Coding multiple viewmodels in WPF XAML MVVM - wpf

Question

for my project, i am trying to create a signal channel generator which connects to a toolset and pushes signals into it.
the issue i have is that i have been given the project in a form where the code for the textboxes are in the codebehind file, and i would like them to be in the xaml.
i have a variable which controls the number of channels (viewmodels) which can be changed. which is able to create multiple instances of the same viewmodel on the window. this allows the ability to select different targets inside the tool whcih it is communicating with and be able to pump signals to each target.
here is the code currently in the XAML:
<Window x:Class="SigGeneratorMVVM.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:SigGeneratorMVVM"
Title="Signal Generator" Height="370" Width="734" >
<StackPanel Name="MyWindow">
<!--<TextBox Height="23" HorizontalAlignment="Left" Margin="91,20,0,0" Name="CurrentValDisplay" VerticalAlignment="Top" Width="120" />-->
</StackPanel>
</Window>
here is the code for the mainwindow.cs
public partial class MainWindow : Window
{
List<ViewModel> gViewModels;
int gNumChannels = 1;
private System.Threading.Timer mViewUpdateTimer;
private TimerCallback mViewTimerCallback;
private UtilityParticipant mParticipant;
public MainWindow()
{
InitializeComponent();
// Connect as UtilityParticipant
ConnectMesh();
gViewModels = new List<ViewModel>();
for (int i = 0; i < gNumChannels; i++)
{
gViewModels.Add(new ViewModel(mParticipant));
TextBlock CurrentValueText = new TextBlock();
CurrentValueText.Text = "Current Value:";
CurrentValueText.Margin = new Thickness(5);
TextBox CurrentValueBox = new TextBox();
CurrentValueBox.Width = 120;
CurrentValueBox.Name = "CurrentValDisplay" + i.ToString();
CurrentValueBox.HorizontalAlignment = System.Windows.HorizontalAlignment.Left;
CurrentValueBox.Margin = new Thickness(10);
CurrentValueBox.SetBinding(TextBox.TextProperty, "CurrentValue");
//CurrentValDisplay.Name = "CurrentValDisplay" + i.ToString();
//CurrentValDisplay.SetBinding(TextBox.TextProperty, "CurrentValue");
TextBlock CurrentFrequencyText = new TextBlock();
CurrentFrequencyText.Text = "Frequency:";
CurrentFrequencyText.Margin = new Thickness(5);
TextBox CurrentFrequencyBox = new TextBox();
CurrentFrequencyBox.Width = 120;
CurrentFrequencyBox.Name = "CurrentFrequencyDisplay" + i.ToString();
CurrentFrequencyBox.HorizontalAlignment = System.Windows.HorizontalAlignment.Left;
CurrentFrequencyBox.Margin = new Thickness(10);
CurrentFrequencyBox.SetBinding(TextBox.TextProperty, "Frequency");
Slider FrequencySlider = new Slider();
FrequencySlider.Width = 200;
FrequencySlider.Name = "FrequencySet" + i.ToString();
FrequencySlider.Value= 10;
FrequencySlider.Maximum = 10;
FrequencySlider.Minimum = 0.1;
FrequencySlider.SetBinding(Slider.ValueProperty, "Frequency");
//Create a new stackpanel
StackPanel sp = new StackPanel();
sp.Orientation = Orientation.Vertical;
//Set DataContext of the StackPanel
sp.DataContext = gViewModels[i];
//Add controls created above to the StackPanel
sp.Children.Add(CurrentValueText);
sp.Children.Add(CurrentValueBox);
sp.Children.Add(CurrentFrequencyText);
sp.Children.Add(CurrentFrequencyBox);
sp.Children.Add(FrequencySlider);
//Add the StackPanel to the window
MyWindow.Children.Add(sp);
}
mViewTimerCallback = this.UpdateView;
mViewUpdateTimer = new System.Threading.Timer(mViewTimerCallback, null, 100, 20);
}
Update: I already have a ViewModel which has get set methods for each property (CurrentValue and Frequency for now), would it be sufficient to bind the DataTemplate and ItemsControl to that instead of creating a new model class?
private SigGenChannel mSigGenChannel;
//Constructor
public ViewModel(UtilityParticipant aParticipant)
{
mSigGenChannel = new SigGenChannel(aParticipant);
}
public string CurrentValue
{
get
{
return mSigGenChannel.CurrentValue.ToString();
}
set
{
mSigGenChannel.CurrentValue = double.Parse(value);
RaisePropertyChanged("CurrentValue");
}
}
public double Frequency
{
get
{
return mSigGenChannel.Frequency;
}
set
{
mSigGenChannel.Frequency = value;
RaisePropertyChanged("Frequency");
}
}
public double Amplitude
{
get
{
return mSigGenChannel.Amplitude;
}
set
{
mSigGenChannel.Amplitude = value;
RaisePropertyChanged("Amplitude");
}
}
public void RefreshValue()
{
//A bit of a cheat, but we provide a means to poke the Viewmodel
//And raise a property change event
RaisePropertyChanged("CurrentValue");
}
also this is the SigChannel model:
class SigGenChannel
{
#region Private members
private UtilityParticipant mParticipant;
private double mCurrentValue;
private double mFrequency;
private double mAmplitude;
private double mTarget;
private double mOffset;
private double mCurrentStepTime;
private DateTime mStartTime;
private System.Threading.Timer mTimer;
private TimerCallback mTCallback;
private int mUpdateInterval = 10;
#endregion
#region Public members
public double CurrentValue
{
get
{
return mCurrentValue;
}
set
{
mCurrentValue = value;
}
}
public double Frequency
{
get
{
return mFrequency;
}
set
{
mFrequency = value;
}
}
public double Amplitude
{
get
{
return mAmplitude;
}
set
{
mAmplitude = value;
}
}
public double Target
{
get
{
return mTarget;
}
set
{
mTarget = value;
}
}
#endregion
//Constructor
public SigGenChannel(UtilityParticipant aParticipant)
{
mParticipant = aParticipant;
mCurrentValue = 10;
mFrequency = 200;
mAmplitude = 100;
mOffset = 0;
mCurrentStepTime = 0;
mStartTime = DateTime.Now;
mTCallback = this.Update;
mTimer = new System.Threading.Timer(mTCallback, null, 500, mUpdateInterval);
//Array enumData = Enum.GetNames;
//RefreshItems();
//Temp Code....!
Collection lCollection = mParticipant.GetCollection("DefaultNodeName.NodeStats");
lCollection.Publish();
}
private void Update(object StateInfo)
{
TimeSpan span = DateTime.Now - mStartTime;
mCurrentStepTime = span.TotalMilliseconds / (double)1000;
mCurrentValue = (Math.Sin(mCurrentStepTime * (mFrequency * 2 * Math.PI)) * mAmplitude / 2) + mOffset;
//Temp Code...!
Collection lCollection = mParticipant.GetCollection("DefaultNodeName.NodeStats");
Parameter lParameter = lCollection.GetParameter("CPUPercent");
lParameter.SetValue(mCurrentValue);
lCollection.Send();

