Flutter state management with provider library and why it's so important? There are lots of topics in flutter which are very important but out of those state management of your flutter application is the most important and little bit complicated as well.
So in this article, I will try to explain how to use the provider package for managing the state of flutter and dart application and how to access the data down the hierarchy of the widget tree without recreating the whole UI.
Before starting the coding I would like to explain some basics about the Flutter application so that you can understand, why it's important to manage the state of your application in the correct way. In Flutter, everything is a widget and whenever the state of your application changes the UI is recreated the UI with the new data. Let's list out the topic or problem that we are going to explore about state management.
I understand that if you are new to flutter then it's difficult to understand the logic of state management and why it's so important. It's okay from small, we don't care about the state management but as application complexity will grow you will realize that we need some model to manage the state of the application. Just, for example, we have two pages in our application. On the first page, we have listed all item which can be added by the user and later when tabbing the user to second screen all the selected item need to show on the second page.
So how you will do this? The easy way is that we can pass the parameter while routing the user to the second page, but what if the same data is required on some other page. We have to write the same again for this page and send the data to the down the hierarchy by sending the data widget by widget at the required place.
If you don't know about how to navigate to the other page in flutter then you can refer our earlier tutorial on Page Navigation In Flutter. This default application increases the counter value when the user taps on the floating action button and show into the text in the center of the home page.
So, first of all, we will break this default application in three parts to convert it into the model. First of all, we need to add the provider library as a dependency in project pubspec. So we are now going to create a model which will we responsible for providing the updated value to our widget and whenever value counter value change due to any event it will notify all the respective widgets to recreate with the latest value.
There two functions inside this model one will increase the value and others will decrease the value of the counter.
If you notice in the above code we use the notifyListeners function and this function is responsible for notifying all the widget about the change whenever counter value will change.
This function comes from the foundation. So don't forget to import this function. When you click on the increment and decrement function then it will do nothing because there is no event added to it on the pressed section of the raised button. Now time to add the provider to our application in the main section of our app. There are two types of providers a single provider in which you can add the only one provider and another one is multi-provider.After experimenting with multiple ways to manage state in flutter, Provider looks solid and easy to use.
A dependency injection system built with widgets for widgets. That's it, enjoy. How can we change data of HomePage from another page? Mobile App Programming. Programming Languages. Get insights on scaling, management, and product development for founders and engineering managers.
State Management With Provider
Read programming tutorials, share your knowledge, and become better developers together. Hot Topics. Sunil Mishra Follow. Published May 12, Here are the various ways of maintaining state in flutter: Scoped Model BLoc Redux MobX Flutter provider with example: A dependency injection system built with widgets for widgets.
Let's walk through most popular ' Counter Widget ': Add this to your package's pubspec. Create your model class. Create your Widget. Here you widget is 'StatelessWidget'. Your Main. Expertise in Software Architecture and scoping product ecosystem. Discover and read more posts from Sunil Mishra. GitHub flavored markdown supported. Good Grief.
Paulo Gorenstein. Simple…the best…could you give an example of multiple Classes Inherited by Multiples Widgets? Sunil Mishra.A mixture between dependency injection DI and state management, built with widgets for widgets. The reason is, widgets are very simple yet robust and scalable. To read more about providersee the documentation. If this is undesired, you can disable lazy-loading by passing lazy: false to the provider of your choice:. See this issue for details on how to migrate.
If this is undesired, you can revert to the old behavior by passing a shouldRebuild parameter to Selector :. DelegateWidget and its family is removed. Instead, for custom providers, directly subclass InheritedProvider or an existing provider. To expose a newly created object, use the default constructor of a provider. Do not use the. See this stackoverflow answer which explains in further details why using the.
If you want to pass variables that can change over time to your object, consider using ProxyProvider :. If you already have an object instance and want to expose it, you should use the. Failing to do so may call the dispose method of your object when it is still in use.
The easiest way to read a value is by using the static method Provider. This method will look up in the widget tree starting from the widget associated with the BuildContext passed and it will return the nearest variable of type T found or throw if nothing is found.
Combined with the first example of exposing a valuethis widget will read the exposed String and render "Hello World.
How to Manage State in Flutter using Provider
Alternatively instead of using Provider. These can be useful for performance optimizations or when it is difficult to obtain a BuildContext descendant of the provider. When injecting many values in big applications, Provider can rapidly become pretty nested:.
The behavior of both examples is strictly the same. MultiProvider only changes the appearance of the code. ProxyProvider is a provider that combines multiple values from other providers into a new object, and sends the result to Provider. The following example uses ProxyProvider to build translations based on a counter coming from another provider.
That digit after the class name is the number of other providers that ProxyProvider depends on. They all work similarly, but instead of sending the result into a Providera ChangeNotifierProxyProvider will send its value to a ChangeNotifierProvider.State management is a hot topic in the Flutter community.
You have the default StatefulWidget and then there are literally hundreds of different libraries to choose from. This article will cut through the noise and, once and for all, explain the principles which are valid across many state management solutions.
