访问这个经理放
let mgr = CachedUserPersistenceManager()
在 ViewModel 或视图中
/// Manager for the Item entity
class CachedUserPersistenceManager: PersistenceManager<CachedUser>{
let sampleUUID = UUID(uuidString: "00000000-0000-0000-0000-000000000000")!
init(isTest: Bool = false) {
super.init(entityType: CachedUser.self, isTest: isTest)
//Preloads the user
preloadSample()
}
///Preloads a sample object to the context
func preloadSample(){
let list = retrieveObjects(sortDescriptors: nil, predicate: NSPredicate(format: "%K == %@", #keyPath(CachedUser.uuid), sampleUUID as CVarArg)
)
if list.isEmpty{
let sampleItem = createObject()
sampleItem.uuid = sampleUUID
save()
}
}
override func addSample() -> CachedUser {
let new = super.addSample() as CachedUser
//add any sample code
return new
}
override func createObject() -> CachedUser {
super.createObject()!
}
override func updateObject(object: CachedUser) -> Bool {
//Replace the uuid if needed
if object.uuid == sampleUUID{
object.uuid = UUID()
}
return super.updateObject(object: object)
}
}
作为此代码一部分的通用类如下所示。你不需要他们说它只是让一些代码可以通过应用程序重用。
//Manager for any Entity
class PersistenceManager<T : NSManagedObject>{
let serviceSD: CoreDataPersistenceService<T>
internal init(entityType: T.Type, isTest: Bool = false) {
self.serviceSD = CoreDataPersistenceService(isTest: isTest, entityType: entityType)
}
//MARK: convenience
func addSample() -> T {
let newItem = createObject()
return newItem!
}
//MARK: Persistence Service Methods
func createObject() -> T? {
let result = serviceSD.createObject()
return result
}
func updateObject(object: T) -> Bool {
return serviceSD.updateObject(object: object)
}
func deleteObject(object: T) -> Bool {
return serviceSD.deleteObject(object: object)
}
func deleteAllObjects(entityName: String, isConfirmed: Bool) -> Bool {
return serviceSD.deleteAllObjects(isConfirmed: isConfirmed)
}
func retrieveObjects(sortDescriptors: [NSSortDescriptor]?, predicate: NSPredicate?) -> [T]{
return serviceSD.retrieveObjects(sortDescriptors: sortDescriptors, predicate: predicate)
}
func retrieveObject(id: String) -> T? {
return serviceSD.retrieveObject(sortDescriptors: nil, id: id).first
}
func resetChanges() {
serviceSD.resetChanges()
}
func save() {
_ = serviceSD.save()
}
}
//Service for Any Entity
class CoreDataPersistenceService<T: NSManagedObject>: NSObject {
var persistenceController: PersistenceController
let entityType: T.Type
required init(isTest: Bool = false, entityType: T.Type) {
if isTest{
self.persistenceController = PersistenceController.preview
}else{
self.persistenceController = PersistenceController.previewAware
}
self.entityType = entityType
super.init()
}
//MARK: CRUD methods
func createObject() -> T? {
let result = entityType.init(context: persistenceController.container.viewContext)
return result
}
func updateObject(object: T) -> Bool {
var result = false
result = save()
return result
}
func deleteObject(object: T) -> Bool {
var result = false
persistenceController.container.viewContext.delete(object)
result = save()
return result
}
func deleteAllObjects(isConfirmed: Bool) -> Bool {
var result = false
//Locked in so only the Generic "Item" can be deleted like this
if entityType == Item.self && isConfirmed == true{
let deleteRequest = NSBatchDeleteRequest(fetchRequest: entityType.fetchRequest())
do {
try persistenceController.container.persistentStoreCoordinator.execute(deleteRequest, with: persistenceController.container.viewContext)
} catch {
print(error)
result = false
}
}
return result
}
func resetChanges() {
persistenceController.container.viewContext.rollback()
_ = save()
}
func save() -> Bool {
var result = false
do {
if persistenceController.container.viewContext.hasChanges{
try persistenceController.container.viewContext.save()
result = true
}else{
result = false
}
} catch {
print(error)
}
return result
}
func retrieveObject(sortDescriptors: [NSSortDescriptor]? = nil, id: String) -> [T]{
return retrieveObjects(sortDescriptors: sortDescriptors, predicate: NSPredicate(format: "id == %@", id))
}
func retrieveObjects(sortDescriptors: [NSSortDescriptor]? = nil, predicate: NSPredicate? = nil) -> [T]
{
let request = entityType.fetchRequest()
if let sortDescriptor = sortDescriptors
{
request.sortDescriptors = sortDescriptor
}
if let predicate = predicate
{
request.predicate = predicate
}
do
{
let results = try persistenceController.container.viewContext.fetch(request)
return results as! [T]
}
catch
{
print(error)
return []
}
}
}
提到的previewAware 变量与PersistenceController 中的Apple 标准代码一致
它会自动为您提供preview 容器，因此您不必担心调整代码以适应 Canvas 中的示例。只需将以下代码添加到PersistenceController
static var previewAware : PersistenceController{
if ProcessInfo.processInfo.environment["XCODE_RUNNING_FOR_PREVIEWS"] == "1" {
return PersistenceController.preview
}else{
return PersistenceController.shared
}
}