这是我在Stackoverflow中的第一个问题。当我们将其作为类构造函数参数传递时,我试图在另一个StatefulWidget中调用一个小部件。
所以我有这个自定义小部件:
class MyTextWidget extends StatelessWidget {
final String text;
MyTextWidget({ @required this.text });
@override
Widget build(BuildContext context) {
return Text(this.text);
}
}
我想在另一个这样的小部件中使用(通过类构造函数参数传递)
import 'package:myproject/MyTextWidget.dart';
.
.
.
// Passing widget like this
child: Example(display: MyTextWidget,text: this.widget.text);
.
.
.
// And use this widget like this
this.widget.display(text: this.widget.text);
这是我的第一个代码:
class Example extends StatefulWidget {
final Widget display;
final String text;
Example({ @required this.display, @required this.text });
@override
State<StatefulWidget> createState() {
return ExampleState();
}
}
class ExampleState extends State<Example> {
@override
Widget build(BuildContext context) {
return this.widget.display(text: this.widget.text); // here we have error
}
}
但是我有这个错误
The expression doesn't evaluate to a function, so it can't be invoked.dart(invocation_of_non_function_expression)
我意识到我需要对此问题进行typedef,所以我改进这样的代码:
typedef Widget DisplayType({ @required String text });
class Example extends StatefulWidget {
final DisplayType display;
final String text;
Example({ @required this.display, @required this.text });
@override
State<StatefulWidget> createState() {
return ExampleState();
}
}
class ExampleState extends State<Example> {
@override
Widget build(BuildContext context) {
return this.widget.display(text: this.widget.text);
}
}
我们的错误已修复,但是当我想在另一个窗口小部件中传递MyTextWidget时:
child: Example(display: MyTextWidget,text: this.widget.text);
最后我得到这个错误:
The argument type 'Type' can't be assigned to the parameter type 'Widget Function({String text})'.dart(argument_type_not_assignable)
我该如何解决这个问题?
我认为您想display
成为一个返回的构建器函数MyTextWidget
。
import 'package:flutter/material.dart';
Future<void> main() async {
return runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(final BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(primarySwatch: Colors.blue),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
@override
Widget build(final BuildContext context) {
return Scaffold(
appBar: AppBar(title: const Text("Home")),
body: Center(
child: Example(
display: ({@required final String text}) {
assert(text != null);
return MyTextWidget(text: text);
},
text: "some text",
),
),
);
}
}
class MyTextWidget extends StatelessWidget {
final String text;
MyTextWidget({@required this.text}) : assert(text != null);
@override
Widget build(final BuildContext context) {
return Text(this.text);
}
}
typedef Widget DisplayType({@required final String text});
class Example extends StatefulWidget {
final DisplayType display;
final String text;
Example({
@required this.display,
@required this.text,
}) : assert(display != null),
assert(text != null);
@override
State<StatefulWidget> createState() {
return ExampleState();
}
}
class ExampleState extends State<Example> {
@override
Widget build(final BuildContext context) {
return this.widget.display(text: this.widget.text);
}
}
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