Swift 5 - 让 tableview 等到来自 api 调用的数据返回（使用多个 tableviews）

Question

Issue: Fatal error when View is loading. I know the problem is because there is no data available when to table view is trying to load. But, because I am using multiple TableViews in one UI I have to force the cell return in CellForRowAt.

Is there a better way of setting up different data for each TableView?

THANKS FOR THE HELP!

import UIKit

class NewCustomTaskVC: UIViewController {


    @IBAction func CancelPressed (_ sender: Any) {
        dismiss(animated: true, completion: nil)
    }
    @IBOutlet weak var taskTypeSelectionBtn: UIButton!
    @IBOutlet weak var FrameSelectionBtn: UIButton!
    @IBOutlet weak var AssignSelectionBtn: UIButton!


    @IBAction func SelecttaskTypePressed(_ sender: Any) {
        if tableViewTaskType.isHidden {
            self.tableViewTaskType.isHidden = false
            self.tableViewTaskType.rowHeight = 43.5
        } else {
            self.tableViewTaskType.isHidden = true
        }
    }


    @IBAction func SelectFramePressed(_ sender: Any) {
        if tableViewFrame.isHidden {
            self.tableViewFrame.isHidden = false
        } else {
            self.tableViewFrame.isHidden = true
        }
    }

    @IBAction func SelectAssignToPressed(_ sender: Any) {
        if tableViewAssignTo.isHidden {
            self.tableViewAssignTo.isHidden = false
        } else {
            self.tableViewAssignTo.isHidden = true
        }
    }





    @IBOutlet weak var tableViewTaskType: UITableView!
    @IBOutlet weak var tableViewFrame: UITableView!
    @IBOutlet weak var tableViewAssignTo: UITableView!



    var cellID = ""
    var array = ["String", "Test", "Next","Test 2", "Test 3"]

    override func viewDidLoad() {
        super.viewDidLoad()

        getData()

        tableViewTaskType.isHidden = true
        tableViewFrame.isHidden = true
        tableViewAssignTo.isHidden = true

        tableViewTaskType.delegate = self
        tableViewFrame.delegate = self
        tableViewAssignTo.delegate = self

        tableViewTaskType.dataSource = self
        tableViewFrame.dataSource = self
        tableViewAssignTo.dataSource = self

        self.tableViewTaskType.register(UITableViewCell.self, forCellReuseIdentifier: "cell1")
        self.tableViewFrame.register(UITableViewCell.self, forCellReuseIdentifier: "cell2")
        self.tableViewAssignTo.register(UITableViewCell.self, forCellReuseIdentifier: "cell3")

    }



    func getData () {
        //dispatchGroup.enter()
        var count = 0
        APICallBack.getFramesData(completion: { success in
            if success == true {
                print("frames success")
             count += 1
            } })

        APICallBack.getTaskTypeData { success in
            if success == true {
                print("task success")
             count += 1
            }
        }

        APICallBack.GETUserData(completion:  { success in
        if success == true {
            print("user success")
            count += 1
        } })

        if count == 3{

            DispatchQueue.main.async {
                self.tableViewTaskType.reloadData()
                self.tableViewAssignTo.reloadData()
                self.tableViewFrame.reloadData()
                print("ALL COMPLETE")

            }
        }
    }


}





   extension NewCustomTaskVC : UITableViewDelegate, UITableViewDataSource {
    func numberOfSections(in tableView: UITableView) -> Int {
       return 1

    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

        var count = 1
               switch tableView {
               case tableViewTaskType:
                   count = TaskTypeData.typeModel.count

               case tableViewFrame:
                   count = FramesData.framesModel.count

               case tableViewAssignTo:
                   count = CustomerData.customerModel.count

               default:
                   print("none")
                   return count
               }
        //return 5
        return count
    }

