = Qt::NoFocus.
However, there are two concepts here that you're mixing - the focused control (per window), and the active window (per desktop). I think in the scenario you're describing (a torn-off popup window), the OS window manager is likely to still change the active top-level window even if Qt doesn't set a focused control. That will result in nobody having keyboard focus (which is a valid state!).
So I think a full answer to your question will involve some non-portable bits. I don't know what GUI environment you're working in, but I know some of the answer for Win32, so I'll keep going and hope that's useful:
Win32
There's a pretty good discussion of the state tracking for Win32 on MSDN in the article Win32 Activation and Focus. I'm not aware that Qt does anything to wrap this level, so you'd have to use QWidget::nativeEvent or QCoreApplication::installNativeEventFilter to get at the low-level event. If you can subclass the window, I'd prefer the former, since it's more self-contained.
bool FooWidget::nativeEvent(const QByteArray & eventType, void * message, long * result)
{
#ifdef Q_OS_WIN
if(eventType == "windows_generic_MSG") {
const MSG *msg = reinterpret_cast<MSG *>(message);
if(msg->message == WM_MOUSEACTIVATE) {
*result = MA_NOACTIVATE;
return true;
}
}
#else
#error Need platform-specific code to suppress click-activation
#endif
return false;
}
This should block the click from activating the window (MA_NOACTIVATE), and block Qt from processing it further (return true), while leaving other all events (including the the click, since we didn't use MA_NOACTIVATEANDEAT to block it too) to be processed into QEvents and Qt signals normally (return false at the end).
If you need further low-level access (though I don't think you will), see also QWidget::effectiveWinId() and QWidget::windowHandle
Thanks a lot to Martin Gräßlin for the answer!
My recommendation: check out the virtual keyboard code in KDE Plasma: http://quickgit.kde.org/?p=kdeplasma-addons.git&a=blob&h=5628d6325afe57f85917dad865a07d4116335726&hb=a658d1e257cfca2a43c12714d026ec26f1fdb755&f=applets%2Fplasmaboard%2Fwidget.cpp
Looks like the key is setWindowFlags(Qt::X11BypassWindowManagerHint) and setFocusPolicy(Qt::NoFocus)
MyVirtualKeyboard::MyVirtualKeyboard(QWidget *parent) :
QDockWidget(parent),
ui(new Ui::MyVirtualKeyboard)
{
ui->setupUi(this);
this->connect(this, SIGNAL(topLevelChanged(bool)), this, SLOT(topLevelChanged()));
}
void MyVirtualKeyboard::topLevelChanged()
{
if(this->isWindow())
{
this->setWindowFlags(Qt::Popup | Qt::WindowStaysOnTopHint | Qt::X11BypassWindowManagerHint);
this->setFocusPolicy(Qt::NoFocus);
this->show();
}
}
I think I've found a better way to do it!
Just use this->setAttribute(Qt::WA_X11DoNotAcceptFocus); and voila!
Example:
MyVirtualKeyboard::MyVirtualKeyboard(QWidget *parent) :
QDockWidget(parent),
ui(new Ui::MyVirtualKeyboard)
{
ui->setupUi(this);
this->setAttribute(Qt::WA_X11DoNotAcceptFocus);
}
I am creating an animation with QGraphicsView, QGraphicsScene and QGraphicsItem. Can someone explain me when the paint function is called? Although I does not change variables of the item, the paint function is called every ≈100 ms. Can I stop that, so i can repaint the item when I want?
You are approaching it the wrong way. The item should be repainted only when needed - when you change how it looks or where it's located. That's when you call the QGraphicsItem::update(). The rest will be handled for you. It seems you're overcomplicating things.
Do note that you need to be determining the current time-dependent parameter of the animation within the paint() method, or "close" to it (say, right before update() is called), using actual time! If your animations are derived from QAbstractAnimation, it's already done for you. If they are not, then you'll have to use QElapsedTimer yourself.
The relevant Qt documentation says:
The animation framework calls updateCurrentTime() when current time has changed. By reimplementing this function, you can track the animation progress. Note that neither the interval between calls nor the number of calls to this function are defined; though, it will normally be 60 updates per second.
This means that Qt will do animations on a best-effort basis. The currentTime reported by the animation is the most recent time snapshot at the moment the animation was updated in the event loop. This is pretty much what you want.
The simplest way to deal with all this would be to use QVariantAnimation with QGraphicsObject. An example is below. Instead of rotating the object, you may have your own slot and modify it in some other way. You can also, instead of using signal-slot connection, have a customized QVariantAnimation that takes your custom QGraphicsItem-derived class as a target.
main.cpp
#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsObject>
#include <QPropertyAnimation>
#include <QGraphicsRectItem>
class EmptyGraphicsObject : public QGraphicsObject
{
public:
EmptyGraphicsObject() {}
QRectF boundingRect() const { return QRectF(0, 0, 0, 0); }
void paint(QPainter *, const QStyleOptionGraphicsItem *, QWidget *) {}
};
class View : public QGraphicsView
{
public:
View(QGraphicsScene *scene, QWidget *parent = 0) : QGraphicsView(scene, parent) {
setRenderHint(QPainter::Antialiasing);
}
void resizeEvent(QResizeEvent *) {
fitInView(-2, -2, 4, 4, Qt::KeepAspectRatio);
}
};
void setupScene(QGraphicsScene &s)
{
QGraphicsObject * obj = new EmptyGraphicsObject;
QGraphicsRectItem * rect = new QGraphicsRectItem(-1, 0.3, 2, 0.3, obj);
QPropertyAnimation * anim = new QPropertyAnimation(obj, "rotation", &s);
s.addItem(obj);
rect->setPen(QPen(Qt::darkBlue, 0.1));
anim->setDuration(2000);
anim->setStartValue(0);
anim->setEndValue(360);
anim->setEasingCurve(QEasingCurve::InBounce);
anim->setLoopCount(-1);
anim->start();
}
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QGraphicsScene s;
setupScene(s);
View v(&s);
v.show();
return a.exec();
}
You can set the viewportUpdateMode of the QGraphicsView to change how it updates. The options are: -
QGraphicsView::FullViewportUpdate
QGraphicsView::MinimalViewportUpdate
QGraphicsView::SmartViewportUpdate
QGraphicsView::BoundingRectViewportUpdate
QGraphicsView::NoViewportUpdate
The Qt docs explains what the different options do, but if you want full control, just set to QGraphicsView::NoViewportUpdate and control it yourself using a QTimer event.