Flutter-Bounty-Hunters/follow_the_leader

Follow the Leader - Widgets following widgets

Built by the Flutter Bounty Hunters

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Getting Started

Select a widget that you want to follow and wrap it with a Leader widget. Give the Leader widget a LeaderLink, to share with Followers.

Leader(
  link: _leaderLink,
  child: YourLeaderWidget(),
);

Add a widget that you want to follow your Leader, and wrap it with a Follower widget.

// Follower appears 20px above the Leader.
Follower.withOffset(
  link: _leaderLink,
  offset: const Offset(0, -20),
  leaderAnchor: Alignment.topCenter,
  followerAnchor: Alignment.bottomCenter,
  child: YourFollowerWidget(),
);

Follower's can position themselves with a constant distance from a Leader using .withOffset(), as shown above. Or, Follower's can choose their exact location on every frame by using .withAligner().

// Follower appears where the aligner says it should.
Follower.withAligner(
  link: _leaderLink,
  aligner: _aligner,
  child: YourFollowerWidget(),
);

To constrain where your Follower is allowed to appear, pass a boundary to your Follower.

// Follower is constrained by the given boundary.
Follower.withAligner(
  link: _leaderLink,
  aligner: _aligner,
  boundary: _boundary,
  child: YourFollowerWidget(),
);

Building multiple widgets without layouts

Building follower widgets is a bit unusual with Flutter. Typically, whenever we build multiple widgets in Flutter, we place them in a layout container, such as Column, Row, or Stack. But follower widgets don't respect ancestor layout rules. That's the whole point.

follow_the_leader introduces a new container widget, which builds children, but doesn't attempt to apply any particular layout rules. The primary purpose of this widget is to make it clear to readers that you aren't trying to layout the children.

BuildInOrder(
  children: [
    MyContentWithALeader(),
    Follower.withOffset(),
    Follower.withDynamics(),
  ],
);

The BuildInOrder widget builds each child widget in the order that it's provided. This fact is important because Leader widgets must be built before their Followers. But BuildInOrder does not impose any Offset on its children. BuildInOrder passes its parent's constraints down to the children.