Animating using AnimatedPositioned Flutter widget

Introduction

AnimatedPositioned widget is the animated version of the Positioned widget.

In this article, we'll see how AnimatedPositioned widget is used to animate an image in it. We'll observe animation behavior for various types of curves.

Target Audience: Beginner

Recipe: Animating an image in AnimatedPositioned widget.

Focus Widget: AnimatedPositioned

Goal: Animate an image inside AnimatedPositioned using various types given AnimationCurves

AnimationCurves:

Checkout YouTube video:

Structure of AnimatedPositioned widget

AnimatedPositioned uses duration and curve properties to animate from previous position to a new position. The duration value controls how long animation would take whereas curve property's value provides the type of animation Curve

AnimatedPositioned(
      width: selected ? 400.0 : 200.0,
      height: selected ? 200.0 : 400.0,
      duration: Duration(seconds: 2),
      curve: dropDownValue != null ? dropDownValue.curveCubic : Curves.linear,
      child: Image.asset('assets/images/sea.jpg'),
    ),

Recipe's Code Structure

I'm using a drop down to choose the different type of curve. Animation curves used in this code recipe are available in the source code as well as here.

AnimatedPositioned needs to be implemented inside a StatefulWidget since it can only animate when position is changed.

AnimationCurve dropDownValue holds the current selection from the AnimationCurves drop down widget.

class AnimatedPositionedDemo extends StatefulWidget {
  @override
  _AnimatedPositionedDemoState createState() => _AnimatedPositionedDemoState();
}

class _AnimatedPositionedDemoState extends State<AnimatedPositionedDemo> {
  AnimationCurve dropDownValue;
  bool selected = false;

  ...
}  

Boolean selected keeps track of when 'Animate' button is pressed or image is touched.

'Animate' button next to dropDown widget. It updates the value of selected as below:

Widget playAnimation(BuildContext context) {
  return RaisedButton(
    color: Colors.blueAccent,
    child: Text("Animate"),
    onPressed: () => setState(() {
      selected = !selected;
    }),
  );
}

Implementing AnimatedPositioned widget

AnimatedPositioned widget's default position or width / height are 200.0 and 400.0 respectively. When user presses 'Animate' button for a selected Curve type in dropDown widget, position or width and height are updated to 400.0 and 200.0 respectively. AnimatedPositioned updates its position to a new value with in 2 seconds as provided in duration attribute using current selection for curve property.

Widget animatedPositionedWidget(BuildContext context) {
  return AnimatedPositioned(
    width: selected ? 400.0 : 200.0,
    height: selected ? 200.0 : 400.0,
    duration: Duration(seconds: 2),
    curve: dropDownValue != null ? dropDownValue.curveCubic : Curves.linear,
    child: Image.asset('assets/images/sea.jpg'),
  );
}

I encourage you to Checkout the code below, and play around with different types of Curve animations to pick an animation that would work best for you.

Source code repo

1. AnimatedPositioned code recipe is available here
2. Source code for all other animation code recipes is available here

References:

1. AnimatedPositioned
2. Animation Curves

Happy cooking with Flutter :)

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