1// Copyright 2014 The Flutter Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5/// @docImport 'package:flutter/material.dart';
6/// @docImport 'package:flutter/rendering.dart';
7/// @docImport 'package:flutter/scheduler.dart';
8///
9/// @docImport 'binding.dart';
10/// @docImport 'widget_inspector.dart';
11library;
12
13import 'dart:collection';
14import 'dart:developer' show Timeline; // to disambiguate reference in dartdocs below
15
16import 'package:flutter/foundation.dart';
17
18import 'basic.dart';
19import 'framework.dart';
20import 'localizations.dart';
21import 'lookup_boundary.dart';
22import 'media_query.dart';
23import 'overlay.dart';
24import 'table.dart';
25
26// Examples can assume:
27// late BuildContext context;
28// List children = [];
29// List items = [];
30
31// Any changes to this file should be reflected in the debugAssertAllWidgetVarsUnset()
32// function below.
33
34/// Log the dirty widgets that are built each frame.
35///
36/// Combined with [debugPrintBuildScope] or [debugPrintBeginFrameBanner], this
37/// allows you to distinguish builds triggered by the initial mounting of a
38/// widget tree (e.g. in a call to [runApp]) from the regular builds triggered
39/// by the pipeline.
40///
41/// Combined with [debugPrintScheduleBuildForStacks], this lets you watch a
42/// widget's dirty/clean lifecycle.
43///
44/// To get similar information but showing it on the timeline available from
45/// Flutter DevTools rather than getting it in the console (where it can be
46/// overwhelming), consider [debugProfileBuildsEnabled].
47///
48/// See also:
49///
50/// * [WidgetsBinding.drawFrame], which pumps the build and rendering pipeline
51/// to generate a frame.
52bool debugPrintRebuildDirtyWidgets = false;
53
54/// Signature for [debugOnRebuildDirtyWidget] implementations.
55typedef RebuildDirtyWidgetCallback = void Function(Element e, bool builtOnce);
56
57/// Callback invoked for every dirty widget built each frame.
58///
59/// This callback is only invoked in debug builds.
60///
61/// See also:
62///
63/// * [debugPrintRebuildDirtyWidgets], which does something similar but logs
64/// to the console instead of invoking a callback.
65/// * [debugOnProfilePaint], which does something similar for [RenderObject]
66/// painting.
67/// * [WidgetInspectorService], which uses the [debugOnRebuildDirtyWidget]
68/// callback to generate aggregate profile statistics describing which widget
69/// rebuilds occurred when the
70/// `ext.flutter.inspector.trackRebuildDirtyWidgets` service extension is
71/// enabled.
72RebuildDirtyWidgetCallback? debugOnRebuildDirtyWidget;
73
74/// Log all calls to [BuildOwner.buildScope].
75///
76/// Combined with [debugPrintScheduleBuildForStacks], this allows you to track
77/// when a [State.setState] call gets serviced.
78///
79/// Combined with [debugPrintRebuildDirtyWidgets] or
80/// [debugPrintBeginFrameBanner], this allows you to distinguish builds
81/// triggered by the initial mounting of a widget tree (e.g. in a call to
82/// [runApp]) from the regular builds triggered by the pipeline.
83///
84/// See also:
85///
86/// * [WidgetsBinding.drawFrame], which pumps the build and rendering pipeline
87/// to generate a frame.
88bool debugPrintBuildScope = false;
89
90/// Log the call stacks that mark widgets as needing to be rebuilt.
91///
92/// This is called whenever [BuildOwner.scheduleBuildFor] adds an element to the
93/// dirty list. Typically this is as a result of [Element.markNeedsBuild] being
94/// called, which itself is usually a result of [State.setState] being called.
95///
96/// To see when a widget is rebuilt, see [debugPrintRebuildDirtyWidgets].
97///
98/// To see when the dirty list is flushed, see [debugPrintBuildScope].
99///
100/// To see when a frame is scheduled, see [debugPrintScheduleFrameStacks].
101bool debugPrintScheduleBuildForStacks = false;
102
103/// Log when widgets with global keys are deactivated and log when they are
104/// reactivated (retaken).
105///
106/// This can help track down framework bugs relating to the [GlobalKey] logic.
107bool debugPrintGlobalKeyedWidgetLifecycle = false;
108
109/// Adds [Timeline] events for every Widget built.
