Flutter Animated Series : Animated Containers

Published in

Flutter Community

4 min readJan 23, 2019

I always wanted to work with neat or crazy animations. I have worked with Android for a couple of years and I was starting to lose my love for animations, because trying to develop them in Android was a huge investment of my time.

Enter Flutter!

And I have fallen in love again.

To celebrate this newfound love, I am starting an Animated Series for Flutter.

YES It’s a SERIES!

I am going to cover everything about animation in Flutter from implicit animations to explicit animations and even Flare! This is the first one in the series.

Animated Containers

Animated Containers are implicit animated widgets.

Wait a second. What are implicit animated widgets again?

So usually to achieve an animation in Flutter, we have to define the Animation and AnimationController objects to manage the animations. There are other complex additions like TickerProviderMixin. You have to manually start the animation, end the animation and various other complexities.

But good news for us, implicit animated widgets have all these logic under the hood, and we don’t have to worry about a thing. Give a duration, define the beginning and end values and let your widgets animaaate!

Example 1 — Bar Charts

Imagine you have to build an application with bar graphs. So there can be a container with increasing or decreasing height depending on the graph values.

Let’s imagine the initial height of your Container is 40.0
var height = 40.0;

And then your Container will be like —

Container(
    width: 60.0,
    height: height,
    color: Color(0xff14ff65),
  ),

And now suppose you have a Button and in the onPressed method, you can change the height of the Container and setState() to rebuild the UI.

onPressed: (){
  setState(() {
    height = 320.0;
  });
},

But sadly, we have this following output.

There is no smooth transition when we change the height values. So this looks weird for a bar chart application.

We want the bar to gradually increase with time.

Let’s see if we can achieve our desired effect with AnimatedContainer.

Let’s see some magic!

Replace your ordinary Container with AnimatedContainer and provide a Duration property and see the magic happen!

AnimatedContainer(
  duration: Duration(seconds: 5),
  width: 60.0,
  height: height,
  color: Color(0xff14ff65),
)

One widget replacement and one extra line of code, and voila! You are animating a Container now!

I showed this example during my DevFest BBSR and DevFest Kolkata talks, and in minutes, Flutter was sold to my audience.

Example 2 — Take Flight

Obviously you can animate the usual Container properties like color, height, and width . But you can also animate a Container’s child, like using the alignment property to align a Container’s child.

Container’s child is an Icon .

Alignment property affects the child of a Container

The initial alignment is Alignment.bottomCenter

On clicking the button, we change the alignment to Alignment.center

And the airplane flies right to the center of the screen!

You can find the entire working code here —

Example 3 — Playing with lots of colors!

Not one color, but many colors. We are going to animate the gradient property of the Container .

Here I defined just two colors and their initial alignment and changed both the properties on setState() .

Code here —

That’s it.

What else do we have in the Animated Series ?

AnimatedContainers
AnimatedOpacity
AnimatedCrossFade (Coming soon)
And many more…

Read the Spanish translation by CarlosMillan here —

Serie Flutter Animated: Containers Animados

Fuente original: https://medium.com/flutter-community/flutter-animated-series-animated-containers-52a5d52c0ad3

medium.com

Read the Portuguese translation by Pedro Massango here —

Série animada do Flutter: Containers Animados

Mais um artigo da série de artigos sobre Flutter em Português. Desta vez temos um artigo originalmente escrito por…