QT knowledge: QT widgets widget class [01]

One 、 summary

         because QWidget Class itself contains attributes 、 Many methods , And we often use this class , So I'm going to open a series to introduce this class a little .
1、QWidget Is the most basic interface

Its basic function is ：

• Receive the mouse from the window system 、 Keyboard and other events ,
• Draw your own representation on the screen .
• The basic shapes are rectangular , They press Z Order .
• A widget is clipped by its parent widget and the widget before it .

2、 Widget without parent window QWidget It's called a window . General properties ：

• Windows have borders
• The title bar
• Geometry

3、QWidget Some properties of are not used directly , But it can be implemented in its inherited descendants .

for example ,QWidget There is a font attribute , But never use it . Instead, it is used by its subclasses .

4、 When implementing a new widget , Overload the following functions ：

• sizeHint() Provide a reasonable default size for widgets .
• Use setSizePolicy() It is useful to set the correct size policy .
• The size policy provides a good default behavior for the layout management system .
• The default size policy indicates size The prompt indicates the preferred size of the widget .

5、 Widgets respond to events that are usually caused by user actions .

Qt By using... That contains information about each event QEvent Subclass instances call specific event handlers , Pass events to the widget to be handled by the widget .

6、QWidget Use double buffering to draw , So there's no need to be in paintEvent() Write double buffered code to avoid flickering .

Two 、 Enum type members

Today is about QWidget Class has a unique enumeration value RenderFlag. At the end of the article, the matching method will be introduced ：

• QWidget::render() Method to render the widget QWidget
• QWidget::setMask() Method .

DrawWindowBackground： If this option is enabled , Even if... Is not set autoFillBackground, The background of the widget is also rendered to the target . By default , This option is enabled .
DrawChildren： If this option is enabled , Then the widget QWidget The children of will be rendered recursively into the target . By default , This option is enabled .
IgnoreMask： If this option is enabled , The widget's... Will be ignored when rendered to the target QWidget::mask(). By default , This option is disabled .

3、 ... and 、 Static attribute members

1、acceptDrops : bool   --    Accept drag and drop Events . The default is false.

2、accessibleDescription : QString --  Description of the widget . The description should provide relatively detailed widget information . The default is an empty string .

3、accessibleName : QString -- The name of the part shown in the auxiliary reading . For most widgets , There is no need to set this property . When the widget does not provide any text , Setting this property is very important . The default is an empty string .

4、autoFillBackground : bool -- Whether to automatically fill the widget background . The default is false.

If enabled , This attribute will result in Qt Fill the background of the widget before calling the draw event . The colors used are determined by the... In the widget palette QPalette::Window Of color Role definition . Besides , Unless set WA_OpaquePaintEvent or WA_NoSystemBackground attribute , Otherwise, the window always uses QPalette::Window fill . If the widget's parent has a static gradient background , You cannot disable this property .

When the widget has a style sheet with a valid background or border image , This property will be automatically disabled .

5、baseSize : QSize  -- The basic size of the widget . If the widget defines sizeIncrement attribute , Use the base size to calculate the appropriate widget size . The default value is QSize(0,0).

6、childrenRect : QRect --  The border of the widget sub object . Does not contain hidden child objects .

By default , For widgets without children , This property contains a rectangle with zero width and height at the origin .

7、childrenRegion : QRegion -- The crop region occupied by the child of the widget . Does not contain hidden child objects .

By default , For widgets without children , This attribute contains an empty area .

8、contextMenuPolicy : Qt::ContextMenuPolicy -- Menu policy （QWidget Menu policy ：Qt::ContextMenuPolicy）.

9、cursor : QCursor --  Mouse style . If the mouse is not set , Or calling unsetCursor() after , Will use the parent's mouse . By default , This property contains a with Qt::ArrowCursor style （ arrow ） The mouse .

10、enabled : bool  --  Is it available . The default is true.

Generally speaking , Enabled widgets handle keyboard and mouse events , Disabled widgets do not handle （QAbstractButton exception ）. Some widgets display differently when disabled . for example , The button may draw its label in gray .

If the widget needs to know when it is enabled or disabled , You can use the type QEvent::EnabledChange Of changeEvent().