110///
111/// The timing information this flag exposes is not representative of the actual
112/// cost of building, because the overhead of adding timeline events is
113/// significant relative to the time each object takes to build. However, it can
114/// expose unexpected widget behavior in the timeline.
115///
116/// In debug builds, additional information is included in the trace (such as
117/// the properties of widgets being built). Collecting this data is
118/// expensive and further makes these traces non-representative of actual
119/// performance. This data is omitted in profile builds.
120///
121/// For more information about performance debugging in Flutter, see
122/// <https://docs.flutter.dev/perf/ui-performance>.
123///
124/// See also:
125///
126/// * [debugPrintRebuildDirtyWidgets], which does something similar but
127/// reporting the builds to the console.
128/// * [debugProfileLayoutsEnabled], which does something similar for layout,
129/// and [debugPrintLayouts], its console equivalent.
130/// * [debugProfilePaintsEnabled], which does something similar for painting.
131/// * [debugProfileBuildsEnabledUserWidgets], which adds events for user-created
132/// [Widget] build times and incurs less overhead.
133/// * [debugEnhanceBuildTimelineArguments], which enhances the trace with
134/// debugging information related to [Widget] builds.
135bool debugProfileBuildsEnabled = false;
136
137/// Adds [Timeline] events for every user-created [Widget] built.
138///
139/// A user-created [Widget] is any [Widget] that is constructed in the root
140/// library. Often [Widget]s contain child [Widget]s that are constructed in
141/// libraries (for example, a [TextButton] having a [RichText] child). Timeline
142/// events for those children will be omitted with this flag. This works for any
143/// [Widget] not just ones declared in the root library.
144///
145/// See also:
146///
147/// * [debugProfileBuildsEnabled], which functions similarly but shows events
148/// for every widget and has a higher overhead cost.
149/// * [debugEnhanceBuildTimelineArguments], which enhances the trace with
150/// debugging information related to [Widget] builds.
151bool debugProfileBuildsEnabledUserWidgets = false;
152
153/// Adds debugging information to [Timeline] events related to [Widget] builds.
154///
155/// This flag will only add [Timeline] event arguments for debug builds.
156/// Additional arguments will be added for the "BUILD" [Timeline] event and for
157/// all [Widget] build [Timeline] events, which are the [Timeline] events that
158/// are added when either of [debugProfileBuildsEnabled] and
159/// [debugProfileBuildsEnabledUserWidgets] are true. The debugging information
160/// that will be added in trace arguments includes stats around [Widget] dirty
161/// states and [Widget] diagnostic information (i.e. [Widget] properties).
162///
163/// See also:
164///
165/// * [debugProfileBuildsEnabled], which adds [Timeline] events for every
166/// [Widget] built.
167/// * [debugProfileBuildsEnabledUserWidgets], which adds [Timeline] events for
168/// every user-created [Widget] built.
169/// * [debugEnhanceLayoutTimelineArguments], which does something similar for
170/// events related to [RenderObject] layouts.
171/// * [debugEnhancePaintTimelineArguments], which does something similar for
172/// events related to [RenderObject] paints.
173bool debugEnhanceBuildTimelineArguments = false;
174
175/// Show banners for deprecated widgets.
176bool debugHighlightDeprecatedWidgets = false;
177
178Key? _firstNonUniqueKey(Iterable<Widget> widgets) {
179 final Set<Key> keySet = HashSet<Key>();
180 for (final Widget widget in widgets) {
181 if (widget.key == null) {
182 continue;
183 }
184 if (!keySet.add(widget.key!)) {
185 return widget.key;
186 }
187 }
188 return null;
189}
190
191/// Asserts if the given child list contains any duplicate non-null keys.
192///
193/// To invoke this function, use the following pattern:
194///
195/// ```dart
196/// class MyWidget extends StatelessWidget {
197/// MyWidget({ super.key, required this.children }) {
198/// assert(!debugChildrenHaveDuplicateKeys(this, children));
199/// }
200///
201/// final List<Widget> children;
202///
203/// // ...
204/// }
205/// ```
206///
207/// If specified, the `message` overrides the default message.
208///
209/// For a version of this function that can be used in contexts where
210/// the list of items does not have a particular parent, see
211/// [debugItemsHaveDuplicateKeys].
