Question 1

When do you use StatelessWidget and what does build mean in it?

Accepted Answer

A StatelessWidget describes the UI from fixed configuration, and build returns a new widget tree when Flutter asks to update it.

Question 2

Explain the basic lifecycle of a StatefulWidget's State.

Accepted Answer

A State usually goes through initState, then didChangeDependencies and build, may receive didUpdateWidget, then dispose on final removal.

Question 3

What is BuildContext and why does its position in the tree matter?

Accepted Answer

BuildContext is a handle to a widget's position inside the element tree, and through it you look up ancestors such as Theme or an InheritedWidget.

Question 4

How do keys help Flutter preserve widget identity?

Accepted Answer

A key lets Flutter match a new widget with a previous element when the order or set of siblings changes, thereby preserving the correct state.

Question 5

Explain the rule constraints go down, sizes go up in Flutter.

Accepted Answer

The parent sends constraints to the child, the child picks a size within them, and then the parent positions it.

Question 6

How do const widgets help reduce the cost of a rebuild?

Accepted Answer

const creates a configuration that can be shared at compile time, which lets Flutter skip static parts and do less checking during an update.

Question 7

What does setState actually do, and how do you avoid a wide rebuild?

Accepted Answer

setState tells the framework that the State changed and requests a rebuild of the StatefulElement and its children; put the state at the nearest logical owner.

Question 8

When do you use InheritedWidget and didChangeDependencies?

Accepted Answer

An InheritedWidget shares a value across the tree, and didChangeDependencies notifies the State when a dependency it registered through the context changes.

Question 9

What are the trade-offs of using GlobalKey in Flutter?

Accepted Answer

A GlobalKey gives access and a unique identity across the tree, but it is more expensive and more tightly coupled than local keys and must not be created inside build.

Question 10

How do you use the child parameter in a Builder to reduce rebuilds?

Accepted Answer

Put the static subtree in child outside the builder and pass it through as is; when the builder is called, only the part that depends on the value is rebuilt.