How to create and use a custom DataGridRow Trigger

Question

I'm using Prism 6 to create my application, and I have a need to color the background of DataGridRows based on the date. I started creating a Blend SDK Trigger to accept two parameters: MinDate and MaxDate. The action would then set the background color. However, I am hitting a roadblock when it comes to using the trigger. It isn't accepted in the collection and I can't seem to get the trigger to execute when I use a DataTemplate.

Here's the code for the trigger. It doesn't actually do anything other than invoke the action because I want to make sure it is executing before coding the logic to check the date.

public class AnniversaryTrigger: TriggerBase<DataGridRow>
{
    public DateTime MaxDate
    {
        get { return (DateTime)GetValue(MaxDateProperty); }
        set { SetValue(MaxDateProperty, value); }
    }

    public DateTime MinDate
    {
        get { return (DateTime)GetValue(MinDateProperty); }
        set { SetValue(MinDateProperty, value); }
    }

    protected override void OnAttached()
    {
        AssociatedObject.Loaded += OnLoaded;
        AssociatedObject.Unloaded += OnUnloaded;
    }

    protected override void OnDetaching()
    {
        AssociatedObject.Loaded -= OnLoaded;
        AssociatedObject.Unloaded -= OnUnloaded;
    }

    private void OnLoaded(object sender, System.Windows.RoutedEventArgs e)
    {
        AssociatedObject.DataContextChanged += OnDataContextChanged;
        Refresh();
    }

    private void OnUnloaded(object sender, System.Windows.RoutedEventArgs e)
    {
        AssociatedObject.DataContextChanged -= OnDataContextChanged;
    }

    private void Refresh()
    {
        base.InvokeActions(null);
    }

    private void OnDataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
    {
        Refresh();
    }

    #region Dependency Properties
    public static readonly DependencyProperty MaxDateProperty =
        DependencyProperty.Register("MaxDate", typeof(DateTime), typeof(AnniversaryTrigger), new PropertyMetadata(null));

    public static readonly DependencyProperty MinDateProperty =
        DependencyProperty.Register("MinDate", typeof(DateTime), typeof(AnniversaryTrigger), new PropertyMetadata(null));
    #endregion
}

The DataTemplate is as follows and was attached to the DataGrid ItemTemplate.

<UserControl.Resources>
    <DataTemplate x:Key="AnniversaryTemplate">
        <DataGridRow>
            <i:Interaction.Triggers>
                <b:AnniversaryTrigger MinDate="{Binding MinDate}" 
                                      MaxDate="{Binding MaxDate}" >
                    <ei:ChangePropertyAction PropertyName="Background">
                        <ei:ChangePropertyAction.Value>
                            <SolidColorBrush Color="Yellow"/>
                        </ei:ChangePropertyAction.Value>
                    </ei:ChangePropertyAction>
                </b:AnniversaryTrigger>
            </i:Interaction.Triggers>
        </DataGridRow>
    </DataTemplate>
</UserControl.Resources>

Here's the DataGrid:

<DataGrid ItemsSource="{Binding FalseAlarmHistory}" AutoGenerateColumns="False" IsReadOnly="True" ItemTemplate="{DynamicResource AnniversaryTemplate}" >
        <DataGrid.Columns>
            <DataGridTextColumn Header="Incident ID" 
                                Binding="{Binding IncidentID}" />
            <DataGridTextColumn Header="Incident Date" 
                                Binding="{Binding IncidentDate, StringFormat=d}" />
            <DataGridTextColumn Header="Incident Time" 
                                Binding="{Binding IncidentTime}" />
            <DataGridTextColumn Header="Notes" 
                                Binding="{Binding Notes}" />
        </DataGrid.Columns>
    </DataGrid>

Any guidance is appreciated.

