Qt usage history

QFileDialog select folder

QString dir = QFileDialog::getExistingDirectory();

Remove the three small dots on the left side of QToolBar

Call setMovable(false);

Remove style

//移除原有样式
QWidget *widget = new QWidget;
style()->unpolish(widget );
//重新设置新的该控件的样式。
style()->polish(widget);

QTreeWidget horizontal scroll bar

QTreeWidget sets the horizontal scroll bar

treeWidget->header()->setSectionResizeMode(QHeaderView::ResizeToContents);
treeWidget->header()->setStretchLastSection(false);

QTableWidgetItem has a black border

When the border styles of QTableWidget and QTableWidgetItem are set to none. There is still a black border.
Solution: QTableWidget object calls setShowGrid(false)to

QPushButton text left aligned

QPushButton  button = new QPushButton;
button->setStyleSheet("text-align:left;");

Set icon in QDateTimeEdit

Looking at the QDateTimeEdit source code, you can see that the middle date editing part is a QLineEdit named qt_spinbox_lineedit . Therefore, you can get this QLineEdit through findChild; at this time, you can set QAction.

  QDateTimeEdit *dateTimeEdit = new QDateTimeEdit;
   QLineEdit *lineEdit = dateTimeEdit->findChild<QLineEdit*>("qt_spinbox_lineedit");
   if(lineEdit)
   {
    
    
       QAction *actionIcon = new QAction(lineEdit);
       actionIcon->setIcon(QIcon("icon.png"));
       lineEdit->addAction(actionIcon,QLineEdit::ActionPosition::LeadingPosition);
   }

Get the width and height of the screen in Qt

QApplication::desktop()->width()  ;
QApplication::desktop()->height() ;

Multiple screens are also available

win7 shadow border

setWindowFlags(windowFlags() | Qt::NoDropShadowWindowHint);

Ignore mouse events

setAttribute(Qt::WA_TransparentForMouseEvents);
Note: Mouse wheel events cannot be ignored;

QComboBo setting style is invalid

Plus setView( new QListView());you can

QComboBox sets the text to be empty

Direct call setCurrentText("")invalid. Can be setCurrentIndex(-1)achieved

Qt signal connection reports warning problem

When using QTimer today, connect its timerout signal. Then the prompt message is always output on the console.

Warning: QObject::connect: invalid null parameter  --File:(kernel\qobject.cpp:46
74, class QMetaObject::Connection __cdecl QObjectPrivate::connectImpl(const clas
s QObject *,int,const class QObject *,void **,class QtPrivate::QSlotObjectBase *
,enum Qt::ConnectionType,const int *,const struct QMetaObject *))

Then I just look at the source code of QTimer directly. Find

Q_SIGNALS:
    void timeout(QPrivateSignal);

I found that timeout has one more parameter, thinking it is a parameter problem, but I remember it has no parameters, which is very strange. Later inspection found that it was because when I called connect, the memory application of the timer object was placed after the connect, which resulted in an empty object. Put new in front of connect, and it's solved.

Qt program running directory and program environment directory acquisition

QString exeDir= QApplication::applicationDirPath();//exe运行目录
QString dirPath = QDir::currentPath().toStdString();//程序运行环境目录

Qt captures the screen and saves it as a picture

	 auto desktopWidget = QApplication::desktop();
	QScreen * pqscreen = QGuiApplication::primaryScreen();
	QPixmap pixmap = pqscreen->grabWindow(desktopWidget->winId(), 0, 0, desktopWidget->width(), desktopWidget->height());
	pixmap.save("data/a.png");

QTread Destroryed while thread is still running

This problem is caused because the thread exit is not handled properly. The following code needs to be added to the main thread:

      _trimeThread  为子类化QThread的对象；
      //quit
        _trimeThread->quit();//退出线程
        _trimeThread->wait();//等待主线程退出  join()

Get its content after editing the item of QTableWidget

After the item of QTableWidget is edited, if the content changes, it will be sent

void QTableWidget::itemChanged(QTableWidgetItem *item)

Signal, associate this signal and then you can get the content of the item

QMenu secondary menu

	 QMenu *menu = new QMenu(nullptr);
	 QAction *actionChildMenu = new QAction(nullptr);
	 actionChildMenu->setText("child menu");
	 QMenu *menuChild = new QMenu(nullptr);//二级菜单
	 QAction *actionChildOne = new QAction(nullptr);
	 actionChildOne->setText("actionChildOne");
	 QAction *actionChildTwo = new QAction(nullptr);
	 actionChildTwo->setText("actionChildTwo");
	 QAction *actionChildThree = new QAction(nullptr);//二级菜单项
	 actionChildTwo->setText("actionChildTwo");
	 menuChild->addAction(actionChildOne);
	 menuChild->addAction(actionChildTwo);
	 menuChild->addAction(actionChildThree);
	 menu->addAction(actionChildMenu);
	 actionChildMenu->setMenu(menuChild);

QWidget deletes sub-controls and sub-layouts in the layout

Qt::Popup flags problem

QAction setting selected

	 QAction *action = new  QAction(nullptr);
	 action->setCheckable(true);
	 action->setChecked(true);

Multiple QAction settings are mutually exclusive when selected

Add it to QActionGroup to be mutually exclusive. The
following code, actionTwo is selected

	 QActionGroup *actionGroup = new QActionGroup(nullptr);
	 QAction *actionOne = new QAction(nullptr);
	 QAction *actionTwo = new QAction(nullptr);
	 QAction *actionThree = new QAction(nullptr);
	 actionGroup->addAction(actionOne);
	 actionGroup->addAction(actionTwo);
	 actionGroup->addAction(actionThree);
	 actionOne->setCheckable(true);
	 actionTwo->setCheckable(true);
	 actionThree->setCheckable(true);
	 actionTwo->setChecked(true);