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multithreadingswiftparsingios9dispatch

Swift iOS9 - dispatch_group - need code to execute in specific order


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My code is not working as expected. I need the code to operate in the order in which it is typed. Currently only the first 2 sections are working as needed. Look at the comments in the code for further details.

tl;dr how can I have the commented sections execute in the order that I type in the comments?

func getResults() {
    resultsFollowingArray.removeAll(keepCapacity: false)
    resultsDisplayNameArray.removeAll(keepCapacity: false)
    resultsProfilePicArray.removeAll(keepCapacity: false)
    resultsNoticeReasonArray.removeAll(keepCapacity: false)
    resultsNoticeDescriptionArray.removeAll(keepCapacity: false)
    resultsDatePostedArray.removeAll(keepCapacity: false)


    let followGroup: dispatch_group_t = dispatch_group_create()
    let profilePicGroup: dispatch_group_t = dispatch_group_create()
    let noticesGroup: dispatch_group_t = dispatch_group_create()

    /*** needs to execute first ***/
    dispatch_group_async(followGroup, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
        let fQ = PFQuery(className: "Following")
        fQ.limit = 30
        fQ.whereKey("follower", equalTo: myEmail)

        do {
            let objs = try fQ.findObjects()
            for obj in objs {
                self.resultsFollowingArray.append(obj.valueForKey("followed") as! String)
            }
            print(self.resultsFollowingArray) //works fine
        } catch _ {

        }
    })

    /*** needs to execute second ***/
    dispatch_group_notify(followGroup, dispatch_get_main_queue(), {
        if (self.resultsFollowingArray.count > 0) {
            dispatch_group_async(profilePicGroup, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
                let uQ = PFQuery(className: "_User")
                uQ.limit = 30
                for (var i = 0; i < self.resultsFollowingArray.count; i++) {
                    uQ.whereKey("username", equalTo: self.resultsFollowingArray[i])
                    do {
                        try self.resultsProfilePicArray.append(uQ.getFirstObject().valueForKey("profile_picture") as! PFFile)
                    } catch _ {

                    }
                }
                print(self.resultsProfilePicArray) //works fine
            })
        }
    })

    /*** needs to execute third ***/
    /*** this section seems to be the first section to execute, therefore it is not working as I need it ***/

    dispatch_group_notify(profilePicGroup, dispatch_get_main_queue(), {
        print(self.resultsFollowingArray) //prints empty array
        if (self.resultsFollowingArray.count > 0) {
            dispatch_group_async(noticesGroup, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), {
                let nQ = PFQuery(className: "Notices")
                nQ.limit = 30
                for (var i = 0; i < self.resultsFollowingArray.count; i++) {
                    nQ.whereKey("poster", equalTo: self.resultsFollowingArray[i])
                    do {
                        let notices = try nQ.findObjects()
                        for notice in notices {
                            self.resultsDisplayNameArray.append(notice.valueForKey("poster_display_name") as! String)
                            self.resultsNoticeReasonArray.append(notice.valueForKey("reason") as! String)
                            self.resultsNoticeDescriptionArray.append(notice.valueForKey("notice_description") as! String)
                            self.resultsDatePostedArray.append(notice.valueForKey("date_posted") as! String)
                        }
                        self.tvMyFeed.reloadData()
                        print(self.resultsDisplayNameArray) //prints nothing
                    } catch _ {

                    }
                }
            })
        }
    })

    /*** needs to execute last ***/
    dispatch_group_notify(noticesGroup, dispatch_get_main_queue(), {
        self.tvMyFeed.reloadData()
    })
}

Updated code: For some odd reason, PFQuery "Notices" gets called twice and it's screwing everything up. This is what I am trying to do but I am trying to do it "in the background," this code still freezes the UI:

let group: dispatch_group_t = dispatch_group_create()

    dispatch_group_enter(group)
    let fQ = PFQuery(className: "Following")
    fQ.limit = 30
    fQ.whereKey("follower", equalTo: myEmail)
    do {
        let objs = try fQ.findObjects()
        for obj in objs {
            self.resultsFollowingArray.append(obj.valueForKey("followed") as! String)
        }
        dispatch_group_leave(group)
    } catch _ {
        dispatch_group_leave(group)
    }

