如何在onDelete中获取当前的CoreData项目 [英] How to get current CoreData item in onDelete

问题描述

有两个实体 Parent 和 Child ，这是一对多的关系.一个父母和多个孩子.

There two entities Parent and Child, which is one to many relationship. One Parent and many Child.

我使用 EditMode 删除 Child 数据，例如:

I use EditMode to delete Child data like:

@ObservedObject private var db = CoreDataDB<Child>(predicate: "parent")

var body: some View {

    VStack {
        Form {

            Section(header: Text("Title")) {
                ForEach(db.loadDB(relatedTo: parent)) { child in

                    if self.editMode == .active {
                        ChildListCell(name: child.name, order: child.order)
                    } else {
                        ...
                    }
                }
                .onDelete { indices in 
                  // how to know which child is by indices here ???
                  let thisChild = child // <-- this is wrong!!!

                  self.db.deleting(at: indices)
                }
            }
        }
    }
}

删除方法是在另一个类中定义的，例如:

The deleting method is defined in another Class like:

public func deleting(at indexset: IndexSet) {

    CoreData.executeBlockAndCommit {

        for index in indexset {
            CoreData.stack.context.delete(self.fetchedObjects[index])
        }
    }
}

当发生 onDelete 时，我还想更新 Parent 和 Child 实体的其他属性.但是我必须找到已删除的当前 Child 项.怎么做?

And I also want to update other Attribute of Parent and Child Entities when onDelete occurs. But I have to locate the current Child item which is deleted. How to make it?

感谢您的帮助.

推荐答案

这里是可行的方法...(假设您的.loadDB返回数组，但通常类似的方法适用于任何随机访问集合)

Here is possible approach... (assuming your .loadDB returns array, but in general similar will work with any random access collection)

使用Xcode 11.4(使用常规的项目数组)进行了测试

Tested with Xcode 11.4 (using regular array of items)

var body: some View {
    VStack {
        Form {
            Section(header: Text("Title")) {
                // separate to standalone function...
                self.sectionContent(with: db.loadDB(relatedTo: parent))
            }
        }
    }
}

// ... to have access to shown container
private func sectionContent(with children: [Child]) -> some View {
    // now we have access to children container in internal closures
    ForEach(children) { child in

        if self.editMode == .active {
            ChildListCell(name: child.name, order: child.order)
        } else {
            ...
        }
    }
    .onDelete { indices in

        // children, indices, and child by index are all valid here
        if let first = indices.first {
            let thisChild = children[first]       // << here !!
            // do something here
        }

        self.db.deleting(at: indices)
    }
}

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