{"id":419,"date":"2022-02-17T21:57:10","date_gmt":"2022-02-17T12:57:10","guid":{"rendered":"https:\/\/engineering.webstudio168.jp\/?p=419"},"modified":"2022-03-18T11:35:55","modified_gmt":"2022-03-18T02:35:55","slug":"flutter-main-dart-key-question","status":"publish","type":"post","link":"https:\/\/engineering.webstudio168.jp\/blog\/flutter-main-dart-key-question\/","title":{"rendered":"Flutter\u30c7\u30d5\u30a9\u30eb\u30c8\u30a2\u30d7\u30ea\u306emain.dart\u306b\u3042\u308b\u300cKey?\u300d\u306e\u610f\u5473"},"content":{"rendered":"<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_86 counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">\u76ee\u6b21<\/p>\n<span class=\"ez-toc-title-toggle\"><a href=\"#\" class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" aria-label=\"Toggle Table of Content\"><span class=\"ez-toc-js-icon-con\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/span><\/a><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/engineering.webstudio168.jp\/blog\/flutter-main-dart-key-question\/#%E3%83%91%E3%83%83%E3%81%A8%E8%A6%8B%E3%81%AF%E4%B8%89%E9%A0%85%E6%BC%94%E7%AE%97%E5%AD%90%E3%81%A0%E3%81%91%E3%81%A9\" >\u30d1\u30c3\u3068\u898b\u306f\u4e09\u9805\u6f14\u7b97\u5b50\u3060\u3051\u3069<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/engineering.webstudio168.jp\/blog\/flutter-main-dart-key-question\/#Dart%E5%85%AC%E5%BC%8F%E3%81%AB%E3%83%89%E3%82%AD%E3%83%A5%E3%83%A1%E3%83%B3%E3%83%88%E3%82%92%E7%99%BA%E8%A6%8B\" >Dart\u516c\u5f0f\u306b\u30c9\u30ad\u30e5\u30e1\u30f3\u30c8\u3092\u767a\u898b<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/engineering.webstudio168.jp\/blog\/flutter-main-dart-key-question\/#%E3%80%8CKey%E3%80%8D%E3%81%AFNull%E3%81%A7%E3%82%82%E3%81%84%E3%81%84%E3%82%88%E3%80%81Key%E5%9E%8B%E3%81%A0%E3%82%88\" >\u300cKey?\u300d\u306fNull\u3067\u3082\u3044\u3044\u3088\u3001Key\u578b\u3060\u3088<\/a><\/li><\/ul><\/nav><\/div>\n\n<p class=\"wp-block-paragraph\">Flutter\u304c\u3069\u3093\u306a\u3082\u306e\u306a\u306e\u304b\u89e6\u3063\u3066\u307f\u305f\u304f\u3066\u958b\u767a\u74b0\u5883\u3092\u5165\u308c\u3066\u307f\u307e\u3057\u305f\u3002<br>\u65e9\u901f\u3001flutter run\u3057\u3066\u30b5\u30f3\u30d7\u30eb\u306e\u6570\u5b57\u304c\u30af\u30ea\u30c3\u30af\u3067+1\u3055\u308c\u3066\u3044\u304f\u30a2\u30d7\u30ea\u3092\u3044\u3058\u3063\u3066\u307e\u3057\u305f\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u3067\u3001Dart\u8a00\u8a9e\u3063\u3066\u5b9f\u969b\u3069\u3046\u306a\u306e\u304b\u306a\u3001\u51fa\u6765\u305d\u3046\u304b\u306a\u3001\u3068\u4e2d\u8eab\u3092\u898b\u59cb\u3081\u30661\u5206\u3067\u8e93\u304d\u307e\u3057\u305f\u7b11<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u30d1\u30c3\u3068\u898b\u306f\u4e09\u9805\u6f14\u7b97\u5b50\u3060\u3051\u3069\"><span class=\"ez-toc-section\" id=\"%E3%83%91%E3%83%83%E3%81%A8%E8%A6%8B%E3%81%AF%E4%B8%89%E9%A0%85%E6%BC%94%E7%AE%97%E5%AD%90%E3%81%A0%E3%81%91%E3%81%A9\"><\/span>\u30d1\u30c3\u3068\u898b\u306f\u4e09\u9805\u6f14\u7b97\u5b50\u3060\u3051\u3069<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u3069\u3053\u3067\u8a70\u307e\u3063\u305f\u304b\u3068\u3044\u3046\u3068\u3001main.dart\u3092\u8aad\u307f\u59cb\u3081\u30668\u884c\u76ee\u3067\u3059\u7b11\u7b11<br>\u3042\u3001\u306a\u3093\u304b\u610f\u5473\u308f\u304b\u3089\u3093\u3063\u3066\u306a\u3063\u3066\u3057\u307e\u3044\u307e\u3057\u305f\u3002\u6b21\u306e\u7b87\u6240\u3067\u3059\u3002<\/p>\n\n\n\n<div class=\"hcb_wrap\"><pre class=\"prism undefined-numbers lang-dart\" data-file=\"main.dart\" data-lang=\"Dart\"><code>const MyApp({Key? key}) : super(key: