I am creating a calendar and I am using MVVM light. When i change the observable Collection the UI is not updated. My goal is if i click on a button in my ItemsControl the observable Collection changes and should trigger the DataTriger in my buttonstyle.

Things from MainWindow:

private ObservableCollection<Dates> _list;
public ObservableCollection<Dates> List
        {
            get { return _list; }
            set
            {
                _list = value;
                RaisePropertyChanged(nameof(List));
            }
        }

public RelayCommand<DateTime> DayClickedCommand { get; private set; }
private void DayClickedeCommandParameterhandling(DateTime s)
        {
            for (int i = 0; i < List.Count; i  )
            {
                if (List[i].Date == s)
                {
                    List[i].IsSelected = true;
                }
            }
        }

Dates class:

public class Dates
    {
        public Dates(DateTime day, int currentMonth)
        {
            Date = day;
            Day = day.Day.ToString();
            if ((int)day.Month == currentMonth)
            {
                IsInactive = false;
            }
            else
            {
                IsInactive = true;
            }
            if (day.DayOfYear == DateTime.Today.DayOfYear)
            {
                IsToday = true;
            }
            else IsToday = false;
        }

        #region Properties
        public DateTime Date { get; set; }
        public string Day { get; set; }
        public bool IsInactive { get; set; }
        public bool IsToday { get; set; }
        public bool IsSelected { get; set; }


        #endregion Properties
    }

My Xaml:

 <ItemsControl ItemsSource="{Binding List}">
                        <ItemsControl.ItemsPanel>
                            <ItemsPanelTemplate>
                                <WrapPanel></WrapPanel>
                            </ItemsPanelTemplate>
                        </ItemsControl.ItemsPanel>
                        <ItemsControl.ItemTemplate>
                            <DataTemplate >
                                <Grid Height="{Binding ElementName=Monday, Path=ActualHeight}" Width="{Binding ElementName=Monday, Path=ActualWidth}" Name="grid">
                                    <Button  Command="{Binding RelativeSource={RelativeSource AncestorType={x:Type Window}}, Path=DataContext.DayClickedCommand}" CommandParameter="{Binding Date}"  VerticalContentAlignment="Center" HorizontalContentAlignment="Center" MinHeight="10" MinWidth="10" FontSize="{Binding ElementName=textblockMonday, Path=FontSize}" Name="Button" BorderThickness="3" Content="{Binding Day}" >
                                            <Button.Style>
                                            <Style TargetType="Button">
                                                <Style.Triggers>
                                                    <DataTrigger Binding="{Binding IsInactive}" Value="True">
                                                        <Setter Property="Foreground" Value="Green" />
                                                        <Setter Property="Background" Value="Transparent" />
                                                    </DataTrigger> 
                                                    <DataTrigger Binding="{Binding IsInactive}" Value="false">
                                                        <Setter Property="Background" Value="Transparent" />
                                                    </DataTrigger>
                                                    <DataTrigger Binding="{Binding IsToday}" Value="true">
                                                        <Setter Property="Background" Value="Yellow" />
                                                        <Setter Property="Foreground" Value="Orange" />
                                                        <Setter Property="BorderBrush" Value="Orange" />
                                                    </DataTrigger> 
                                                    <DataTrigger Binding="{Binding IsToday}" Value="false">
                                                        <Setter Property="BorderBrush" Value="Transparent" />
                                                    </DataTrigger>
                                                    <DataTrigger Binding="{Binding IsSelected}" Value="true">
                                                        <Setter Property="Background" Value="Green" />
                                                        <Setter Property="Foreground" Value="Purple" />
                                                        <Setter Property="BorderBrush" Value="Orange" />
                                                    </DataTrigger>
                                                </Style.Triggers>
                                                </Style>
                                        </Button.Style>
                                    </Button>
                                </Grid>
                            </DataTemplate>
                        </ItemsControl.ItemTemplate>
                    </ItemsControl>

The command is working and the collection is changed, but the ui is not informed.

CodePudding user response：

Your Dates class should implement INotifyPropertyChanged and raise the PropertyChanged event for the IsSelected property:

public class Dates : INotifyPropertyChanged
{
    public Dates(DateTime day, int currentMonth)
    {
        Date = day;
        Day = day.Day.ToString();
        if ((int)day.Month == currentMonth)
        {
            IsInactive = false;
        }
        else
        {
            IsInactive = true;
        }
        if (day.DayOfYear == DateTime.Today.DayOfYear)
        {
            IsToday = true;
        }
        else IsToday = false;
    }

    #region Properties
    public DateTime Date { get; set; }
    public string Day { get; set; }
    public bool IsInactive { get; set; }
    public bool IsToday { get; set; }

    private bool _isSelected;
    public bool IsSelected
    {
        get { return _isSelected; }
        set { _isSelected = value; NotifyPropertyChanged(); }
    }
    #endregion Properties

    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged([System.Runtime.CompilerServices.CallerMemberName]
        string propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

An ObservableCollection<T> doesn't raise change notifications when the T items in it are modified. It raises an event when you add or remove items to and from it only.