Xamarin中使用CorePlot的饼图显示白色空白屏幕

Question

I got the component off the Xamarin Component Store and have successfully managed to make a line and bar chart but having a little difficulty with a pie chart.

Code for Pie Chart:

protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);
        var view = NativeView;
        var graph = new CPTXYGraph
        {
            Title = "Pie Chart",
            TitleTextStyle = new CPTMutableTextStyle
            {
                FontSize = 50,
                Color = CPTColor.GreenColor,
            },
        };

        var plotSpace = (CPTXYPlotSpace)graph.DefaultPlotSpace;
        plotSpace.AllowsUserInteraction = true;     

        graph.ApplyTheme(CPTTheme.ThemeNamed((NSString)"Plain Black"));
        graph.PlotAreaFrame.BorderLineStyle.LineColor = CPTColor.BlackColor;

        var plot = new CPTPieChart
        {
            DataSource = new PiePlotDataSource()
        };                   

        graph.AddPlot(plot);

        view.AddSubview(new CPTGraphHostingView
        {
            HostedGraph = graph
        });       
    }

Code for Data Source:

class PiePlotDataSource : CPTPieChartDataSource
{
    public override int NumberOfRecordsForPlot(CPTPlot plot)
    {
        return DummyData.Data.Length;
    }

    public override NSNumber NumberForPlot(CPTPlot plot, CPTPlotField forFieldEnum, uint index)
    {
        return forFieldEnum == CPTPlotField.PieChartWidth ? DummyData.Data[index] : index;
    }
}

All I get is just a white blank screen with a misplaced title that cannot be zoomed or scrolled (I apologize for the big image, I'm not sure how to resize it):

The line and bar charts were implmeneted in a similar manner and they work fine. I have put break points in and checked if it was stopping in anywhere of the code but execution also seemed to be working fine.

The thing that it is not doing however is that the PiePlotDataSource methods are not getting called. I have verified they are getting called in the line and bar charts but for some reason they are not getting called here.

It has taken me several days to just get a few generic graphs working for Android and iOS due to so little documentation. This is the last chart I need to do so I would greatly appreciate any help.

Answer 1

I have managed to get it working and I am 90% sure what may have been the underlying problem. I originally thought that the order of setting up the host view, graph and plot may have been the problem but it turns out it was not the case.

The revised code is:

protected override void OnElementChanged(VisualElementChangedEventArgs e)
{
    base.OnElementChanged(e);
    var view = NativeView;

    var graph = new CPTXYGraph
    {
        Title = "Pie Chart",

    };

    var hostView = new CPTGraphHostingView(view.Bounds);
    view.AddSubview(hostView);

    var plot = new CPTPieChart
    {
        DataSource = new PiePlotDataSource(),
        PieRadius = hostView.Bounds.Size.Height / 4,
    };

    graph.AddPlot(plot);   

    hostView.HostedGraph = graph;            
}

What I have changed is that when creating a CPTGraphHostingView() , I pass in the parent's View.Bounds as a parameter and then assign the result to the variable hostView , which will be used later. I believe this was what was causing the layout problems.

The hostView is then used when setting the PieRadius property of the pie chart. If this property isn't set, the pie chart does not show (only a set of X and Y axes are shown).

In terms of the PiePlotDataSource methods not being called, a simple clean and rebuild fixed that problem. The updated code for its NumberForPlot() method is here:

public override NSNumber NumberForPlot(CPTPlot plot, CPTPlotField forFieldEnum, uint index)
{
    return forFieldEnum == CPTPlotField.BarLocation ? DummyData.Data[index] : index;
}

Notice that I am comparing forFieldEnum to CPTPlotField.BarLocation instead of CPTPlotField.PieChartWidth . This was because I put some break points in and stepped through the method, only to find that forFieldEnum was always CPTPlotField.BarLocation . I believe this is a binding error of some sort to the Xamarin CorePlot Compoenent.

Answer 2

Not sure with your coreplot version in xamarin component. I'm using version 1.5.1.2

But I found out that i could not use your method to run public override NSNumber NumberForPlot(CPTPlot plot, CPTPlotField forFieldEnum, uint index)

Solve by :

public override NSNumber NumberForPlot(CPTPlot plot, CPTPlotField forFieldEnum, nuint index)
            {
                int i = Convert.ToInt32(index);
                return forFieldEnum == CPTPlotField.BarLocation ? data[i].X : data[i].Y;
            }