根据DateTime更改ListBox项

Question

I have a ListBox with some items bound to it. Those items are read from files like so:

        private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
        {
            bindList();
        }

        private void bindList()
        {
            var appStorage = IsolatedStorageFile.GetUserStoreForApplication();

            string[] fileList = appStorage.GetFileNames();

            List<Activity> activities = new List<Activity>();


            foreach (string file in fileList)
            {

                string fileName = file;

                string cYear = file.Substring(0, 4);
                string cMonth = file.Substring(5, 2);
                string cDay = file.Substring(8, 2);
                string cHour = file.Substring(11, 2);
                string cMinute = file.Substring(14, 2);
                string cSeconds = file.Substring(17, 2);

                DateTime dateCreated = new DateTime(int.Parse(cYear), int.Parse(cMonth), int.Parse(cDay), int.Parse(cHour), int.Parse(cMinute), int.Parse(cSeconds));

                string dYear = file.Substring(20, 4);
                string dMonth = file.Substring(25, 2);
                string dDay = file.Substring(28, 2);

                DateTime dateDeadline = new DateTime(int.Parse(dYear), int.Parse(dMonth), int.Parse(dDay));

                string aTitle = file.Substring(31);
                aTitle = aTitle.Substring(0, aTitle.Length - 4);
                activities.Add(new Activity() { Title = aTitle, DateCreated = dateCreated.ToLongDateString(), Deadline = dateDeadline.ToLongDateString(), FileName = fileName });

            }

            activityListBox.ItemsSource = activities;

        }

As you can see I'm reading dates and a title from the file name. Afterwards I bind them to the ListBox. What I want to do is change ListBox item (2 textbox and a hyperlink) color each time the dateDeadline is past the current date.

Here is how my ListBox looks like:

        <ListBox HorizontalAlignment="Stretch"
                 Name="activityListBox"
                 VerticalAlignment="Stretch">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel>
                        <HyperlinkButton Name="activityTitle"
                                         FontSize="40"
                                         Content="{Binding Title}"
                                         HorizontalContentAlignment="Left"
                                         Tag="{Binding FileName}"
                                         Click="activityTitle_Click"
                                          />

                        <TextBlock Name="activityDateCreated"
                                   Text="{Binding DateCreated, StringFormat='Stworzono: {0}'}"
                                   Margin="10" />

                        <TextBlock Name="activityDeadline"
                                   Text="{Binding Deadline, StringFormat='Deadline: {0}'}"
                                   Margin="10" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

Every guide I found was dealing with particular ListBox item (like changing 3rd item, 4th item etc.) and it does not solve my problem. I want to be able to check if the Deadline is past the current date each time files are loaded to the app and change it accordingly.

I'll greatly appreciate your help.

Answer 1

In order to achieve this, you would first want to add a property Forecolor to your Activity class. This property will be a getter property that returns a color based on your condition (In this case, if the current date is greater than the deadline, return Red else Green). Note that I have changed your Deadline data type to Date to allow comparison of dates.

public DateTime Deadline { get; set; }
public Color Forecolor
{
    get
    {
        if (DateTime.Now > Deadline)
            return Colors.Red;
        else
            return Colors.Green;
    }
}

Now bind you controls Foreground property to this property Forecolor

Foreground="{Binding Forecolor, Converter={StaticResource ColorToSolidColorBrush_ValueConverter}}"

Since the Foreground property expects a Brush, it will not work with just a color binding, you will need to use a converter that converts a Color to a Brush.

Define a Converter class in your project.

    public class ColorToSolidColorBrushValueConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (null == value)
        {
            return null;
        }
        // For a more sophisticated converter, check also the targetType and react accordingly..
        if (value is Color)
        {
            Color color = (Color)value;
            return new SolidColorBrush(color);
        }
        // You can support here more source types if you wish
        // For the example I throw an exception

        Type type = value.GetType();
        throw new InvalidOperationException("Unsupported type [" + type.Name + "]");
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        // If necessary, here you can convert back. Check if which brush it is (if its one),
        // get its Color-value and return it.

        throw new NotImplementedException();
    }
}

Finally define the converter in your window resources.

<Window.Resources>
    <local:ColorToSolidColorBrushValueConverter  x:Key="ColorToSolidColorBrush_ValueConverter"/>
</Window.Resources>

Note: I have put in code from a WPF project. There may be a few syntax issues if your project is in WP7 (Though I think, it should work). However the principle is the same.

Answer 2

You can use a converter for just such a thing.

<UserControl.Resources>
    <ResourceDictionary>
        <local:DateToColorConverter x:Key="DateToColorConverter"/>
    </ResourceDictionary>
</UserControl.Resources>

...

<TextBlock Name="activityDateCreated"
    Text="{Binding DateCreated, StringFormat='Stworzono: {0}'}"                                  
    Margin="10"
    Foreground="{Binding Deadline, Converter={StaticResource DateToColorConverter}" />


...


Your Converter (put this in your code behind)...

public class DateToColorConverter : IValueConverter
{
    static SolidColorBrush _normalColor = new SolidColorBrush(Colors.Black);
    static SolidColorBrush _pastDeadlineColor = new SolidColorBrush(Colors.Red);

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value is DateTime)
        {
            var deadline = value as DateTime;
            return deadline < DateTime.Now ? _pastDeadlineColor : _normalColor;
        }

        return _normalColor;
    }
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

BTW - you should use an ObservableCollection instead of a List to hold your activity objects. Also, make sure your activity object supports INotifyPropertyChanged and that all your property methods call PropertyChanged.