Disabling a widget implicitly disables all its children , Enable will enable all child widgets , Unless they have been explicitly disabled . When the parent widget remains disabled , It is not possible to explicitly enable child widgets that are not window types .

11、focus : bool --  Whether there is keyboard input focus . The default is false.

12、focusPolicy : Qt::FocusPolicy -- Focus strategy （QWidget Focus strategy ：Qt::FocusPolicy）.

13、font : QFont -- typeface （QFont Detailed explanation ）.

14、frameGeometry : QRect

15、frameSize : QSize --frameGeometry() The width and height of , See above .

16、fullScreen : bool  -- Whether the status is displayed in full screen .

17、geometry : QRect -- See above .

18、height : int / width : int / x : int / y : int -- See above .

19、inputMethodHints : Qt::InputMethodHints  --  Input prompt for input type part .

This is only relevant for input widgets . Input methods use it to retrieve tips about how the input method should operate . for example , If set Qt::ImhFormattedNumbersOnly sign , The IME may change its visual components to reflect that only numbers can be entered .

Be careful ： The sign is just a reminder , Therefore, specific ime implementations are free to ignore them . If you want to make sure you enter a certain type of character , You should also set... On the widget QValidator. see TextEdit.

To set a flag , Please perform ：

w->setInputMethodHints(w->inputMethodHints()|f);
instead of ：

w->setInputMethodHints(f);
22、​isActiveWindow : bool  -- Whether the widget's window is active . An active window is a window that contains widgets with keyboard focus .

21、layoutDirection : Qt::LayoutDirection --QWidget On layout() The layout direction of .（Qt： Layout direction ）

22、locale : QLocale -- Area （ practical QLocale）.

23、maximized : const bool / minimized : const bool  Whether it is currently maximized / Minimized .

24、maximumHeight : int

       maximumWidth : int

       maximumSize : QSize

Maximum height / Width /size（ Pixel values ）, Maximum height / The default value for width is 16777215.

25、minimumHeight : int

       minimumWidth : int

Minimum height / Width . The default value is 0.

26、minimumSize : QSize

Minimum size. The default is (0,0). The minimum size set by this property will override QLayout Minimum size defined .

27、minimumSizeHint : QSize

Tips for minimum size of layout manager .

When QWidget No layout is set （ namely layout() == nullptr） when , Returns an invalid value （QSize(-1,-1)）.
Otherwise return to layout() Minimum size of （ And layout The subassemblies in and layout The spacing of the ）.
28、modal : bool

Whether the modal part .

29、mouseTracking : bool.

Whether to enable mouse tracking . The default is false.

If mouse tracking is disabled , The widget only receives mouse movement events when at least one mouse button is pressed while the mouse is moving .
If mouse tracking is enabled , Even if no button is pressed , The widget also receives mouse movement events .
30、normalGeometry : const QRect.

When QWidget As a top-level widget Geometry().
Returns null when treated as a subassembly QRect().
31、palette : QPalette

palette （ practical QPalette）. You cannot match a palette with Qt Use with style sheets .

32、pos : QPoint

The position of the widget within its parent widget . If the widget is a window , Its location is the location of the widget on the desktop （ See above ）.

Change position ：

The widget （ If visible ） Will immediately receive a mobile event （moveEvent()）.
If not currently visible , Then a move event will be received before the display .
By default , This property contains a position pointing to the origin .

stay moveEvent() Call in move() or setGeometry() May result in infinite recursion .

33、rect : QRect

be equal to QRect(0,0,width(),height()). See above .

34、size : QSize

be equal to QSize(width(),height()).

If the widget is visible while resizing , It will immediately receive a resizing event （resizeEvent()）.
If the widget is not currently visible , An event will be received before the display .
If the size exceeds that specified by minimumSize() and maximumSize() Defined scope , It will be adjusted . The default value of this attribute depends on the user's platform and screen geometry .

stay resizeEvent() Call in resize() or setGeometry() May result in infinite recursion .

Set the size to QSize(0,0) Will cause the widget not to appear on the screen .

35、sizeHint : QSize

and minimumSizeHint be similar .layout() Null returns an invalid value , Otherwise return to layout() Recommended size .

The following is a good way to write ：

resize(this->sizeHint());
36、sizeIncrement : QSize

Save the increment of widget size .

