57 lines
2.0 KiB
Dart
57 lines
2.0 KiB
Dart
// Copyright 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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import 'package:flutter/foundation.dart';
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import 'framework.dart';
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import 'scroll_controller.dart';
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/// Associates a [ScrollController] with a subtree.
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///
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/// When a [ScrollView] has [ScrollView.primary] set to true and is not given
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/// an explicit [ScrollController], the [ScrollView] uses [of] to find the
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/// [ScrollController] associated with its subtree.
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///
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/// This mechanism can be used to provide default behavior for scroll views in a
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/// subtree. For example, the [Scaffold] uses this mechanism to implement the
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/// scroll-to-top gesture on iOS.
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class PrimaryScrollController extends InheritedWidget {
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/// Creates a widget that associates a [ScrollController] with a subtree.
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const PrimaryScrollController({
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Key key,
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@required this.controller,
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@required Widget child
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}) : assert(controller != null),
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super(key: key, child: child);
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/// Creates a subtree without an associated [ScrollController].
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const PrimaryScrollController.none({
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Key key,
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@required Widget child
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}) : controller = null,
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super(key: key, child: child);
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/// The [ScrollController] associated with the subtree.
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final ScrollController controller;
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/// Returns the [ScrollController] most closely associated with the given
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/// context.
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///
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/// Returns null if there is no [ScrollController] associated with the given
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/// context.
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static ScrollController of(BuildContext context) {
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final PrimaryScrollController result = context.inheritFromWidgetOfExactType(PrimaryScrollController);
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return result?.controller;
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}
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@override
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bool updateShouldNotify(PrimaryScrollController old) => controller != old.controller;
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@override
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void debugFillDescription(List<String> description) {
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super.debugFillDescription(description);
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description.add('${controller ?? "no controller"}');
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}
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}
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