升级到 Flutter 3.22.0 之后,在 Chrome 上运行 Flutter Web 应用程序时收到以下警告:
1 2 3 |
Launching lib/main.dart on Chrome in debug mode... Waiting for connection from debug service on Chrome... Warning: In index.html:40: Local variable for "serviceWorkerVersion" is deprecated. Use "{{flutter_service_worker_version}}" template token instead. See https://docs.flutter.dev/platform-integration/web/initialization for more details. |
这个警告的原因是,新版本的 Flutter Web 应用加载 service_worker.js 的方式发生了变化,原来的加载脚本被 {{flutter_bootstrap_js}} 替代。
调整为新的初始化代码即可解决此问题。
原始的代码如下:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 |
<!DOCTYPE html> <html> <head> <!-- If you are serving your web app in a path other than the root, change the href value below to reflect the base path you are serving from. The path provided below has to start and end with a slash "/" in order for it to work correctly. For more details: * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base This is a placeholder for base href that will be replaced by the value of the `--base-href` argument provided to `flutter build`. --> <base href="$FLUTTER_BASE_HREF"> <meta charset="UTF-8"> <meta content="IE=Edge" http-equiv="X-UA-Compatible"> <meta name="description" content="A new Flutter project."> <!-- iOS meta tags & icons --> <meta name="apple-mobile-web-app-capable" content="yes"> <meta name="apple-mobile-web-app-status-bar-style" content="black"> <meta name="apple-mobile-web-app-title" content="xxxx"> <link rel="apple-touch-icon" href="icons/Icon-192.png"> <!-- Favicon --> <link rel="icon" type="image/png" href="favicon.png"/> <title>xxxx</title> <link rel="manifest" href="manifest.json"> </head> <body> <!-- This script installs service_worker.js to provide PWA functionality to application. For more information, see: https://developers.google.com/web/fundamentals/primers/service-workers --> <script> var serviceWorkerVersion = null; var scriptLoaded = false; function loadMainDartJs() { if (scriptLoaded) { return; } scriptLoaded = true; var scriptTag = document.createElement('script'); scriptTag.src = 'main.dart.js'; scriptTag.type = 'application/javascript'; document.body.append(scriptTag); } if ('serviceWorker' in navigator) { // Service workers are supported. Use them. window.addEventListener('load', function () { // Wait for registration to finish before dropping the <script> tag. // Otherwise, the browser will load the script multiple times, // potentially different versions. var serviceWorkerUrl = 'flutter_service_worker.js?v=' + serviceWorkerVersion; navigator.serviceWorker.register(serviceWorkerUrl) .then((reg) => { function waitForActivation(serviceWorker) { serviceWorker.addEventListener('statechange', () => { if (serviceWorker.state == 'activated') { console.log('Installed new service worker.'); loadMainDartJs(); } }); } if (!reg.active && (reg.installing || reg.waiting)) { // No active web worker and we have installed or are installing // one for the first time. Simply wait for it to activate. waitForActivation(reg.installing || reg.waiting); } else if (!reg.active.scriptURL.endsWith(serviceWorkerVersion)) { // When the app updates the serviceWorkerVersion changes, so we // need to ask the service worker to update. console.log('New service worker available.'); reg.update(); waitForActivation(reg.installing); } else { // Existing service worker is still good. console.log('Loading app from service worker.'); loadMainDartJs(); } }); // If service worker doesn't succeed in a reasonable amount of time, // fallback to plaint <script> tag. setTimeout(() => { if (!scriptLoaded) { console.warn( 'Failed to load app from service worker. Falling back to plain <script> tag.', ); loadMainDartJs(); } }, 4000); }); } else { // Service workers not supported. Just drop the <script> tag. loadMainDartJs(); } </script> </body> </html> |
调整后的代码如下:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 |
<!DOCTYPE html> <html> <head> <!-- If you are serving your web app in a path other than the root, change the href value below to reflect the base path you are serving from. The path provided below has to start and end with a slash "/" in order for it to work correctly. For more details: * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base This is a placeholder for base href that will be replaced by the value of the `--base-href` argument provided to `flutter build`. --> <base href="$FLUTTER_BASE_HREF"> <meta charset="UTF-8"> <meta content="IE=Edge" http-equiv="X-UA-Compatible"> <meta name="description" content="A new Flutter project."> <!-- iOS meta tags & icons --> <meta name="apple-mobile-web-app-capable" content="yes"> <meta name="apple-mobile-web-app-status-bar-style" content="black"> <meta name="apple-mobile-web-app-title" content="xxxx"> <link rel="apple-touch-icon" href="icons/Icon-192.png"> <!-- Favicon --> <link rel="icon" type="image/png" href="favicon.png"/> <title>xxxx</title> <link rel="manifest" href="manifest.json"> </head> <body> <!-- This script installs service_worker.js to provide PWA functionality to application. For more information, see: https://developers.google.com/web/fundamentals/primers/service-workers --> <script> {{flutter_bootstrap_js}} </script> </body> </html> |