What is the difference between `context.watch` and `context.select` in flutter_bloc?

Question

I’m interested in understanding the distinctions between context.watch and context.select in the context of blocs. Can you provide insights into when it is more appropriate to utilize watch and when select would be the better choice in a bloc scenario?

Thank you for your assistance in clarifying this matter.

Answer 1

In flutter_bloc, context.watch and context.select are both useful for interacting with the states of your blocs, but they have slightly different use cases.

context.watch: Use context.watch when you want to listen to changes in the state of any bloc or Cubit and rebuild your widget whenever the state changes. This can be useful when you need to rebuild your widget based on any change in the bloc state, regardless of which part of the state changed. context.watch ensures that your widget rebuilds if any state in the observed bloc changes.

context.select: Use context.select when you only want to listen to specific parts of the state and rebuild your widget when those specific parts change. This can be more efficient than context.watch because it allows you to be more selective about which state changes trigger a rebuild. By selecting only specific parts of the state to listen to, you can avoid unnecessary rebuilds when other parts of the state change. In summary:

Use context.watch when you want to rebuild your widget on any state change in the observed bloc.

Use context.select when you want to be more selective about which state changes trigger a rebuild in your widget.

It’s generally better to use context.watch when you need to react to changes in various parts of the state, and context.select when you only care about specific parts of the state. Choose the one that best fits your specific use case to improve performance and minimize unnecessary widget rebuilds.