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The QDialog class is the base class of dialog windows. More...

There is no equivalent of the QINVOKABLE macro of Qt since PySide2 slots can actually have return values. If you need to create a invokable method that returns some value, declare it as a slot, e.g. In contrast to the previous example, our new class also uses a return value for the increment slot. No further adjustments are required to receive the return value in QML. Qt automatically maps basic C types to QML types for all method parameters and return values.

Public Types

Properties

• modal : bool
• sizeGripEnabled : bool

• 58 properties inherited from QWidget
• 1 property inherited from QObject

Public Functions

Reimplemented Public Functions

• 211 public functions inherited from QWidget
• 31 public functions inherited from QObject
• 14 public functions inherited from QPaintDevice

Public Slots

• 19 public slots inherited from QWidget
• 1 public slot inherited from QObject

Signals

• 3 signals inherited from QWidget
• 2 signals inherited from QObject

Reimplemented Protected Functions

• 35 protected functions inherited from QWidget
• 9 protected functions inherited from QObject
• 1 protected function inherited from QPaintDevice

Additional Inherited Members

• 1 public variable inherited from QObject
• 5 static public members inherited from QWidget
• 10 static public members inherited from QObject
• 35 protected functions inherited from QWidget
• 9 protected functions inherited from QObject
• 1 protected function inherited from QPaintDevice
• 1 protected slot inherited from QWidget
• 2 protected variables inherited from QObject
• 1 protected type inherited from QPaintDevice

Detailed Description

The QDialog class is the base class of dialog windows.

A dialog window is a top-level window mostly used for short-term tasks and brief communications with the user. QDialogs may be modal or modeless. QDialogs can provide a return value, and they can have default buttons. QDialogs can also have a QSizeGrip in their lower-right corner, using setSizeGripEnabled().

Note that QDialog (and any other widget that has type Qt::Dialog) uses the parent widget slightly differently from other classes in Qt. A dialog is always a top-level widget, but if it has a parent, its default location is centered on top of the parent's top-level widget (if it is not top-level itself). It will also share the parent's taskbar entry.

Use the overload of the QWidget::setParent() function to change the ownership of a QDialog widget. This function allows you to explicitly set the window flags of the reparented widget; using the overloaded function will clear the window flags specifying the window-system properties for the widget (in particular it will reset the Qt::Dialog flag).

Modal Dialogs

A modal dialog is a dialog that blocks input to other visible windows in the same application. Dialogs that are used to request a file name from the user or that are used to set application preferences are usually modal. Dialogs can be application modal (the default) or window modal.

When an application modal dialog is opened, the user must finish interacting with the dialog and close it before they can access any other window in the application. Window modal dialogs only block access to the window associated with the dialog, allowing the user to continue to use other windows in an application.

The most common way to display a modal dialog is to call its exec() function. When the user closes the dialog, exec() will provide a useful return value. Typically, to get the dialog to close and return the appropriate value, we connect a default button, e.g. OK, to the accept() slot and a Cancel button to the reject() slot. Alternatively you can call the done() slot with Accepted or Rejected.

An alternative is to call setModal(true) or setWindowModality(), then show(). Unlike exec(), show() returns control to the caller immediately. Calling setModal(true) is especially useful for progress dialogs, where the user must have the ability to interact with the dialog, e.g. to cancel a long running operation. If you use show() and setModal(true) together to perform a long operation, you must call QApplication::processEvents() periodically during processing to enable the user to interact with the dialog. (See QProgressDialog.)

Modeless Dialogs

A modeless dialog is a dialog that operates independently of other windows in the same application. Find and replace dialogs in word-processors are often modeless to allow the user to interact with both the application's main window and with the dialog.

Modeless dialogs are displayed using show(), which returns control to the caller immediately.

If you invoke the show() function after hiding a dialog, the dialog will be displayed in its original position. This is because the window manager decides the position for windows that have not been explicitly placed by the programmer. To preserve the position of a dialog that has been moved by the user, save its position in your closeEvent() handler and then move the dialog to that position, before showing it again.

Default Button

A dialog's default button is the button that's pressed when the user presses Enter (Return). This button is used to signify that the user accepts the dialog's settings and wants to close the dialog. Use QPushButton::setDefault(), QPushButton::isDefault() and QPushButton::autoDefault() to set and control the dialog's default button.

Escape Key

If the user presses the Esc key in a dialog, QDialog::reject() will be called. This will cause the window to close: The close event cannot be ignored.

Extensibility

Extensibility is the ability to show the dialog in two ways: a partial dialog that shows the most commonly used options, and a full dialog that shows all the options. Typically an extensible dialog will initially appear as a partial dialog, but with a More toggle button. If the user presses the More button down, the dialog is expanded. The Extension Example shows how to achieve extensible dialogs using Qt.

