Qt 5.13 | Use Case - Responding To User Input in QML

Qt 5.13.2 Reference Documentation

# Use Case - Responding To User Input in QML

## Supported types of user input

The Qt Quick module provides support for the most common types of user input, including mouse and touch events, text input, and key-press events. Other modules provide support for other types of user input for example, the Qt Sensors module provides support for shake-gestures in QML applications.

This article covers how to handle basic user input; for further information about motion-gesture support, see the Qt Sensors documentation. For information about audio-visual input, see the Qt Multimedia documentation.

### Mouse and touch events

The input handlers let QML applications handle mouse and touch events. For example, you could create a button by adding a TapHandler to an Image, or to a Rectangle with a Text object inside. The TapHandler responds to taps or clicks on any type of pointing device.

      import QtQuick 2.12

      Item {
          id: root

          width: 320
          height: 480

          Rectangle {
              color: "#272822"
              width: 320
              height: 480
          }

          Rectangle {
              id: rectangle
              x: 40
              y: 20
              width: 120
              height: 120
              color: "red"

              TapHandler {
                  onTapped: rectangle.width += 10
              }
          }
      }

For more advanced use cases such as, drag, pinch and zoom gestures, see documentation for the DragHandler and PinchHandler types.

Note: Some types have their own built-in input handling. For example, Flickable responds to mouse dragging and mouse wheel scrolling. It handles touch dragging and flicking via synthetic mouse events that are created when the touch events are not handled.

### Keyboard and button events

Button and key presses, from buttons on a device, a keypad, or a keyboard, can all be handled using the Keys attached property. This attached property is available on all Item derived types, and works with the Item::focus property to determine which type receives the key event. For simple key handling, you can set the focus to true on a single Item and do all your key handling there.

      import QtQuick 2.3

      Item {
          id: root

          width: 320
          height: 480

          Rectangle {
              color: "#272822"
              width: 320
              height: 480
          }

          Rectangle {
              id: rectangle
              x: 40
              y: 20
              width: 120
              height: 120
              color: "red"

              focus: true
              Keys.onUpPressed: rectangle.y -= 10
              Keys.onDownPressed: rectangle.y += 10
              Keys.onLeftPressed: rectangle.x += 10
              Keys.onRightPressed: rectangle.x -= 10
          }
      }

For text input, we have several QML types to choose from. TextInput provides an unstyled single-line editable text, while TextField is more suitable for form fields in applications. TextEdit can handle multi-line editable text, but TextArea is a better alternative as it adds styling.

The following snippet demonstrates how to use these types in your application:

      import QtQuick 2.12
      import QtQuick.Controls 2.4
      import QtQuick.Layouts 1.3

      ApplicationWindow {
          width: 300
          height: 200
          visible: true

          ColumnLayout {
              anchors.fill: parent
              TextField {
                  id: singleline
                  text: "Initial Text"
                  Layout.alignment: Qt.AlignHCenter | Qt.AlignTop
                  Layout.margins: 5
                  background: Rectangle {
                     implicitWidth: 200
                     implicitHeight: 40
                     border.color: singleline.focus ? "#21be2b" : "lightgray"
                     color: singleline.focus ? "lightgray" : "transparent"
                  }
              }

              TextArea {
                  id: multiline
                  placeholderText: "Initial text\n...\n...\n"
                  Layout.alignment: Qt.AlignLeft
                  Layout.fillWidth: true
                  Layout.fillHeight: true
                  Layout.margins: 5
                  background: Rectangle {
                     implicitWidth: 200
                     implicitHeight: 100
                     border.color: multiline.focus ? "#21be2b" : "lightgray"
                     color: multiline.focus ? "lightgray" : "transparent"
                  }
              }
          }
      }