charley charley - 5 days ago 4
C# Question

"live chart" x axis not updating with along with time WPF c#

I have just started exploring the live chart library however can't seem to get the x axis to update as time passes. I have gone over this time and time again and can't seem to find the problem. The data points update correctly which is what I am finding so confusing!

I will at a later date be replacing the DateTime with a timer that displays how long the test has been running instead, if that makes the solution any simpler?

Part of me thinks this must be something simple I am missing!?

I appreciate any help on this one!

public partial class MainWindow : Window
{

private double _axisMax;
private double _axisMin;
Stopwatch stopwatch = new Stopwatch();


public MainWindow()
{
InitializeComponent();
//To handle live data easily, in this case we built a specialized type
//the MeasureModel class, it only contains 2 properties
//DateTime and Value
//We need to configure LiveCharts to handle MeasureModel class
//The next code configures MEasureModel globally, this means
//that livecharts learns to plot MeasureModel and will use this config every time
//a ChartValues instance uses this type.
//this code ideally should only run once, when application starts is reccomended.
//you can configure series in many ways, learn more at http://lvcharts.net/App/examples/v1/wpf/Types%20and%20Configuration


var mapper = Mappers.Xy<MeasureModel>()
.X(model => model.DateTime.Ticks) //use DateTime.Ticks as X
.Y(model => model.Value); //use the value property as Y

//lets save the mapper globally.
Charting.For<MeasureModel>(mapper);


//the values property will store our values array
ChartValues = new ChartValues<MeasureModel>();

//lets set how to display the X Labels
DateTimeFormatter = value => new DateTime((long)value).ToString("hh:mm:ss");

AxisStep = TimeSpan.FromSeconds(1).Ticks;
SetAxisLimits(DateTime.Now);

//The next code simulates data changes every 300 ms
Timer = new DispatcherTimer
{
Interval = TimeSpan.FromMilliseconds(300)
};
Timer.Tick += TimerOnTick;
IsDataInjectionRunning = false;
R = new Random();
DataContext = this;
}

public ChartValues<MeasureModel> ChartValues { get; set; }
public Func<double, string> DateTimeFormatter { get; set; }

public double AxisStep { get; set; }

public double AxisMax
{
get { return _axisMax; }
set
{
_axisMax = value;
OnPropertyChanged("AxisMax");
}
}
public double AxisMin
{
get { return _axisMin; }
set
{
_axisMin = value;
OnPropertyChanged("AxisMin");
}
}

public DispatcherTimer Timer { get; set; }
public bool IsDataInjectionRunning { get; set; }
public Random R { get; set; }

private void RunDataOnClick(object sender, RoutedEventArgs e)
{
if (IsDataInjectionRunning)
{
stopwatch.Stop();
Timer.Stop();
IsDataInjectionRunning = false;
}
else
{
stopwatch.Start();
Timer.Start();
IsDataInjectionRunning = true;
}
}

private void TimerOnTick(object sender, EventArgs eventArgs) // Class is referencing from here!
{
var now = DateTime.Now;

ChartValues.Add(new MeasureModel
{
DateTime = DateTime.Now,
Value = R.Next(0, 10)
});

SetAxisLimits(DateTime.Now);

//lets only use the last 30 values
if (ChartValues.Count > 30) ChartValues.RemoveAt(0);
}

private void SetAxisLimits(DateTime now)
{
AxisMax = now.Ticks + TimeSpan.FromSeconds(20).Ticks; // lets force the axis to be 100ms ahead
AxisMin = now.Ticks - TimeSpan.FromSeconds(8).Ticks; //we only care about the last 8 seconds
}

public event PropertyChangedEventHandler PropertyChanged;

protected virtual void OnPropertyChanged(string propertyName = null)
{
if (PropertyChanged != null) // if subrscribed to event
PropertyChanged.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}





public class MeasureModel
{
public DateTime DateTime { get; set; }
public double Value { get; set; }
}





<Window
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:graph_test_6"
xmlns:lvc="clr-namespace:LiveCharts.Wpf;assembly=LiveCharts.Wpf"
xmlns:chart="http://mindfusion.eu/charting/wpf" x:Class="graph_test_6.MainWindow"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"></RowDefinition>
<RowDefinition Height="*"></RowDefinition>
</Grid.RowDefinitions>
<Button Grid.Row="0" Height="30" Click="RunDataOnClick">
Inject/Stop Data
</Button>
<lvc:CartesianChart Grid.Row="1">
<lvc:CartesianChart.Series>
<lvc:LineSeries Values="{Binding ChartValues}" PointGeometrySize="18" StrokeThickness="4" />
</lvc:CartesianChart.Series>
<lvc:CartesianChart.AxisX>
<lvc:Axis LabelFormatter="{Binding DateTimeFormatter}"
MaxValue="{Binding AxisMax}"
MinValue="{Binding AxisMin}"
DisableAnimations="True">
<lvc:Axis.Separator>
<lvc:Separator Step="{Binding AxisStep}"></lvc:Separator>
</lvc:Axis.Separator>
</lvc:Axis>
</lvc:CartesianChart.AxisX>
</lvc:CartesianChart>
<TextBox x:Name="textBox" HorizontalAlignment="Left" Height="23" Margin="323,-71,0,0" TextWrapping="Wrap" Text="TextBox" VerticalAlignment="Top" Width="120"/>
</Grid>




Screen shot of problem

Answer

In Xaml you are binding for AxisX properties MaxValue and MinValue:

 MaxValue="{Binding AxisMax}" 
 MinValue="{Binding AxisMin}"

When window is loaded WPF mechanism reads the values that are bound: that's how you are getting initial values for X Axes. Later in code you are changing these values:

 AxisMax = now.Ticks + TimeSpan.FromSeconds(20).Ticks; // lets force the axis to be 100ms ahead
 AxisMin = now.Ticks - TimeSpan.FromSeconds(8).Ticks; //we only care about the last 8 seconds

Xaml should be notified about these changes and it's done via:

 OnPropertyChanged("AxisMin");
 OnPropertyChanged("AxisMax");

The problem is that window control itself doesn't declare, that it supports change notifications: it's missing INotifyPropertyChanged.

So to fix your issue change

public partial class MainWindow : Window

to

 public partial class MainWindow  : Window, INotifyPropertyChanged
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