CODEWITHSUNDEEP
c#wpfdatatrigger
Paul
Paul

Reputation: 23

WPF DataTrigger only working 1 time

I'm trying out WPF and I have an application with an ObservableCollection hooked up to a ListView. It adds the items perfectly and everything is falling together. It is taking in data from a live source and so item values are getting updated and rows are getting added. But now I want the most recent rows to be highlighted, text changed, something to show that this certain row is being changed. So I set up a data trigger and added a value to the DataType in the ObservableCollection called RecentlyChanged. If its true, then set the text to red, otherwise text is black.

When I run this code the list items change to red and then never change back and I have tried everything and it is ticking me off. I've checked the debugger to and even when the value is no (I'm using strings yes and no because i wanted to try all sorts of data types) it stays red. Code for the data trigger is below:

--Edit: Added in the second datatrigger that i tried using before to no avail. 

<ListView ItemsSource="{Binding DataTable, UpdateSourceTrigger=PropertyChanged}">
    <ListView.Resources>
        <Style TargetType="ListViewItem">
            <Setter Property="Foreground" Value="Black"/>
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=RecentlyChanged}" Value="yes">
                    <Setter Property="Foreground" Value="Red" />
                </DataTrigger>
                <DataTrigger Binding="{Binding Path=RecentlyChanged}" Value="no">
                    <Setter Property="Foreground" Value="Black" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ListView.Resources>

Upvotes: 2

Views: 2227

Answers (1)

Austin Mullins
Austin Mullins

Reputation: 7437

The issue is that the ObservableCollection only reports changes to the collection itself, in other words, it fires a CollectionChanged event whenever items are added or removed, but not when properties of those items change. In order to achieve the desired result - updating a data trigger when an item's property changes - the item itself must implement the INotifyPropertyChanged interface and fire the PropertyChanged event when the desired property is set.

In this case, you can use the following:

using System.ComponentModel;

public class ListViewItem : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void OnPropertyChanged(string name)
    {
        var propChanged = PropertyChanged;
        if(propChanged != null)
        {
            propChanged(this, new PropertyChangedEventArgs(name));
        }
    }

    private string recentlyChanged = "yes"; // Recently changed on creation
    public string RecentlyChanged
    {
        get { return recentlyChanged; }
        set {
            recentlyChanged = value;
            OnPropertyChanged("RecentlyChanged");
        }
    }

    // ... define the rest of the class as usual

}

WPF magic should take care of the rest.

Upvotes: 4

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