When the user resizes the window , The size will be in the horizontal direction in sizeIncrement().width() Pixels and vertical direction in sizeIncrement.height() Pixel by pixel , With baseSize() Based on . The preferred widget size applies to non negative integers i and j：

width = baseSize().width() + i * sizeIncrement().width();
height = baseSize().height() + j * sizeIncrement().height();
Although you can set the size increment for all widgets , But it only affects windows .

By default , This property contains the size with zero width and height .

37、sizePolicy : QSizePolicy

Size strategy （QSizePolicy Detailed explanation ）.

38、statusTip : QString

When the mouse is over the control, a prompt message is displayed in the status bar of the window , If the window has no status bar, it does not display .

39、styleSheet : QString

Style sheets , See ：https://blog.csdn.net/kenfan1647/category_10854729.html 

40、tabletTracking : bool

Whether to enable digital board tracking .

If you disable （ default setting ） When you move the pen , The widget receives tablet movement events only when the stylus contacts the tablet or at least one of the stylus buttons is pressed .

If enabled , Even if you hover the mouse nearby , Widgets also receive tablet movement events .

41、toolTip : QString

The tool tip . By default , Show tooltips only for child widgets of the active window . If you want to control the behavior of tooltips , You can capture QEvent::ToolTip event . By default , This property contains an empty string .

42、toolTipDuration : int

Tooltip display time for widget （ Company ： millisecond ）. If the value is -1（ The default value is ）, The duration is calculated according to the length of the tooltip .

43、updatesEnabled : bool        【 Be careful 】

Whether to enable update . If update is disabled , Call update() and repaint() Invalid . The default is true.

Disabling a widget implicitly disables all its children . Enabling widgets enables all child widgets except the top-level widget or all child widgets that have been explicitly disabled . Re enabling updates implicitly invokes... On the widget update().

setUpdatesEnabled() Usually used to disable updates for a short period of time , for example , Avoid screen flickering when making large changes .

  setUpdatesEnabled(false);
  bigVisualChanges();
  setUpdatesEnabled(true);
44、visible : bool

Whether the widget is visible .

When the visibility state of the control changes , It receives show and hide Events . Between hiding events and showing Events , No waste CPU Cycle to prepare or display information to the user .

Widgets that are obscured by other windows on the screen are considered visible .

A spontaneous hidden event occurs when the user minimizes the window , And a spontaneous display event occurs when the window is restored again .

45、whatsThis : QString

Of components “What's This” Help text messages . The default is empty. .

46、windowFilePath : QString

The file path associated with the widget . It associates the file path with the window . If the file path is set , But the window title has not been set , be Qt Will set the window title to use QFileInfo::fileName() Gets the file name of the specified path .

    setWindowFilePath(QStringLiteral("D:\\ Study OPenCV3.pdf"));

47、windowFlags : Qt::WindowFlags

Window sign .

When changing the window's flag , Will call setParent(), This causes the widget to be hidden . Must call show() To make the widget visible again .

48、windowIcon : QIcon

Widget icon . If no icon is set , be windowIcon() Return to the application icon （QApplication::windowIcon()）.

49、windowModality : Qt::WindowModality

Window modal type . The default is Qt::NonModal.

Qt::Window This attribute is only meaningful for widgets of type .

It is invalid to change this property when the window is visible , Must first hide() The widget , And then again show().

Qt::NonModal： Modeless .
Qt::WindowModal： Mode of a single window hierarchy , Block input to its parent window 、 All grandparent windows 、 All peer windows of its parent window and grandparent window .
Qt::ApplicationModal： Application mode , Block input from all windows .
50、windowOpacity : double

The opacity level of the window . The effective range of opacity is 1.0（ Completely opaque ） To 0.0（ Completely transparent ）. By default , The value of this property is 1.0.

Warning ： Changing this property from not transparent to transparent may cause a paint event , You need to process the window correctly to display the window correctly . This mainly affects QScreen::grabWindow() Use . Also pay attention to , Translucent windows are much slower to update and resize than opaque windows .

51、windowTitle : QString

Window title . This property is only available for top-level widgets （ Such as windows and dialog boxes ） meaningful . If no title is set , Then the title is based on windowFilePath. If none of them are set , The title is an empty string .

（ To be continued ）