如何修复附加函数的异步性质?
How to fix the asynchronous nature of my appending function?
我设置了一个查询以从数据库(由 heroku 托管的 Parse-server)中提取数据并将其附加到数组;在此查询中是另一个查询,用于从不同的 class 中提取信息,但也用于附加另一个数组。我认为因为我使用 .findObjectsinBackground
它是异步发生的,这导致了一个问题。这是代码(通用):
func getQueries(completion: (() -> Void)?){
let searchQuery = PFQuery(className: "Etc")
searchQuery.findObjectsInBackground(block: { (objects, error) in
if let objectss = objects{
for object in objectss {
//append some arrays
let otherQuery = PFQuery(className: "OtherClass")
otherQuery.whereKey("user", equalTo: object["User"] as String)
otherQuery.findObjectsInBackground(block: {(objects, error) in
if let objectss = objects{
for object in objectss{
array.append(object["ProfPic"] as PFFile)
print("\(array) and its count is \(array.count)") //this returns a non 0 value
}
}
completion!()
})
print("\(array) and its count is \(array.count)") //this returns 0
}
}
})
}
array
的计数一旦被附加到它自己的闭包中就返回为非 0,但在其闭包之外返回为 0。这是一个问题,因为数组用于迭代显示信息。无论如何要确保在完成 searchQuery
的整体关闭之前,otherQuery
的追加已经完成?
(另外,它是异步发生导致问题的事实是一个猜测......我可能是错的)
在后一种情况下,您将在获取数据之前打印计数,例如在 findObjectsInBackground
.
的完成块之外
您可以将整个事情包装在一个带有完成块的自己的方法中:
func fetchData(_ completion: () -> Void) {
searchQuery.findObjectsInBackground(block: { (objects, error) in
guard let objectss = objects else {
completion()
}
for object in objectss {
let otherQuery = PFQuery(className: "OtherClass")
otherQuery.whereKey("user", equalTo: object["User"] as String)
otherQuery.findObjectsInBackground(block: {(objects, error) in
guard let objectss = objects else {
completion()
}
for object in objectss{
array.append(object["ProfPic"] as PFFile)
}
print("In loop: \(array) and its count is \(array.count)")
completion()
})
}
})
}
比这更重要的是:
fetchData() {
print("After completing: \(array) and its count is \(array.count)")
// do stuff with your fetched data and display it
// "use in iterating through to display information" here
}
更新:
在您更新的问题中,您仅在成功案例中调用 completion!()
。在任何情况下你都必须调用它:
...
if let objectss = objects
...
completion!()
} else {
completion!()
}
...
我设置了一个查询以从数据库(由 heroku 托管的 Parse-server)中提取数据并将其附加到数组;在此查询中是另一个查询,用于从不同的 class 中提取信息,但也用于附加另一个数组。我认为因为我使用 .findObjectsinBackground
它是异步发生的,这导致了一个问题。这是代码(通用):
func getQueries(completion: (() -> Void)?){
let searchQuery = PFQuery(className: "Etc")
searchQuery.findObjectsInBackground(block: { (objects, error) in
if let objectss = objects{
for object in objectss {
//append some arrays
let otherQuery = PFQuery(className: "OtherClass")
otherQuery.whereKey("user", equalTo: object["User"] as String)
otherQuery.findObjectsInBackground(block: {(objects, error) in
if let objectss = objects{
for object in objectss{
array.append(object["ProfPic"] as PFFile)
print("\(array) and its count is \(array.count)") //this returns a non 0 value
}
}
completion!()
})
print("\(array) and its count is \(array.count)") //this returns 0
}
}
})
}
array
的计数一旦被附加到它自己的闭包中就返回为非 0,但在其闭包之外返回为 0。这是一个问题,因为数组用于迭代显示信息。无论如何要确保在完成 searchQuery
的整体关闭之前,otherQuery
的追加已经完成?
(另外,它是异步发生导致问题的事实是一个猜测......我可能是错的)
在后一种情况下,您将在获取数据之前打印计数,例如在 findObjectsInBackground
.
您可以将整个事情包装在一个带有完成块的自己的方法中:
func fetchData(_ completion: () -> Void) {
searchQuery.findObjectsInBackground(block: { (objects, error) in
guard let objectss = objects else {
completion()
}
for object in objectss {
let otherQuery = PFQuery(className: "OtherClass")
otherQuery.whereKey("user", equalTo: object["User"] as String)
otherQuery.findObjectsInBackground(block: {(objects, error) in
guard let objectss = objects else {
completion()
}
for object in objectss{
array.append(object["ProfPic"] as PFFile)
}
print("In loop: \(array) and its count is \(array.count)")
completion()
})
}
})
}
比这更重要的是:
fetchData() {
print("After completing: \(array) and its count is \(array.count)")
// do stuff with your fetched data and display it
// "use in iterating through to display information" here
}
更新:
在您更新的问题中,您仅在成功案例中调用 completion!()
。在任何情况下你都必须调用它:
...
if let objectss = objects
...
completion!()
} else {
completion!()
}
...