Subclassing QWidget in Visual C#

Create ECC200 in Visual C# Subclassing QWidget

Subclassing QWidget
Draw ECC200 In Visual C#.NET
Using Barcode encoder for VS .NET Control to generate, create Data Matrix image in .NET framework applications.
www.OnBarcode.com
Read Data Matrix In C#.NET
Using Barcode scanner for VS .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
To begin, your custom widget needs to implement QWidget and include the Q_OBJECT declaration. Listing 5 1 shows a trivial example:
2D Generation In Visual C#
Using Barcode generator for .NET framework Control to generate, create Matrix Barcode image in .NET framework applications.
www.OnBarcode.com
QR Code 2d Barcode Generator In C#
Using Barcode creator for .NET Control to generate, create QR Code JIS X 0510 image in .NET applications.
www.OnBarcode.com
Listing 5 1. A trivial widget class MyWidget : public QWidget { Q_OBJECT public: explicit MyWidget (QWidget *parent = 0) : QWidget(parent) {} protected: void paintEvent(QPaintEvent *) { QPainter painter(this); painter.setPen(Qt::blue); painter.setFont(QFont("Arial", 18)); painter.drawText(rect(), Qt::AlignCenter, "Hello world"); } private: Q_DISABLE_COPY(MyWidget) };
Print USS Code 128 In Visual C#
Using Barcode encoder for .NET framework Control to generate, create Code 128A image in .NET framework applications.
www.OnBarcode.com
Draw PDF-417 2d Barcode In C#
Using Barcode generation for .NET Control to generate, create PDF 417 image in .NET applications.
www.OnBarcode.com
CHAPTER 5: Doing More with Qt
GS1 - 13 Generator In C#
Using Barcode generator for .NET Control to generate, create EAN-13 Supplement 5 image in .NET applications.
www.OnBarcode.com
USPS Confirm Service Barcode Encoder In Visual C#
Using Barcode creator for .NET Control to generate, create Planet image in .NET applications.
www.OnBarcode.com
This widget simply paints the message Hello World at its origin. It does, however, demonstrate the basic requirements you must fulfill to provide your own widget: Your custom widget must inherit QWidget. Like any QObject-based class, your widget must include the Q_OBJECT declaration in its class definition. Your custom widget implements its functionality by overriding parent methods in QWidget. As you ll see in the section Handling Incoming Events later in the chapter, many of these methods are event handlers for specific Qt-based events passed to your widget. Instances of widgets are best thought of as unique objects, and thus can t be copied. To prevent the compiler from including default copy constructors for your widget, use the Q_DISABLE_COPY macro in private declarations in your class to ensure that the copy constructors for your widget remain private.
Reading ECC200 In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Data Matrix Drawer In Objective-C
Using Barcode encoder for iPad Control to generate, create DataMatrix image in iPad applications.
www.OnBarcode.com
Specifying Your Widget s Size Hints and Policies
QR Code Decoder In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
EAN / UCC - 13 Recognizer In Visual C#
Using Barcode scanner for .NET framework Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
Previously you ve learned about Qt s system of layouts, which let you specify how widgets arrange themselves in a container. A key part of the layout system is how widgets indicate their size preference and policies to the layout manager. They communicate this using two methods: sizeHint and sizePolicy. The sizeHint method provides a hint to the layout manager how big the widget would like to be. It returns a QSize, which has width and height member functions to provide the dimensions, along with an isValid function that indicates whether the size is valid or not. (It also has convenience methods for performing arithmetic on sizes, including scaling a size to fit within a predetermined width and height.) How the layout system interprets the sizeHint depends on the sizePolicy, which can have the following values for each of the horizontal and vertical axes: When the value is QSizePolicy::Fixed, the sizeHint-returned value is the only acceptable alternative, so the widget can never grow or shrink. When the value is QSizePolicy::Minimum, the sizeHint-returned value is minimal and sufficient. The widget can be expanded, but there is no advantage to it being larger. When the value is QSizePolicy::Maximum, the sizeHint-returned value is a maximum, and the widget can be shrunk if other widgets require the space. When the value is QSizePolicy::Preferred, the sizeHint-returned value is best, but the widget can be shrunk or expanded and still be useful.
EAN128 Creation In None
Using Barcode creator for Microsoft Excel Control to generate, create GS1-128 image in Office Excel applications.
www.OnBarcode.com
Recognize UPC - 13 In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
CHAPTER 5: Doing More with Qt
Barcode Reader In C#.NET
Using Barcode decoder for .NET framework Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
Create Barcode In VS .NET
Using Barcode creator for Reporting Service Control to generate, create Barcode image in Reporting Service applications.
www.OnBarcode.com
When the value is QSizePolicy::Expanding, the sizeHint-returned value is a sensible size, but the widget should get as much space as possible. When the value is QSizePolicy::MinimumExpanding, the sizeHintreturned value is minimal and sufficient. The widget can make use of extra space, so it should get as much space as possible. When the value is QSizePolicy::Ignored, the sizeHint-returned value is ignored and the widget be made as large as possible. The widget returns these values when the layout invokes sizePolicy, which returns a QSizePolicy instance. Of course, you can override a specific widget s desired horizontal or vertical size policy by calling setSizePolicy. But in general when creating your own widget, it s easier to override sizePolicy altogether. Expanding our previous example, Listing 5 2 shows what we might write, with the methods you ve already seen elided for brevity.
Barcode Maker In None
Using Barcode creation for Word Control to generate, create Barcode image in Microsoft Word applications.
www.OnBarcode.com
GS1 - 12 Recognizer In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Listing 5 2. Handling size preferences in a custom widget class MyWidget : public QWidget { Q_OBJECT public: explicit MyWidget (QWidget *parent = 0) QSize sizeHint() { return QSize(80, 60); } QSizePolicy sizePolicy() { return QSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::MinimumExpanding); } protected: void paintEvent(QPaintEvent *event) private: Q_DISABLE_COPY(MyWidget) };
Paint Data Matrix In VB.NET
Using Barcode creation for VS .NET Control to generate, create DataMatrix image in .NET applications.
www.OnBarcode.com
Data Matrix 2d Barcode Encoder In Java
Using Barcode drawer for Java Control to generate, create Data Matrix 2d barcode image in Java applications.
www.OnBarcode.com
A widget with these methods would start small, filling a rectangle 80 pixels wide and 60 pixels tall, and grow to fit whatever space the layout could provide.
Copyright © OnBarcode.com . All rights reserved.