212///
213/// Does nothing if asserts are disabled. Always returns false.
214bool debugChildrenHaveDuplicateKeys(Widget parent, Iterable<Widget> children, {String? message}) {
215 assert(() {
216 final Key? nonUniqueKey = _firstNonUniqueKey(children);
217 if (nonUniqueKey != null) {
218 throw FlutterError(
219 "${message ?? 'Duplicate keys found.\n'
220 'If multiple keyed widgets exist as children of another widget, they must have unique keys.'}"
221 '\n$parent has multiple children with key $nonUniqueKey.',
222 );
223 }
224 return true;
225 }());
226 return false;
227}
228
229/// Asserts if the given list of items contains any duplicate non-null keys.
230///
231/// To invoke this function, use the following pattern:
232///
233/// ```dart
234/// assert(!debugItemsHaveDuplicateKeys(items));
235/// ```
236///
237/// For a version of this function specifically intended for parents
238/// checking their children lists, see [debugChildrenHaveDuplicateKeys].
239///
240/// Does nothing if asserts are disabled. Always returns false.
241bool debugItemsHaveDuplicateKeys(Iterable<Widget> items) {
242 assert(() {
243 final Key? nonUniqueKey = _firstNonUniqueKey(items);
244 if (nonUniqueKey != null) {
245 throw FlutterError('Duplicate key found: $nonUniqueKey.');
246 }
247 return true;
248 }());
249 return false;
250}
251
252/// Asserts that the given context has a [Table] ancestor.
253///
254/// Used by [TableRowInkWell] to make sure that it is only used in an appropriate context.
255///
256/// To invoke this function, use the following pattern, typically in the
257/// relevant Widget's build method:
258///
259/// ```dart
260/// assert(debugCheckHasTable(context));
261/// ```
262///
263/// Always place this before any early returns, so that the invariant is checked
264/// in all cases. This prevents bugs from hiding until a particular codepath is
265/// hit.
266///
267/// This method can be expensive (it walks the element tree).
268///
269/// Does nothing if asserts are disabled. Always returns true.
270bool debugCheckHasTable(BuildContext context) {
271 assert(() {
272 if (context.widget is! Table && context.findAncestorWidgetOfExactType<Table>() == null) {
273 throw FlutterError.fromParts(<DiagnosticsNode>[
274 ErrorSummary('No Table widget found.'),
275 ErrorDescription('${context.widget.runtimeType} widgets require a Table widget ancestor.'),
276 context.describeWidget('The specific widget that could not find a Table ancestor was'),
277 context.describeOwnershipChain('The ownership chain for the affected widget is'),
278 ]);
279 }
280 return true;
281 }());
282 return true;
283}
284
285/// Asserts that the given context has a [MediaQuery] ancestor.
286///
287/// Used by various widgets to make sure that they are only used in an
288/// appropriate context.
289///
290/// To invoke this function, use the following pattern, typically in the
291/// relevant Widget's build method:
292///
293/// ```dart
294/// assert(debugCheckHasMediaQuery(context));
295/// ```
296///
297/// Always place this before any early returns, so that the invariant is checked
298/// in all cases. This prevents bugs from hiding until a particular codepath is
299/// hit.
300///
301/// Does nothing if asserts are disabled. Always returns true.
302bool debugCheckHasMediaQuery(BuildContext context) {
303 assert(() {
304 if (context.widget is! MediaQuery &&
305 context.getElementForInheritedWidgetOfExactType<MediaQuery>() == null) {
306 throw FlutterError.fromParts(<DiagnosticsNode>[
307 ErrorSummary('No MediaQuery widget ancestor found.'),
308 ErrorDescription(
309 '${context.widget.runtimeType} widgets require a MediaQuery widget ancestor.',
310 ),
311 context.describeWidget('The specific widget that could not find a MediaQuery ancestor was'),
312 context.describeOwnershipChain('The ownership chain for the affected widget is'),
313 ErrorHint(
314 'No MediaQuery ancestor could be found starting from the context '
315 'that was passed to MediaQuery.of(). This can happen because the '
316 'context used is not a descendant of a View widget, which introduces '
317 'a MediaQuery.',
318 ),
319 ]);
320 }
321 return true;
322 }());
323 return true;
324}
325
326/// Asserts that the given context has a [Directionality] ancestor.
