ios - swift ，parse.com : how to pass data from query

Question

我对 parse.com 有这样的查询。 为什么numObjects变量在findObjectsInBackgroundWithBlock内部和函数退出时有不同的值

func searchUserInParse () -> Int {

    var numObjects : Int = 0 // the num return objects from query

    var query = PFQuery(className:"Bets")
    query.whereKey("user", equalTo: "Bob")
    query.findObjectsInBackgroundWithBlock {
        (objects: AnyObject[]!, error: NSError!) -> Void in
        if !error {
            numObjects = objects.count
            println(numObjects) // at this point the value = 1
        } else {
            // Log details of the failure
            NSLog("Error: %@ %@", error, error.userInfo)
        }
    }
    println(numObjects) // at this point the value = 0

    return numObjects
}

Answer 1

不要使用异步运行的findObjectsInBackgroundWithBlock，而是尝试使用同步运行的findObjects:

//Set up query...
var objects = query.findObjects()
numObjects = objects.count
println(numObjects)

然后在运行你的函数时，这样做:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) {
    //Search users
    searchUserInParse()

    dispatch_async(dispatch_get_main_queue()) {
        //Show number of objects etc.
    }
}