Flutter, pasing parameters on StatefulWidget - flutter

Question

Can someone tell me what is happening in this program?
body: new ListView.builder(
itemBuilder: (BuildContext context, int index) {
return new StuffInTiles(listOfTiles[index]);
},
itemCount: listOfTiles.length,
),
),
);
}
}
class StuffInTiles extends StatefulWidget{
final MyTile myTile;
const StuffInTiles(this.myTile);
#override
StuffInTilesState createState() => StuffInTilesState();
}
class StuffInTilesState extends State<StuffInTiles> {
#override
Widget build(BuildContext context) {
return Container(child:
//Text(widget.myTile.title),);
_buildTiles(widget.myTile));
}
Widget _buildTiles(MyTile t) {
I want to understand how passing parameters works,why i have
const StuffInTiles(this.myTile);
in this program, what this code is doing?
in my class StuffInTilesState extends State<StuffInTiles> i don't have any constructor, so how this code is working? why my parameters just happen to be there? before i was learning C++, so this is like a magic to me

Answer 1

If you learned C++ you are probably familiar with initializer list, which Dart has as well. In C++ you could do something:
MyClass {
MyClass(MyTitle title) : this.myTitle = title;
final MyTitle myTitle;
}
Which is also valid in Dart. However, Dart allows you to shorthand the call, by automatically assigning the reference to the new class property, without using any intermediate variable.
MyClass(this.myTitle);
Which is basically the same but ensures that any given property won't be null unless you explicitly pass null.
There are other type of constructors available on Dart, such as private constructors, factory constructors and named constructors. You may want to check the official documentation to learn more about it.

Answer 2

By default, when you create classes in Dart, there is just a default constructor implemented.
For example, if you have a class named AwesomeWidget. It will have a default constructor AwesomeWidget() that lets you create an instance of this widget.
So you could use a default constructor in code like so:
//Example 1
return AwesomeWidget();
//Example 2
AwesomeWidget myWidget = AwesomeWidget();
//Example 3
//...
Row(
children: [
Text("Example Code!"),
AwesomeWidget(),
Text("Example Footer Code!"),
],
),
//...
Now if you want to pass some values or some data to your Widget classes then you use the code you have posted above in your question.
The question is: Why would we want to send data to our widgets?
Answer: The biggest use case is when we make our list items as separate widgets. For example, in my food app, I have to show my user's order history in a ListView, so for the UI of each individual list item, I will just make a reusable Widget called OrderHistoryListItem.
In that OrderHistoryListItem, you want to show the date and time of the object. And the order id, and how much the user paid in that order or any other details, so to display this, we send this data to our Reusable Widget List Item, which displays it. Simple as that.
And that is one of the reasons why we pass values to Widgets. As a programmer, you can make use of this handy feature for more complex scenarios, be creative!