“状态”class 构造函数在 Flutter 中是什么样子的？

Question

What does super.didChangeDependencies(); do in the following code?

  void didChangeDependencies() {
    if (_isInit) {
      setState(() {
        _isLoading = true;
      });
      Provider.of<Contests>(context).fetchAndSetContests().then((_) {
        setState(() {
          _isLoading = false;
        });
      });
    }
    _isInit = false;
    super.didChangeDependencies();
  }

I know it should call the constructor of the State class but I can't find the constructor's definition and don't understand what is the purpose of calling that?

Answer 1

From the Flutter docs for didChangeDependencies :

Called when a dependency of this State object changes.

For example, if the previous call to build referenced an InheritedWidget that later changed, the framework would call this method to notify this object about the change.

This method is also called immediately after initState. It is safe to call BuildContext.dependOnInheritedWidgetOfExactType from this method.

Subclasses rarely override this method because the framework always calls build after a dependency changes. Some subclasses do override this method because they need to do some expensive work (eg,.network fetches) when their dependencies change, and that work would be too expensive to do for every build.