Swift 与核心数据一起使用时预览崩溃
我试图用swiftui和核心数据创建一个简单的任务待办应用程序,但在添加视图时遇到了一些问题。我有一个Swift 与核心数据一起使用时预览崩溃,swift,core-data,swiftui,Swift,Core Data,Swiftui,我试图用swiftui和核心数据创建一个简单的任务待办应用程序,但在添加视图时遇到了一些问题。我有一个TaskView视图,用于显示列表中任务的一些信息(标题、日期等)。但是,当尝试使用演示任务对象为视图创建预览时,预览崩溃(正在运行的应用程序仍然有效) 抱歉,如果这是一个普通的问题,对swift和一般编程来说都是新问题 TaskView.swift import SwiftUI struct TaskView: View { @Environment(\.managedObjectC
TaskView
视图,用于显示列表中任务的一些信息(标题、日期等)。但是,当尝试使用演示<代码>任务代码>对象为视图创建预览时,预览崩溃(正在运行的应用程序仍然有效)
抱歉,如果这是一个普通的问题,对swift和一般编程来说都是新问题
TaskView.swift
import SwiftUI
struct TaskView: View {
@Environment(\.managedObjectContext) var managedObjectContext
var task: Task
var body: some View {
HStack {
Image(systemName: task.checked == true ? "circle" : "checkmark.circle.fill")
VStack {
Text(task.name ?? "unknown name")
Text(String(task.streak))
}
}
}
}
struct TaskView_Previews: PreviewProvider {
static var previews: some View {
let task = Task()
task.name = "Washing up"
task.desc = "Wash the dishes"
task.checked = false
task.streak = 2
return TaskView(task: task)
.previewLayout(.fixed(width: 375, height: 60))
}
}
import SwiftUI
struct ContentView: View {
@Environment(\.managedObjectContext) var managedObjectContext
@FetchRequest(entity: Task.entity(), sortDescriptors: [
NSSortDescriptor(keyPath: \Task.checked, ascending: false),
NSSortDescriptor(keyPath: \Task.name, ascending: true)
]) var tasks: FetchedResults<Task>
var body: some View {
NavigationView {
List {
ForEach(tasks, id: \.self) { task in
TaskView(task: task).environment(\.managedObjectContext, self.managedObjectContext)
}
.onDelete(perform: deleteTask)
}
.navigationBarTitle("Today")
}
}
func deleteTask(at indexSet: IndexSet) {
indexSet.forEach { TaskUtils.delete(task: tasks[$0], using: self.managedObjectContext)}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
ContentView.swift
import SwiftUI
struct TaskView: View {
@Environment(\.managedObjectContext) var managedObjectContext
var task: Task
var body: some View {
HStack {
Image(systemName: task.checked == true ? "circle" : "checkmark.circle.fill")
VStack {
Text(task.name ?? "unknown name")
Text(String(task.streak))
}
}
}
}
struct TaskView_Previews: PreviewProvider {
static var previews: some View {
let task = Task()
task.name = "Washing up"
task.desc = "Wash the dishes"
task.checked = false
task.streak = 2
return TaskView(task: task)
.previewLayout(.fixed(width: 375, height: 60))
}
}
import SwiftUI
struct ContentView: View {
@Environment(\.managedObjectContext) var managedObjectContext
@FetchRequest(entity: Task.entity(), sortDescriptors: [
NSSortDescriptor(keyPath: \Task.checked, ascending: false),
NSSortDescriptor(keyPath: \Task.name, ascending: true)
]) var tasks: FetchedResults<Task>
var body: some View {
NavigationView {
List {
ForEach(tasks, id: \.self) { task in
TaskView(task: task).environment(\.managedObjectContext, self.managedObjectContext)
}
.onDelete(perform: deleteTask)
}
.navigationBarTitle("Today")
}
}
func deleteTask(at indexSet: IndexSet) {
indexSet.forEach { TaskUtils.delete(task: tasks[$0], using: self.managedObjectContext)}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
导入快捷界面
结构ContentView:View{
@环境(\.managedObjectContext)变量managedObjectContext
@FetchRequest(实体:Task.entity(),排序描述符:[
NSSortDescriptor(密钥路径:\Task.checked,升序:false),
NSSortDescriptor(键路径:\Task.name,升序:true)
