
# Common Core Data Issues

While using Core Data with [[swift]] and [[swiftui]] I've ran into a few _gotchas_. This page documents those and how I fixed them.

### Merge Conflicts

`Could not merge changes ... with oldVersion = 5 and newVersion = 6`

refresh object before updating and saving new changes

```swift
let myObject = viewContext.objectWithID(managedObjectId)
viewContext.refresh(myObject, mergeChanges: true)
myObject.property = newValue
```

https://stackoverflow.com/questions/39508077/coredata-merge-conflict-shows-managed-object-version-change-not-data

### Observed Object

When passing an Core Data object into a child view, make sure the variable is marked as observable, otherwise it won't receive updates if modified.

```swift
struct ChildView: View {
	@ObservedObject var myModel: MyModel
	
 	var body: some View {
   		// ...
  	}
}
```

### Disable Core Data and CloudKit Debug Logs

```shell
-com.apple.CoreData.Logging.stderr 0
-com.apple.CoreData.CloudKitDebug 0
```

https://stackoverflow.com/a/59125651/1345618


core-data-common-issues


# Core Data Enums

One way to store an enum in [[core data]] is to actually store an Int value and then translate the integer into the enum when used.

Create a new Integer 16 attribute

![[Pasted image 20201130114721.png]]

Define your enum. If you make the enum `Equatable` and `CaseIterable` you can use a `Picker` to change its values.

```swift
public enum MyEnum: Int16, Equatable, CaseIterable {
    case zero = 0
    case one = 1
    case two = 2
    
    var stringValue: String {
        switch self {
        case .zero:
            return "Zero"
        case .one:
            return "First"
        case .two:
            return "Second"
    }
}
```

Create a getter and setter, in the class or extension for your model, that converts the value stored in core data to an instance of `MyEnum`. Optionally provide a default value if the conversion fails.

```swift
public var myEnum: MyEnum {
	get {
    	return MyEnum(rawValue: myEnumValue) ?? .zero
	}
    set {
    	self.myEnumValue = newValue.rawValue
	}
}
```

You can then write to and read from the enum like a normal swift value.

## SwiftUI Picker

If you want the user to be able to modify the value themselves, you can use a [Picker](https://developer.apple.com/documentation/swiftui/picker) in [[swiftui]].

```swift
Picker (
    selection : Binding (
        get : { myModel.myEnum },
        set : { value in
            self.myModel.myEnum = value
        }
    ),
    label : Text ("Select value")
) {
    ForEach (MyEnum.allCases, id: \.self.rawValue) {
        value in Text (value.stringValue).tag (value.rawValue)
    }
}
```


core-data-enums


# SwiftUI Custom Bindings

In [[swiftui]] you can create custom bindings

https://www.hackingwithswift.com/quick-start/swiftui/how-to-create-custom-bindings

```swift
struct ContentView: View {
    @State private var username = ""

    var body: some View {
        let binding = Binding(
            get: { self.username },
            set: { self.username = $0 }
        )

        return VStack {
            TextField("Enter your name", text: binding)
        }
    }
}
```

This may seem obvious, but when I was learning this wasn't clear to me at all. Learning this (and about [[property-wrappers]] in general) helped open my eyes to how data is handled in SwiftUI and enabled me to build more complex and composable views.

swiftui-custom-bindings


# Modal Indicator

Show a [[SwiftUI]] view at the top of the modal to indicator it is draggable.

![[Pasted image 20201213162649.png]]

```swift
private var indicator: some View {
    RoundedRectangle(cornerRadius: Constants.radius)
        .fill(Color.secondary)
        .frame(
            width: Constants.indicatorWidth,
            height: Constants.indicatorHeight
    ).onTapGesture {
        self.isOpen.toggle()
    }
}
```

Referenced from [this blog post](https://swiftwithmajid.com/2019/12/11/building-bottom-sheet-in-swiftui) with the source from [here](https://gist.github.com/mecid/78eab34d05498d6c60ae0f162bfd81ee#file-bottomsheetview-swift-L30).


swiftui-modal-indicator


# SwiftUI

Reactive framework for creating user interfaces for [[ios]] and macOS in [[swift]].

SwiftUI

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