This manages the lifecycle of the value it provides, using a Provider pattern.

Here are some of the Providers you can work with: Provider

With information about your Provider in this new context, you can now access it from within this new scope.

This build method creates a new BuildContext that contains information about your Provider.

You can do that by creating a new file (Widget) with its own build method, then calling it as one of the children between your Provider and where you use it.

You get that by running a build method between where you create the Provider and wherever it is you’re trying to use it.

In short, you need a new context one with information about the Provider in it. But you can’t use a Provider unless it’s in the context where you’re trying to use it. This means the context is created before the Provide, so the Provider can’t possibly be part of the information contained in that context since it didn’t exist yet when that context was created. When you create a Provider, it’s declared within the BuildContext of the build method it’s in. The widgets using the data will only grab that data from the nearest one, and so never see any others. An important thing to know is you can’t use more than one of these for the same type, in the same scope. It has been recommended to keep these as far down the tree as possible, to avoid “polluting the scope”. After all, you can’t use it if it’s not there to use. You place it above where you’re going to use it. These handle putting an access point into your tree, exposing the objects you need to use. When is replaced with something that is not equal to the old value as evaluated by the equality operator =, this class notifies its listeners.”

ChangeNotifier uses the notifyListeners function whenever there is any change in the class/model/object.

is optimized for small numbers (one or two) of listeners.” - change_notifier.dart

“A class that can be extended or mixed in that provides a change notification API using for notifications.

Here are the main two most people use, but these aren’t the only way to do it: ChangeNotifier You can only use one of these with any one Type/Object/Model. A ChangeNotifier is going to notify of any changes in the class, as it is tracking the object as a whole. Which one you use will depend on what you’re trying to listen for. These handle notifying the Providers that something has changed. Which classes you use will depend on what you need to do in your situation. You have three jobs, and each of those classes can do one of them.

The other people are the Consumers of fire, and a Provider.of water.

If door is closed, so someone has to open it and Provide access (expose the fire).

Sound the alarm (Notify people things Changed, that we now have a fire).

I like to explain it as a firefighting team. This all becomes a lot easier to understand when you stop thinking there are a lot of classes and start thinking there are only three jobs that need to be done. But, after Remi kindly took a lot of his time to help me understand (and didn’t laugh at me) I realized something. When someone first looks at this, they often get intimidated. I mean, you could make a word cloud out of all the classes you can use with it: Provider looks daunting when you first dig into it. If you don’t understand, no explanation can help. If you understand, no explanation is necessary. You remember InheritedWidget, right? I like to call it “Flutter’s Monad”: In short, Provider is like a way to use InheritedWidget that humans can understand. They even said so in their talk, “Pragmatic State Management”, at I/O 2019

In fact, they recommend Remi Rousselet’s Provider over their own version of it, which was called Package Provider. We had asked him if the Flutter team recommended any one method of State Management approach over others, and yes, they do. That’s a direct quote from Chris, from when he was on #HumpDayQandA. – Chris Sells – Product Manager, Flutter. Provider is the recommended way to do State Management for apps of all sizes.

Flutter provider clearing up