327///
328/// Used by various widgets to make sure that they are only used in an
329/// appropriate context.
330///
331/// To invoke this function, use the following pattern, typically in the
332/// relevant Widget's build method:
333///
334/// ```dart
335/// assert(debugCheckHasDirectionality(context));
336/// ```
337///
338/// To improve the error messages you can add some extra color using the
339/// named arguments.
340///
341/// * why: explain why the direction is needed, for example "to resolve
342/// the 'alignment' argument". Should be an adverb phrase describing why.
343/// * hint: explain why this might be happening, for example "The default
344/// value of the 'alignment' argument of the $runtimeType widget is an
345/// AlignmentDirectional value.". Should be a fully punctuated sentence.
346/// * alternative: provide additional advice specific to the situation,
347/// especially an alternative to providing a Directionality ancestor.
348/// For example, "Alternatively, consider specifying the 'textDirection'
349/// argument.". Should be a fully punctuated sentence.
350///
351/// Each one can be null, in which case it is skipped (this is the default).
352/// If they are non-null, they are included in the order above, interspersed
353/// with the more generic advice regarding [Directionality].
354///
355/// Always place this before any early returns, so that the invariant is checked
356/// in all cases. This prevents bugs from hiding until a particular codepath is
357/// hit.
358///
359/// Does nothing if asserts are disabled. Always returns true.
360///
361/// See also:
362///
363/// * [debugCheckHasDirectionality], which is a similar, but more general
364/// painting-library level function.
365bool debugCheckHasDirectionality(
366 BuildContext context, {
367 String? why,
368 String? hint,
369 String? alternative,
370}) {
371 assert(() {
372 if (context.widget is! Directionality &&
373 context.getElementForInheritedWidgetOfExactType<Directionality>() == null) {
374 why = why == null ? '' : ' $why';
375 throw FlutterError.fromParts(<DiagnosticsNode>[
376 ErrorSummary('No Directionality widget found.'),
377 ErrorDescription(
378 '${context.widget.runtimeType} widgets require a Directionality widget ancestor$why.\n',
379 ),
380 if (hint != null) ErrorHint(hint),
381 context.describeWidget(
382 'The specific widget that could not find a Directionality ancestor was',
383 ),
384 context.describeOwnershipChain('The ownership chain for the affected widget is'),
385 ErrorHint(
386 'Typically, the Directionality widget is introduced by the MaterialApp '
387 'or WidgetsApp widget at the top of your application widget tree. It '
388 'determines the ambient reading direction and is used, for example, to '
389 'determine how to lay out text, how to interpret "start" and "end" '
390 'values, and to resolve EdgeInsetsDirectional, '
391 'AlignmentDirectional, and other *Directional objects.',
392 ),
393 if (alternative != null) ErrorHint(alternative),
394 ]);
395 }
396 return true;
397 }());
398 return true;
399}
400
401/// Asserts that the `built` widget is not null.
402///
403/// Used when the given `widget` calls a builder function to check that the
404/// function returned a non-null value, as typically required.
405///
406/// Does nothing when asserts are disabled.
407void debugWidgetBuilderValue(Widget widget, Widget? built) {
408 assert(() {
409 if (built == null) {
410 throw FlutterError.fromParts(<DiagnosticsNode>[
411 ErrorSummary('A build function returned null.'),
412 DiagnosticsProperty<Widget>(
413 'The offending widget is',
414 widget,
415 style: DiagnosticsTreeStyle.errorProperty,
416 ),
417 ErrorDescription('Build functions must never return null.'),
418 ErrorHint(
419 'To return an empty space that causes the building widget to fill available room, return "Container()". '
420 'To return an empty space that takes as little room as possible, return "Container(width: 0.0, height: 0.0)".',
421 ),
422 ]);
423 }
424 if (widget == built) {
425 throw FlutterError.fromParts(<DiagnosticsNode>[
426 ErrorSummary('A build function returned context.widget.'),
427 DiagnosticsProperty<Widget>(
428 'The offending widget is',
429 widget,
430 style: DiagnosticsTreeStyle.errorProperty,
431 ),
432 ErrorDescription(
433 'Build functions must never return their BuildContext parameter\'s widget or a child that contains "context.widget". '
434 'Doing so introduces a loop in the widget tree that can cause the app to crash.',
435 ),
436 ]);
437 }
438 return true;
439 }());
440}
441
442/// Asserts that the given context has a [Localizations] ancestor that contains
443/// a [WidgetsLocalizations] delegate.
