- Qt 6.9
- Qt Quick
- QML Types
- Behavior
- Qt 6.9.0 Reference Documentation

# Behavior QML Type

Defines a default animation for a property change. More...

Import Statement: | `import QtQuick`

- List of all members, including inherited members

## Properties

- animation : Animation
- enabled : bool
- targetProperty `(since QtQuick 2.15)`
  - targetProperty.name : string `(since QtQuick 2.15)`
  - targetProperty.object : QtObject `(since QtQuick 2.15)`
- targetValue : Variant `(since QtQuick 2.13)`

## Detailed Description

A Behavior defines the default animation to be applied whenever a particular property value changes.

For example, the following Behavior defines a NumberAnimation to be run whenever the Rectangle's `width` value changes. When the MouseArea is clicked, the `width` is changed, triggering the behavior's animation:

     import QtQuick

     Rectangle {
         id: rect
         width: 100; height: 100
         color: "red"

         Behavior on width {
             NumberAnimation { duration: 1000 }
         }

         MouseArea {
             anchors.fill: parent
             onClicked: rect.width = 50
         }
     }

Note that a property cannot have more than one assigned Behavior. To provide multiple animations within a Behavior, use ParallelAnimation or SequentialAnimation.

If a state change has a Transition that matches the same property as a Behavior, the Transition animation overrides the Behavior for that state change. For general advice on using Behaviors to animate state changes, see Using Qt Quick Behaviors with States.

See also Animation and Transitions in Qt Quick, Behavior example, and Qt Qml.

## Property Documentation

animation : Animation `[default]`

This property holds the animation to run when the behavior is triggered.

enabled : bool

This property holds whether the behavior will be triggered when the tracked property changes value.

By default a Behavior is enabled.

targetProperty group
targetProperty.name : string `[read-only, since QtQuick 2.15]`
targetProperty.object : QtObject `[read-only, since QtQuick 2.15]`

Property | Description
--- | ---
name | This property holds the name of the property being controlled by this Behavior.
object | This property holds the object of the property being controlled by this Behavior.

This property can be used to define custom behaviors based on the name or the object of the property being controlled.

The following example defines a Behavior fading out and fading in its target object when the property it controls changes:

     // FadeBehavior.qml
     import QtQuick 2.15

     Behavior {
         id: root
         property Item fadeTarget: targetProperty.object
         SequentialAnimation {
             NumberAnimation {
                 target: root.fadeTarget
                 property: "opacity"
                 to: 0
                 easing.type: Easing.InQuad
             }
             PropertyAction { } // actually change the controlled property between the 2 other animations
             NumberAnimation {
                 target: root.fadeTarget
                 property: "opacity"
                 to: 1
                 easing.type: Easing.OutQuad
             }
         }
     }

This can be used to animate a text when it changes:

     import QtQuick 2.15

     Text {
         id: root
         property int counter
         text: counter
         FadeBehavior on text {}
         Timer {
             running: true
             repeat: true
             interval: 1000
             onTriggered: ++root.counter
         }
     }

This QML property was introduced in QtQuick 2.15.

targetValue : Variant `[read-only, since QtQuick 2.13]`

This property holds the target value of the property being controlled by the Behavior. This value is set by the Behavior before the animation is started.

This property was introduced in QtQuick 2.13.