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Building Expense Tracker Apple Watch App with SwiftUI & Core Data

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This tutorial is part 3 of the tutorial series on how to build an expense tracker cross-platform App with SwiftUI, Core Data, & CloudKit. I recommend all of you to read the previous tutorials first before continuing, here are the previous tutorials:

Introduction

With the introduction of watchOS 6 in WWDC 2019, Apple finally provided the capability for developers to create a fully independent App Experience on Apple Watch without a companion app on iOS. Also, users can discover and download apps directly from the built-in App Store without an iPhone.

WatchOS 6 SDK also provides SwiftUI support for developers to build native and optimized Apple Watch user experience complete with custom views, animation, and digital crown haptic support out of the box. It also supports many native frameworks and features such as Core Data, CloudKit, Sign in with Apple, and many more. To learn more about developing Apps for watchOS, you can visit Apple Developer Website on watchOS.

What We Will Build


In this tutorial, we'll be focusing on building the Expense Tracker independent watchOS App. Similar to the iOS & macOS app in the previous article, our App will also have the dashboard and expense log list screen as well as the form to create and edit log.

When developing an Apple Watch App, we need to consider several design guidelines provided by Apple in their Human Interface Guidelines such as:

  1. Lightweight interactions. The App needs to provide simplified, focused, and essential information where users can interact at a glance without too much visual distraction. We won't need features such as multi categories filer and sort selection from the log list so users can take a glance at essential information from the App.
  2. Holistic design. We'll use native SwiftUI List with watchOS Carousel so users can seamlessly scroll the content the digital crown on Apple Watch with smooth native animation.


Here are the main components that we'll be focusing to build in this tutorial:

  • Building Page Based Navigation with SwiftUI in WatchOS
  • Building Log List View.
  • Building Log Form View.
  • Building Dashboard View Containing Pie Chart and Category total expenses sum.


You can download the completed project from the GitHub Repository.

The Starter Project

To begin this tutorial, please download the starter project from GitHub Repository. The starter project has already provided several components such as:

  • Completed Expense Tracker iOS and MacOS App targets from the previous tutorials. To learn more about the Core Data part, please refer to the part 1 of this tutorial series, Building Expense Tracker iOS App with Core Data & SwiftUI
  • WatchOS App Target with empty implementation.
  • Shared Models, Core Data Managed Object Model, Utils, as well as extensions to help us build the project. These source files uses target membership to target macOS, iOS, and watchOS platforms.


Make sure to select ExpenseTrackerWatchOS WatchKit App and Apple Watch simulator from the scheme to build and run the project. Let's move on to the next section, where we will create the root page based navigation for our App.

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Building Page Based Navigation for Dashboard and Log Views

WatchOS uses WKInterfaceController as an equivalent of UIViewController in UIKit as the View Controller. To enable SwiftUI in watchOS, Apple provides WKHostingController as the subclass of WKInterfaceController where we can return SwiftUI View by overriding body computed property. The API doesn't use Swift Opaque type, so we need to fill the generic placeholder using the concrete View.

Navigate to the ExpenseTrackerWatchOS WatchKit Extension folder, create a new file named DashboardView.swift and copy the following code.

import SwiftUI
import CoreData

struct DashboardView: View {

    var context: NSManagedObjectContext

    var body: some View {
        Text("Dashboard")
    }
}

Next, create a file named DashboardController.swift and copy the following code.

import WatchKit
import SwiftUI

class DashboardController: WKHostingController<DashboardView> {
    
    override var body: DashboardView {
        return DashboardView(context: CoreDataStack.shared.viewContext)
    }
}

Here, we just return the DashboardView passing the managed object context from CoreDataStack singleton—the managed object context itself used by the fetch request to query our data later.