444///
445/// To call this function, use the following pattern, typically in the
446/// relevant Widget's build method:
447///
448/// ```dart
449/// assert(debugCheckHasWidgetsLocalizations(context));
450/// ```
451///
452/// Always place this before any early returns, so that the invariant is checked
453/// in all cases. This prevents bugs from hiding until a particular codepath is
454/// hit.
455///
456/// Does nothing if asserts are disabled. Always returns true.
457bool debugCheckHasWidgetsLocalizations(BuildContext context) {
458 assert(() {
459 if (Localizations.of<WidgetsLocalizations>(context, WidgetsLocalizations) == null) {
460 throw FlutterError.fromParts(<DiagnosticsNode>[
461 ErrorSummary('No WidgetsLocalizations found.'),
462 ErrorDescription(
463 '${context.widget.runtimeType} widgets require WidgetsLocalizations '
464 'to be provided by a Localizations widget ancestor.',
465 ),
466 ErrorDescription(
467 'The widgets library uses Localizations to generate messages, '
468 'labels, and abbreviations.',
469 ),
470 ErrorHint(
471 'To introduce a WidgetsLocalizations, either use a '
472 'WidgetsApp at the root of your application to include them '
473 'automatically, or add a Localization widget with a '
474 'WidgetsLocalizations delegate.',
475 ),
476 ...context.describeMissingAncestor(expectedAncestorType: WidgetsLocalizations),
477 ]);
478 }
479 return true;
480 }());
481 return true;
482}
483
484/// Asserts that the given context has an [Overlay] ancestor.
485///
486/// To call this function, use the following pattern, typically in the
487/// relevant Widget's build method:
488///
489/// ```dart
490/// assert(debugCheckHasOverlay(context));
491/// ```
492///
493/// Always place this before any early returns, so that the invariant is checked
494/// in all cases. This prevents bugs from hiding until a particular codepath is
495/// hit.
496///
497/// This method can be expensive (it walks the element tree).
498///
499/// Does nothing if asserts are disabled. Always returns true.
500bool debugCheckHasOverlay(BuildContext context) {
501 assert(() {
502 if (LookupBoundary.findAncestorWidgetOfExactType<Overlay>(context) == null) {
503 final bool hiddenByBoundary = LookupBoundary.debugIsHidingAncestorWidgetOfExactType<Overlay>(
504 context,
505 );
506 throw FlutterError.fromParts(<DiagnosticsNode>[
507 ErrorSummary(
508 'No Overlay widget found${hiddenByBoundary ? ' within the closest LookupBoundary' : ''}.',
509 ),
510 if (hiddenByBoundary)
511 ErrorDescription(
512 'There is an ancestor Overlay widget, but it is hidden by a LookupBoundary.',
513 ),
514 ErrorDescription(
515 '${context.widget.runtimeType} widgets require an Overlay '
516 'widget ancestor within the closest LookupBoundary.\n'
517 'An overlay lets widgets float on top of other widget children.',
518 ),
519 ErrorHint(
520 'To introduce an Overlay widget, you can either directly '
521 'include one, or use a widget that contains an Overlay itself, '
522 'such as a Navigator, WidgetApp, MaterialApp, or CupertinoApp.',
523 ),
524 ...context.describeMissingAncestor(expectedAncestorType: Overlay),
525 ]);
526 }
527 return true;
528 }());
529 return true;
530}
531
532/// Returns true if none of the widget library debug variables have been changed.
533///
534/// This function is used by the test framework to ensure that debug variables
535/// haven't been inadvertently changed.
536///
537/// See [the widgets library](widgets/widgets-library.html) for a complete list.
538bool debugAssertAllWidgetVarsUnset(String reason) {
539 assert(() {
540 if (debugPrintRebuildDirtyWidgets ||
541 debugPrintBuildScope ||
542 debugPrintScheduleBuildForStacks ||
543 debugPrintGlobalKeyedWidgetLifecycle ||
544 debugProfileBuildsEnabled ||
545 debugHighlightDeprecatedWidgets ||
546 debugProfileBuildsEnabledUserWidgets) {
547 throw FlutterError(reason);
548 }
549 return true;
550 }());
551 return true;
552}
553