key);<\/code><\/pre><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">\u3093\u30fc\u3001\u4e00\u77ac\u76ee\u306b\u5165\u3063\u305f\u611f\u3058\u3060\u3068\u4e09\u9805\u6f14\u7b97\u5b50\u3060\u3063\u305f\u306e\u3067\u3059\u304c\u3001\u3088\u304f\u3088\u304f\u898b\u308b\u3068\u30ab\u30c3\u30b3\u306e\u4f4d\u7f6e\u3084\u3089\u3064\u3058\u3064\u307e\u304c\u5408\u308f\u306a\u3044\u3002<br>MyApp()\u304c\u30b3\u30f3\u30b9\u30c8\u30e9\u30af\u30bf\u3060\u304b\u3089()\u5185\u306e\u300c<code>Key ? key<\/code>\u300d\u3063\u3066\u4e00\u4f53\u2026\u2026<code>super(key: key)<\/code>\u306f\u5206\u304b\u308a\u307e\u3059\u3088\u3001\u3067\u3082\u300cKey ? key\u300d\u3063\u3066\u306a\u3093\u3084\u306d\u3093\u3001\u3063\u3066\u306a\u3063\u3066\u3057\u307e\u3044\u307e\u3057\u305f\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u3082\u3057\u304b\u3057\u3066\u3001Dart\u3063\u3066\u4e09\u9805\u6f14\u7b97\u5b50\u306e\u7701\u7565\u304c\u51fa\u6765\u308b\u306e\u304b\uff1f\uff08<code>Key ? true<\/code>\u306e\u307f\u7684\u306a\uff09\u3068\u601d\u3044\u8272\u3005\u30b0\u30b0\u3063\u305f\u3093\u3067\u3059\u304c\u3001\u305d\u3093\u306a\u4f7f\u3044\u65b9\u306f\u3057\u306a\u3044\u307f\u305f\u3044\u3067\u3059\u3002\u666e\u901a\u306b<code>Key ? true : false;<\/code>\u306e\u5f62\u3057\u304b\u306a\u3044\u3067\u3059\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u3080\u30fc\u3093\u3001\u3068\u60a9\u307f\u306b\u60a9\u307f\u30b0\u30b0\u308a\u7d9a\u3051\u308b\u3053\u306830\u5206\u2026\u2026\u3084\u3063\u3068\u898b\u3064\u3051\u307e\u3057\u305f\u3002<br>\u65e5\u672c\u8a9e\u30c9\u30ad\u30e5\u30e1\u30f3\u30c8\u304c\u5c11\u306a\u3059\u304e\u3066\u691c\u7d22\u306b\u5f15\u3063\u304b\u304b\u3089\u306a\u304b\u3063\u305f\u3093\u3067\u3059\u3002\u8ab0\u3082\u7591\u554f\u306b\u601d\u308f\u306a\u3044\u306e\u304b\u3057\u3089\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"dart\u516c\u5f0f\u306b\u30c9\u30ad\u30e5\u30e1\u30f3\u30c8\u3092\u767a\u898b\"><span class=\"ez-toc-section\" id=\"Dart%E5%85%AC%E5%BC%8F%E3%81%AB%E3%83%89%E3%82%AD%E3%83%A5%E3%83%A1%E3%83%B3%E3%83%88%E3%82%92%E7%99%BA%E8%A6%8B\"><\/span>Dart\u516c\u5f0f\u306b\u30c9\u30ad\u30e5\u30e1\u30f3\u30c8\u3092\u767a\u898b<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\"><p>Sound null safety is available in Dart 2.12 and Flutter 2.<\/p><cite>https:\/\/dart.dev\/null-safety<\/cite><\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">Dart\u8a00\u8a9e\u306b\u6700\u8fd1\u8ffd\u52a0\u3055\u308c\u305fNullPointerException\u3092\u56de\u907f\u3059\u308b\u300cSound null safety\u300d\u3068\u3044\u3046\u4ed5\u7d44\u307f\u3060\u305d\u3046\u3067\u3001<strong>\u578b\u306e\u5f8c\u308d\u306b\u300c?\u300d\u3092\u4ed8\u3051\u308b\u3068nullable\uff08null\u3067\u3082\u3044\u3044\u3088\uff09\u306b\u306a\u308b<\/strong>\u3068\u306e\u3053\u3068\u3002<br>\uff08\u53c2\u8003\uff1a<a href=\"https:\/\/dart.dev\/null-safety\" target=\"_blank\" rel=\"noreferrer noopener nofollow\">https:\/\/dart.dev\/null-safety<\/a>\uff09<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u306a\u306e\u3067\u3001\u5148\u307b\u3069\u66f8\u3044\u305f\u300c<code>Key ? key<\/code>\u300d\u306f\u9593\u9055\u3044\u3067\u3001\u6b63\u3057\u304f\u306f\u300c<code>Key? key<\/code>\u300d\u306a\u3093\u3067\u3059\u306d\u3002\u300cKey?