How to set datasource and delegate Outside of View Controller

Question

This might sound like an odd question but I'm trying to implement the BEMSimpleLineGraph library to generate some graphs that I have place in a UITableView. My question is how I reference an external dataSource and Delegate to have different graphs placed in each cell (BEMSimpleLineGraph is modelled after UITableView and UICollectionView). I currently have something like this:

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

    let cell: FlightsDetailCell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as FlightsDetailCell

    cell.userInteractionEnabled = false

    if indexPath.section == 0 {

        cell.graphView.delegate = GroundspeedData()
        cell.graphView.dataSource = GroundspeedData()
        return cell

    }
    if indexPath.section == 1 {

        cell.graphView.delegate = self
        cell.graphView.dataSource = self
        return cell

    }
    return cell
}

My dataSource and Delegate for section 1 is setup properly below this and the GroundspeedData class looks like this:

class GroundspeedData: UIViewController, BEMSimpleLineGraphDelegate, BEMSimpleLineGraphDataSource {

func lineGraph(graph: BEMSimpleLineGraphView!, valueForPointAtIndex index: Int) -> CGFloat {
    let data = [1.0,2.0,3.0,2.0,0.0]
    return CGFloat(data[index])
    }

func numberOfPointsInLineGraph(graph: BEMSimpleLineGraphView!) -> Int {
    return 5
    }
}

For some reason when I run the app, Xcode reports that it cannot find the dataSource for section 0, specifically "Data source contains no data.". How should I otherwise reference this alternate dataSource?

matt matt · Accepted Answer · 2015-01-15T00:16:13

    cell.graphView.delegate = GroundspeedData()
    cell.graphView.dataSource = GroundspeedData()

One problem is: the delegate and data source are weak references. That means they do not retain what they are set to. Thus, each of those lines creates a GroundspeedData object which instantly vanishes in a puff of smoke. What you need to do is make a GroundspeedData object and retain it, and then point the graph view's delegate and data source to it.

Another problem is: do you intend to create a new GroundspeedData object or use one that exists already elsewhere in your view controller hierarchy? Because GroundspeedData() creates a new one - with no view and no data. You probably mean to use a reference to the existing one.

How to set datasource and delegate Outside of View Controller

1 Answers