0Pricing
Flutter Mobile Development · 课时

Hero 转场与共享元素运动

协调 Hero 组件和自定义飞行动画，实现精致的屏幕转场。

Hero 转场与共享元素运动 是 CoddyKit 上的免费 Flutter Mobile Development 课时。 这是第 3 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Flutter Mobile Development 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Flutter Mobile Development 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

What Shared Element Motion Means

A Hero transition animates a single widget so it appears to fly from one screen to another during a route push or pop. Instead of the user losing track of an element across screens, the same visual object morphs in place.

  • Think of a thumbnail in a list that expands into a full-screen detail image.
  • Flutter computes the start and end rectangles and tweens the widget between them.
  • This continuity is what designers call shared element motion.

In this lesson you will coordinate Hero widgets and customize the flight shuttle that actually renders during the in-between frames.

The Hero Widget Contract

To create a Hero animation you wrap the source and destination widgets in a Hero widget and give both the same tag. The tag is how Flutter pairs them across routes.

  • Tags must be unique per screen but identical between the two screens.
  • If two Heroes on the same screen share a tag, Flutter throws an assertion at navigation time.

Below, a product thumbnail on the list screen uses the product id as its tag.

Hero(
  tag: 'product-${product.id}',
  child: Image.network(
    product.thumbnailUrl,
    width: 80,
    height: 80,
    fit: BoxFit.cover,
  ),
)

Matching the Destination Hero

The detail screen must wrap its large image in a Hero with the exact same tag. When you push the detail route, Flutter detects both Heroes and starts the flight automatically.

  • The child widgets do not have to be identical — only the tag must match.
  • Here the destination is a full-width image, while the source was an 80x80 thumbnail.
Hero(
  tag: 'product-${product.id}',
  child: Image.network(
    product.imageUrl,
    width: double.infinity,
    height: 320,
    fit: BoxFit.cover,
  ),
)

How Tags Drive Pairing

During a route transition Flutter scans both the outgoing and incoming routes for Heroes, then builds a map keyed by tag. Only tags present on both routes animate; an unmatched Hero simply fades with its page.

Because tags are matched by equality, you can use any object as a tag — strings, ints, or enums — as long as == and hashCode behave correctly.

bool heroesMatch(Object tagA, Object tagB) {
  return tagA == tagB;
}

void main() {
  print(heroesMatch('product-7', 'product-7')); // true -> flies
  print(heroesMatch('product-7', 'product-9')); // false -> fades
  print(heroesMatch(42, 42));                    // true
}

The Default Flight Shuttle

The widget rendered during the flight is called the flight shuttle. By default Flutter uses the destination Hero's child for the entire flight, cross-fading where needed.

This works well when the two children look alike. But when the source and destination have very different shapes — for example a square avatar becoming a rounded banner — the default can look like an abrupt swap. That is when you supply a custom flightShuttleBuilder.

Customizing the Flight Shuttle

The flightShuttleBuilder lets you control exactly what is painted mid-flight. Its signature gives you the animation, the direction (push or pop), and both Hero contexts.

  • flightDirection is HeroFlightDirection.push or .pop.
  • Return any widget; it will be positioned inside the interpolated rectangle for you.

Here we rotate the child slightly as it flies to add polish.

Hero(
  tag: 'product-${product.id}',
  flightShuttleBuilder: (
    BuildContext flightContext,
    Animation<double> animation,
    HeroFlightDirection direction,
    BuildContext fromContext,
    BuildContext toContext,
  ) {
    return RotationTransition(
      turns: Tween<double>(begin: 0, end: 0.05).animate(animation),
      child: toContext.widget,
    );
  },
  child: Image.network(product.imageUrl, fit: BoxFit.cover),
)

Cross-Fading Between Two Children

A common shuttle pattern is cross-fading from the source child to the destination child so the morph reads smoothly. You can drive a FadeTransition from the same flight animation.

  • On push, fade the source out and the destination in.
  • On pop, reverse the roles using flightDirection.
Widget buildShuttle(
  BuildContext flightContext,
  Animation<double> animation,
  HeroFlightDirection direction,
  BuildContext fromContext,
  BuildContext toContext,
) {
  final Widget fromHero = (fromContext.widget as Hero).child;
  final Widget toHero = (toContext.widget as Hero).child;
  final bool isPush = direction == HeroFlightDirection.push;
  return Stack(
    fit: StackFit.expand,
    children: [
      FadeTransition(
        opacity: Tween<double>(begin: isPush ? 1 : 0, end: isPush ? 0 : 1)
            .animate(animation),
        child: fromHero,
      ),
      FadeTransition(
        opacity: Tween<double>(begin: isPush ? 0 : 1, end: isPush ? 1 : 0)
            .animate(animation),
        child: toHero,
      ),
    ],
  );
}

Shaping the Flight Path

By default the Hero moves along a straight line. You can bend that path with createRectTween, which controls how the bounding rectangle is interpolated.