\u300d\u3063\u3066\u3053\u3068\u3067\u3001Null\u3067\u3082OK\u306aKey\u578b\uff08\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\uff09\u306e\u5909\u6570\u3001\u3068\u3067\u3082\u8a00\u3044\u307e\u3057\u3087\u3046\u304b\u3002\u3061\u306a\u307f\u306bVisual Studio Code\u3067\u300cKey ? key\u300d\u3067\u81ea\u52d5\u30b3\u30fc\u30c9\u6574\u5f62\u3059\u308b\u3068\u304d\u3061\u3093\u3068\u300cKey? key\u300d\u306b\u6574\u3048\u3089\u308c\u307e\u3059\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">int\u578b\u3067\u3042\u308c\u3070 <code>int? anything<\/code> String\u578b\u3060\u3068 <code>String? something<\/code> \u306b\u306a\u308a\u307e\u3059\u306d\u3002<br>\u305f\u3069\u308a\u7740\u304f\u307e\u3067\u9060\u304b\u3063\u305f\u2026\u2026<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"key-\u306fnull\u3067\u3082\u3044\u3044\u3088-key\u578b\u3060\u3088\"><span class=\"ez-toc-section\" id=\"%E3%80%8CKey%E3%80%8D%E3%81%AFNull%E3%81%A7%E3%82%82%E3%81%84%E3%81%84%E3%82%88%E3%80%81Key%E5%9E%8B%E3%81%A0%E3%82%88\"><\/span>\u300cKey?\u300d\u306fNull\u3067\u3082\u3044\u3044\u3088\u3001Key\u578b\u3060\u3088<span class=\"ez-toc-section-end\"><\/span><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u3068\u3044\u3046\u3053\u3068\u3067\u300cKey?\u300d\u306fNull safety\uff08Null\u5b89\u5168\uff09\u306e\u4ed5\u69d8\u306b\u3088\u308b\u8a18\u8ff0\u3068\u3044\u3046\u3053\u3068\u3067\u3057\u305f\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u3061\u306a\u307f\u306bNull safety\uff08Null\u5b89\u5168\uff09\u306f\u300cSwift\u300d\u300cPython\u300d\u300cTypeScript\u300d\u306a\u3069\u306e\u8a00\u8a9e\u3067\u3082\u63a1\u7528\u3055\u308c\u3066\u3044\u308b\u3088\u3046\u3067\u3059\u3002Null\u5b89\u5168\u306a\u3093\u3066\u8a00\u8449\u521d\u3081\u3066\u805e\u304d\u307e\u3057\u305f\u2026\u2026\u307e\u3060\u307e\u3060\u52c9\u5f37\u3059\u308b\u3053\u3068\u305f\u304f\u3055\u3093\u3042\u308a\u307e\u3059\u306d\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Null\u5b89\u5168\u306b\u3064\u3044\u3066\u306f<a href=\"https:\/\/qiita.com\/koher\/items\/e4835bd429b88809ab33\" target=\"_blank\" rel=\"noreferrer noopener nofollow\">Qiita\u306e\u8a18\u4e8b<\/a>\u3092\u62dd\u898b\u3055\u305b\u3066\u3044\u305f\u3060\u304d\u307e\u3057\u305f\u3002\u8208\u5473\u306e\u3042\u308b\u65b9\u306f\u3088\u304f\u307e\u3068\u307e\u3063\u3066\u3044\u308b\u306e\u3067\u898b\u3066\u307f\u3066\u304f\u3060\u3055\u3044\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Flutter\u304c\u3069\u3093\u306a\u3082\u306e\u306a\u306e\u304b\u89e6\u3063\u3066\u307f\u305f\u304f\u3066\u958b\u767a\u74b0\u5883\u3092\u5165\u308c\u3066\u307f\u307e\u3057\u305f\u3002\u65e9\u901f\u3001flutter run\u3057\u3066\u30b5\u30f3\u30d7\u30eb\u306e\u6570\u5b57\u304c\u30af\u30ea\u30c3\u30af\u3067+1\u3055\u308c\u3066\u3044\u304f\u30a2\u30d7\u30ea\u3092\u3044\u3058\u3063\u3066\u307e\u3057\u305f\u3002 \u3067\u3001Dart\u8a00\u8a9e\u3063\u3066\u5b9f\u969b\u3069\u3046\u306a\u306e\u304b\u306a\u3001\u51fa\u6765\u305d\u3046\u304b\u306a [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":423,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[45],"tags":[47,36,49,48],"class_list":["post-419","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-flutter","tag-dart","tag-flutter","tag-49","tag-48"],"_links":{"self":[{"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/posts\/419","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/comments?post=419"}],"version-history":[{"count":6,"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/posts\/419\/revisions"}],"predecessor-version":[{"id":428,"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/posts\/419\/revisions\/428"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/media\/423"}],"wp:attachment":[{"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/media?parent=419"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/categories?post=419"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/engineering.webstudio168.jp\/blog\/wp-json\/wp\/v2\/tags?post=419"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}