You're also going to see examples of some of the most popular patterns and libraries. This single set of fields forces you to do crazy hacks for simple things like an initial or "empty" state - will you create a separate isInitial field Imagine how you'd store the history of state changes if you can update any of the fields independently from one another.
Not a very soothing idea to think about indeed. This mitigates all the issues outlined when we talked about ChangeNotifier. Since BLoC can separate the states into multiple classes instead of putting everything into one pile of fairly unrelated fields, representing an initial state has never been easier.
The UI will receive only one of these states at a point of time. You don't need to worry about null checking everything or looking for the value of particular field such as isInitial. All you do is check if state is Initial or state is Success and go from there. You've already seen how states are separated into individual classes.
The same goes for events, which are the "methods" of a Bloc - they control what's going to happen next. Sure, there may be more code in absolute terms but its complexity is never overwhelming because it's spread out across classes and files, usually. You don't need to track the individual fields, you just keep record of the MyState subclasses which are emitted from the Stream. Sure, you need to shell out money for the car and you need to take care of it, but at the same time, it allows you to get where you want much more quickly.
If you want to go across the street, hopping into a car would be crazy. If you're going to a destination which is kilometers Similarly, if you're building an app which is more for display than for functionality, going with the least boilerplatey option makes sense. Building a complex production-grade app requires different solutions altogether. So, if you want to have the benefits of immutable stateclosely work with Stream s whether for the purposes of testing or integration with other code, observe state changes happening across the app from a single place BlocDelegate easily to allow for pain-free analytics and at the same time keep your code as simple as possible, BLoC is truly the best available option out there.To understand it best, perhaps we should look at another, similar question:.Provider state management in flutter with Todo Application
How am I supposed to know what you like on your pizza, and how am I supposed to know which State Management approach is going to be best for your app AND for your personal ability to get that app out the door?
And therein lies the problem, grasshopper. There are plenty of good State Management solutions out there but not all of them are going to be a good fit for younot just your app.
If you can create a solid, bug-free solution with ScopedModel using an MVSP architecture and get the app out the door 40 hours faster then this needs to be your thinking:. That said, each State Management solution has its own characteristics and each person has different preferences.
Flutter Tutorial: Provider Overview for Humans
A word about code examples: I had hoped to make a lot more examples for this article but it quickly started to get out of hand since most of the techniques required three or more separate sets of example code with explanations of how they interact. This is not an exhaustive list, not even close. These are just some of the more commonly used approaches:. When I first started using it, I was confused about exactly what it was doing but then I had a realization:.
So, you can think of it as setStateWith or setStateAfter. InheritedWidget is one of those strange things in the Universe that some people understand instantly and others struggle with for years. Everyone can understand the basic idea, the block diagram is easy.
Almost no one uses it directly anymore and you get the same benefits from ScopedModel and Provider, anyway. In short, without a better way to do things, a Flutter UI can would pass data all the way down the tree from parent to child, down to the point where you use it. To say this is wasteful can be an understatement, especially once your app gets to be any respectable size. Here, what happens is these three make a path for your State data that is much shorter than passing it down the tree.
Think of it this way. These two might seem redundant because the big difference is that Provider gives you a lot more options, and it can use ChangeNotifier which is part of the Flutter framework. ScopedModel is a lot more simplified and you extend Model, which is a specific class within the ScopedModel package. Think of it this way: ScopedModel is like a version of Provider for Dummies. Provider is a lot more flexible, but not quite as easy to use.
BLoC implements the Observer pattern, with it your events are fed into a Stream that is the input into a logic block. The logic block figures out what response it needs to give and then sends that response back out. It simply processes the input and outputs a result.
But what does it do? Anything you want.
On the other side, the Stateful widgets are dynamic and have a state, which we can be modified easily throughout their life-cycle without re-initiation. The state of widget is the information that can be read synchronously when the widget is built and change during the lifetime of the widget. In order to change widget, you need to update the state object which can be update by using setState function of Stateful widgets.
In this post, we'll see another way to update screen widget without calling setState of a widget. It is a dependency injection system that is built with widgets for widgets. With the help of this package, we'll create a small example that will show background color change, as shown below:. We're Social. Popular Tags Blog Archives. Flutter - Capture Image from camera or gallery and apply crop. So, you should implement user profile pic and allow a user to set and chan Flutter - Drop down menu list with example.
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In fact, they recommend Remi Rousselet's Provider over their own version of it, which was called Package Provider. In short, Provider is like a way to use InheritedWidget that humans can understand. You remember InheritedWidget, right? If you understand, no explanation is necessary. If you don't understand, no explanation can help.
Provider looks daunting when you first dig into it. I mean, you could make a word cloud out of all the classes you can use with it:. When someone first looks at this, they often get intimidated. But, after Remi kindly took a lot of his time to help me understand and didn't laugh at me I realized something.
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. That's it. You have three jobs, and each of those classes can do one of them. Which classes you use will depend on what you need to do in your situation. These handle notifying the Providers that something has changed.
Which one you use will depend on what you're trying to listen for. A ChangeNofier is going to notify of any changes in the class, as it is tracking the object as a whole.
Here are the main two most people use, but these aren't the only way to do it:.