Implicit Flutter Animations

Oct 4 2022 Dart 2.17, Flutter 3.0, Visual Studio Code 1.7

Part 2: Implicit Animations in Action

6. Create a Custom PageView Animation

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Previous episode: 5. Animate a Social Share Button Next episode: 7. Create a Card Flip Animation

The student materials have been reviewed and are updated as of August 2022.

The updated material uses null safety and also deploys the use coding practises encouraged by the Flutter as per the Flutter lint rules and a few addons of practises that are considered good here at raywenderlich (see analysis_options.yaml in the material for more info).

Also, the value type passed in the builder parameter of TweenAnimationBuilder is explicitly mentioned otherwise dart assumes the value as generic datatype after the release of Flutter 2.

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In this episode, we would be using implicit animations to affect how the offers slider animates. The offers slider is used inside the homescreen widget. Scroll to it then hold down the ctrl key then click on it to navigate to its file.

int _selectedIndex = 0;
...
onPageChanged: (index) {
    setState(() {
        _selectedIndex = index;
    });
},
...

itemBuilder: (context, index) {
    final offer = offers[index];
    // New Code
    final scale = _selectedIndex == index ? 1.0 : 0.8;
    return TweenAnimationBuilder(
        duration: const Duration(milliseconds: 350),
        curve: Curves.ease,
        tween: Tween(begin: scale, end: scale),
        child: Item(offer: offer),
        builder: (context, value, child) {
            return Transform.scale(
                scale: value,
                child: child,
            );
        },
    );
},

Row(
...
    children: <Widget>[
    for (int i = 0; i < offers.length; i++)
        if (i == _selectedIndex)
            const Indicator(isActive: true)
        else
            const Indicator(isActive: false),
    ],
),

...
return AnimatedContainer(
    duration: const Duration(milliseconds: 350),
...