UITableView numberOfRows - ios

Question

I want to update a tableview with server data.
class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
#IBOutlet weak var tableView: UITableView!
var aedList = [AED]()
override func viewDidLoad() {
super.viewDidLoad()
}
override func viewWillAppear(animated: Bool) {
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return self.aedList.count
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cellIdentifier = "Cell"
let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath)
Server().getJsonInformationFromServer(url: "aeds") { (response) -> Void in
self.aedList = JSONHelper().parseAEDInformation(json: response["data"])
dispatch_async(dispatch_get_main_queue(), { () -> Void in
cell.textLabel?.text = self.aedList[indexPath.row].street
self.tableView.reloadData()
})
}
return cell
}
The data is being downloaded correctly, but the tableview is empty.
I guess this is due to the async behaviour of my download and the numberOfRowsmethod tries to count an still empty array.
How do I correct this to display the data correctly? Do I need to use a dispatch_async there as well?

Answer 1

cellForRowAtIndexPath as the method name implies, its called by the table view for each cell so you should not fetch your entire data there, its for populating the cells individually. Here are a couple of fixes in your code:
class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
#IBOutlet weak var tableView: UITableView!
var aedList = [AED]()
//In addition to viewDidLoad, you can call this method whenever you wanna update your table
func fetchData() {
Server().getJsonInformationFromServer(url: "aeds") { (response) -> Void in
self.aedList = JSONHelper().parseAEDInformation(json: response["data"])
self.aedList = JSONHelper().parseAEDInformation(json: response["data"])
dispatch_async(dispatch_get_main_queue()) { [weak self] in
self?.tableView.reloadData()
}
})
}
override func viewDidLoad() {
super.viewDidLoad()
fetchData()
}
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return aedList.count
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cellIdentifier = "Cell"
let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath)
cell.textLabel?.text = self.aedList[indexPath.row].street
return cell
}

Answer 2

Loading data from tableView:cellForRowAtIndexPath: won't never work. This method is called for every cell, that means:
If there are no cells (data is not loaded yet), the method won't never be called and your data won't be loaded (which is what is happening now).
If the data were loaded, you would trigger a new loading for every displayed cell, that is, if you have 5 items, you trigger 5 loadings. And that's recursive because reloadData will redisplay all cells.
Solution:
Put your loading code to a better place, e.g. viewDidAppear method of your controller.
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
Server().getJsonInformationFromServer(url: "aeds") { (response) -> Void in
self.aedList = JSONHelper().parseAEDInformation(json: response["data"])
dispatch_async(dispatch_get_main_queue(), { () -> Void in
self.tableView.reloadData()
})
}
}
func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cellIdentifier = "Cell"
let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath)
cell.textLabel?.text = self.aedList[indexPath.row].street
return cell
}