问用于StatelessWidget的横条等效
EN

Stack Overflow用户

提问于 2022-11-20 04:23:23

回答 1查看 26关注 0票数 1

创建条时要扩展哪个类？

比如说，我有一个类FooSliver，它返回一个小部件。

class FooSliver extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaybeSliverWidget(...);
  }
}

但是，如果上面的类返回一个非条小部件(即RenderObject )，那么我不能直接在我的代码条中使用这个类。

CustomScrollView(
  slivers: [
    FooSliver(),
  ],
)

那么，我应该扩展哪个sliver类而不是StatelessWidget，以确保始终从它返回一个sliver小部件？

flutter-sliver

flutter

flutter-layout

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回答 1

Stack Overflow用户

回答已采纳

发布于 2022-11-20 05:22:05

您可以创建自定义条。您需要创建一个自定义RenderSliverSingleBoxAdapter和SingleChildRenderObjectWidget

class FooSliver extends SingleChildRenderObjectWidget {
  const FooSliver({super.key, super.child});

  @override
  RenderObject createRenderObject(BuildContext context) => FooRenderSliver();
}

class BarSliver extends SingleChildRenderObjectWidget {
  const BarSliver({super.key, super.child = const Text("Hello from Bar")});

  @override
  RenderObject createRenderObject(BuildContext context) => FooRenderSliver();
}

class FooRenderSliver extends RenderSliverSingleBoxAdapter {
  FooRenderSliver({super.child});

  @override
  void performLayout() {
    /// from  [RenderSliverToBoxAdapter]
    if (child == null) {
      geometry = SliverGeometry.zero;
      return;
    }
    final SliverConstraints constraints = this.constraints;
    child!.layout(constraints.asBoxConstraints(), parentUsesSize: true);
    final double childExtent;
    switch (constraints.axis) {
      case Axis.horizontal:
        childExtent = child!.size.width;
        break;
      case Axis.vertical:
        childExtent = child!.size.height;
        break;
    }
    assert(childExtent != null);
    final double paintedChildSize =
        calculatePaintOffset(constraints, from: 0.0, to: childExtent);
    final double cacheExtent =
        calculateCacheOffset(constraints, from: 0.0, to: childExtent);

    assert(paintedChildSize.isFinite);
    assert(paintedChildSize >= 0.0);
    geometry = SliverGeometry(
      scrollExtent: childExtent,
      paintExtent: paintedChildSize,
      cacheExtent: cacheExtent,
      maxPaintExtent: childExtent,
      hitTestExtent: paintedChildSize,
      hasVisualOverflow: childExtent > constraints.remainingPaintExtent ||
          constraints.scrollOffset > 0.0,
    );
    setChildParentData(child!, constraints, geometry!);
  }
}

并使用类似的

home: Scaffold(
  body: CustomScrollView(
    slivers: [
      FooSliver(
        child: Text("Hi From Foo sliver"),
      ),
      BarSliver()
    ],
  ),
),