])var任务:FetchedResults
var body:一些观点{
导航视图{
名单{
ForEach(tasks,id:\.self){task in
TaskView(任务:task).environment(\.managedObjectContext,self.managedObjectContext)
}
.onDelete(执行:deleteTask)
}
.navigationBarTitle(“今天”)
}
}
func deleteTask(在indexSet:indexSet处){
index.forEach{TaskUtils.delete(任务:tasks[$0],使用:self.managedObjectContext)}
}
}
结构内容视图\u预览:PreviewProvider{
静态var预览:一些视图{
ContentView()
}
}
我修复了TaskView,首先添加了一个上下文常量,然后使用init初始化预览中使用的任务常量
import SwiftUI
struct TaskView: View {
@Environment(\.managedObjectContext) var managedObjectContext
var task: Task
var body: some View {
HStack {
Image(systemName: task.checked == true ? "circle" : "checkmark.circle.fill")
VStack {
Text(task.name ?? "unknown name")
Text(String(task.streak))
}
}
}
}
struct TaskView_Previews: PreviewProvider {
static var previews: some View {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext // IMPORTANT
let task = Task.init(context: context) // IMPORTANT
task.name = "Washing up"
task.desc = "Wash the dishes"
task.checked = false
task.streak = 2
return TaskView(task: task).environment(\.managedObjectContext, context)
.previewLayout(.fixed(width: 375, height: 60))
}
}
至于您的ContentView,我做了一些小改动以使其正常工作—添加了一个按钮以向CoreData模型添加对象
import SwiftUI
struct ContentView: View {
@Environment(\.managedObjectContext) var managedObjectContext
@FetchRequest(entity: Task.entity(), sortDescriptors: [
NSSortDescriptor(keyPath: \Task.checked, ascending: false),
NSSortDescriptor(keyPath: \Task.name, ascending: true)
]) var tasks: FetchedResults<Task>
var body: some View {
NavigationView {
List {
ForEach(tasks, id: \.self) { task in
TaskView(task: task).environment(\.managedObjectContext, self.managedObjectContext)
}
//.onDelete(perform: deleteTask)
}
.navigationBarTitle("Today")
.navigationBarItems(trailing:
Button("Add") {
let task = Task(context: self.managedObjectContext)
task.name = "Washing up"
task.desc = "Wash the dishes"
task.checked = false
task.streak = Int32(Int.random(in: 0...10))
try? self.managedObjectContext.save()
}
)
}
}
// func deleteTask(at indexSet: IndexSet) {
// indexSet.forEach { TaskUtils.delete(task: tasks[$0], using: self.managedObjectContext)}
// }
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
return ContentView().environment(\.managedObjectContext, context)
}
}
导入快捷界面
结构ContentView:View{
@环境(\.managedObjectContext)变量managedObjectContext
@FetchRequest(实体:Task.entity(),排序描述符:[
NSSortDescriptor(密钥路径:\Task.checked,升序:false),
NSSortDescriptor(键路径:\Task.name,升序:true)
])var任务:FetchedResults
var body:一些观点{
导航视图{
名单{
ForEach(tasks,id:\.self){task in
TaskView(任务:task).environment(\.managedObjectContext,self.managedObjectContext)
}
//.onDelete(执行:deleteTask)
}
.navigationBarTitle(“今天”)
.navigationBarItems(尾部:
按钮(“添加”){
让任务=任务(上下文:self.managedObjectContext)
task.name=“洗碗”
task.desc=“洗碗”
task.checked=false
task.streak=Int32(Int.random(in:0…10))
try?self.managedObjectContext.save()
}
)
}
}
//func deleteTask(在indexSet:indexSet处){
//index.forEach{TaskUtils.delete(任务:tasks[$0],使用:self.managedObjectContext)}
// }
}
结构内容视图\u预览:PreviewProvider{
静态var预览:一些视图{
让上下文=(UIApplication.shared.delegate为!AppDelegate)。persistentContainer.viewContext
返回ContentView().environment(\.managedObjectContext,context)
}
}
您无法创建不带上下文的核心数据对象,因此请考虑使用协议/模拟方法来测试/预览视图,而不带数据库对象。您的核心数据实体的名称是什么?那是“任务”吗?是的,那是正确的。我还添加了我的ContentView代码,如果该帮助我进行了更改,请运行它