With Dependency Injection, it's not possible to enforce a single instance in compile-time. That can break API in existing projects, if it's something important, or be an additional step in the development process. For instance, to access the object, you need to add a property or parameter to hold its reference. The disadvantages of Dependency Injection are debatable, depending on your use case. Hence, you get to think twice about where to access it.ĭependency Injection doesn't add a global state to your code, so it becomes more reusable.
#Swift share singleton throughout project code
Additionally, you're not locking yourself out of using multiple instances at the same time in case it's necessary now or in the future.Īn injected dependency behavior is also more predictable since its accesses are restricted to pieces of code that explicitly hold an instance to it.
Since instantiation is not limited, it's possible to create mock instances to use in unit testing. There are multiple advantages to the Dependency Injection pattern. It would be best if you prefer using the initializer approach to avoid making the property public. Alternatively, we can assign the ViewController's chatClient property after initialization. This property can be assigned during instantiation or after.Ĭheck out the snippet below to instantiate a ChatClient and a ViewController with the former going into its initializer. Instead of providing a shared instance that can be accessed without restriction throughout the app, each component or class that needs access to an instance must hold its reference via a parameter or property. Dependency Injectionĭependency Injection can be a great alternative to the Singleton pattern for medium to high complexity apps as it scales with your app with less risk of adding unpredictability. The last point is not valid for Stream Chat Swift SDK's ChatClient, since its initializer is public to support the Dependency Injection pattern, which we'll discuss next. It's also harder to write unit tests without the possibility of instantiating a mock instance of your class. It's also possible that limiting the Facade class to a single instance is not what you'll want as your app scales up, and it can be tough to undo that choice. Though it can be handy for more uncomplicated use cases, it's often considered an anti-pattern by those who want to be more careful with their code and increase predictability. The more places in your app access the shared instance, the more unpredictable your app's behavior becomes and the harder it is to keep all your code in sync with the singleton's global state. The disadvantages of the singleton pattern become apparent the more complex your app gets.
That is a simple way to avoid common conflicts such as concurrent writes to a database. It's also possible to enforce a single instance if you make the Facade class's initializer private. Wherever you need the shared instance, you can access it without modifying your code further. The main advantage of the singleton pattern is its ease of access. Generally, the Facade's class initializer is made private, so the shared instance is the only one in the app.Ĭheck out the snippet below to create a shared instance for Stream Chat's ChatClient class by extending it with the shared static property. It consists of a Facade class with a public static instance, often called shared, accessible throughout the app's code via MyFacade.shared. The Singleton pattern is known for its simplicity.
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