如何分配未来<>小部件颤动? [英] how to assign future<> to widget in flutter?

问题描述

假设我有一个 SingleChildScrollView，它的内容是从一个文件中读取的:

Suppose I have a SingleChildScrollView, its content is read from a file:

singleChildScrollView(
        padding: EdgeInsets.all(8.0),
        child: nw Text(
          getTextFromFile(), //<---read from file
          style: TextStyle(
            fontWeight: FontWeight.bold,
            fontSize: 19.0,
          ),
        ));

  Future<String> getFileData(String path) async {
    return await rootBundle.loadString(path);
  }

  Future<String> getTextFromFile() async {
      return getFileData("test.txt");
  }

我收到以下错误:

The argument type 'Future<String>' can't be assigned to the parameter
type 'String'.

如何解决问题?

推荐答案

StatefulWidget 可用于此目的.声明一个成员变量 String _textFromFile = "";在您的 State 类中，并使用 setState() 更新其在未来解析时的值 方法.

StatefulWidget can be used for this purpose. Declare a member variable String _textFromFile = ""; in your State class and update its value on future resolve by using setState() method.

我从构造函数调用了您的 getTextFromFile() 方法，但您可以从任何地方调用它.

I called your getTextFromFile() method from the constructor, but you may call it from anywhere.

运行代码:

import 'package:flutter/material.dart';
import 'dart:async';

class StatefullWidgetDemo extends StatefulWidget {
  @override
  _StatefulWidgetDemoState createState() {
    return new _StatefulWidgetDemoState();
  }
}

class _StatefulWidgetDemoState extends State<StatefullWidgetDemo> {
  String _textFromFile = "";

  _StatefulWidgetDemoState() {
    getTextFromFile().then((val) => setState(() {
          _textFromFile = val;
        }));
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Stateful Demo'),
      ),
      body: new SingleChildScrollView(
        padding: new EdgeInsets.all(8.0),
        child: new Text(
          _textFromFile,
          style: new TextStyle(
            fontWeight: FontWeight.bold,
            fontSize: 19.0,
          ),
        ),
      ),
    );
  }

  Future<String> getFileData(String path) async {
    return "your data from file";
  }

  Future<String> getTextFromFile() async {
    return await getFileData("test.txt");
  }
}

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