AnimatedSwitcher class

A widget that by default does a FadeTransition between a new widget and the widget previously set on the AnimatedSwitcher as a child.

If they are swapped fast enough (i.e. before duration elapses), more than one previous child can exist and be transitioning out while the newest one is transitioning in.

If the "new" child is the same widget type and key as the "old" child, but with different parameters, then AnimatedSwitcher will not do a transition between them, since as far as the framework is concerned, they are the same widget and the existing widget can be updated with the new parameters. To force the transition to occur, set a Key on each child widget that you wish to be considered unique (typically a ValueKey on the widget data that distinguishes this child from the others).

The same key can be used for a new child as was used for an already-outgoing child; the two will not be considered related. (For example, if a progress indicator with key A is first shown, then an image with key B, then another progress indicator with key A again, all in rapid succession, then the old progress indicator and the image will be fading out while a new progress indicator is fading in.)

Sample code

class ClickCounter extends StatefulWidget {
  const ClickCounter({Key key}) : super(key: key);

  @override
  _ClickCounterState createState() => _ClickCounterState();
}

class _ClickCounterState extends State<ClickCounter> {
  int _count = 0;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Material(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            AnimatedSwitcher(
              duration: const Duration(milliseconds: 500),
              transitionBuilder: (Widget child, Animation<double> animation) {
                return ScaleTransition(child: child, scale: animation);
              },
              child: Text(
                '$_count',
                // This key causes the AnimatedSwitcher to interpret this as a "new"
                // child each time the count changes, so that it will begin its animation
                // when the count changes.
                key: ValueKey<int>(_count),
                style: Theme.of(context).textTheme.display1,
              ),
            ),
            RaisedButton(
              child: const Text('Increment'),
              onPressed: () {
                setState(() {
                  _count += 1;
                });
              },
            ),
          ],
        ),
      ),
    );
  }
}

See also:

Inheritance

Constructors

AnimatedSwitcher({Key key, Widget child, @required Duration duration, Curve switchInCurve: Curves.linear, Curve switchOutCurve: Curves.linear, AnimatedSwitcherTransitionBuilder transitionBuilder: AnimatedSwitcher.defaultTransitionBuilder, AnimatedSwitcherLayoutBuilder layoutBuilder: AnimatedSwitcher.defaultLayoutBuilder })
Creates an AnimatedSwitcher. [...]
const

Properties

child Widget
The current child widget to display. If there was a previous child, then that child will be faded out using the switchOutCurve, while the new child is faded in with the switchInCurve, over the duration. [...]
final
duration Duration
The duration of the transition from the old child value to the new one. [...]
final
layoutBuilder AnimatedSwitcherLayoutBuilder
A function that wraps all of the children that are transitioning out, and the child that's transitioning in, with a widget that lays all of them out. This is called every time this widget is built. The function must not return null. [...]
final
switchInCurve Curve
The animation curve to use when transitioning in a new child. [...]
final
switchOutCurve Curve
The animation curve to use when transitioning a previous child out. [...]
final
transitionBuilder AnimatedSwitcherTransitionBuilder
A function that wraps a new child with an animation that transitions the child in when the animation runs in the forward direction and out when the animation runs in the reverse direction. This is only called when a new child is set (not for each build), or when a new transitionBuilder is set. If a new transitionBuilder is set, then the transition is rebuilt for the current child and all previous children using the new transitionBuilder. The function must not return null. [...]
final
hashCode int
The hash code for this object. [...]
read-only, inherited
key Key
Controls how one widget replaces another widget in the tree. [...]
final, inherited
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited

Methods

createState() → _AnimatedSwitcherState
Creates the mutable state for this widget at a given location in the tree. [...]
override
createElement() StatefulElement
Creates a StatefulElement to manage this widget's location in the tree. [...]
inherited
debugDescribeChildren() List<DiagnosticsNode>
Returns a list of DiagnosticsNode objects describing this node's children. [...]
@protected, inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void
Add additional properties associated with the node. [...]
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
inherited
toDiagnosticsNode({String name, DiagnosticsTreeStyle style }) DiagnosticsNode
Returns a debug representation of the object that is used by debugging tools and by toStringDeep. [...]
inherited
toString({DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns a string representation of this object.
inherited
toStringDeep({String prefixLineOne: '', String prefixOtherLines, DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns a string representation of this node and its descendants. [...]
inherited
toStringShallow({String joiner: ', ', DiagnosticLevel minLevel: DiagnosticLevel.debug }) String
Returns a one-line detailed description of the object. [...]
inherited
toStringShort() String
A short, textual description of this widget.
inherited

Operators

operator ==(dynamic other) bool
The equality operator. [...]
inherited

Static Methods

defaultLayoutBuilder(Widget currentChild, List<Widget> previousChildren) Widget
The layout builder used as the default value of layoutBuilder. [...]
defaultTransitionBuilder(Widget child, Animation<double> animation) Widget
The transition builder used as the default value of transitionBuilder. [...]