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Writing Reusable QML Components - Avnee Nathani


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These slides are from my talk - "Writing Reusable QML Components" at - KDE INDIA Conference at DAIICT, Gandhinagar
QML is a declarative language used to design and develop the application user interface. While developing UI one needs to maintain design consistency and code redundancy. Writing reusable components is one such way to do this. The practice to develop reusable components make efficient developers who write less buggy code. It saves coding time and efforts. Reusable components such as buttons and lists provide the end user with a consistent look and performance.

The presentation covers the basic techniques to implement such custom QML components.

Also, the presentation would cover how to use these custom components in your projects with example from KDE Game - KDiamond.

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Writing Reusable QML Components - Avnee Nathani

  1. 1. Reusable QML Components Avnee Nathani @AvneeNathani
  2. 2. About me… ● Avnee Nathani ● Post-graduate student of Computer applications ● Open-source enthusiast ● Nokia Developer Champion (2012, 2013) ● Qt Ambassador (2011) What do I work on? ● Qt Projects ( ● KDE Games (KDiamond) ● Mobile applications (Windows Phone, Android) ● Research on Handwriting recognition (
  3. 3. Agenda ● QML application development in brief ● QML basic components ● Need for custom QML components ● Custom components in KDiamond game ● Demo – Creating custom UI components ● Writing QML components ● ‘Reusability’ is the key when designing ● Importing Reusable components ● Conclusion
  4. 4. What does Qt Quick offer? ● Qt Quick = QML UI Creation Kit ● New way to create Qt User Interfaces ● ● ● QML works on UI, Qt helps with backend code implementation Declarative language: “QML” - CSS & JavaScript like syntax Supports states and transitions
  5. 5. QML Basic Components • Rectangle (basic component, holds other components) • Image • BorderImage • Text • ListView These are some of the primary components. Complex components are built by grouping primary components e.g. List with attributes such as icon, name and description
  6. 6. QML Basic Components Rectangle Rectangle { width: 100 height: 100 color: "red" border.color: "black" border.width: 5 radius: 10 } Shows the effects of some of the common properties on a Rectangle item, which in this case is used to create a square
  7. 7. QML Basic Components - Images Image { source: "pics/borderframe.png" } An unscaled image is displayed using an Image. A BorderImage is used to display the image, and it is given a size that is larger than the original image. BorderImage { width: 180 height: 180 border { left: 30; top: 30; right: 30; bottom: 30 } source: "pics/borderframe.png" }
  8. 8. QML Basic Components - Text Text items can display both plain and rich text. Red text with a specific font and size Text { text: "Hello World!" "Helvetica" font.pointSize: 24 color: "red” } Rich text is defined using HTML-style markup Text { text: "<b>Hello</b> <i>World!</i>" }
  9. 9. QML Basic Components - ListView A ListView has a model, which defines the data to be displayed, and a delegate, which defines how the data should be displayed. Displays data from models created from built-in QML types like ListModel and XmlListModel, or custom model classes defined in C++ ListView with Model and Delegate ListView { width: 180; height: 200 model: contactModel delegate: Text { text: name + ": " + number } Model for the list view - ListModel ListModel { id: contactModel ListElement { name: ”Avnee" number: ”876 5432" } ListElement { name: ”Neha" number: ”345 8426" } } … }
  10. 10. Need for custom QML components What is a custom QML component? A custom component is essentially a QML document that defines a single QML component that you can use in an application. Even though Qt Quick 2.0 comes with lots of useful controls right out of the box, you will likely come to a point where you must create your own custom components. For example, in your QML applications, you may need to use custom Dialog boxes, prompts, toasts, notifications, buttons, labels, etc. Custom – in terms of look and feel Custom – in terms of functionality
  11. 11. Custom components in KDiamond KDiamond is a single player puzzle game. The object of the game is to build lines of three similar diamonds. Some of the custom QML components used, • Buttons • List Dialog • Popup Dialog • Quit Dialog
  12. 12. Custom components in KDiamond List Dialog: A list dialog provides a dialog box with a list of items to choose from. Basically, a dialog that prompts for one element out of a list of elements. Fig: ListDialog for selecting Difficulty Level Fig: Screenshot of ListDailog in KDiamond
  13. 13. Custom components in KDiamond Popup Dialog: A popup is used to show small info or notifications to the user. Fig: Screenshot of pause game popup in KDiamond
  14. 14. Custom components in KDiamond Quit Dialog: Quit Dialog is a component which is a used to ask for confirmation before exiting an application or a game. Fig: Using quit dialog in KDiamond
  15. 15. Demo – Creating custom UI components Lets create some simple custom UI components! This is a line edit | Custom Line Edit Custom Button ListDialog from KDiamond
  16. 16. Custom Button Basic functionality, • Triggers an event on clicking • Allows a text caption Image{ id: buttonbase width: caption.width + 10 height: caption.height + 20 signal clicked property bool pressed: mousearea.pressed property alias buttonText: caption.text property string buttonPressed: buttonbase.source property string buttonReleased : buttonbase.source source: pressed ? buttonPressed : buttonReleased Text { id: caption color: "white" text: buttonText font.pointSize: 12 font.bold: true anchors.centerIn: parent } Update MouseArea { id: mousearea anchors.fill: parent onClicked: parent.clicked() } }
  17. 17. Writing QML components Summarizing basic steps to create custom QML components • Create a .qml for the component. File name needs to start with a capital letter. For e.g. ‘Button.qml’ • Define the component UI • Define the interactions Import and use this component in your applications. Make them reusable…
  18. 18. Reusability is the key If everyone keeps writing the same components, there would be too many versions of such components. • Expose the component properties using property alias. This allows customization of components. For example, allow to change the color, background image, text caption of a Button component by property alias. • Make your components public Share the components with the community, put them on github if possible. Others can fork them and make them more versatile. Remember, reusability is the key when writing custom components.
  19. 19. Questions?