Return Value (Modal Dialogs)

Modal dialogs are often used in situations where a return value is required, e.g. to indicate whether the user pressed OK or Cancel. A dialog can be closed by calling the accept() or the reject() slots, and exec() will return Accepted or Rejected as appropriate. The exec() call returns the result of the dialog. The result is also available from result() if the dialog has not been destroyed.

In order to modify your dialog's close behavior, you can reimplement the functions accept(), reject() or done(). The closeEvent() function should only be reimplemented to preserve the dialog's position or to override the standard close or reject behavior.

Code Examples

A modal dialog:

A modeless dialog:

See also QDialogButtonBox, QTabWidget, QWidget, QProgressDialog, GUI Design Handbook: Dialogs, Standard, Extension Example, and Standard Dialogs Example.

Member Type Documentation

enum QDialog::DialogCode

The value returned by a modal dialog.

Property Documentation

modal : bool

This property holds whether show() should pop up the dialog as modal or modeless.

By default, this property is false and show() pops up the dialog as modeless. Setting his property to true is equivalent to setting QWidget::windowModality to Qt::ApplicationModal.

exec() ignores the value of this property and always pops up the dialog as modal.

Access functions:

See also QWidget::windowModality, show(), and exec().

sizeGripEnabled : bool

This property holds whether the size grip is enabled.

A QSizeGrip is placed in the bottom-right corner of the dialog when this property is enabled. By default, the size grip is disabled.

Access functions:

Member Function Documentation

QDialog::QDialog(QWidget *parent = Q_NULLPTR, Qt::WindowFlagsf = Qt::WindowFlags())

Constructs a dialog with parent parent.

A dialog is always a top-level widget, but if it has a parent, its default location is centered on top of the parent. It will also share the parent's taskbar entry.

The widget flags f are passed on to the QWidget constructor. If, for example, you don't want a What's This button in the title bar of the dialog, pass Qt::WindowTitleHint Qt::WindowSystemMenuHint in f.

See also QWidget::setWindowFlags().

QDialog::~QDialog()

Destroys the QDialog, deleting all its children.

[virtual slot] void QDialog::accept()

Hides the modal dialog and sets the result code to Accepted.

See also reject() and done().

[signal] void QDialog::accepted()

This signal is emitted when the dialog has been accepted either by the user or by calling accept() or done() with the QDialog::Accepted argument.

Note that this signal is not emitted when hiding the dialog with hide() or setVisible(false). This includes deleting the dialog while it is visible.

This function was introduced in Qt 4.1.

See also finished() and rejected().

[virtual protected] void QDialog::closeEvent(QCloseEvent *e)

Reimplemented from QWidget::closeEvent().

[virtual protected] void QDialog::contextMenuEvent(QContextMenuEvent *e)

Reimplemented from QWidget::contextMenuEvent().

[virtual slot] void QDialog::done(intr)

Closes the dialog and sets its result code to r. If this dialog is shown with exec(), done() causes the local event loop to finish, and exec() to return r.

As with QWidget::close(), done() deletes the dialog if the Qt::WA_DeleteOnClose flag is set. If the dialog is the application's main widget, the application terminates. If the dialog is the last window closed, the QApplication::lastWindowClosed() signal is emitted.

See also accept(), reject(), QApplication::activeWindow(), and QCoreApplication::quit().

[virtual protected] bool QDialog::event(QEvent *e)

Reimplemented from QObject::event().

[virtual protected] bool QDialog::eventFilter(QObject *o, QEvent *e)

Reimplemented from QObject::eventFilter().

[virtual slot] int QDialog::exec()

Shows the dialog as a modal dialog, blocking until the user closes it. The function returns a DialogCode result.

If the dialog is application modal, users cannot interact with any other window in the same application until they close the dialog. If the dialog is window modal, only interaction with the parent window is blocked while the dialog is open. By default, the dialog is application modal.

See also open(), show(), result(), and setWindowModality().

[signal] void QDialog::finished(intresult)

This signal is emitted when the dialog's result code has been set, either by the user or by calling done(), accept(), or reject().

Note that this signal is not emitted when hiding the dialog with hide() or setVisible(false). This includes deleting the dialog while it is visible.

This function was introduced in Qt 4.1.

See also accepted() and rejected().

[virtual protected] void QDialog::keyPressEvent(QKeyEvent *e)

Reimplemented from QWidget::keyPressEvent().

[virtual] QSize QDialog::minimumSizeHint() const

Reimplemented from QWidget::minimumSizeHint().

[virtual slot] void QDialog::open()

Shows the dialog as a window modal dialog, returning immediately.

This function was introduced in Qt 4.5.

See also exec(), show(), result(), and setWindowModality().

[virtual slot] void QDialog::reject()

Hides the modal dialog and sets the result code to Rejected.

See also accept() and done().

[signal] void QDialog::rejected()

This signal is emitted when the dialog has been rejected either by the user or by calling reject() or done() with the QDialog::Rejected argument.