**PROBLEM IS HERE 
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        var cell:UITableViewCell?

        if tableView == self.tableViewTaskType{
            cell = tableView.dequeueReusableCell(withIdentifier: "cell1", for: indexPath)
            cell!.textLabel!.text = TaskTypeData.typeModel[indexPath.row].TaskTypeName
           // cell!.textLabel?.text = array[indexPath.row]
        }

        if tableView == tableViewFrame{
             cell = tableView.dequeueReusableCell(withIdentifier: "cell2", for: indexPath)
            cell!.textLabel!.text = FramesData.framesModel[indexPath.row].FrameName
           // cell!.textLabel?.text = array[indexPath.row]
        }
        if tableView ==  self.tableViewAssignTo {
             cell = tableView.dequeueReusableCell(withIdentifier: "cell3", for: indexPath)
            cell!.textLabel!.text = UserData.userModel[indexPath.row].UserFirst
          //  cell.textLabel?.text = array[indexPath.row]
        }
//       let cell = tableView.dequeueReusableCell(withIdentifier: "cell1", for: indexPath)
//        cell.textLabel?.text = array[indexPath.row]


        return cell!
    }
** TO HERE!



    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        let item = array[indexPath.row]
        print(item)
        tableViewTaskType.isHidden = true

    }



   }

My UI View:

The error I get if I don't force it:

Answer 1

I assume that you want to display an empty "placeholder" cell if the data source array is empty. You need to check explicitly for that condition in your cellForRow function.

As far as co-ordinating the fetch from multiple API endpoints, you can use a DispatchGroup - Some commented code indicates you may have tried this.

override func viewDidLoad() {
    super.viewDidLoad()

    tableViewTaskType.isHidden = true
    tableViewFrame.isHidden = true
    tableViewAssignTo.isHidden = true

    tableViewTaskType.delegate = self
    tableViewFrame.delegate = self
    tableViewAssignTo.delegate = self

    tableViewTaskType.dataSource = self
    tableViewFrame.dataSource = self
    tableViewAssignTo.dataSource = self

    self.tableViewTaskType.register(UITableViewCell.self, forCellReuseIdentifier: "cell1")
    self.tableViewFrame.register(UITableViewCell.self, forCellReuseIdentifier: "cell2")
    self.tableViewAssignTo.register(UITableViewCell.self, forCellReuseIdentifier: "cell3")

    getData()
}

func getData () {
    let dispatchGroup = DispatchGroup()

    dispatchGroup.enter()
    APICallBack.getFramesData(completion: { success in
        if success == true {
            print("frames success")
        } 
        dispatchGroup.leave()
    })

    APICallBack.getTaskTypeData { success in
        if success == true {
            print("task success")
        }
        dispatchGroup.leave()
    }

    APICallBack.GETUserData(completion:  { success in
        if success == true {
            print("user success")
        } 
        dispatchGroup.leave()
    })

    dispatchGroup.notify {
            self.tableViewTaskType.reloadData()
            self.tableViewAssignTo.reloadData()
            self.tableViewFrame.reloadData()
            print("ALL COMPLETE")
    }
}


extension NewCustomTaskVC : UITableViewDelegate, UITableViewDataSource {
func numberOfSections(in tableView: UITableView) -> Int {
   return 1
}

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

    switch tableView {
        case tableViewTaskType:
            return max(1,TaskTypeData.typeModel.count)

        case tableViewFrame:
            return max(1,FramesData.framesModel.count)

        case tableViewAssignTo:
            return max(1,CustomerData.customerModel.count)

        default:
            fatalError("Unexpected table view")
    } 
}


func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

    switch tableView {
        case self.tableViewTaskType:
            let cell = tableView.dequeueReusableCell(withIdentifier: "cell1", for: indexPath)
            if !TaskTypeData.typeModel.isEmpty {
                cell.textLabel!.text = TaskTypeData.typeModel[indexPath.row].TaskTypeName
            }
            return cell

