1// Copyright (C) 2021 The Qt Company Ltd.
2// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
7\brief An introduction to the basic concepts and features of QML.
8\nextpage QML Tutorial 1 - Value Types
10This tutorial gives an introduction to QML, the language for Qt Quick UIs. It doesn't cover everything;
11the emphasis is on teaching the key principles, and features are introduced as needed.
13Through the different steps of this tutorial we will learn about QML value types, we will create our own QML component
14with properties and signals, and we will create a simple animation with the help of states and transitions.
16Chapter one starts with a minimal "Hello world" program and the following chapters introduce new concepts.
18The tutorial's source code is located in the \c{examples/quick/tutorials/helloworld} directory.
23\li \l {QML Tutorial 1 - Value Types}{Value Types}
24\li \l {QML Tutorial 2 - QML Components}{QML Components}
25\li \l {QML Tutorial 3 - States and Transitions}{States and Transitions}
31\page qml-tutorial1.html
32\title QML Tutorial 1 - Value Types
33\previouspage QML Tutorial
34\nextpage QML Tutorial 2 - QML Components
36This first program is a very simple "Hello world" example that introduces some basic QML concepts.
37The picture below is a screenshot of this program.
39\image declarative-tutorial1.png
41Here is the QML code for the application:
43\snippet tutorials/helloworld/tutorial1.qml 0
49First, we need to import the types that we need for this example. Most QML files will import the built-in QML
50types (like \l{Rectangle}, \l{Image}, ...) that come with Qt, using:
52\snippet tutorials/helloworld/tutorial1.qml 3
54\section2 Rectangle Type
56\snippet tutorials/helloworld/tutorial1.qml 1
58We declare a root object of type \l{Rectangle}. It is one of the basic building blocks you can use to create an application in QML.
59We give it an \c{id} to be able to refer to it later. In this case, we call it "page".
60We also set the \c width, \c height and \c color properties.
61The \l{Rectangle} type contains many other properties (such as \c x and \c y), but these are left at their default values.
65\snippet tutorials/helloworld/tutorial1.qml 2
67We add a \l Text type as a child of the root Rectangle type that displays the text 'Hello world!'.
69The \c y property is used to position the text vertically at 30 pixels from the top of its parent.
71The \c anchors.horizontalCenter property refers to the horizontal center of an type.
72In this case, we specify that our text type should be horizontally centered in the \e page element (see \l{anchor-layout}{Anchor-Based Layout}).
74The \c font.pointSize and \c font.bold properties are related to fonts and use the dot notation.
77\section2 Viewing the Example
79To view what you have created, run the
80\l{Prototyping with the QML Runtime Tool}{qml tool} (located in the
81\c bin directory) with your filename as the first argument. For example, to run
82the provided completed Tutorial 1 example from the install location, you would type:
85qml tutorials/helloworld/tutorial1.qml
90\page qml-tutorial2.html
91\title QML Tutorial 2 - QML Components
92\previouspage QML Tutorial 1 - Value Types
93\nextpage QML Tutorial 3 - States and Transitions
95This chapter adds a color picker to change the color of the text.
97\image declarative-tutorial2.png
99Our color picker is made of six cells with different colors.
100To avoid writing the same code multiple times for each cell, we create a new \c Cell component.
101A component provides a way of defining a new type that we can re-use in other QML files.
102A QML component is like a black-box and interacts with the outside world through properties, signals and functions and is generally
103defined in its own QML file. (For more details, see the \l Component documentation).
104The component's filename must always start with a capital letter.
106Here is the QML code for \c Cell.qml:
108\snippet tutorials/helloworld/Cell.qml 0
112\section2 The Cell Component
114\snippet tutorials/helloworld/Cell.qml 1
116The root type of our component is an \l Item with the \c id \e container.
117An \l Item is the most basic visual type in QML and is often used as a container for other types.
119\snippet tutorials/helloworld/Cell.qml 4
121We declare a \c cellColor property. This property is accessible from \e outside our component, this allows us
122to instantiate the cells with different colors.
123This property is just an alias to an existing property - the color of the rectangle that compose the cell
124(see \l{Property Binding}).
126\snippet tutorials/helloworld/Cell.qml 5
128We want our component to also have a signal that we call \e clicked with a \e cellColor parameter of type \e color.
129We will use this signal to change the color of the text in the main QML file later.
131\snippet tutorials/helloworld/Cell.qml 2
133Our cell component is basically a colored rectangle with the \c id \e rectangle.
135The \c anchors.fill property is a convenient way to set the size of a visual type.
136In this case the rectangle will have the same size as its parent (see \l{anchor-layout}{Anchor-Based Layout}).
138\snippet tutorials/helloworld/Cell.qml 3
140In order to change the color of the text when clicking on a cell, we create a \l MouseArea type with
141the same size as its parent.
143A \l MouseArea defines a signal called \e clicked.
144When this signal is triggered we want to emit our own \e clicked signal with the color as parameter.
146\section2 The Main QML File
148In our main QML file, we use our \c Cell component to create the color picker:
150\snippet tutorials/helloworld/tutorial2.qml 0
152We create the color picker by putting 6 cells with different colors in a grid.
154\snippet tutorials/helloworld/tutorial2.qml 1
156When the \e clicked signal of our cell is triggered, we want to set the color of the text to the \e cellColor passed as a parameter.
157We can react to any signal of our component through a property of the name \e 'onSignalName' (see \l{Signal Attributes}).
161\page qml-tutorial3.html
162\title QML Tutorial 3 - States and Transitions
163\previouspage QML Tutorial 2 - QML Components
165In this chapter, we make this example a little bit more dynamic by introducing states and transitions.
167We want our text to move to the bottom of the screen, rotate and become red when clicked.
169\image declarative-tutorial3_animation.gif
173\snippet tutorials/helloworld/tutorial3.qml 0
177\snippet tutorials/helloworld/tutorial3.qml 2
179First, we create a new \e down state for our text type.
180This state will be activated when the \l MouseArea is pressed, and deactivated when it is released.
182The \e down state includes a set of property changes from our implicit \e {default state}
183(the items as they were initially defined in the QML).
184Specifically, we set the \c y property of the text to \c 160, the rotation to \c 180 and the \c color to red.
186\snippet tutorials/helloworld/tutorial3.qml 3
188Because we don't want the text to appear at the bottom instantly but rather move smoothly,
189we add a transition between our two states.
191\c from and \c to define the states between which the transition will run.
192In this case, we want a transition from the default state to our \e down state.
194Because we want the same transition to be run in reverse when changing back from the \e down state to the default state,
195we set \c reversible to \c true.
196This is equivalent to writing the two transitions separately.
198The \l ParallelAnimation type makes sure that the two types of animations (number and color) start at the same time.
199We could also run them one after the other by using \l SequentialAnimation instead.
201For more details on states and transitions, see \l {Qt Quick States} and the
202\l{Qt Quick Examples - Animation#States}{states and transitions example}.