    dispatch_group_enter(group)
    let uQ = PFQuery(className: "_User")
    uQ.limit = 30
    for (var i = 0; i < self.resultsFollowingArray.count; i++) {
        uQ.whereKey("username", equalTo: self.resultsFollowingArray[i])
        do {
            try self.resultsProfilePicArray.append(uQ.getFirstObject().valueForKey("profile_picture") as! PFFile)
        } catch _ {
            dispatch_group_leave(group)
        }
    }
    dispatch_group_leave(group)

    dispatch_group_enter(group)
    let nQ = PFQuery(className: "Notices")
    nQ.limit = 30
    for (var i = 0; i < self.resultsFollowingArray.count; i++) {
        nQ.whereKey("poster", equalTo: self.resultsFollowingArray[i])
        do {
            let notices = try nQ.findObjects()
            for notice in notices {
                self.resultsDisplayNameArray.append(notice.valueForKey("poster_display_name") as! String)
                self.resultsNoticeReasonArray.append(notice.valueForKey("reason") as! String)
                self.resultsNoticeDescriptionArray.append(notice.valueForKey("notice_description") as! String)
                self.resultsDatePostedArray.append(notice.valueForKey("date_posted") as! String)
            }
            dispatch_group_leave(group)
        } catch _ {
            dispatch_group_leave(group)
        }
    }

    dispatch_group_notify(group, dispatch_get_main_queue(), {
        self.tvMyFeed.reloadData()
    })

Solution

  • I have found a solution. You who dedicate your being to this purpose feel free to post yours, I will gladly accept your wisdom, granted it works as needed.

    Here is my final solution, the one I was looking for (thank God I was able to find it on my own!): It works FANTASTICALLY!

    func getResults() {
        resultsFollowingArray.removeAll(keepCapacity: false)
        resultsDisplayNameArray.removeAll(keepCapacity: false)
        resultsProfilePicArray.removeAll(keepCapacity: false)
        resultsNoticeReasonArray.removeAll(keepCapacity: false)
        resultsNoticeDescriptionArray.removeAll(keepCapacity: false)
        resultsDatePostedArray.removeAll(keepCapacity: false)
    
        let followGroup: dispatch_group_t = dispatch_group_create()
    
        dispatch_group_async(followGroup, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
            let fQ = PFQuery(className: "Following")
            fQ.limit = 30
            fQ.whereKey("follower", equalTo: myEmail)
    
            do {
                let objs = try fQ.findObjects()
                for obj in objs {
                    if (obj.valueForKey("followed") as! String != myEmail) {
                        self.resultsFollowingArray.append(obj.valueForKey("followed") as! String)
                    }
                }
                if (self.resultsFollowingArray.count > 0) {
                    let nQ = PFQuery(className: "Notices")
                    nQ.limit = 30
                    for (var i = 0; i < self.resultsFollowingArray.count; i++) {
                        nQ.whereKey("poster", equalTo: self.resultsFollowingArray[i])
                        do {
                            let notices = try nQ.findObjects()
                            for notice in notices {
                                self.resultsDisplayNameArray.append(notice.valueForKey("poster_display_name") as! String)
                                self.resultsNoticeReasonArray.append(notice.valueForKey("reason") as! String)
                                self.resultsNoticeDescriptionArray.append(notice.valueForKey("notice_description") as! String)
                                self.resultsDatePostedArray.append(notice.valueForKey("date_posted") as! String)
                            }
                            self.tvMyFeed.reloadData()
                        } catch _ {
    
                        }
                    }
                }
            } catch _ {
    
            }
        })
    
        dispatch_group_notify(followGroup, dispatch_get_main_queue(), {
            if (self.resultsFollowingArray.count > 0) {
                let uQ = PFQuery(className: "_User")
                uQ.limit = 30
                for (var i = 0; i < self.resultsFollowingArray.count; i++) {
                    uQ.whereKey("username", equalTo: self.resultsFollowingArray[i])
                    do {
                        try self.resultsProfilePicArray.append(uQ.getFirstObject().valueForKey("profile_picture") as! PFFile)
                    } catch _ {
    
                    }
                }
                self.tvMyFeed.reloadData()
            }
        })
    }