Flutter，如何将值从一个函数传递到另一页上的另一个函数 [英] Flutter, How to pass value from one function to another function on a different page

问题描述

我试图从单击按钮时传递一个值，我想要在代码中传递的是将值从Button窗口小部件传递给另一个名为pdfNo的页面变量.这是我的代码:

I a trying to pass a Value from when a button is clicked, What I want in the code is to pass the value from the Button Widget to another Page's Variable named pdfNo. Here's my code:

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');
          },
        ),`

这是首页上的按钮，在按下时我想将一个值传递给一个子函数，所以我创建了一个变量，但无法弄清楚下一步如何做:

This is the Button on the First Page , On Pressed I would like to pass a Value to a function which is child, so I have created a variable , but cant figure out how to go about this next:

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int从第1页的Staleful Class的按钮传递给第二页的Stateful Class，以更改PDF(此处).

So, I would like to pass a int from the button on page 1 Staleful Class to a Stateful Class on second page to changePDF(here).

请帮帮我.PS Flutter，Dart的新手

Please help me out. PS New to Flutter,Dart

推荐答案

您可以创建 to 参数...

You can create a to arguments...

类似这样的东西

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: "[e-mail]");

编辑

也许很简单...

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();
   }
...
}

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