A raw string can be used to avoid escaping only backslashes and dollars.

Do

var s = r'This is demo string \ and $';

Don't

var s = 'This is demo string \\ and \$';

When use relative and absolute imports together then It is possible to create confusion when the same class gets imported from two different ways. To avoid this case we should use a relative path in the lib/ folder.

Do

import '../../../utils/dialog_utils.dart';

Don't

import 'package:demo/src/utils/dialog_utils.dart';

When existing items are already stored in another collection, spread collection syntax leads to simpler code.

Do

var y = [4,5,6];
var x = [1,2,...y];

Don't

var y = [4,5,6];
var x = [1,2];

x.addAll(y);

class someAPI {
  Future<int> getThings() => Future.value(3000);
  Future<int> getItems() => Future.value(300);
  Future<int> getStuff() => Future.value(30);
}

final api = someAPI();
final values = await Future.wait(
  [
    api.getThings(),
    api.getItems(),
    api.getStuff()
  ]
);

Flexible(
  child: GridView.count(
    crossAxisCount: (orientation == Orientaation.portrait) ? 2 : 3,
    mainAxisSpacing: 4.0,
    crossAxisSpacing: 4.0,
    padding: const EdgeInsets.all(4.0),
    childAspectRatio: (orientation == Orientaation.portrait) ? 1.0 : 1.3,
    children: someList.map(
      (catData) => aListItemWidget(catData)
    ).toList()
  )
);

import 'package:flutter/servics.dart';

...

void main() async {
  await SystemChrome.setPreferredOrientations([DeviceOrientation.portraitUp]);

  runApp(App());
}

Widget to the list of children, you will need to change the height of the Sizedbox whenever you add a widget.

Don't

SizedBox(
  height: 20,
  child: Column(
    children: [
      Text(Hey),
      Text(You)
    ]
  ) 
)

Do

Column(
  mainAxisSize: MainAxisSize.min,
  child: Column(
    children: [
      Text(Hey),
      Text(You)
    ]
  ) 
)

You can use the print0 function to view it in the system console. If your output is too much, then Android sometimes discards some log lines. To avoid this, you can use debugPrint().

You can also log your print calls to disk if you're doing long-term or background work.

Just wrap the widget with the Theme Widget and pass the ThemeData().

Theme(
  data: ThemeData(...),
  child: TextFormField(
    decoration: const InputDecoration(
      icon: Icon(Icons.person),
      hintText: 'What do people call you ?',
      labelText: 'Name *',
    )
    validator: (value) {
      return value!.contains('@') ? 'Do not use the @ char' : null;
    }
  )
)

1. You can set your JAVA_HOME to an older version of Java and then run your Flutter build. You would also need to have this JAVA_HOME available anywhere you build from (command line, IDE, CI/CD, etc)
2. Update your allprojects section of android/build.gradle to look like the following:

allprojects {
  repositories {
    google()
    mavenCentral()
  }

  tasks.withType(JavaCompile).configureEach {
    javaCompiler = javaToolchains.compilerFor {
      languageVersion = JavaLanguageVersion.of(8)
    }
  }
}

Add triggers to your Content Blocker

initialSettings: InAppWebViewSettings(contentBlockers: [
  ContentBlocker(
    trigger: ContentBlockerTrigger(
      urlFilter: ".*",
      resourceType: [
        ContentBlockerTriggerResourceType.IMAGE,
        ContentBlockerTriggerResourceType.STYLE_SHEET
      ],
      unlessDomain: ["example.com", "github.com", "pub.dev"]
    ),
    action: ContentBlockerAction(
      type: ContentBlockerActionType.BLOCK
    )
  )
]),

For deeper trigger customization, you can use the other properties of ContentBlockerTrigger :

• urlFilterIsCaseSensitive: If the URL matching should be case-sensitive. By default, it is case insensitive.
• resourceType: A list of “ContentBlockerTriggerResourceType” representing the resource types (how the browser intends to use the resource) that the rule should match. If not specified, the rule matches all resource types.
• ifDomain: A list of strings matched to a URL’s domain; limits action to a list of specific domains. Values must be lowercase ASCII, or punycode for non-ASCII. Add * in front to match domain and subdomains. It can’t be used with “unlessDomain”.
• unlessDomain: A list of strings matched to a URL’s domain; acts on any site except domains in a provided list. Values must be lowercase ASCII, or punycode for non-ASCII. Add * in front to match domain and subdomains. It can’t be used with “ifDomain”.
• loadType: A list of “ContentBlockerTriggerLoadType” that can include one of two mutually exclusive values. If not specified, the rule matches all load types. “ContentBlockerTriggerLoadType.FIRST_PARTY” triggers only if the resource has the same scheme, domain, and port as the main page resource. “ContentBlockerTriggerLoadType.THIRD_PARTY” triggers if the resource isn’t from the same domain as the main page resource.
• ifTopUrl: A list of strings matched to the entire main document URL; limits the action to a specific list of URL patterns. Values must be lowercase ASCII, or punycode for non-ASCII. It can’t be used with “unlessTopUrl”.
• unlessTopUrl: An array of strings matched to the entire main document URL; acts on any site except URL patterns in the provided list. Values must be lowercase ASCII, or punycode for non-ASCII. It can’t be used with “ifTopUrl”.
• loadContext: An array of strings that specify loading contexts.
• ifFrameUrl: A list of regular expressions to match iframes URL against.

