我在单个用户 tapGesture 中运行多个 Firestore 查询，这要求我确保应用程序中运行的同时 Firestore 查询最少或没有。我已经阅读了关于这个问题的多个答案（等待任务完成），但我的查询没有按照我想要的顺序运行。
感谢您帮助指导我使用 DispatchGroup 以确保代码和查询的逻辑顺序。
我想确保函数checkAndCreateUserWorkoutProfile中的 Firestore 查询在DispatchGroup.notify(...)中的 2 个打印语句之前完成，从“Firestore Sequence”方法开始。相反，查询在两个打印语句启动后完成。
下面是我的 Xcode 调试器的代码和屏幕截图。如屏幕截图所示，问题在于使用“ DispatchGroup.notify(...) ”并没有等到函数 checkAndCreateUserWorkoutProfile中的 Firestore 查询完成。
alert.addAction(UIAlertAction(title: "Select", style: .default, handler: { [self]_ in
let dispatchGroup = DispatchGroup()
dispatchGroup.enter()
DispatchQueue.main.async {
print("Firestore Sequence 2 Initiated")
startActivityIndicator()
if let user = Auth.auth().currentUser {
let userID = user.uid
db.collection("user").whereField("author_uid", isEqualTo: userID).getDocuments { snapshot, error in
if error == nil && snapshot != nil {
for document in snapshot!.documents {
let docID = document.documentID
db.collection("user")
.document(docID)
.setData(["selectedWorkoutID" : workoutRow.workoutId], merge: true)
print("Firestore Sequence 2 Success - user selectedWorkoutID updated")
}
}
dispatchGroup.leave()
if let user = Auth.auth().currentUser {
let userID = user.uid
checkAndCreateUserWorkoutProfile(selectedWorkout: workoutRow, userID: userID)
}
}
}
}
dispatchGroup.notify(queue: .main) {
print("Firestore Sequence 4 Initiated")
print("Firestore Sequence 5 Initiated - Create/Read User Specific Dayprogram data")
}
}))
func checkAndCreateUserWorkoutProfile(selectedWorkout: Workout, userID: String) {
print("Firestore Sequence 3 Initiated - createORread user specific workout profile")
let dispatchGroup = DispatchGroup()
dispatchGroup.enter()
db.collection("Workout")
.whereField("workoutId", isEqualTo: selectedWorkout.workoutId)
.whereField("userID", isEqualTo: userID)
.getDocuments() { (querySnapshot, err) in
if querySnapshot?.count == 0 {
var ref: DocumentReference? = nil
ref = self.db.collection("Workout").addDocument(data:
[
"author_uid": selectedWorkout.author_uid!,
"workoutId": selectedWorkout.workoutId,
"userID": userID
])
{ err in
if let err = err {
print("Error adding user specific workout profile: \(err)")
dispatchGroup.leave()
} else {
print("Firestore Sequence 3 Success - User specific workout profile added/created with ID: \(ref!.documentID)")
dispatchGroup.leave()
}
}
}
}
}
使用@Kiril S. 的回答，代码已得到更正，如下所示。
class WorkoutViewController: UIViewController {
let dispatchGroup = DispatchGroup()
alert.addAction(UIAlertAction(title: "Select", style: .default, handler: { [self]_ in
dispatchGroup.enter()
DispatchQueue.main.async {
print("Firestore Sequence 2 Initiated")
startActivityIndicator()
if let user = Auth.auth().currentUser {
let userID = user.uid
db.collection("user").whereField("author_uid", isEqualTo: userID).getDocuments { snapshot, error in
if error == nil && snapshot != nil {
for document in snapshot!.documents {
let docID = document.documentID
db.collection("user")
.document(docID)
.setData(["selectedWorkoutID" : workoutRow.workoutId], merge: true)
print("Firestore Sequence 2 Success - user selectedWorkoutID updated")
}
}
if let user = Auth.auth().currentUser {
let userID = user.uid
checkAndCreateUserWorkoutProfile(selectedWorkout: workoutRow, userID: userID)
dispatchGroup.leave()
}
}
}
}
dispatchGroup.notify(queue: .main) {
print("Firestore Sequence 4 Initiated")
print("Firestore Sequence 5 Initiated - Create/Read User Specific Dayprogram data")
}
}))
func checkAndCreateUserWorkoutProfile(selectedWorkout: Workout, userID: String) {
print("Firestore Sequence 3 Initiated - createORread user specific workout profile")
dispatchGroup.enter()
db.collection("Workout")
.whereField("workoutId", isEqualTo: selectedWorkout.workoutId)
.whereField("userID", isEqualTo: userID)
.getDocuments() { (querySnapshot, err) in
if querySnapshot?.count == 0 {
var ref: DocumentReference? = nil
ref = self.db.collection("Workout").addDocument(data:
[
"author_uid": selectedWorkout.author_uid!,
"workoutId": selectedWorkout.workoutId,
"userID": userID
])
{ err in
if let err = err {
print("Error adding user specific workout profile: \(err)")
self.dispatchGroup.leave()
} else {
print("Firestore Sequence 3 Success - User specific workout profile added/created with ID: \(ref!.documentID)")
self.dispatchGroup.leave()
}
}
}
}
}
Xcode 控制台显示更正的代码/查询序列。