Navigate to the ExpenseTrackerWatchOS WatchKit Extension folder, create a new file named LogView.swift and copy the following code.

import SwiftUI
import CoreData

struct LogListView: View {
    
    @Environment(\.managedObjectContext)
    var context
    
    var body: some View {
        Text("Logs")
    }
}    

Next, create a file name LogController.swift and copy the following code.

import WatchKit
import SwiftUI
import CoreData

class LogController: WKHostingController<LogView> {
    
    override var body: LogView {
        return LogView(context: CoreDataStack.shared.viewContext)
    }
}

struct LogView: View {
    
    var context: NSManagedObjectContext
    
    var body: some View {
        LogListView()
            .environment(\.managedObjectContext, context)
    }
}

Here, we need to create proxy LogView where we'll return in the LogController body property passing the managed object context. There are two reasons:

  1. WKHostingController doesn't support Swift Opaque type for SwiftUI View. If we just return a view by applying an environment modifier to pass the managed object context, the compiler will raise an error because the type is View.
  2. To be able to use @FetchRequest property wrapper, we need to pass the managed object context via @Environment property wrapper by injecting it from the parent View.


Navigate to the ExpenseTrackerWatchOS WatchKit App, and click on the Interface.storyboard. We'll put our initial controller and create page-based navigation.

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From the object library, drag a HostingController into the storyboard, click on the Identity Inspector and assign DashboardController as the class. Then, click on the Attributes Inspector and check Is Initial Controller.

Next, drag the second HostingController into the storyboard. Assign LogController as the class from Identity Inspector.

To create page-based navigation, Hold Ctrl key on the DashboardController and drag the blue line to the LogController. It will ask you to create relationship segue with next page as the only option, make sure to check it.

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We have successfully build page based navigation for our watchOS app for the Dashboard and Log View. Build and run App in the simulator, and you should be able to navigate between pages using the swipe gesture.

Building Category Image View

Before creating the LogListView, let's create the CategoryImageView first. This View displays the category image in our Dashboard and Log page.

Create a new file named CategoryImageView.swift. Copy the following code.

struct CategoryImageView: View {
    
    let category: Category
    var color: Color = .white
    
    var body: some View {
        Image(systemName: category.systemNameIcon)
            .resizable()
            .aspectRatio(contentMode: .fit)
            .frame(width: 15, height: 15)
            .padding(.all, 4)
            .foregroundColor(color)
            .overlay(
                Circle()
                    .stroke(color, style: StrokeStyle(lineWidth: 1)
                )
        )
    }
}

Here, we use the category systemNameIcon property to retrieve the image using SF Symbols system name for the respective category. We constrained the frame to have the width and height of 15 and add 4-pts of padding around. At last, we add an Overlay containing the Circle Shape, which we stroke with the the color property. Default color is white, but it can be costumized by injecting it from the initializer.

Building Log List View

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Next, navigate to LogListView.swift file. This main view shows the list of expense logs sorted by a recent date. Copy the following code.

import SwiftUI
import CoreData

struct LogListView: View {
    
    // 1
    @Environment(\.managedObjectContext)
    var context
    
    @State private var logToEdit: ExpenseLog?
    @State private var isAddPresented: Bool = false
    
    // 2
    @FetchRequest(
        entity: ExpenseLog.entity(),
        sortDescriptors: [
            NSSortDescriptor(keyPath: \ExpenseLog.date, ascending: false)
        ]
    )
    private var result: FetchedResults<ExpenseLog>
    
    var body: some View {
        // 3
        ZStack {
            // 4
            ScrollView {
                Button(action: {
                     self.isAddPresented = true
                }) {
                     HStack {
                         Spacer()
                         Image(systemName: "plus.circle")
                         Text("Add Log")
                         Spacer()
                     }
                     .foregroundColor(Color(hexString: "#F92365"))
                }
                 
