macOSアプリ [SwiftUI] toolbar で CoreData 扱うサンプル

# やること

- toolbar にボタンを配置して
- クリックすると CoreData の User に user が追加される

![image.png](https://qiita-image-store.s3.ap-northeast-1.amazonaws.com/0/45822/47449d71-9fda-b22d-08b9-376f08f091c2.png)


# コード

```swift:Titlebar.swift
import Foundation
import SwiftUI

struct ToolbarButtonView: View {
    
    @Environment(\.managedObjectContext) var moc
    
    var body: some View {
        ZStack {
            Color.clear
            HStack {
                Button(action: {
                    let names = ["taro", "yuki", "ken", "bob", "john"]
                      let user = User(context: self.moc)
                      
                      user.id = UUID()
                      user.name = names.randomElement()
                      do {
                          try self.moc.save()
                      } catch {
                          print(error)
                      }
                }) {
                    Text("新規作成").offset(x: 0, y: 1)
                }
            }.font(.caption)
        }
        .padding()
        .edgesIgnoringSafeArea(.all)
    }
}
```

```swift:ContentView.swift
import SwiftUI

func getAllUsers() -> NSFetchRequest<User> {
  let request: NSFetchRequest<User> = User.fetchRequest()
  request.sortDescriptors = []
  return request
}

struct ContentView: View {
    @Environment(\.managedObjectContext) var moc
    @FetchRequest(fetchRequest: getAllUsers()) var users: FetchedResults<User>
    
    var body: some View {
        List(users, id: \.self.id) { user in
            Text(user.name ?? "?")
        }
    }
}
```

```swift:AppDelegate.swift
import Cocoa
import SwiftUI

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

    var window: NSWindow!

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        // Create the SwiftUI view and set the context as the value for the managedObjectContext environment keyPath.
        // Add `@Environment(\.managedObjectContext)` in the views that will need the context.
        let contentView = ContentView().environment(\.managedObjectContext, persistentContainer.viewContext)

        // Create the window and set the content view. 
        window = NSWindow(
            contentRect: NSRect(x: 0, y: 0, width: 480, height: 300),
            styleMask: [.titled, .closable, .miniaturizable, .resizable, .fullSizeContentView],
            backing: .buffered, defer: false)
        window.center()
        window.setFrameAutosaveName("Main Window")
        window.contentView = NSHostingView(rootView: contentView)
        window.makeKeyAndOrderFront(nil)
        
        // toolbar の設定
        window.toolbar = .init()
        window.titleVisibility = .hidden
        let titlebarAccessory = NSTitlebarAccessoryViewController()
        let toolbarView = ToolbarButtonView().environment(\.managedObjectContext, persistentContainer.viewContext)
        let toolbarHostingView = NSHostingView(rootView: toolbarView)
        toolbarHostingView.frame.size = toolbarHostingView.fittingSize
        titlebarAccessory.view = toolbarHostingView
        titlebarAccessory.layoutAttribute = .leading
        window.addTitlebarAccessoryViewController(titlebarAccessory)
    }

    func applicationWillTerminate(_ aNotification: Notification) {
        // Insert code here to tear down your application
    }

    // MARK: - Core Data stack

    lazy var persistentContainer: NSPersistentContainer = {
        /*
         The persistent container for the application. This implementation
         creates and returns a container, having loaded the store for the
         application to it. This property is optional since there are legitimate
         error conditions that could cause the creation of the store to fail.
        */
        let container = NSPersistentContainer(name: "macosToolbarCoreData")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                 
                /*
                 Typical reasons for an error here include:
                 * The parent directory does not exist, cannot be created, or disallows writing.
                 * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                 * The device is out of space.
                 * The store could not be migrated to the current model version.
                 Check the error message to determine what the actual problem was.
                 */
                fatalError("Unresolved error \(error)")
            }
        })
        return container
    }()

    // MARK: - Core Data Saving and Undo support

    @IBAction func saveAction(_ sender: AnyObject?) {
        // Performs the save action for the application, which is to send the save: message to the application's managed object context. Any encountered errors are presented to the user.
        let context = persistentContainer.viewContext

        if !context.commitEditing() {
            NSLog("\(NSStringFromClass(type(of: self))) unable to commit editing before saving")
        }
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                // Customize this code block to include application-specific recovery steps.
                let nserror = error as NSError
                NSApplication.shared.presentError(nserror)
            }
        }
    }

    func windowWillReturnUndoManager(window: NSWindow) -> UndoManager? {
        // Returns the NSUndoManager for the application. In this case, the manager returned is that of the managed object context for the application.
        return persistentContainer.viewContext.undoManager
    }

    func applicationShouldTerminate(_ sender: NSApplication) -> NSApplication.TerminateReply {
        // Save changes in the application's managed object context before the application terminates.
        let context = persistentContainer.viewContext
        
        if !context.commitEditing() {
            NSLog("\(NSStringFromClass(type(of: self))) unable to commit editing to terminate")
            return .terminateCancel
        }
        
        if !context.hasChanges {
            return .terminateNow
        }
        
        do {
            try context.save()
        } catch {
            let nserror = error as NSError

            // Customize this code block to include application-specific recovery steps.
            let result = sender.presentError(nserror)
            if (result) {
                return .terminateCancel
            }
            
            let question = NSLocalizedString("Could not save changes while quitting. Quit anyway?", comment: "Quit without saves error question message")
            let info = NSLocalizedString("Quitting now will lose any changes you have made since the last successful save", comment: "Quit without saves error question info");
            let quitButton = NSLocalizedString("Quit anyway", comment: "Quit anyway button title")
            let cancelButton = NSLocalizedString("Cancel", comment: "Cancel button title")
            let alert = NSAlert()
            alert.messageText = question
            alert.informativeText = info
            alert.addButton(withTitle: quitButton)
            alert.addButton(withTitle: cancelButton)
            
            let answer = alert.runModal()
            if answer == .alertSecondButtonReturn {
                return .terminateCancel
            }
        }
        // If we got here, it is time to quit.
        return .terminateNow
    }

}
```

# 参考

https://github.com/toph-allen/VibeChecker-v0

こちらのおかげです。ありがとうございます。