I want to pass to my Widget a function that returns a future:
class CircularButtonWithIcon extends StatefulWidget {
CircularButtonWithIcon(
{Key key,
#required this.onPress,
this.activeStatus})
: super(key: key);
final Function activeStatus;
class _CircularButtonWithIconState extends State<CircularButtonWithIcon> {
bool active;
#override
void initState() {
super.initState();
widget.activeStatus.then(...);
}
However Dart's class Function has no way to specify that the function's return type.
Is it possible to do such thing?
You can add the return type front of the Function
i.e.
class CircularButtonWithIcon extends StatefulWidget {
Future<void> Function() activeStatus;
CircularButtonWithIcon({Key key, #required this.onPress, this.activeStatus,}) : super(key: key);
}
Related
I want to set default function in my child Widget in a constructor.
Basically, I have two widgets
Login (Parent Widget)
AppButton (Child Widget)
Here is my AppButton.dart
And I am calling this child widget in Login.dart (Parent) like this:
AppButton(title: "Login")
Please give me a way that to set default function without making "onPress" required for it's Parent (Login.dart)
TIA
Only static value can be set as default value in constructor, so you need define you function as static like this:
class AppButton extends StatefulWidget {
final Function onPress;
const AppButton({Key? key, this.onPress = _onPress}) : super(key: key);
static void _onPress(){}
#override
State<AppButton> createState() => _AppButtonState();
}
just make it nullable:
class MyButton extends StatefulWidget {
final void Function()? onPress;
final String title;
const MyButton({Key? key, this.onPress, required this.title}) : super(key: key);
#override
State<MyButton> createState() => _MyButtonState();
}
class _MyButtonState extends State<MyButton> {
void Function() defaultOnPress = (){
// your default function here
};
#override
Widget build(BuildContext context) {
return ElevatedButton(onPressed: widget.onPress ?? defaultOnPress, child: const Text("my button"));
}
}
still you can get const constructor
you could put "static" before childOnPress()
It's the first time a use Flutter (2.8.1) and I'having problems trying to undestrand what's going wrong.
I have a Stateful widget like this:
class SimpleWidget extends StatefulWidget {
const SimpleWidget({Key key, #required this.aValue}) : super(key: key);
final Type2 aValue;
#override
_SimpleWidgetState createState() => _SimpleWidgetState();
}
class _SimpleWidgetState extends State<SimpleWidget> {
Type1 from;
Type1 to;
#override
void initState() {
print('mounted: $mounted'); // true
print('widget.aValue: ${widget.aValue}'); // null <-- WHY IS THIS NULL?
super.initState();
from = ...;
to = ...;
}
...
}
that I call in this way:
List<Type1> breakTimes = await showDialog(
context: context,
builder: (context) {
print('currentElement.aValue: ${currentElement.aValue}'); // not null
return SimpleWidget(aValue: currentElement.aValue);
},
);
Why is widget.aValue == null in initInstance()? How can I solve it?
There is wrong in your code :
Chane this to this:
class SimpleWidget extends StatefulWidget {
final Type2 aValue; // initialize 1st
const SimpleWidget({Key key, #required this.aValue}) : super(key: key);
#override
_SimpleWidgetState createState() => _SimpleWidgetState();
}
I installed flutter_lints plugin in my project, after installing then it shows a warning message "Don't put any logic in createState". How to solve this issue?
class OverviewPage extends StatefulWidget {
final int id;
const OverviewPage({Key? key, required this.id}) : super(key: key);
#override
_OverviewPageState createState() => _OverviewPageState(id); // Warning on this line
}
class _OverviewPageState extends State<OverviewPage>{
late final int id;
_OverviewPageState(this.id);
}
Don't pass anything to _OverviewPageState in the constructor.
class OverviewPage extends StatefulWidget {
final int id;
const OverviewPage({Key? key, required this.id}) : super(key: key);
#override
_OverviewPageState createState() => _OverviewPageState();
}
class _OverviewPageState extends State<OverviewPage>{
// if you need to reference id, do it by calling widget.id
}
I someone want to initiate a variable inside the state from the main class you can use for example, cause you can't use it in constructor class.
#override
void initState() {
super.initState();
id = widget.id;
code = widget.code;
//your code here
}
I have a stateful widget that has one method called in initialisation. I wanna know how to be able to get a parameter from the previous screen and pass it in initState to my initialisation method
class LabDetalheWidget extends StatefulWidget {
final String path;
const LabDetalheWidget({
Key key,
this.path,
}) : super(key: key);
You can pass parameter like that
class MyWidget extends StatefulWidget {
final String param;
const MyWidget({
Key key,
this.param,
}) : super(key: key);
#override
_MyWidgetState createState() => _MyWidgetState();
}
class _MyWidgetState extends State<MyWidget> {
#override
void initState() {
print(widget.param);
super.initState();
}
#override
Widget build(BuildContext context) {
return Container(
);
}
}
Inside the state you can access the parameter like that
print(widget.param)
I believe you wanna pass data across routes.. If so then read this flutter cookbook's section you might get the idea
https://flutter.dev/docs/cookbook/navigation/passing-data
When I use VSCode snippet Extract Widget, I have the following :
class MyExtractedWidget extends StatelessWidget {
const MyExtractedWidget({
Key key,
#required T someVariable,
}) : _someVariable = someVariable,
super(key: key);
final T _someVariable;
#override
Widget build(BuildContext context){ return Container(); }
}
However, I am used to write constructors the following way :
class MyExtractedWidget extends StatelessWidget {
const MyExtractedWidget({
Key key,
#required this.someVariable, // Directly accessing variable using "this"
}) : super(key: key);
final T someVariable;
#override
Widget build(BuildContext context){ return Container(); }
}
Do you know why snippets' constructors use a temporary variable instead of directly writing in the variable?
Is it related to encapsulation? If yes, I cannot understand why, as an extracted Widget is written in the same file, and that "underscored" variables are accessible in whole file.
EDIT
I tried with another widget and I have a kind of mix :
class Test extends StatelessWidget {
const Test({
Key key,
#required List<SortedExpense> sortedExpenses,
#required this.expensesSink,
}) : _sortedExpenses = sortedExpenses, super(key: key);
final List<SortedExpense> _sortedExpenses;
final StreamSink<List<Expense>> expensesSink;
...
This is based on the privacy of the variables you're extracting.
For example, the following widget:
Text(_count.toString())
will generate:
class MyName extends StatelessWidget {
const MyName({
Key key,
#required int count,
}) : _count = count, super(key: key);
final int _count;
#override
Widget build(BuildContext context) {
return Text(_count.toString());
}
}
while this widget:
Text(count.toString())
will create:
class MyName extends StatelessWidget {
const MyName({
Key key,
#required this.count,
}) : super(key: key);
final int count;
#override
Widget build(BuildContext context) {
return Text(count.toString());
}
}