How Flutter renders Widgets
Why Stack Overflow recommends it
Stack Overflow users link it when answering questions about why widgets rebuild, how state is preserved, and how the three trees fit together.
Recommended by 9 people across 9 different months, 2019 to 2022.
What it is
A Google Developer Days China 2019 talk by Flutter team members Andrew Fitz Gibbon and Matt Sullivan on how Flutter works internally. It explains the Widget, Element and RenderObject trees and how they relate during builds and rebuilds.
What people said
Recommends Jay Dangar · 2020-04 · Stack Overflow · on “Flutter : Understading Widget,Element and Render tree”
I have been trying to understand Flutter and How rendering works under the hood. I have watched a video regarding "How flutter renders a widget?" How Flutter Rendering works? [this video] I got to know that there are 3 (Widget, Element and Render Tree) trees being built. In the Video Widget is the blueprint of the layout, Element is the configuration and Render Tree does the actual paining. I am still not been able to understand as in the video, Matt Sulliman says about these three as follows : Widget : Immutable Description of UI (Means It won't change?), also It describe configuration of Element. Element : Instantiation of the widget in a widget tree at particular location. (BuildContext?) Rend
Recommends Gazihan Alankus · 2020-05 · Stack Overflow · on “Does whole subtree rebuilds on setState in flutter”
Yes, MyWidget1 is rebuilt upon that setState . Just trust the code. After you call setState , build is called, which calls the constructor of MyWidget1 . After each setState , the entire subtree is rebuilt. Old widgets are thrown away. States are not thrown away, though. State instances live on, they are not recreated (see didUpdateWidget). So, yes. After each setState , the entire subtree is rebuilt. This is OK, don't worry. The widget classes here are very lightweight classes. Dart's garbage collector is optimized to instantiate many such objects and throw them away together. This tree that you get to recreate again and again is just a facade. There are two more parallel trees that are not
Recommends Lulupointu · 2020-06 · Stack Overflow · on “How should I pause the camera when navigating to new screen?”
Flutter philosophy is to add/remove widget constantly from the widget tree, it is build to be efficient at doing so. I would advise you to watch this video where the Flutter team explain this better than I could : [this video]
Recommends Tox · 2020-08 · Stack Overflow · on “Flutter - UI is not updated correctly when removing an element”
This is not a solution but an explanation, refer to Marcin Szałek's comment for the solution. The reason that the ListView does not rerender as expected is that the TextFormField is a stateful widget. When you rebuild the widgets, you need to take note that there are 3 trees under the hood, which are the Widget, Element and RenderObject tree. The RenderObject is the visual representation, and is directly based on the Element. Whereas the Element is directly based on the Widget, and the Widget is just the configuration, i.e. what you type in code. When first instantiating a widget, a corresponding element is created. However, when you call setState() to change the _items list, the widget is r
Recommends easeccy · 2020-12 · Stack Overflow · on “How to rebuild only a spesific item in the Listview?”
You should consider how widget, element and render trees work in order to be concerned. There is a great video [this video] about Flutter's rendering mechanism. When rebuilding a tree, framework compares [LINK] the two versions of widgets by using only the key [LINK] and runtime type values. This means that if you change string value of the Text widget, the same render object with mutated data will be used again. New render object won't be created, which means no unnecessary rebuilds will happen on the render tree. Rebuilding the widget tree is not expensive compared to the render tree. There is a limit on minimizing the the build scope in the ListView . ListView itself should be rebuilt in order
Recommends Rohan Thacker · 2021-04 · Stack Overflow · on “Is it possible to somehow indicate that the two widgets have the same state?”
Specify that such a widget already exists in the tree and I should use its state and change What you're trying to do is actually, what the flutter framework does, and the way flutter does it is with the use of Elements and RenderObjects . To understand this in more detail do check this video [this video] from the flutter team explaining how flutter renders UI's. A common paradigm used in in flutter, is the flux architecture which is that of data-down actions up. So to summarize, you should not need to do this activity of deduplication of your widgets as the framework will take care of it for you. Being that the data is passed from a parent widget to the child, and the parent widget is where the s
Recommends Cosneanu Cristian · 2021-05 · Stack Overflow · on “How does the Widget Lifecycle work in Flutter?”
Rather the me butchering a nice explanation from the developers themselves, here is a short clip explaining the widget lifecycle [LINK] A more detailed explanation was made in 2019 At Google Developer Days China [this video] If you talk about performance, the functional approach is better. Consider this: class TestWidget extends StatelessWidget { @override Widget build(BuildContext context) { final streamController = StreamController<String>.broadcast(); Future.delayed(Duration(seconds: 3)).then((_) { streamController.sink.add('new value to received'); streamController.close(); }); return StreamBuilder( stream: streamController.stream, builder: (BuildContext context, AsyncSnapshot<String> snapsho
Recommends Ma Jeed · 2022-02 · Stack Overflow · on “Are Statefull widget deleted and replaced when being rebuild using setState()?”
there are 3 trees : Widget Tree, Element Tree and Render Object Tree. watch this: How Flutter renders Widgets [this video]
Recommends Omatt · 2022-08 · Stack Overflow · on “A RenderConstrainedBox expected a child of type RenderBox but received a child of type RenderSliverPadding”
RenderBox and RenderSliver are different layout protocols for Rendering. You can watch this video [this video] to learn more about this. The issue here is that a Sliver is being used as a child in SizedBox - which is a RenderBox. This isn't allowed since SizedBox is a RenderBox and expects a 'RenderBox' widget, not RenderSliver. If you need to set Slivers inside a RenderBox, you can wrap the Sliver first in CustomScrollView [LINK] .
Cites Joshua de Guzman · 2019-12 · Stack Overflow · on “Preserve widget state when temporarily removed from tree in Flutter”
Widgets are meant to store transient data of their own within their scope and lifetime. Based on what you have provided, you are trying to re-create CounterButton child widget , by removing and adding it back to the widget tree. In this case, the counter value that is under the CounterButton was not saved or not saving in the MyHomePage screen, the parent widget , without any reference to a view model or any state management within or at the top level. A more technical overview how Flutter renders your widgets Ever wonder what is the key if you try to create a constructor for a widget? class CounterButton extends StatefulWidget { const CounterButton({Key key}) : super(key: key); @override _C