Create instance of unknown type

Question

I have class that draw three types of charts, and i want to update it by function public void GetData(PlotModel PlotModel). The main problem is that every series (AreaSeries,CandleStickSeries,HighLowSeries) has different interfaces. How can i update different types in function public void GetData(PlotModel PlotModel). What should i use Activator? Generic?

I think that something like is bad idea:

public void GetData(PlotModel PlotModel) {
    while(true) {
        System.Threading.Thread.Sleep(1000);
        // Add new Item?
        switch(PlotModel.Series.First().ToString()) {
            case "OxyPlot.Series.AreaSeries":
                Console.WriteLine("AreaSeries");
                break;
            case "OxyPlot.Series.CandleStickSeries":
                Console.WriteLine("CandleStickSeries");
                break;
            case "OxyPlot.Series.HighLowSeries":
                Console.WriteLine("HighLowSeries");
                break;
        }
    }
}

Code:

 namespace WpfApplication20 {
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    /// 
    public partial class MainWindow : Window {
        public MainWindow() {
            InitializeComponent();
            DataContext = new PlotClass();
        }
    }
    public class PlotClass {
        public PlotModel PlotModel { get; set; }
        public PlotClass() {
            PlotModel = new PlotModel();
            DrawCandleChart(PlotModel);
            UpdateChartAsync(PlotModel);
        }
        public void DrawSimpleChart(PlotModel PlotModel) {
            Random rnd = new Random();
            LineSeries LS = new LineSeries();
            for (int i=0;i<10;i++) {
                LS.Points.Add(new DataPoint(i,rnd.NextDouble()));
            }
            PlotModel.Series.Add(LS);
            PlotModel.InvalidatePlot(false);
        }

        public void DrawCandleChart(PlotModel PlotModel) {
            Random rnd = new Random();
            CandleStickSeries CSS = new CandleStickSeries();
            for (int i=0;i<10;i++) {
                CSS.Items.Add(new HighLowItem { Close = rnd.NextDouble(), High = rnd.NextDouble(), Low = rnd.NextDouble(), Open = rnd.NextDouble(), X = i });
            }
            PlotModel.Series.Add(CSS);
            PlotModel.InvalidatePlot(false);
        }

        public void DrawHighLowChart(PlotModel PlotModel) {
            Random rnd = new Random();
            HighLowSeries HLS = new HighLowSeries();
            for (int i = 0; i < 10; i++) {
                HLS.Items.Add(new HighLowItem { Close = rnd.NextDouble(), High = rnd.NextDouble(), Low = rnd.NextDouble(), Open = rnd.NextDouble(), X = i });
            }
            PlotModel.Series.Add(HLS);
            PlotModel.InvalidatePlot(false);
        }

        public void UpdateChartAsync(PlotModel PlotModel) {
            Action<PlotModel> Update = new Action<PlotModel>(GetData);
            IAsyncResult result = Update.BeginInvoke(PlotModel, null, null);
        }

        public void GetData(PlotModel PlotModel) {
            while(true) {
                System.Threading.Thread.Sleep(1000);
                // Add new Item?
            }
        }
    }
}

It sounds like your function to update them should belong to the classes themselves. — Matt Burland
– Matt Burland, Commented Nov 5, 2015 at 14:38
You should use a timer instead of an infinite while loop. Its not clear though what you mean by add a new item, since your code doesn't really show the different "interfaces" to the plots, its hard to tell you how to make a proxy or adapter to solve the issue. — Ron Beyer
– Ron Beyer, Commented Nov 5, 2015 at 14:44
Using dynamic properties can be performance costly. Do you have a base interface in which all models derive from? You could add a Draw method there. Then, as long as your primary method accepts the interface, you call the Draw method on the object. — SILENT
– SILENT, Commented Nov 5, 2015 at 15:32
No all models derive from different parents and they do not intersect. — A191919
– A191919, Commented Nov 5, 2015 at 15:33

Sergey Kalinichenko · Accepted Answer · 2015-11-05 14:44:27Z

C# 4 and up offers a nice way of processing situations like this: use cast to dynamic, and call a method with one overload per subtype, like this:

private void Process(AreaSeries arSer) {
    ...
}
private void Process(CandleStickSeries csSer) {
    ...
}
private void Process(HighLowSeries hlSer) {
    ...
}
...
while(true) {
    System.Threading.Thread.Sleep(1000);
    Process((dynamic)PlotModel.Series.First());
    //      ^^^^^^^^^
}

The cast to dynamic makes the "magic" happen: C# will examine the run-time type of PlotModel.Series.First(), and dispatch to one of the three Process methods that you supplied.

There is a danger in this approach: if PlotModel.Series.First() happens to not match any of the overloads, you get a run-time exception. The compiler cannot perform static analysis to tell you that your call would not succeed. Consider adding a catch-all method for the common superclass of your plots, too, so that you could handle unexpected sub-types more gracefully.

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