'A Deeper Look into Clean Architecture: Flutter vs Kotlin' fluttertutorial advantagesoffluttermobile
Now it's time to make our application work. For the Riverpod magic to work, you need to wrap the entire ProviderScope application with a widget:Since _counterProvider is a global constant, we can access it from anywhere .
You usually hear in programming that you shouldn't use global variables. One reason is that it's easy to get subtle errors if different parts of your code change a variable. However, this global variable is immutable, so there is no danger of changing it. Another reason to be careful with globals is to create dependency problems. Riverpod has many different providers. In this example, we are using the StateNotifierProvider because the state is in the StateNotifier class . MyHomePage is currently a successor to StatelessWidget. Change the StatelessWidget to a ConsumerWidget to get a "ref" object. This object allows us to interact with providers, be it a widget or another provider. Every time the counter value changes, it would be a good idea to display this in the user interface. To do this, we need to learn how to observe changes..watch will listen for changes to _counterProvider.state, which is an instance of CounterModel. And accordingly, we can access the .count field, in which CounterModel stores the counter value.Counter update. When the user clicks the + button, we need to call the increment method in our counter state management class .onPressed: =>ref.read .increment , The ref object has a read method. Unlike watch, the read method gives you a reference to your state management class without tracking changes in state. The reason this is important is that the watch behind the CounterNotifier will cause the widget's build method to rerun when the state changes. If the widget, in this case FAB , does not visually change in any way, it is somehow useless to redraw it. However, the current build method is already in use and will be called because there is a watch call inside the widget. This means that all widgets in this build method will still be rebuilt. We'll optimize this later. Let's try to launch the application, and the counter starts responding to clicks.The application may already be working, but there is no limit to perfection. Let's try to add a feature - let us have another counter that will show how many even numbers the user has seen. We will solve the problem head-on, as if we have a KPI for the number of lines. We will store the value and add it to a new counter, let's call it EvenCounter, every time Counter is divisible by two without a remainder. And then we start EvenCounterNotifier and EvenCounterModel by analogy with Counter. As a provider, in full analogy with _counterProvider});final _isEvenProvider=Provider { final counter=ref.watch ; return ; }); It will transmit on an even or odd number the change in the _counterProvider value. We noticed earlier that it is not optimal to redraw the widget every time the provider changes. Since new providers pass values twice less often than _counterProvider, we will create new widgets for new providers: CounterIsEven and EvenCounter . Their system can redraw only when the corresponding provider will transfer values.
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