Problem Statement
What is the difference between Consumer and Selector widgets in Provider? When should you use each?
Explanation
Consumer rebuilds whenever any part of the provided value changes because it listens to the entire object. If your model has multiple properties and only one changes, Consumer still rebuilds even if the widget only uses properties that didn't change. This can cause unnecessary rebuilds when working with large models where widgets only care about specific properties.
Selector solves this by allowing you to specify exactly which part of the model to listen to using a selector function. It only rebuilds when the selected value changes, determined by comparing old and new selected values. For example, Selector<CounterModel, int>(selector: (context, model) => model.count) only rebuilds when count changes, ignoring changes to other properties in CounterModel.
Use Consumer when the widget depends on the entire model or when the model is small with few properties. Use Selector for fine-grained control, especially with large models where widgets only care about specific properties. Selector improves performance by minimizing rebuilds, but adds complexity with the selector function. The shouldRebuild parameter provides even more control, allowing custom comparison logic beyond default equality.
Consumer2, Consumer3, etc., listen to multiple providers, while Selector can select from one provider. For multiple providers with fine-grained control, use Selector with a selector returning a tuple of values. Understanding the tradeoff between Consumer's simplicity and Selector's performance optimization helps you choose appropriately - default to Consumer for simplicity, use Selector when profiling shows rebuild performance issues.
