从 CoreData 中删除数据 [英] Delete data from CoreData
本文介绍了从 CoreData 中删除数据的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我想马上说我是 Swift 的新手.我的任务是通过单击按钮删除某些数据附言单击按钮并删除框架"，如何为此重写函数(在 SwiftUI、AppDelegate 中工作)
I want to say right away that I'm new to Swift. My task is to delete certain data by clicking on a button P.s. Clicked the button and removed the "frame", how to rewrite a function for this (Working in SwiftUI, AppDelegate)
//MARK: - PROPERTIES
@FetchRequest(entity: TodoDB.entity(), sortDescriptors: [NSSortDescriptor(keyPath: \TodoDB.name, ascending: true)]) var manyTasksTodo: FetchedResults<TodoDB>
实现了删除功能，但是在按钮动作中调用该功能时，出现错误
Implemented the delete function, but when you call the function in the button action, an error appears
//MARK: - FUNCTION
public func deleteTodo(at offsets: IndexSet){
for index in offsets{
let todoDB = manyTasksTodo[index]
managedObjectContext.delete(todoDB)
do{
try managedObjectContext.save()
} catch{
print(error)
}
}
}
完整代码:
import SwiftUI
struct ContentView: View {
//MARK: - PROPERTIES
@Environment(\.managedObjectContext) var managedObjectContext
@FetchRequest(entity: TodoDB.entity(), sortDescriptors: [NSSortDescriptor(keyPath: \TodoDB.name, ascending: true)]) var manyTasksTodo: FetchedResults<TodoDB>
@State public var AddTodo: Bool = false
@State private var animationButton: Bool = false
@Namespace var animationID
//MARK: - BODY
var body: some View {
ScrollView(.vertical, showsIndicators: false){
VStack{
ForEach(self.manyTasksTodo, id: \.self) { (todoDB: TodoDB) in
VStack(alignment: .leading, spacing: 5){
ZStack{
Button(action: {
}, label: {
Image(systemName: "trash")
.frame(maxWidth: .infinity, alignment: .bottomTrailing)
.padding(.bottom,30)
.foregroundColor(.black)
})
Divider()
Text(todoDB.attribute ?? "unknown attribute")
.foregroundColor(.black)
.font(.callout)
.padding(.bottom, 30)
}
Text(todoDB.name ?? "unknown task")
.foregroundColor(.black)
.padding(.bottom)
Text(todoDB.date ?? Date(), style: .date)
.foregroundColor(.black)
.font(.callout)
HStack{
Spacer()
}
}//VStack
.padding()
.background(Color("Red"))
.cornerRadius(10)
.padding()
}//: FOREACH
.onDelete(perform: deleteTodo(at:))
Spacer()
}
.shadow(color: Color.black.opacity(0.3), radius: 10, x: 0, y: 10)
.shadow(color: Color.black.opacity(0.2), radius: 5, x: 0, y: 2)
}
.padding(.top, 45)
.background(Color("Bg"))
.edgesIgnoringSafeArea(.all)
.overlay(
ZStack{
Group{
Circle()
.fill(Color.black)
.opacity(self.animationButton ? 0.2 : 0)
.scaleEffect(self.animationButton ? 1 : 0)
.frame(width: 68, height: 68, alignment: .center)
Circle()
.fill(Color.black)
.opacity(self.animationButton ? 0.15 : 0)
.scaleEffect(self.animationButton ? 1 : 0)
.frame(width: 88, height: 88, alignment: .center)
}
.animation(Animation.easeInOut(duration: 2).repeatForever(autoreverses: true), value: self.animationButton)
Button(action: {
self.AddTodo.toggle()
}, label: {
Image(systemName: "plus.circle.fill")
.resizable()
.scaledToFit()
.background(Circle().fill(Color.white))
.foregroundColor(Color.black)
.frame(width: 48, height: 48, alignment: .center)
})
.sheet(isPresented: $AddTodo){
AddTodoView().environment(\.managedObjectContext, self.managedObjectContext)}
.onAppear(perform: {
self.animationButton.toggle()
})
}//: ZSTACK
.padding(.bottom, 15)
.padding(.trailing, 15)
, alignment: .bottomTrailing
)
//}//: NAVIGATON
}
//MARK: - FUNCTION
public func deleteTodo(at offsets: IndexSet){
for index in offsets{
let todoDB = manyTasksTodo[index]
managedObjectContext.delete(todoDB)
do{
try managedObjectContext.save()
} catch{
print(error)
}
}
}
}
//MARK: - PREIVIEW
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
return ContentView()
.environment(\.managedObjectContext, context)
}
}
推荐答案
IndexSet 方法在您使用 onDelete 和 ForEach 时有效循环.
The IndexSet method works when you are using onDelete with a ForEach loop.
由于您无法使用 Button 访问 IndexSet，因此您传递了实际项目.
Since you don't have access to the IndexSet with a Button you pass the actual item.
将您的功能更改为此.
public func deleteTodo(todoDB: TodoDB){
managedObjectContext.delete(todoDB)
do{
try managedObjectContext.save()
} catch{
print(error)
}
}
然后将此代码放入垃圾箱按钮的操作中，如下所示.
And put this code within the trash button's action like this.
deleteTodo(todoDB: todoDB)
这篇关于从 CoreData 中删除数据的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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