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Easy Publishers

Ever wondered how to create a simple publisher?

In this blog i’ll try to show you the basics

Firstly we need to import the required frameworks

// Used for the ObservableObject
import Combine

// The easiest for publishers
import SwiftUI

Published object

We’re going to create a class what subclasses ObservableObject and contains a @Published variable. (for this example it is also using a timer to update the value)

class MyObject: ObservableObject {
    // This published variable will be updated several times.
    @Published var y: String

    // Set a default value to y, and start the timer
    init() {
        // Set the value of y to Loading...
        y = "Loading..."

        // Run this function after 5 seconds on the main thread.
        DispatchQueue.main.asyncAfter(deadline: .now() + 5) { 
            self.upd() // Update
        }
    }

    func upd() {
        // Set the value of y to Published World
        y = "Published World"

        // Tell the system that this ObservableObject class is updated.
        self.objectWillChange
    }
}

(SwiftUI) View

struct MyView: View {
    // Define our object(class) as Observed
    @ObservedObject var v = MyObject()

    var body: some View {
        Text(v.y) // This will change automatically if y is changed
    }
}

Full code

import Combine
import SwiftUI

class MyObject: ObservableObject {
    @Published var y: String
    init() {
        y = "Loading..."
        DispatchQueue.main.asyncAfter(deadline: .now() + 5) { 
            self.upd()
        }
    }
    func upd() {
        y = "Published World"
        self.objectWillChange
    }
}

struct MyView: View {
    @ObservedObject var v = MyObject()
    var body: some View {
        Text(v.y)
    }
}

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