Material's MaterialRectArcTween gives a curved, more natural arc — the same motion Material Design recommends for shared element transitions.

import 'package:flutter/material.dart';

RectTween arcTween(Rect? begin, Rect? end) {
  return MaterialRectArcTween(begin: begin, end: end);
}

// Usage on the Hero:
// Hero(
//   tag: 'product-7',
//   createRectTween: arcTween,
//   child: ...,
// )

Avoiding Tag Collisions in Lists

The most frequent Hero bug is a duplicate tag on a single screen. In a ListView of items, every Hero needs a tag unique to its data row.

  • Never use a constant string like 'hero' for all items.
  • Derive the tag from a stable identity such as the model id.

This helper guarantees uniqueness when building list rows.

String heroTagFor(String screen, Object id) {
  return '$screen::$id';
}

void main() {
  final ids = [1, 2, 2, 3];
  final tags = <String>{};
  for (final id in ids) {
    final tag = heroTagFor('list', id);
    if (!tags.add(tag)) {
      print('Collision on $tag');
    } else {
      print('OK $tag');
    }
  }
}

Wrapping Heroes in Material

When a Hero's child has elevation, rounded corners, or ink — like a Card or Material surface — the flight can show clipped or square corners because the in-flight widget is detached from its original ancestors.

Wrap the shuttle (or the children) in a Material with type: MaterialType.transparency so text, shadows, and clipping render correctly mid-flight.

Hero(
  tag: 'card-${item.id}',
  flightShuttleBuilder: (ctx, anim, dir, from, to) {
    return Material(
      type: MaterialType.transparency,
      child: (to.widget as Hero).child,
    );
  },
  child: Material(
    type: MaterialType.transparency,
    child: ProductCard(item: item),
  ),
)

Coordinating Hero with Rive

In this track we pair Hero transitions with Rive animations for richer motion. A clean approach is to let the Hero handle position and size, while a Rive state machine plays a micro-animation on arrival.

  • Drive a Rive SMITrigger when the destination route finishes its transition.
  • Use animation.addStatusListener on the flight to fire the trigger at AnimationStatus.completed.

Keep the Hero shuttle simple; let Rive own the expressive part so the two systems do not fight over the same frames.

void fireOnArrival(Animation<double> animation, void Function() onArrived) {
  animation.addStatusListener((status) {
    if (status == AnimationStatus.completed) {
      onArrived(); // e.g. riveTrigger.fire();
    }
  });
}

Quick Check

You have a grid of avatars; tapping one pushes a profile screen. The avatar is a 56x56 circle, and the destination is a 200-tall rounded banner. The default flight looks like an abrupt swap and the corners flicker square during motion. Which combination best fixes this?

Recap

You now know how to build polished shared element transitions:

  • Matching tags on source and destination Heroes drive the pairing; tags must be unique per screen and identical across screens.
  • The flight shuttle is what renders mid-flight; customize it with flightShuttleBuilder to cross-fade differing children.
  • Wrap shuttle content in a transparent Material to keep shadows, text, and rounded corners correct.
  • Bend the path with createRectTween and MaterialRectArcTween for a natural arc.
  • Let Hero own position and hand expressive micro-motion to a Rive state machine, fired on AnimationStatus.completed.

Combine these to make screen changes feel continuous and intentional.

常见问题解答

「Hero 转场与共享元素运动」课时是免费的吗？

是的 — 「Hero 转场与共享元素运动」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Flutter Mobile Development 课程的其余内容，请升级到 CoddyKit PRO。 Flutter Mobile Development 课程共包含 4 节课。

「Hero 转场与共享元素运动」这节课中我会学到什么？

协调 Hero 组件和自定义飞行动画，实现精致的屏幕转场。 你通过在浏览器中直接运行的动手代码来练习 Flutter Mobile Development，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Flutter Mobile Development 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Flutter Mobile Development 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 3 节课，共 4 节。

「Hero 转场与共享元素运动」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 Flutter Mobile Development 课中编写并运行代码吗？

能。每节 Flutter Mobile Development 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

此课程中的所有课时

  1. 嵌入 Rive 资源与控制器
  2. 状态机与输入驱动的运动
  3. Hero 转场与共享元素运动
  4. 交错动画与编排式 AnimationControllers
← 返回 Flutter Mobile Development