Flutter Stack

Widgets are the central class hierarchy in the Flutter framework . A widget is an immutable description of part of a user interface. Widgets can be inflated into elements, which manage the underlying render tree. Widgets themselves have no mutable state (all their fields must be final).

Single-child layout widgets Align . A widget that aligns its child within itself and optionally sizes itself based on the child’s size . AspectRatio. A widget that attempts to size the child to a specific aspect ratio.

In Flutter, almost everything is a widget—even layout models are widgets . The images, icons, and text that you see in a Flutter app are all widgets. But things you don’t see are also widgets, such as the rows, columns, and grids that arrange, constrain, and align the visible widgets.

In Flutter, LayoutBuilder Widget is similar to the Builder widget except that the framework calls the builder function at layout time and provides the parent widget’s constraints.