Add actions to your Content Blocker

initialSettings: InAppWebViewSettings(contentBlockers: [
  ContentBlocker(
    trigger: ContentBlockerTrigger(
      urlFilter: "https://flutter.dev/.*",
    ),
    action: ContentBlockerAction(
      type: ContentBlockerActionType.CSS_DISPLAY_NONE,
      selector: '.notification, .media, #developer-story'
    )
  )
]),

Valid types are:

• BLOCK: Stops loading of the resource. If the resource was cached, the cache is ignored.
• BLOCK_COOKIES: Strips cookies from the header before sending it to the server. This only blocks cookies otherwise acceptable to WebView’s privacy policy. Combining with “IGNORE_PREVIOUS_RULES” doesn’t override the browser’s privacy settings.
• CSS_DISPLAY_NONE: Hides elements of the page based on a CSS selector. A selector field contains the selector list. Any matching element has its display property set to none, which hides it.
• MAKE_HTTPS: Changes a URL from http to https. URLs with a specified (nondefault) port and links using other protocols are unaffected.
• IGNORE_PREVIOUS_RULES: Ignores previously triggered actions.

Creating a simple Ad Blocker

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter_inappwebview/flutter_inappwebview.dart';

Future main() async {
  WidgetsFlutterBinding.ensureInitialized();
  if (!kIsWeb &&
      kDebugMode &&
      defaultTargetPlatform == TargetPlatform.android) {
    await InAppWebViewController.setWebContentsDebuggingEnabled(kDebugMode);
  }
  runApp(const MaterialApp(home: MyApp()));
}

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  final GlobalKey webViewKey = GlobalKey();

  // list of Ad URL filters to be used to block ads loading.
  final adUrlFilters = [
    ".*.doubleclick.net/.*",
    ".*.ads.pubmatic.com/.*",
    ".*.googlesyndication.com/.*",
    ".*.google-analytics.com/.*",
    ".*.adservice.google.*/.*",
    ".*.adbrite.com/.*",
    ".*.exponential.com/.*",
    ".*.quantserve.com/.*",
    ".*.scorecardresearch.com/.*",
    ".*.zedo.com/.*",
    ".*.adsafeprotected.com/.*",
    ".*.teads.tv/.*",
    ".*.outbrain.com/.*"
  ];

  final List<ContentBlocker> contentBlockers = [];
  var contentBlockerEnabled = true;

  InAppWebViewController? webViewController;

  @override
  void initState() {
    super.initState();

    // for each Ad URL filter, add a Content Blocker to block its loading.
    for (final adUrlFilter in adUrlFilters) {
      contentBlockers.add(ContentBlocker(
          trigger: ContentBlockerTrigger(
            urlFilter: adUrlFilter,
          ),
          action: ContentBlockerAction(
            type: ContentBlockerActionType.BLOCK,
          )));
    }

    // apply the "display: none" style to some HTML elements
    contentBlockers.add(ContentBlocker(
        trigger: ContentBlockerTrigger(
          urlFilter: ".*",
        ),
        action: ContentBlockerAction(
            type: ContentBlockerActionType.CSS_DISPLAY_NONE,
            selector: ".banner, .banners, .ads, .ad, .advert")));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text("Ads Content Blocker"),
          actions: [
            TextButton(
              onPressed: () async {
                contentBlockerEnabled = !contentBlockerEnabled;
                if (contentBlockerEnabled) {
                  await webViewController?.setSettings(
                      settings: InAppWebViewSettings(
                          contentBlockers: contentBlockers));
                } else {
                  await webViewController?.setSettings(
                      settings: InAppWebViewSettings(contentBlockers: []));
                }
                webViewController?.reload();

                setState(() {});
              },
              style: TextButton.styleFrom(foregroundColor: Colors.white),
              child: Text(contentBlockerEnabled ? 'Disable' : 'Enable'),
            )
          ],
        ),
        body: SafeArea(
            child: Column(children: <Widget>[
          Expanded(
            child: Stack(
              children: [
                InAppWebView(
                  key: webViewKey,
                  initialUrlRequest:
                      URLRequest(url: WebUri('https://www.tomshardware.com/')),
                  initialSettings:
                      InAppWebViewSettings(contentBlockers: contentBlockers),
                  onWebViewCreated: (controller) {
                    webViewController = controller;
                  },
                ),
              ],
            ),
          ),
        ])));
  }
}

Do

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Column(
      children: const [
        Widget(),
        Widget(),
        Widget()
      ]
    )
  );
}

Don't

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Column(
      children: [
        WidgetFunction(),
        WidgetFunction(),
        WidgetFunction()
      ]
    )
  );
}

Conclusion: Extracting widgets to a method is considered as a Flutter anti-pattern, because when Flutter rebuilds widget tree, it calls the function all the time, making more processor time for the operations while widgets they will be rendered once and will not update themselves.