如何在View Controller外部设置数据源和委托

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?

Answer 1

    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.