System.NullReferenceException thrown in the MouseMove

[Kountree]

To whomever it may concern:

As of the past two weeks, users of the arction tool are receiving an error

************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
at Arction.LightningChartUltimate.Views.ViewXY.ViewXY.MouseMoved(MouseEventArgs eventArguments, MouseEventType eventType, LightningChartUltimate chart)
at Arction.LightningChartUltimate.Views.ViewBase.KQB(MouseEventArgs A, MouseEventType B, LightningChartUltimate C)
at Arction.LightningChartUltimate.LightningChartUltimate.OnMouseMove(MouseEventArgs eventArgs)
at System.Windows.Forms.Control.WmMouseMove(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
at System.Windows.Forms.ContainerControl.WndProc(Message& m)
at System.Windows.Forms.UserControl.WndProc(Message& m)
at Arction.LightningChartUltimate.LightningChartUltimate.WndProc(Message& message)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

Here is the picture.

This is the error message that appears at random occurances

Capture.PNG (223.15 KiB) Viewed 12288 times

Usually, I would provide a set of steps in order to repeat the error. Unfortunately, this exception is thrown randomly.

Thank you
Kountree

[ArctionPasi]

These kinds of errors are typically caused by forgetting to use Control.Invoke when updating the chart from background thread. Can you check you are using Invoke correctly?

[Kountree]

Thanks for the response. The Invoke member takes a delegate as a parameter. Is there an example on how to do this? And the biggest question, is how to recreate this error

[ArctionPasi]

In WinForms demo application, there's
- ViewXY->RealTime-> Thread-fed multi-channel example
- ViewXY->RealTime-> Historic data review example

Invoke is used there correctly.


Or just use this simpler example. It's using a Task as background thread.

Code: Select all

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Threading; 
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using Arction.WPF.LightningChartUltimate; 
using Arction.WPF.LightningChartUltimate.SeriesXY;
using Arction.WPF.LightningChartUltimate.Axes;
using Arction.WPF.LightningChartUltimate.Views;
using Arction.WPF.LightningChartUltimate.Views.ViewXY; 

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        
        System.Threading.CancellationTokenSource m_cancel = new CancellationTokenSource();
        LightningChartUltimate m_chart;
        int ChannelCount = 10;
        Random m_rand = new Random(); 

        public MainWindow()
        {
            InitializeComponent();

            CreateChart();

            Task task = new Task(() => { ThreadProc(); }, m_cancel.Token);
            task.Start();

            this.Closing += new System.ComponentModel.CancelEventHandler(MainWindow_Closing);
        }

        void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
        {
            m_cancel.Cancel(); 
        }


        void CreateChart()
        {
            m_chart = new LightningChartUltimate();


            m_chart.BeginUpdate();
            ViewXY v = m_chart.ViewXY;

            AxisX xAxis = v.XAxes[0];
            xAxis.SetRange(0, 10);
                        
            v.YAxes.Clear(); 

            for (int iCh = 0; iCh < ChannelCount; iCh++)
            {
                AxisY yAxis = new AxisY(v);
                yAxis.AxisColor = DefaultColors.SeriesForBlackBackgroundWPF[iCh % DefaultColors.SeriesForBlackBackgroundWPF.Length]; 
                v.YAxes.Add(yAxis);

                SampleDataSeries s = new SampleDataSeries(v, xAxis, yAxis);
                s.SamplingFrequency = 1000;
                s.FirstSampleTimeStamp = 0; 
                s.LineStyle.Color = DefaultColors.SeriesForBlackBackgroundWPF[iCh % DefaultColors.SeriesForBlackBackgroundWPF.Length];
                s.LineStyle.Width = 1; 
                s.MouseInteraction = false; 
                v.SampleDataSeries.Add(s); 
            }

            v.AxisLayout.YAxesLayout = YAxesLayout.Stacked;
            v.LegendBox.Visible = false; 

            m_chart.EndUpdate();

            gridMain.Children.Add(m_chart); 
        }

        void ThreadProc()
        {
            while (!m_cancel.IsCancellationRequested)
            {
                int iSampleCount = 10*1000; //X axis lenght * sampling frequency 
                List<double[]> dataForAllChannels  = new List<double[]>(); 
                for (int iCh = 0; iCh < ChannelCount; iCh++)
                { 
                    
                    double[] data = new double[iSampleCount]; 
                    for(int i=0; i<iSampleCount;i ++)
                    {
                        data[i] = m_rand.NextDouble()* 10.0; 
                    }

                    dataForAllChannels.Add(data); 
                }

                
                Dispatcher.Invoke((Action)delegate { UpdateChart(dataForAllChannels); });
                
                Thread.Sleep(1); 

            }

            if (m_chart != null)
            {
                m_chart.Dispose();
                m_chart = null;
            }
        }

        void UpdateChart(List<double[]> dataForAllChannels)
        {
            m_chart.BeginUpdate();

            int iChCount = dataForAllChannels.Count;

            for (int iCh = 0; iCh < iChCount; iCh++)
            {
                m_chart.ViewXY.SampleDataSeries[iCh].SamplesDouble = dataForAllChannels[iCh]; 
            } 

            m_chart.EndUpdate(); 

        }

    }
}

There's Dispatcher.Invoke((Action)delegate { UpdateChart(dataForAllChannels); });

For WinForms, just replace Dispatcher with 'this', and it uses the Form:
this.Invoke((Action)delegate { UpdateChart(dataForAllChannels); });

[Kountree]

Dood,

When it comes to tech support, you are making the competition look really horrible.

Thank you for the example. Those were the examples that I used, but I did not call the invoke, but instead the method from the thread
this.UIThread(delegate
{
// populate my array
this.Invoke((Action)delegate { FeedNewDataToChart(aMultiChannelData); });
}

I added the Invoke which is already nested in my UIThread.

I am not quit sure that this is a fix. Reason being is that I cannot reproduce the error.

[Kountree]

Hi ArctionPasi,

After careful analysis of my code, I do infact call the Control.Invoke. In fact, the examples you provided, I used them in my code.

It appears to happen when I set my plot to sweep. In the debugger, I get the mousemove exception even when I do not move the mouse.

Thanks
Kountree

[ArctionPasi]

Are you setting the XAxis.ScrollMode = Sweeping in background thread?

Please send us a small VS project to reproduce the issue.