Qt: 窗口的显示和隐藏

隐藏窗口

1. hide()

Hides the widget.

This function is equivalent to setVisible(false).

Note: If you are working with QDialog or its subclasses and you invoke the show() function after this function, the dialog will be displayed in its original position.

2. setVisible(false)

Calling setVisible(false) or hide() hides a widget explicitly.

An explicitly hidden widget will never become visible, even if all its ancestors become visible, unless you show it.

3. lower()

Lowers the widget to the bottom of the parent widget’s stack.

After this call the widget will be visually behind (and therefore obscured by) any overlapping sibling widgets.

4. close()

Closes this widget.

Returns true if the widget was closed; otherwise returns false.

First it sends the widget a QCloseEvent. The widget is hidden if it accepts the close event. If it ignores the event, nothing happens. The default implementation of QWidget::closeEvent() accepts the close event.

If the widget has the Qt::WA_DeleteOnClose(widget attribute, which is set and cleared with void QWidget::setAttribute(Qt::WidgetAttribute attribute, bool on = true)) flag, the widget is also deleted. (the difference with hide())

this->setAttribute(Qt::WA_DeleteOnCLose, true);

A close events is delivered to the widget no matter if the widget is visible or not.

The QApplication::lastWindowClosed() signal is emitted when the last visible primary window (i.e. window with no parent) with the Qt::WA_QuitOnClose attribute set is closed. By default this attribute is set for all widgets except transient windows such as splash screens, tool windows, and popup menus.

5. hideEvent()

This event handler is called with the given event when Qt receives a window close request for a top-level widget from the window system.

By default, the event is accepted and the widget is closed.

You can reimplement this function to change the way the widget responds to window close requests. For example, you can prevent the window from closing by calling ignore() on all events.

  void MainWindow::closeEvent(QCloseEvent *event)
  {
      if (maybeSave()) {
          writeSettings();
          event->accept();
      } else {
          event->ignore();
      }
  }

 

显示窗口

1. show()

Shows the widget and its child widgets.

This is equivalent to calling showFullScreen(), showMaximized(), or setVisible(true), depending on the platform’s default behavior for the window flags.

2. setVisible(true)

Calling setVisible(true) or show() sets the widget to visible status if all its parent widgets up to the window are visible.

If an ancestor is not visible, the widget won’t become visible until all its ancestors are shown.

If its size or position has changed, Qt guarantees that a widget gets move and resize events just before it is shown.

If the widget has not been resized yet, Qt will adjust the widget’s size to a useful default using adjustSize().

A widget that happens to be obscured by other windows on the screen is considered to be visible.

3. raise()

Raises this widget to the top of the parent widget’s stack.

After this call the widget will be visually in front of any overlapping sibling widgets.

4. exec()

 int QDialog::exec()

Shows the dialog as a modal dialog, blocking until the user closes it.

The function returns a DialogCode result.

QDialog::Accepted 1

QDialog::Rejected 0

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.

用法

当需要一直显示一个窗口时，用 exec()，不同于 show()，exec() 显示的只能是 模态窗口，且只要去关闭窗口，操作权会一直在该窗口，开启事件循环，直到关闭该窗口。

关闭窗口常用函数有：
1、accept()

void QDialog::accept()

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

该函数只隐藏窗口，并不删除窗口，并设置返回值为 Accepted。

2、reject()

void QDialog::reject()

Hides the modal dialog and sets the result code to Rejected.
该函数同样隐藏窗口，并返回值 Rejected。

3、done(int r)

 void QDialog::done(int r)

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.

该函数 close 窗口，窗口会隐藏，是否删除取决于是否设置 Qt::WA_DeleteOnClose 。且该函数可以自己设置返回值。

这样可以利用返回值做出相应判断，如显示一个需要根据用户选择而决定下一步操作的对话框，如有三个选项：A， B， C，可以根据不同选择用 done() 函数设置不同返回值，从而进行不同处理。

4、setResult(int i)

void QDialog::setResult(int i)

Sets the modal dialog’s result code to i.

5. showEvent() ?

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

This event handler can be reimplemented in a subclass to receive widget show events which are passed in the event parameter.

Non-spontaneous show events are sent to widgets immediately before they are shown.

The spontaneous show events of windows are delivered afterwards.

Note: A widget receives spontaneous show and hide events when its mapping status is changed by the window system, e.g. a spontaneous hide event when the user minimizes the window, and a spontaneous show event when the window is restored again.

After receiving a spontaneous hide event, a widget is still considered visible in the sense of isVisible(). (why???)