                // 5
                ForEach(result) { (log: ExpenseLog) in
                    Button(action: {
                        self.logToEdit = log
                    }) {
                        LogRowView(log: .constant(log))
                    }
                }
                .sheet(item: self.$logToEdit) { (log: ExpenseLog) in
                    // TODO: return LogFormView for editing log
                }
            }

            if result.isEmpty {
                Text("No expenses data\nPlease add an expense first.")
                    .multilineTextAlignment(.center)
                    .font(.headline)
                    .padding(.horizontal)
            }
        }
        .navigationBarTitle("Expenses")
        .sheet(isPresented: $isAddPresented) {
            // TODO: return LogFormView for adding log
        }
    }
    
    private func onDelete(with indexSet: IndexSet) {
        indexSet.forEach { index in
            let log = result[index]
            context.delete(log)
        }
        try? context.saveContext()
    }
}

struct LogRowView: View {
    
    @Binding var log: ExpenseLog
    
    var body: some View {
        VStack(alignment: .leading) {
            HStack {
                CategoryImageView(category: log.categoryEnum, color: log.categoryEnum.color)
                Text(log.nameText)
                    .font(.body)
            }
            HStack(alignment: .firstTextBaseline) {
                Text(log.amountText)
                    .font(.headline)
                
                Spacer()
                Text(log.dateText)
                    .font(.footnote)
            }
        }
        .padding(.horizontal, 2)
        .padding(.vertical)
        .listRowPlatterColor(log.categoryEnum.color)
    }
}

Here are the explanations for all the points in the code above:

  1. We declared several properties. We'll use @Environment property wrapper to pass the managed object context from a parent. To handle presenting the LogFormView sheet, we declare isAddPresented state property for adding log and logToEdit for editing log.
  2. We use @FetchRequest property wrapper passing the expense log entity and default sort descriptor by a recent date. It will use the @Environment managed object context to fetch the request automatically.
  3. A ZStack is the main container view. With this, we can add a Text to inform the user to add a new log in case the fetched result is empty.
  4. An Add Log button located at the top where the user can use it to add a new log using the Log Form View we'll build in the next section.
  5. To display the expense logs, we use a ScrollView instead of List because currently it crashes when adding/updating/deleting with List . We pass the FetchedResults so the list will be updated whenever the logs get added, updated, or deleted automatically. We'll add onTapGesture to assign the logToEdit property when the user taps on each row to present the LogFormView in a sheet. Finally, we'll add onDelete modifier to delete the respective row whenever the user swipes on the row.
  6. For each of the fetched expense log, we put it in LogRowView. It uses a combination of HStack and VStack to show the image of the log's category, name, amount, and date. Notice that we pass the log using @Binding so the row can be updated whenever the item changes.


Try to build and run the project, and you should be able to navigate to the Log View. Currently, it only shows an Add Log button with a text telling the user to add a new expense log. Next, we'll be going to build the Log Form View so the user can add and edit log.

Building Log Form View

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Next, create a file named LogFormView.swift. The LogFormView uses Form containing text fields for name, amount, and a picker for selecting a category. Copy the following code into the file.

import SwiftUI
import CoreData

struct LogFormView: View {
   
    // 1
    var logToEdit: ExpenseLog?
    var context: NSManagedObjectContext
    
    @Environment(\.presentationMode)
    var presentationMode
    
    // 2
    @State var name: String = ""
    @State var amount: Double = 0
    @State var category: Category = .utilities

    var body: some View {
        // 3
        Form {
            Section {
                TextField("Name", text: $name)
                TextField("Amount", value: $amount, formatter: Utils.numberFormatter)
                Picker(selection: $category, label: Text("Category")) {
                    ForEach(Category.allCases) { category in
                        Text(category.rawValue.capitalized).tag(category)
                    }
                }
            }
            
            // 4
            Section {
               Button(action: self.onSaveTapped) {
                   HStack {
                       Spacer()
                       Text("Save")
                           .foregroundColor(Color.white)
                       Spacer()
                   }
               }
               .listRowPlatterColor(Color.blue)
               
               if self.logToEdit != nil {
                   Button(action: self.onDeleteTapped) {
                       HStack {
                           Spacer()
                           Text("Delete")
                               .foregroundColor(Color.white)
                           Spacer()
                       }
                   }
                   .listRowPlatterColor(Color.red)
               }
           }
        }
    }
    
