Separating Data Source to another class in Swift

Question

I'm trying to keep my view controllers clean as described in this article objc.io Issue #1 Lighter View Controllers. I tested this method in Objective-C and it works fine. I have a separate class which implements

UITableViewDataSource

methods.

#import "TableDataSource.h"



@interface TableDataSource()



@property (nonatomic, strong) NSArray *items;

@property (nonatomic, strong) NSString *cellIdentifier;



@end



@implementation TableDataSource



- (id)initWithItems:(NSArray *)items cellIdentifier:(NSString *)cellIdentifier {

    self = [super init];

    if (self) {

        self.items = items;

        self.cellIdentifier = cellIdentifier;

    }

    return self;

}



- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {

    return self.items.count;

}



- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:self.cellIdentifier forIndexPath:indexPath];



    cell.textLabel.text = self.items[indexPath.row];



    return cell;

}



@end

From the tableview controller, all I have to do is instantiate a instance of this class and set it as the tableview's data source and it works perfectly.

self.dataSource = [[TableDataSource alloc] initWithItems:@[@"One", @"Two", @"Three"] cellIdentifier:@"Cell"];

self.tableView.dataSource = self.dataSource;

Now I'm trying to do the same in Swift. First here's my code. Its pretty much of a translation of the Objective-C code above.

import Foundation

import UIKit



public class TableDataSource: NSObject, UITableViewDataSource {



    var items: [AnyObject]

    var cellIdentifier: String



    init(items: [AnyObject]!, cellIdentifier: String!) {

        self.items = items

        self.cellIdentifier = cellIdentifier



        super.init()

    }



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

        return items.count

    }



    public func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier, forIndexPath: indexPath) as UITableViewCell



        cell.textLabel?.text = items[indexPath.row] as? String



        return cell

    }



}

And I call it like this.

let dataSource = TableDataSource(items: ["One", "Two", "Three"], cellIdentifier: "Cell")

tableView.dataSource = dataSource

But the app crashes with the following error.

-[NSConcreteNotification tableView:numberOfRowsInSection:]: unrecognized selector sent to instance

I checked the

init

method of

TableDataSource

and the items and the cell identifier gets passed fine. I had to declare the

UITableViewDataSource

methods

public

and remove the

override

keyword otherwise it would give compile time errors.

I'm clueless on what's going wrong here. Can anyone please help me out?

Thank you.

Answer 1

Create a property for data source and use it with your tableview.

class ViewController: UIViewController {

  @IBOutlet weak var tableView: UITableView!
  var dataSource:TableDataSource!

  override func viewDidLoad() {
    super.viewDidLoad()

    dataSource = TableDataSource(items: ["One", "Two", "Three"], cellIdentifier: "Cell")

   tableView.dataSource = dataSource

  }
}

Separating Data Source to another class in Swift

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