Example on when to use didUpdateWidget

Question

I think I understand all other StatefulWidget lifecycle callbacks, but didUpdateWidget is one that I never had to use, neither can think of a specific use case, as I just get information about the Widget using the widget getter at build.

So on which cases didUpdateWidget is useful and desired to be used?

Answer 1

didUpdateWidget exists for when you want to trigger side-effects when one of the parameters of your stateful widget change.

A typical use-case is implicitly animated widgets. These are implemented using didUpateWidget like so:

@override
void didUpdateWidget(MyWidget oldWidget) {
  super.didUpdateWidget(oldWidget);
  if (widget.value != oldWidget.value) {
    // TODO: start a transition between the previous and new value
  }
}