Flutter，如何将值从一个函数传递到不同页面上的另一个函数

Question

我试图在单击按钮时传递一个值，我在代码中想要的是将值从按钮小部件传递到另一个页面的名为 pdfNo 的变量。这是我的代码:

FlatButton(
          padding: EdgeInsets.fromLTRB(2, 5, 5, 5),
          child: ListTile(
            leading: Icon(Icons.book, color: Color(0xFFEB3549)),
            title: Text('Book5'),
          ),
          onPressed: () {
            Navigator.push(
                context,
                MaterialPageRoute(
                builder: (context) => PDFPage() ));
            print('Pressed 6');
          },
        ),`

这是第一页上的按钮，按下时我想将一个值传递给子函数，因此我创建了一个变量，但不知道接下来如何进行:

var pdfNo = 2;
bool _isLoading = true;
PDFDocument document;
@override
   void initState() {
      super.initState();
        changePDF(pdfNo);
        loadDocument();
         }

changePDF(value) async {
setState(() => _isLoading = true);
if (value == 1) {
  document = await PDFDocument.fromAsset('assets/sample2.pdf');
} else if (value == 2) {
  document = await PDFDocument.fromURL(
      "http://conorlastowka.com/book/CitationNeededBook-Sample.pdf");
} else {
  document = await PDFDocument.fromAsset('assets/sample.pdf');
}
setState(() => _isLoading = false);
}

因此，我想将第 1 页 Staleful Class 上的按钮中的 int 传递到第二页上的 Stateful Class 以更改 PDF(此处)。

请帮帮我。 PS Flutter、Dart 新手

Answer 1

您可以创建一个to参数...

类似这样的事情

class LoginWidgetArguments {
  final String username;

  LoginWidgetArguments(
      {this.username});
}

class LoginWidget extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _LoginWidgetState();
}

class _LoginWidgetState extends State<LoginWidget>{
  LoginWidgetArguments args;

  @override
  void initState() {
    //Get context
    // I do this because sometimes it doesn't get the context without the FutureDelay... This workaround I used with the first flutter versions, maybe now its not needed
    Future.delayed(Duration.zero, () {
      args = ModalRoute.of(context).settings.arguments;
      if (args != null) {
        print(args.username)
      }
    });
  }

....
}

并导航

Navigator.pushNamed(context, LoginPage.routeName,
                    arguments: LoginWidgetArguments(
                        user: "<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="ea9f998f98aa938b93c4898587" rel="noreferrer noopener nofollow">[email protected]</a>");

编辑

也许这很简单......

FlatButton(
          padding: EdgeInsets.fromLTRB(2, 5, 5, 5),
          child: ListTile(
            leading: Icon(Icons.book, color: Color(0xFFEB3549)),
            title: Text('Book5'),
          ),
          onPressed: () {
            Navigator.push(
                context,
                MaterialPageRoute(
                builder: (context) => PDFPage(pageNumber: 6) ));
            print('Pressed 6');
          },
        )

class PDFPage extends StatefulWidget {
  final int pageNumber;
  PDFPage({this.pageNumber});
  @override
  _PDFPageStage createState() => _PDFPageStage();
}

class _PDFPageStage extends State<PDFPage> {
...
    @override
   void initState() {
      super.initState();
      changePDF(widget.pageNumber);
      loadDocument();
   }
...
}