        case tableViewFrame:
            let cell = tableView.dequeueReusableCell(withIdentifier: "cell2", for: indexPath)
            if !FramesData.framesModel.isEmpty {
                cell!.textLabel!.text = FramesData.framesModel[indexPath.row].FrameName
            }
            return cell

        case self.tableViewAssignTo:     
           let cell = tableView.dequeueReusableCell(withIdentifier: "cell3", for: indexPath)
           if !UserData.userModel.isEmpty {
               cell!.textLabel!.text = UserData.userModel[indexPath.row].UserFirst
           }
           return cell

        default:
           fatalError("Unexpected Tableview")
    }
}

Answer 2

you can set tableView.dataSource & tableView.delegate to self when your data is back

Answer 3

There is multiple problems with your code.
1) You call get data before your table view had registered it cells. So if your API would load data immediately table view will be call dataSource methods

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int  
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell  

but since the

self.tableViewTaskType.register(UITableViewCell.self, forCellReuseIdentifier: "cell1")
self.tableViewFrame.register(UITableViewCell.self, forCellReuseIdentifier: "cell2")
self.tableViewAssignTo.register(UITableViewCell.self, forCellReuseIdentifier: "cell3")

called in the end of viewDidLoad, your would get crash when you dequeue your cells in cellForAtIndexPath method.

The solution is to move getData call to the end of viewDidLoad method.

2) If you want to display all tables data at one time (when API is complete loading getFramesData, getTaskTypeData and GETUserData) you would need to synchronise this callbacks. You could do this with DispatchGroup.

    func getData () {
        let apiDispatchGroup = DispatchGroup()

        APICallBack.getFramesData { success in
            apiDispatchGroup.leave()
        }
        apiDispatchGroup.enter()

        APICallBack.getTaskTypeData { success in
            apiDispatchGroup.leave()
        }
        apiDispatchGroup.enter()

        APICallBack.GETUserData { success in
            apiDispatchGroup.leave()
        }
        apiDispatchGroup.enter()

        apiDispatchGroup.notify(queue: DispatchQueue.main) {
            self.tableViewTaskType.reloadData()
            self.tableViewAssignTo.reloadData()
            self.tableViewFrame.reloadData()
        }
    }

3) It's not good idea to use one dataSOurce class for mutltiple UITableView, because of dataSource become god object. The better approach is to use one ContainerViewController that contains three child UITableViewController, and pass data to the childs when data has loaded from the API.

Answer 4

It is perfectly fine to have multiple view controllers in one screen. So I suggest that you create three view controllers, one for each table view. And each table view has its own datasource. Then use a custom container view controller as described here: https://developer.apple.com/documentation/uikit/view_controllers/creating_a_custom_container_view_controller

Answer 5

Try to reload TableView data this way,

    func getData () {
        //dispatchGroup.enter()
        var count = 0
        APICallBack.getFramesData(completion: { success in
            if success == true {
                print("frames success")
             count += 1
             self.reloadTableViewsIfNeeded(count)
            } })

        APICallBack.getTaskTypeData { success in
            if success == true {
                print("task success")
             count += 1
             self.reloadTableViewsIfNeeded(count)
            }
        }

        APICallBack.GETUserData(completion:  { success in
        if success == true {
            print("user success")
            count += 1
            self.reloadTableViewsIfNeeded(count)
        } })


    }

    func reloadTableViewsIfNeeded (_ conunt: Int) {
        if count == 3{

            DispatchQueue.main.async {
                self.tableViewTaskType.reloadData()
                self.tableViewAssignTo.reloadData()
                self.tableViewFrame.reloadData()
                print("ALL COMPLETE")

            }
        }
    }

By using this, you will get an event to reload the tableviews after getting all the data.

Let me know if this helps.

Enjoy and Share...

Answer 6

You can always return a default non styled UITableViewCell. Also stop force unwrapping. You should always guard with if let or guard let.

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        var cell:UITableViewCell?


        ...

        return UITableViewCell()
    }