Answer 1

The current code is written in a way that does not follow the WPF suggested practices, and swimming against the current makes things a lot harder than then should be.
What the code should be doing is:
Create a (view)model class for a channel
For example:
class ChannelModel
{
public int Value { get; set; }
public int Frequency { get; set; }
}
Use an ItemsControl instead of a StackPanel
The WPF way of doing things like this is to bind controls to collections, so replace the StackPanel with an ItemsControl.
Bind the ItemsControl to an ObservableCollection of the models
Your main viewmodel should expose an ObservableCollection<ChannelModel> property and the control should bind to that directly:
<ItemsControl ItemsSource="{Binding CollectionOfChannelModels}"/>
This ensures that the control is automatically updated with any changes made to your collection without your needing to do anything else.
Use a DataTemplate to specify how each model should render
So far we 've gotten the control to stay in sync with your channel collection, but we also need to tell it how each item (channel model) should be displayed. To do this, add a DataTemplate to the Resources collection of the ItemsControl:
<ItemsControl.Resources>
<DataTemplate DataType={x:Type local:ChannelModel}>
<StackPanel Orientation="Horizontal">
<TextBlock Text="Value" />
<TextBox Text="{Binding Value}" />
</StackPanel>
</DataTemplate>
</ItemsControl.Resources>

Answer 2

Generally the idea is to create a DataTemplate for a specific type, in your case it is for ViewModel.
Create a DataTemplate for your ViewModel, for instance:
<DataTemplate DataType={x:Type local:ViewModel}>
<TextBox Text="{Binding ViewModelTextProperty}" />
</DataTemplate>
And also in your XAML you must bind your list of ViewModels
<ItemsControl ItemsSource="{Binding myListOfViewModels}"/>