    // 5
    private func onSaveTapped() {
        let log: ExpenseLog
        if let logToEdit = self.logToEdit {
            log = logToEdit
        } else {
            log = ExpenseLog(context: self.context)
            log.id = UUID()
            log.date = Date()
        }
        
        log.name = self.name
        log.category = self.category.rawValue
        log.amount = NSDecimalNumber(value: self.amount)
        do {
            try context.saveContext()
        } catch let error as NSError {
            print(error.localizedDescription)
        }
        self.presentationMode.wrappedValue.dismiss()
    }
    
    // 6
    private func onDeleteTapped() {
         guard let logToEdit = self.logToEdit else { return }
         self.context.delete(logToEdit)
         try? context.saveContext()
         self.presentationMode.wrappedValue.dismiss()
     }
}

Here are the explanations for all the points in the code above:

  1. We declare several properties for this form of view. The logToEdit is an optional property that will be passed when the user taps on the row in the LogList View for editing a log. We use NSManagedObjectContext so we can save the created or updated log after user taps on the save button. At last, we use @Environment to access PresentationMode to dismiss the sheet after save.
  2. We declare 3 @State properties for name, amount, and category. These will be used as bindings for the text fields and picker in the Form.
  3. The Form is the main container for all the text fields and picker. We have text fields to bind the name and amount state. Notice, for amount we are passing a NumberFormatter with currency type so the String can be converted to Double after the user commits the change. As for the category selection, we use Picker passing the Category enum using CaseIterable protocol to retrieve all the cases.
  4. We have a Save button that triggers the onSaveTapped method when the user taps. Also, we show a Delete button when user edit an item.
  5. In the onSaveTapped method, we create a new log if logToEdit value is nil, otherwise we use it as the log. We'll assign all the state properties such as name, amount, and category to the log. Notice that we're assigning a current date for the new log to simplify the form. At last, we invoke the managed object context save method and dismiss the sheet.
  6. In the onDeleteTapped method, we delete the logToEdit from the managed object context, then save, and dismiss the sheet.


Before we try our new LogFormView, we'll need to add it in 2 places inside LogListView:

  1. In the sheet that uses logToEdit binding. This property will be used in the case when the user taps on the log row. Here, we need to pass the logToEdit as well the states for name, amount, category to the initializer. Those states are going to populate the text fields and picker.
  2. In the sheet that uses isAddPresented binding. This property will be used in the case when the user taps on the Add Log button, we need to pass the managed object context.
struct LogListView: View {
    
    // ...
    var body: some View {
        ZStack {
            ScrollView {
                
                // ..
                .sheet(item: self.$logToEdit) { (log: ExpenseLog) in
                    // 1
                    LogFormView(
                        logToEdit: log,
                        context: self.context,
                        name: log.name ?? "",
                        amount: log.amount?.doubleValue ?? 0,
                        category: Category(rawValue: log.category ?? "") ?? .food
                    )
                }
            }
            // ...
        }
        // ..
        .sheet(isPresented: $isAddPresented) {
            // 2
            LogFormView(context: self.context)
        }
    }
    // ...
}

Try to build and run the project, create several new logs to make sure the list gets updated. Also, try to edit and delete several logs to make sure it's working properly.

Building Dashboard View

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Try to build and run the project, create several new logs to make sure the list gets updated. Also, try to edit and delete several logs to make sure it's working correctly.

import SwiftUI
import CoreData

struct DashboardView: View {
    
    // 1
    var context: NSManagedObjectContext
    
    @State var totalExpenses: Double?
    @State var categoriesSum: [CategorySum]?
    
    var body: some View {
        // 2
        List {
            // 3
             if totalExpenses != nil && totalExpenses! > 0 {
                VStack(alignment: .center, spacing: 2) {
                    
                    Text("Total expenses")
                        .font(.footnote)
                    Text(totalExpenses!.formattedCurrencyText)
                        .font(.headline)
                    
                    if categoriesSum != nil {
                        PieChartView(
                            data: categoriesSum!.map { ($0.sum, $0.category.color) },
                            style: Styles.pieChartStyleOne,
                            form: CGSize(width: 160, height: 110),
                            dropShadow: false
                        ).padding()
                    }
                }
                .listRowPlatterColor(.clear)
            }
            
