Flutter is a Google-developed open-source UI toolkit that enables developers to build natively compiled applications for mobile, web, and desktop from a single codebase. Its declarative UI framework allows developers to describe the desired user interface state and structure using a tree of widgets, promoting expressive designs, consistent experiences, and efficient development workflows.
As Flutter developers you might have read about how Flutter works internally and have wondered what the difference is between Repaint and Rebuild in Flutter. In this article, we are gonna explain to you in detail the difference and how Flutter does it Internally.
What do you mean by Rebuilding in Flutter?
Rebuilding refers to the process of recreating the widget tree or parts of the widget tree due to changes in the widget properties(i.e. state of a widget) or hierarchy. When a widget’s state changes(i.e due to a change in the value of a state that the widget is dependent on by a button press). Flutter marks that widget and its descendants as dirty. For each dirty widget, Flutter calls its build method to create a new instance of the widget(i.e. description or the UI of the widget changes). Rebuilding can be computationally more expensive compared to repainting since it involves recalculating the layout of the widget that is marked as dirty and its descendants.
What do you mean by Repainting in Flutter?
Repainting refers to the process of taking the new widget tree and translating it to pixels. It occurs after rebuilding the widgets. It uses RenderObjects created during the build to paint the widget. When a widget needs to change its appearance due to an update in its state or properties then the paint method is called to redraw itself. Repainting typically occurs when the visual properties of a widget change, such as its color, size, or shape. Repainting is efficient because it doesn’t involve recomputing the layout of the widget or its children.
Differences and Similarities
In Flutter, repaint refers to updating the visual appearance of a widget without changing its layout, typically triggered by changes in properties like color or size. Rebuild involves recreating part or all of the widget tree due to changes in structure or properties, potentially affecting layout and requiring more computational resources.
In Flutter, both repaint and rebuild processes are essential for updating the user interface in response to changes. Both processes involve updating the visual appearance of widgets, albeit repaint focuses on visual changes without affecting layout, while rebuild may involve layout changes due to modifications in structure or properties.
Best Practices for Optimizations
To optimize repainting and rebuilding in Flutter apps, minimize unnecessary widget rebuilds by utilizing stateless widgets where possible and leveraging the setState method judiciously to update only the necessary parts of the widget tree. Additionally, reduce unnecessary repaints by using const constructors for widgets with static properties and employing techniques like ValueNotifier and AnimatedBuilder to limit repaints to only the relevant portions of the UI.
You can also use repaint boundaries for optimizing Flutter apps. By encapsulating parts of the widget tree within repaint boundaries using widgets like RepaintBoundary or LayoutBuilder, you can prevent unnecessary repaints of those subtrees, thus improving performance by minimizing the scope of repaint operations to only the areas that require updating.
Conclusion
We learned what is repainting and rebuilding in Flutter. You can use this knowledge to minimize widget rebuilds as much as possible to make performant flutter apps. You can also use Flutter dev tools for widget profiling and optimize even further. So Flutter developers experiment as much as possible and play around with these concepts to get clarity around it.
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