@EnviornmentObject to share data between views

SwiftUI to share data between the Views

Struggling to share data between views in SwiftUI?

• Apple introduced new SwiftUI.
• There is shift in programming paradigm from Imperative to Declarative.
• Autoupdating the view whenever there are changes in the model.

SwiftUI provides way to share data across all views within app, using @EnviornmentObject. This enables the app to update the views automatically whenever data changes.

Scenerios:

• If we want to pass data from A -> B -> C, instead of creating protocols or singleton objects, we can create @EnvironmentObject and put into the environment object so that views B, C and D can automatically have access to it.

Precaution:

• Environment objects must be supplied by an ancestor views, if wont find the object, it may lead to crash.

Usage:

• Object or Model that needs to be shared across views must confirms to protocol ObservableObject.
• Change in the model also communicated with the help of @Published property wrappers.

By default an ObservableObject synthesizes an objectWillChange publisher that emits the changed value before any of its @Published properties changes.

Example

 class Contact: ObservableObject {
    @Published var name: String
    @Published var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }

    func haveBirthday() -> Int {
        age += 1
        return age
    }
}

let john = Contact(name: "John Appleseed", age: 24)
john.objectWillChange.sink { _ in print("\(john.age) will change") }
print(john.haveBirthday())
// Prints "24 will change"
// Prints "25"