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// Copyright 2014 The Flutter 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 '../widgets/framework.dart';
/// Indicates the visual level for a piece of content. Equivalent to `UIUserInterfaceLevel`
/// from `UIKit`.
/// See also:
/// * `UIUserInterfaceLevel`, the UIKit equivalent:
enum CupertinoUserInterfaceLevelData {
/// The level for your window's main content.
/// The level for content visually above [base].
/// Establishes a subtree in which [CupertinoUserInterfaceLevel.of] resolves to
/// the given data.
/// Querying the current elevation status using [CupertinoUserInterfaceLevel.of]
/// will cause your widget to rebuild automatically whenever the [CupertinoUserInterfaceLevelData]
/// changes.
/// If no [CupertinoUserInterfaceLevel] is in scope then the [CupertinoUserInterfaceLevel.of]
/// method will throw an exception, unless the `nullOk` argument is set to true,
/// in which case it returns null.
/// See also:
/// * [CupertinoUserInterfaceLevelData], specifies the visual level for the content
/// in the subtree [CupertinoUserInterfaceLevel] established.
class CupertinoUserInterfaceLevel extends InheritedWidget {
/// Creates a [CupertinoUserInterfaceLevel] to change descendant Cupertino widget's
/// visual level.
const CupertinoUserInterfaceLevel({
Key key,
@required CupertinoUserInterfaceLevelData data,
Widget child,
}) : assert(data != null),
_data = data,
super(key: key, child: child);
final CupertinoUserInterfaceLevelData _data;
bool updateShouldNotify(CupertinoUserInterfaceLevel oldWidget) => oldWidget._data != _data;
/// The data from the closest instance of this class that encloses the given
/// context.
/// You can use this function to query the user interface elevation level within
/// the given [BuildContext]. When that information changes, your widget will
/// be scheduled to be rebuilt, keeping your widget up-to-date.
static CupertinoUserInterfaceLevelData of(BuildContext context, { bool nullOk = false }) {
assert(context != null);
assert(nullOk != null);
final CupertinoUserInterfaceLevel query = context.dependOnInheritedWidgetOfExactType<CupertinoUserInterfaceLevel>();
if (query != null)
return query._data;
if (nullOk)
return null;
throw FlutterError(
'CupertinoUserInterfaceLevel.of() called with a context that does not contain a CupertinoUserInterfaceLevel.\n'
'No CupertinoUserInterfaceLevel ancestor could be found starting from the context that was passed '
'to CupertinoUserInterfaceLevel.of(). This can happen because you do not have a WidgetsApp or '
'MaterialApp widget (those widgets introduce a CupertinoUserInterfaceLevel), or it can happen '
'if the context you use comes from a widget above those widgets.\n'
'The context used was:\n'
' $context'
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
properties.add(EnumProperty<CupertinoUserInterfaceLevelData>('user interface level', _data));