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flutter开发实战-使用FutureBuilder异步数据更新Widget
在开发过程中，经常遇到需要依赖异步数据更新Widget的情况，如下载图片后显示Widget，获取到某个数据时候，显示在对应的UI界面上，都可以使用FutureBuilder异步数据更新Widget。
一、FutureBuilder
FutureBuilder是一个Widget，该Widget基于与Future]交互的最新快照构建的。
/// Creates a widget that builds itself based on the latest snapshot of/// interaction with a [Future].////// The [builder] must not be null.const FutureBuilder({super.key,this.future,this.initialData,required this.builder,}) : assert(builder != null);
其中
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future：final Future? future; 是一个异步的任务；
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builder：final AsyncWidgetBuilder builder;是创建显示的Widget，可以根据AsyncSnapshot<String?> snapshot来确定显示的Widget，可以在Future执行过程中被调用多次。
二、使用FutureBuilder
这里使用FutureBuilder的示例，我是通过加载网页时候，需要将Webview中设置cookie，cookie中需要设置token。token需要获取到再设置到Webview中的cookie中。
获取token
Future<String?> _getToken() async {final token = (await SessionDataService.sessionData)?.token;if (token == null) return null;return token;}
使用FutureBuilder用来在获取token后更新Webview，先判断snapshot.hasData是否有数据。如果有数据，则直接显示Webview，如果没有数据，则显示默认的Container。
FutureBuilder<String?>(future: _getToken(),builder: (BuildContext context, AsyncSnapshot<String?> snapshot) {if (snapshot.hasData) {final token = snapshot.data;if (token == null) return Container();return WebView(javascriptMode: JavascriptMode.unrestricted,initialUrl: url,initialCookies: [WebViewCookie(name: "auth", value: "token", domain: "inice.cn"),],userAgent: "inice.cn",onWebViewCreated: (controller) {cookieManager.setCookies([Cookie('auth', token)..domain = 'inice.cn'..httpOnly = false,]);webController = controller;},);}return Container();},),
完整代码如下
class WebViewScreen extends StatelessWidget {WebViewScreen({Key? key, required this.url}) : super(key: key);final String url;WebViewController? webController;final cookieManager = WebviewCookieManager();Future<String?> _getToken() async {// final token = (await SessionDataService.sessionData)?.token;final token = ApiAuth().token;if (token == null) return null;return token;}Widget build(BuildContext context) {return Scaffold(body: Stack(children: [Container(color: Colors.amber,),SafeArea(bottom: false,child: FutureBuilder<String?>(future: _getToken(),builder: (BuildContext context, AsyncSnapshot<String?> snapshot) {if (snapshot.hasData) {final token = snapshot.data;if (token == null) return Container();return WebView(javascriptMode: JavascriptMode.unrestricted,initialUrl: url,initialCookies: [WebViewCookie(name: "auth", value: "token", domain: "inice.cn"),],userAgent: "inice.cn",onWebViewCreated: (controller) {cookieManager.setCookies([Cookie('auth', token)..domain = 'inice.cn'..httpOnly = false,]);webController = controller;},);}return Container();},),),],),);}
}
三、小结
flutter开发实战-使用FutureBuilder异步数据更新Widget。描述可能不是特别准确，请见谅。
https://blog.csdn.net/gloryFlow/article/details/133490457
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