Flutter framework lets developers develop visually appealing native apps on iOS & Android that too from a single code base. Every single Flutter mobile app’s main building is a widget and the objective of this blog is to provide the mobile app developer with information about different kinds of widgets, their hierarchy, as well as how Flutter utilizes widgets to render native-like UIs.
Widget basic information
A widget is a User Interface component or simply a component that directly interacts with a UI layer of applications. Flutter Widget is lightweight, unlike iOS UI-Widget or Android View.
An Element represents the widget’s utilization to configure a specific location in the tree. The root element is the mobile app, which is a Widget itself. Let us have a glance at a typical widgets tree utilizing a nice visualizing and exploring tool Widget Inspector:
To manage or control how one widget replaces another widget in the tree it utilizes the Key property. A newly built widget will merely be utilized to update an element which is already existing. Keys must be ideal amongst the elements that too with the same parent.
Elements have the following lifecycle:
Types of Widget
Let us have a deep look at different kinds of widgets. The Widget class itself has 5 implementers, named
PreferredSizeWidget
ProxyWidget
RenderObjectWidget
StatefulWidget
StatelessWidget
with its own subclasses.
Mostly you’ll be working with StatefulWidget & StatelessWidget. In short, if there are user interactions with a widget or its state changes over time with it, for example — it’s StatefulWidget. If there is no internal state to manage & the widget just displays certain static information — it’s StatelessWidget. These 2 kinds of widgets give a build() method. While creating or updating an element tree, the Flutter calls those build() methods recursively.
The build method has just one parameter BuildContext which is an Element object . The BuildContext interface was introduced to dispirit direct manipulation of Element objects. There are typically 3 scenarios while a build method might be called:
- Widget is inserted into the tree
- When the widget or parent of the widget changes its configuration,
- When an InheritedWidget (see description below) it depends on alterations.
Now, let us have a glance at StatefulWidget as it has a bit very much complex structure.
StatefulWidget
To build a Stateful Widget we require to create 2 classes, one extends the StatefulWidget class & overrides the createState method. Another is a generic State<> class extension where we require to override a build method to actually build our widget.
A Stateful Widget can be loaded multiple times by calling the setState method. This will trigger the build() method to be called again.
Now let us move to a less-known type of widget.
PreferredSizeWidget
The most widely utilized implementers are CupertinoTabBar, AppBar, &TabBar.
ProxyWidget
Extends with just one required child property to utilize it, rather than building the latest one. This widget does not have real usage. Its 2 implementers InheritedWidget & ParentDataWidget are the most interesting part for us.
InheritedWidget
The InheritedWidget works in conjunction with a StatefulWidget as well as lets you pass its state to every descendant. One good instance of usage of InheritedWidget is when you require to pass data across your mobile app. To achieve it you can make your mobile app class a StatefulWidget with a state which returns an InheritedWidget implementation in its build method.
ParentDataWidget
Base class for widgets that hook ParentData information to RenderObjectWidgets’s children (see below). The most widely utilized implementers are
- Flexible — It simply controls how a child of a Flex flexes, Column, or Row.
- Positioned — Its’ a widget that simply controls where a stack’s child is positioned
- TableCell — This one is a widget that simply controls how a child of a Table is aligned.
RenderObjectWidget
If you’re familiar with gaming engines, Flutter renders User Interface in a very similar way. Flutter updates the User Interface at a certain frames-per-second rate (usually at 60fps) & utilizes the GPU for maximum of the work. Rendering is where trually our Flutter widgets convert into pixels on a device screen.
We already know that Widgets generate Element objects, or in more detail, Stateful- & StatelessWidget creates RenderObjectWidget which creates RenderObjectElement with associated RenderObject widget in the render tree, which simply handles concrete rendering operations such as laying out, painting, & composing:
- Layout — does both positioning & sizing elements on a screen.
- Painting — is about figuring out what those elements actually look like.
- Composite — the stacks elements together in draw order so that these can be composed on the screen as single one thing.
To conclude
As we can see there is an entirely new world behind the widgets of Flutter and we completely hope this blog was useful to you to provide you with a basic understanding of widgets structure. We thank you for reading this blog, we hope you enjoyed the blog. However, if you are looking for a flutter app development company India, then Get Widget is surely a good choice you can ever make.
Get Widget
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