我有我的主页，当我按Enter键时，将打开另一页，然后在中间一个按钮中，当按下该按钮时，该功能将返回主页。但是当我按下它时，出现此错误：
错误：“ package：flutter / src / widgets / text.dart”：失败的断言：第253行 pos 10：“数据！= null”：必须为文本提供非null的字符串 小部件。带有星号的线是错误线。
import 'package:flutter/material.dart';
import './SecondPage.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'BelaBlock',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.cyan,
),
home: MyHomePage(title: "Bela Block"),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
//Inputs
var _counter = "0";
var _counter1 = "0";
var text1;
//Select tim
var tim1 = 0;
var tim2 = 0;
//Contacts
String contacts = "";
//Points
var count1 = 0;
var count2 = 0;
var input1 = 0;
var input2 = 0;
var cons = 162;
var t1 = 0;
var t2 = 0;
@override
void dispose() {
tim1 = 0;
tim2 = 0;
contacts = "";
super.dispose();
}
void contact1 (){
setState(() {
tim1 = 1;
tim2 = 0;
});
}
void contact2 (){
setState(() {
tim2 = 1;
tim1 = 0;
});
}
void clear (){
setState(() {
_counter = "0";
_counter1 = "0";
contacts = "";
tim1 = 0;
tim2 = 0;
});
}
void fall(){
if (contacts == "Tim1") {
if (t1 <= t2){
input1 = 0;
input2 = 162;
setState(() {
_counter = 0.toString();
_counter1 = 162.toString();
});
print("Tim 1 je pao.");
}
else{
print("Tim 1 je prosao.");
}
}
if (contacts == "Tim2") {
if (t2 <= t1){
input1 = 162;
input2 = 0;
setState(() {
_counter = 162.toString();
_counter1 = 0.toString();
});
print("Tim 2 je pao.");
}
else{
print("Tim 2 je prosao.");
}
}
}
void _incrementCounter(String buttonText) {
if (tim1 == 1){
setState(() {
_counter = _counter + buttonText.toString();
count2 = int.parse(_counter);
print(count2);
input2 = cons - count2;
t1 = count2;
t2 = input2;
_counter1 = input2.toString();
});
}
if(tim2 == 1){
setState(() {
_counter1 = _counter1 + buttonText.toString();
count1 = int.parse(_counter1);
print(count1);
input1 = cons - count1;
t2 = count1;
t1 = input1;
_counter = input1.toString();
});
}
}
Widget buildButton (String buttonText){
return new Expanded(
child: new MaterialButton(
color: Colors.black,
padding: new EdgeInsets.all(20),
child: new Text(buttonText,
style: TextStyle(
backgroundColor: Colors.black,
color: Colors.white,
fontSize: 24,
fontWeight: FontWeight.bold,
),),
onPressed: () => _incrementCounter(buttonText)
),
);
}
@override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return Scaffold(
appBar: AppBar(
// Here we take the value from the MyHomePage object that was created by
// the App.build method, and use it to set our appbar title.
title: Text(widget.title),
),
body: Center(
// Center is a layout widget. It takes a single child and positions it
// in the middle of the parent.
child: Column(
children: <Widget>[
new Row(children: [
Expanded(
child: new MaterialButton(
color: Colors.black,
textColor: Colors.white,
padding: new EdgeInsets.only(left: 20, right: 100),
child: new Text("Tim 1",
style: TextStyle(
color: Colors.white,
fontSize: 20,
fontWeight: FontWeight.bold),),
onPressed: () {
contacts = "Tim1";
fall();}
),
),
Expanded(child: new MaterialButton(
color: Colors.black,
padding: new EdgeInsets.only(left: 100, right: 20),
child: new Text("Tim 2",
style: TextStyle(
color: Colors.white,
fontSize: 20,
fontWeight: FontWeight.bold),),
onPressed: () {
contacts = "Tim2";
fall();
}
),
),
],
),
new Row(children: [
Expanded(
child: new GestureDetector(
onTap: (contact1),
child: text1 = Text(_counter, maxLines: 1,
textAlign: TextAlign.left, style: TextStyle(
fontSize: 50,
fontWeight: FontWeight.bold,
),),
),
),
Expanded (
child: new GestureDetector(
onTap: (contact2),
child: Text(_counter1, maxLines: 1,
**textAlign: TextAlign.right, style: TextStyle(**
fontSize: 50,
fontWeight: FontWeight.bold)
),
),
),
],
),
new Row(
children: <Widget>[
Expanded(
child: new MaterialButton(
padding: EdgeInsets.only(left: 15,right: 15, bottom: 25, top: 18),
color: Colors.black,
textColor: Colors.white,
onPressed: () {},
child: Text("Points",
style: TextStyle(
fontSize: 40,
fontWeight: FontWeight.bold,
),),
),
),
Expanded(
child: new MaterialButton(
padding: EdgeInsets.only(left: 15,right: 15, bottom: 26, top: 23),
color: Colors.black,
textColor: Colors.white,
onPressed: () {},
child: Text("Contacts", textAlign: TextAlign.end,
style: TextStyle(
fontSize: 35,
fontWeight: FontWeight.bold,
),),
),
)
],
),
new Row(children: [
buildButton("1"),
buildButton("2"),
buildButton("3"),
],
),
new Row(children: [
buildButton("4"),
buildButton("5"),
buildButton("6"),
],
),
new Row(children: [
buildButton("7"),
buildButton("8"),
buildButton("9"),
],
),
new Row(children: [
buildButton(">"),
buildButton("0"),
new Expanded(
child: new MaterialButton(
color: Colors.black,
textColor: Colors.white,
padding: new EdgeInsets.all(20),
child: new Text("<",
style: TextStyle(
fontSize: 24,
fontWeight: FontWeight.bold,
),),
onPressed: () => clear(),
),
),
],
),
new Row(children: [
new Expanded(
child: new MaterialButton(
padding: new EdgeInsets.all(10),
color: Colors.cyan,
child: new Text("ENTER",
style: TextStyle(
color: Colors.black,
fontSize: 48,
fontWeight: FontWeight.bold,
),),
onPressed: () {
Navigator.push(context,
MaterialPageRoute(builder: (context) => FirstPage()),
);
}
),
),
],
),
],
),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}
}
答案 0 :(得分：1)
如果您确定要从该行中获取例外，只需将其替换为Text(_counter1 ?? ‘’)，以确保它将包含数据。无论如何，通过查看您的代码，我看不到_counter1可能被分配给null的位置，而且，将其用作var不会产生影响，因为它将隐式转换为String。
答案 1 :(得分：0)
点击“ Enter”后，我可以导航到另一个页面。我认为这是被执行的行为。
最近，我在标准的小部件/代码中遇到了类似的问题。我要做的就是运行flutter clean，关闭IDE，然后重新打开。如果仍然不能解决问题，请再次运行flutter clean并重新启动计算机。
答案 2 :(得分：0)
异常来自文本小部件，给您的行号是Text类内的行号，它检查数据是否为空。
您只需要仔细检查Text()小部件是否获得了不为空的数据。尽管您可以这样使用??运算符来完成此操作：Text(data ?? "")（如果data为空，它将用空字符串替换data）找出null的来源，并正确处理数据源。
还有另一个问题。似乎您是在将FirstPage()推入导航器而不导入实际的类。