Incident history view model:

public class FalseAlarmHistoryViewModel : ValidatingBindableBase, IConfirmNavigationRequest
{
    private IFalseAlarmService _service;
    private ICustomerService _custsvc;

    private string _title;
    private IEventAggregator _eventAggregator;

    public string Title { get => _title; set => SetProperty(ref _title, value); }

    public FalseAlarmHistoryViewModel(IFalseAlarmService service, ICustomerService custsvc, IEventAggregator eventAggregator)
    {
        _service = service;
        _custsvc = custsvc;
        _eventAggregator = eventAggregator;
        Title = "False Alarms History";

        _eventAggregator.GetEvent<PermitSelectedChangedEvent>().Subscribe(PermitIdChanged);
    }

    //todo Color DataGrid Rows based on the anniversary year the false alarm occurred.  
    // See https://stackoverflow.com/questions/14997250/datagrid-row-background-color-mvvm
    // Add unmapped item to the FalseAlarmHistory entity that returns the year based on the anniversary year. 0 = current year, 1 = 1 year ago, etc.
    // Translate the year number into a color that will be used on the DataGrid row.  Make the color configurable (in app.config at least).

    //todo Initial sort should be most recent first.
    private void PermitIdChanged(int obj)
    {
        FalseAlarmHistory = new ListCollectionView(_service.GetFalseAlarmHistoryByPermitId(_custsvc.CurrentPermitId).ToList());
        RaisePropertyChanged(nameof(FalseAlarmHistory));
    }

    public void ConfirmNavigationRequest(NavigationContext navigationContext, Action<bool> continuationCallback)
    {
        continuationCallback(true);
    }

    public void OnNavigatedTo(NavigationContext navigationContext)
    {
        FalseAlarmHistory = new ListCollectionView(_service.GetFalseAlarmHistoryByPermitId(_custsvc.CurrentPermitId).ToList());
        RaisePropertyChanged(nameof(FalseAlarmHistory));
    }

    public bool IsNavigationTarget(NavigationContext navigationContext)
    {
        return true;
    }

    public void OnNavigatedFrom(NavigationContext navigationContext)
    {
    }

    #region Commands
    #endregion
    #region Event Handlers
    #endregion
    #region Bound Controls
    public ICollectionView FalseAlarmHistory { get; private set; }


    #endregion
    #region Bound Commands
    #endregion
}

Answer 1

So, what I am thinking is that you add a property to the incident model that would be calculated based on the incident and anniversary date. By the sounds of it, you would have to get the anniversary date into the incident model somehow. You could do that from your data, or pass it to the incident model via a property, constructor, a function, etc.

Say you call the property IncidentAgeBucket and make of type AgeBucket.

// Inside Incident Model
public AgeBucket IncidentAgeBucket { get {
    // AgeBucket calculation logic goes here
    // Check to make sure you have an anniversary date first...
    // There are a few ways to approach setting this value, use one that you are comfortable with 
    }
}

// New enumeration to use (name these something more to your liking)
public enum AgeBucket{
    OneYear,
    TwoYear,
    ThreeYear
}

So, if the date is within the year of the anniversary date, then make the value of IncidentAgeBucket return AgeBucket.OneYear, when two years then return AgeBucket.TwoYear, etc.

In the XAML, add a RowStyle based on the value in the property:

<DataGrid x:Name="IncidentList" ItemsSource="{Binding Incidents}" ...>
    <DataGrid.Columns>
        <DataGridTextColumn Header="Incident Number" Binding="{Binding IncidentNumber}"/>
        ...
    </DataGrid.Columns>
    <DataGrid.RowStyle>
        <Style TargetType="DataGridRow">
            <Style.Triggers>
                <DataTrigger Binding="{Binding IncidentAgeBucket}" Value="{x:Static local:AgeBucket.OneYear}">
                    <Setter Property="Background" Value="LightGreen"></Setter>
                </DataTrigger>
                <DataTrigger Binding="{Binding IncidentAgeBucket}" Value="{x:Static local:AgeBucket.TwoYear}">
                    <Setter Property="Background" Value="LightBlue"></Setter>
                </DataTrigger>
                <DataTrigger Binding="{Binding IncidentAgeBucket}" Value="{x:Static local:AgeBucket.ThreeYear}">
                    <Setter Property="Background" Value="LightPink"></Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </DataGrid.RowStyle>
</DataGrid>

You may have to play around with the {x:Static local:AgeBucket.OneYear} syntax a bit. The local namespace may not be what you use. If you end up nesting the enum, then there are other things you will have to do to get this to work. A seemingly good reference for that.

I am hoping that this will give you an idea of a direction to go with this other than the trigger route. This seems more straight forward to me.

If this is way off base, let me know and I will scrap this answer. Too much for a comment! Hope this helps.