Flutter 检测传递给有状态小部件的值何时发生变化

Question

I have a statefull widget where am passing an integer to. I would like to execute a method when the value passed to the widget changes

class Test extends StatefulWidget {
 final String item;
 const Test({
  Key? key,
  required this.item,
 }) : super(key: key);

@override
_TestState createState() => _TestState();
}

class _TestState extends State<Test> {
 List<String> hh = [];

 @override
 void initState() {
  super.initState();
  print("init state value is  ${widget.item}");
 }

 @override
 Widget build(BuildContext context) {
  return Container();
 }

 void getDataItems() {
  print("value passed is ${widget.item}");

  setState(() {
    hh = [widget.item];
  });
 }
}

So on the above i would like to detect when the value of string item passed to the widget changes and call the method getDataItems which will later update the list hh. How can i detect when the value passed statefull widget has changed?

Answer 1

You can check the useEffect , which is based on the React hook useEffect.

Or you can hardcode it.

Create other integer: late int lastCalledInteger;

And check this in the build:

@override
Widget build(BuildContext context) {
  if(lastCalledInteger != integer) {
    getDataItems();
    lastCalledInteger = integer;
  }

  return Container();
}

Answer 2

You can simply override didUpdateWidget on State to be informed of every change of passed in arguments. If you have multiple arguments you of course need to change what changed. For this didUpdateWidget provides you with the oldWidget as only parameter.

From the documentation:

Called whenever the widget configuration changes.

[...]

Override this method to respond when the widget changes (eg, to start implicit animations).