我的 viewDidLoad 函数中有一个 observeSingleEvent,我想将其更改为带有 .childAdded 的 observe,以便它会持续监听并在对象添加到数据库时添加它们。
这是从 firebase 读取的代码:
let parentRef = Database.database().reference().child("Recipes")
parentRef.observeSingleEvent(of: .value, with: { snapshot in
// PROCESSES VALUES RECEIVED FROM SERVER
if ( snapshot.value is NSNull ) {
// DATA WAS NOT FOUND
print("– – – Data was not found – – –")
} else {
// DATA WAS FOUND
for user_child in (snapshot.children) {
let user_snap = user_child as! DataSnapshot
let dict = user_snap.value as! [String: String?]
// DEFINE VARIABLES FOR LABELS
let recipeName = dict["Name"] as? String
let recipeDescription = dict["Description"] as? String
food.append(Element(name: recipeName!, description: recipeDescription!))
self.tableView.reloadData()
}
}
})
我现在遇到的另一个问题(除了它只加载一次)是,每当我转到应用程序中的另一个 View 然后返回时,它会再次读取所有内容,所以我会在我的 tableView 中获得所有内容的副本,这是否仍然会发生用观察?
编辑:
这是我的数据库的样子:
Recipes
-Kv7FAqgLtDrRoyGd-99
Description: "food description"
Name: "food name"
-KvBuzMUnIQXn8gpG2WL
Description: "food description2"
Name: "food name2"
-KvH6yYeJaThK7oP8xBj
Description: "food description3"
Name: "food name3"
最佳答案
- 更改 observeSingleEvent 以进行观察。
- 每当观察到新值时清空食物数组。
在 for 循环之外重新加载您的食物数组,以便仅在将所有项目加载到数组中时才重新加载。
let parentRef = Database.database().reference().child("Recipes") // 1. Change to observe parentRef.observe(.value, with: { snapshot in // PROCESSES VALUES RECEIVED FROM SERVER if ( snapshot.value is NSNull ) { // DATA WAS NOT FOUND print("– – – Data was not found – – –") } else { // 2. Empty food array self.food = [] // DATA WAS FOUND for user_child in (snapshot.children) { let user_snap = user_child as! DataSnapshot let dict = user_snap.value as! [String: String?] // DEFINE VARIABLES FOR LABELS let recipeName = dict["Name"] as? String let recipeDescription = dict["Description"] as? String food.append(Element(name: recipeName!, description: recipeDescription!)) } // 3. reload tableview outside loop self.tableView.reloadData() } })
通过在每次观察到新值时清空食物数组,您可以确保只显示数据库中存在的值,因此绝不会出现重复元素。
关于ios - (Swift + Firebase) 将 observeSingleEvent 转换为观察 .childAdded,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46515454/