            // 4
            if categoriesSum != nil {
                ForEach(self.categoriesSum!) {
                    CategoryRowView(category: $0.category, sum: $0.sum)
                }
            }
            
            // 5
            if totalExpenses == nil && categoriesSum == nil {
                Text("No expenses data\nPlease add your expenses from the logs page.")
                    .multilineTextAlignment(.center)
                    .font(.headline)
                    .padding()
            }
            
        }
        .listStyle(CarouselListStyle())
        .navigationBarTitle("Dashboard")
        .onAppear(perform: fetchTotalSums)
    }
    
    // 6
    func fetchTotalSums() {
        ExpenseLog.fetchAllCategoriesTotalAmountSum(context: self.context) { (results) in
            guard !results.isEmpty else {
                self.totalExpenses = nil
                self.categoriesSum = nil
                return
            }
            
            let totalSum = results.map { $0.sum }.reduce(0, +)
            self.totalExpenses = totalSum
            self.categoriesSum = results.map({ (result) -> CategorySum in
                return CategorySum(sum: result.sum, category: result.category)
            })
        }
    }
}

struct CategoryRowView: View {
    let category: Category
    let sum: Double
    
    var body: some View {
        HStack {
            CategoryImageView(category: category)
            VStack(alignment: .leading) {
                Text(category.rawValue.capitalized)
                Text(sum.formattedCurrencyText).font(.headline)
            }
        }
        .listRowPlatterColor(category.color)
        .padding(.vertical)
    }
}

Here are the explanations for all the points in the code above:

  1. For the view properties, we have a managed object context without @Environment property wrapper because we don't use @FetchRequest to fetch our total categories sum data. We have two state properties, one for the total expense sum for all categories. The other state property is an array of CategorySum which stores the total sum for a category.
  2. We use List with CarouselListStyle to display the data, an onAppear modifier is added, so we can fetch the data when the view appears. With CarouselListStyle, we can have digital crown animation and animation as user scrolls the content.
  3. For the first row in the List, we use a VStack to display the total sum expense for all categories using a Text. We'll also show the total sum for each category inside a PieChart. We are using a conditional statement only to render this row if totalExpense state is not nil.
  4. For the other rows, we check if the categoriesSum array is not nil, then using ForEach, we pass the categoriesSum array. In the ViewBuilder closure, we return the CategoryRowView. You can see the declaration of this view at the bottom of the source code. It's using HStack to display the image of the category using CategoryImageView, then VStack as a sibling containing the text of category name as well as the total formatted sum.
  5. If the data haven't been fetched or empty, we display a text containing the information for the user to add a new log from the logs page.
  6. The fetchTotalSums will be invoked onAppear. In this case, we'll use ExpenseLog static method to fetch all the categories with the total sum for each category. In the closure, we assign the totalExpense property using reduce to sum all the value. At last, we transform the results and assign it to the categoriesSum array. These assignments will trigger a view update.


That's it! Try to build and run the project, and you should be able to see the total expenses sum, pie chart, and the list containing the amount of spending for each category.

Setup Core Data CloudKit Syncing in WatchOS Target

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To make sure Core Data CloudKit syncing is working, you need to add a valid CloudKit container with the same identifier to all the targets. To try this, make sure you sign in into iCloud in the simulator or your physical devices when you want to test.

Try to add items on iOS. In 1 minute, it should sync the data to the other platforms.

Conclusion

Congratulations! You have successfully built the watchOS Expense Tracker App with SwiftUI. With Core Data + CloudKit, we're able to persist data locally as well as syncing the data to iCloud across all our Apple devices.

With SwiftUI, building an independent watch App has never become so much simple and fast! We're able to apply our learning to create unique app experiences across Apple platform. With simple modifiers such as passing CarouselListStyle for the listStyle, we're able to use the digital crown combined with sliding animation to provide an immersive experience and focus to the users when they use the app at a glance.

Until the next one! Let's keep the lifelong learning goes on!