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