Note that this signal is not emitted when hiding the dialog with hide() or setVisible(false). This includes deleting the dialog while it is visible.

This function was introduced in Qt 4.1.

See also finished() and accepted().

[virtual protected] void QDialog::resizeEvent(QResizeEvent *)

Reimplemented from QWidget::resizeEvent().

int QDialog::result() const

In general returns the modal dialog's result code, Accepted or Rejected.

Note: When called on a QMessageBox instance, the returned value is a value of the QMessageBox::StandardButton enum.

Do not call this function if the dialog was constructed with the Qt::WA_DeleteOnClose attribute.

See also setResult().

void QDialog::setResult(inti)

Sets the modal dialog's result code to i.

Note: We recommend that you use one of the values defined by QDialog::DialogCode.

See also result().

[virtual] void QDialog::setVisible(boolvisible)

Reimplemented from QWidget::setVisible().

[virtual protected] void QDialog::showEvent(QShowEvent *event)

Reimplemented from QWidget::showEvent().

Qt Slot Return Value

[virtual] QSize QDialog::sizeHint() const

Reimplemented from QWidget::sizeHint().

Qt Signal Slot Return Value

As Qt WebKit is replaced by Qt WebEngine(you can refer to this post about porting issues), accessing html elements from C++ directly becomes impossible. Many works originally done by QWebKit classes are now transferred to javascript. Javascript is used to manipulate web content. And you need to call runJavaScript from C++ code to run javascript on the web page loaded by QWebEngineView.To get web elements, a communication mechanism is invented to bridge the C++ world and the javascript world. The bridging mechanism is more than obtaining the values of web page elements. It provides the ways in which C++ code can call javascript functions, and javascript can invoke C++ functions as well.The values of variables can also be passed from C++ to javascript, and vice versa. Let’s consider the following application scenarios:

javascript code calls C++ function

C++ code should provide a class which contains the to-be-called function(as a slot), then register an object of this class to a QWebChannel object, and set the web channel object to the web page object in the QWebEngineView

To invoke the C++ function jscallme, javascript should new an instance of QWebChannel object.

QWebChannel is defined in qwebchannel.js(you can find this file in the example folder of Qt installation directory) so the script should be loaded first. In the function passed as the second parameter of function QWebChannel, the exposed object from C++ world(webobj in C++) channel.objects.webobj is assigned to the javascript variable webobj, and then assigned to window.foo so you can use foo elsewhere to refer to the object. After the function is executed, javascript can call the C++ slot function jscallme as follows:

Pass data from javascript to C++

We’ve known how to call C++ function from javascript. You should be able to figure out a way to pass data from javascript to C++, i.e., as parameter(s) of function. We re-implement jscallme as follows:

Qt Slot Return Value Guide

, and invoking of the function from js would be:

Note that the “const” before the parameter can not be omitted, otherwise, you will get the following error:
Could not convert argument QJsonValue(string, “sd”) to target type .

Although data can be passed as parameters of function, it would be more convenient if we can pass data by setting an attribute of an object like:

We expect after the code is executed, “somedata” will be stored in a member variable of the exposed object (webobj) in C++. This is done by delaring a qt property in C++ class:

Now if you execute foo.someattribute=”somedata” in javascript, m_someattribute in C++ will be “somedata”.

Pass data from C++ to javascript

We can send data from C++ to javascript using signals. We emit a signal with the data to send as the parameter of the signal. Javascript must connect the signal to a function to receive the data.

The line “webobj.someattributeChanged.connect(updateattribute)” connects the C++ signal someattributeChanged to the javascript function updateattribute. Note that although updateattribute takes one parameter “text”, we did not provide the parameter value in connect. In fact, we do not know the parameter value passed to updateattribute until the signal is received. The signal is accompanied by a parameter “attr” which is passed as the “text” parameter of updateattribute. Now, if you call webobj->setsomeattribute(“hello”), you will see the value of the html element with id “#attrid” is set to “hello”. Note that although we connect the member m_someattribute to the qt property someattribute in the above example, it is not a required step. The signal mechanism alone can realize the delivery of data.
We can make things even simpler by adding the NOTIFY parameter when declaring the someattribute property.

Now, if you call webobj->setProperty(“someattribute”,”hello”) somewhere in C++, the signal “someattributeChanged” is automatically emitted and our web page gets updated.

Qt Slot Return Value Kelley Blue Book

C++ invokes javascript function

This is much straightforward compared with invoking C++ function from js. Just use runJavaScript passing the function as the parameter as follows:

It assumes the jsfun is already defined on your web page, otherwise, you have to define it in the string parameter. The return value is asynchronously passed to the lambda expression as the parameter v.

Now, back to the question raised at the beginning of the post: How to get the value of an html element in C++? It can be done as follows:

It uses jQuery functions so make sure jQuery lib is running on your web page.