How to force Flutter to rebuild / redraw all widgets?

Is there a way to force Flutter to redraw all widgets (e.g. after locale change)?

Solution 1:

Your Widget should have a setState() method, everytime this method is called, the widget is redrawn.

Documentation : Widget setState()

Solution 2:

This type of use case, where you have data that children can read but you don't want to explicitly pass the data to the constructor arguments of all your children, usually calls for an InheritedWidget. Flutter will automatically track which widgets depend on the data and rebuild the parts of your tree that have changed. There is a LocaleQuery widget that is designed to handle locale changes, and you can see how it's used in the Stocks example app.

Briefly, here's what Stocks is doing:

• Put a callback on root widget (in this case, StocksApp) for handling locale changes. This callback does some work and then returns a customized instance of LocaleQueryData
• Register this callback as the onLocaleChanged argument to the MaterialApp constructor
• Child widgets that need locale information use LocaleQuery.of(context).
• When the locale changes, Flutter only redraws widgets that have dependencies on the locale data.

If you want to track something other than locale changes, you can make your own class that extends InheritedWidget, and include it in the hierarchy near the root of your app. Its parent should be a StatefulWidget with key set to a GlobalKey that accessible to the children. The State of the StatefulWidget should own the data you want to distribute and expose methods for changing it that call setState. If child widgets want change the State's data, they can use the global key to get a pointer to the State (key.currentState) and call methods on it. If they want to read the data, they can call the static of(context) method of your subclass of InheritedWidget and that will tell Flutter that these widgets need to rebuilt whenever your State calls setState.

Solution 3:

Old question, but here is the solution:

In your build method, call the rebuildAllChildren function and pass it the context:

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

void rebuildAllChildren(BuildContext context) {
  void rebuild(Element el) {
    el.markNeedsBuild();
    el.visitChildren(rebuild);
  }
  (context as Element).visitChildren(rebuild);
}

This will visit all children and mark them as needing to rebuild. If you put this code in the topmost widget in your widgets tree, it will rebuild everything.

Also note you must order that specific widget to rebuild. Also you could have some boolean so that the rebuild of that widget only rebuilds all of its children when you really need it (it's an expensive operation, of course).

IMPORTANT: This is a hack, and you should only do this if you know what you are doing, and have strong reason to do so. One example where this is necessary is in my internationalization package: i18_extension. As Collin Jackson explained in his answer, you are really not supposed to do this in general.

Solution 4:

I explain how to create a custom 'AppBuilder' widget in this post.

https://hillelcoren.com/2018/08/15/flutter-how-to-rebuild-the-entire-app-to-change-the-theme-or-locale/

You can use the widget by wrapping your MaterialApp with it, for example:

Widget build(BuildContext context) {
  return AppBuilder(builder: (context) {
    return MaterialApp(
      ...
    );
  });
}

You can tell the app to rebuild using:

AppBuilder.of(context).rebuild();

Solution 5:

Refreshing the whole widget tree might be expensive and when you do it in front of the users eyes that wouldn't seem sweet.

so for this purpose flutter has ValueListenableBuilder<T> class. It allows you to rebuild only some of the widgets necessary for your purpose and skip the expensive widgets.

you can see the documents here ValueListenableBuilder flutter docs
or just the sample code below:

  return Scaffold(
  appBar: AppBar(
    title: Text(widget.title)
  ),
  body: Center(
    child: Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        Text('You have pushed the button this many times:'),
        ValueListenableBuilder(
          builder: (BuildContext context, int value, Widget child) {
            // This builder will only get called when the _counter
            // is updated.
            return Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: <Widget>[
                Text('$value'),
                child,
              ],
            );
          },
          valueListenable: _counter,
          // The child parameter is most helpful if the child is
          // expensive to build and does not depend on the value from
          // the notifier.
          child: goodJob,
        )
      ],
    ),
  ),
  floatingActionButton: FloatingActionButton(
    child: Icon(Icons.plus_one),
    onPressed: () => _counter.value += 1,
  ),
);

And also never forget the power of setState(() {});