Bind to certain item in ObservableCollection by checking value of string property - wpf

Question

In my View Model (VM) I have an ObservableCollection of items. In my view I am binding to the collection. I have created a few user controls that have a dependency property that i am binding to called STCode. So for example a "Tag" object will have a "Name" property of type String and a "value" property of type integer.
In my ViewModel
Constructor
Tags.Add(new Tag("Tag1",111));
Tags.Add(new Tag("Tag2",222));
Tags.Add(new Tag("Tag3",333));
Tags.Add(new Tag("Tag4",444));
public ObservableCollection<Tag> Tags
{
get
{
return _TagList;
}
set
{
if (value != _TagList)
{
_TagList = value;
}
}
}
In my View
<my:UserControl1 x:Name="control1" Margin="12,89,0,0" HorizontalAlignment="Left" Width="257" Height="249" VerticalAlignment="Top" STCode="{Binding Path=Value}"/>
This will bind to the First items value property in the ObservableCollection (Showing "Tag1" value). Is there anyway that I can get a specific "tag" object from the observableCollection by specifying the string Name property? So basically if I had 3 instances of my usercontrol in the view, on each control I would like to specify the "Name" property of the Tag object as a string in XAML, and in return bind that specific control to that specific tags integer "Value" property?
I hope this makes sense
Model
public class Tag : ModelBase
{
private int _value;
public string Tagname { get; set; }
public int Value
{
get
{
return _value;
}
set
{
_value = value;
NotifyPropertyChanged("Value");
}
}
}
ModelBase
public class ModelBase :INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void NotifyPropertyChanged(string propertyName)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
}
}

Answer 1

Since your UserControls are bound to the Collection itself and not the Item on the collection (the converter does this job internally) you must call PropertyChanged on the whole Collection when you want to refresh the bindings on your usercontrols.
Edit: Full solution
ViewModel:
public class MainWindowViewModel : INotifyPropertyChanged
{
public ObservableCollection<Tag> Tags { get; private set; }
public MainWindowViewModel()
{
Tags = new ObservableCollection<Tag>();
Tags.Add(new Tag("Tag1", 111));
Tags.Add(new Tag("Tag2", 222));
Tags.Add(new Tag("Tag3", 333));
Tags.Add(new Tag("Tag4", 444));
}
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
public void ChangeRandomTag()
{
var rand = new Random();
var tag = Tags[rand.Next(0, Tags.Count - 1)];
tag.Value = rand.Next(0, 1000);
OnPropertyChanged("Tags");
}
}
View XAML:
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:wpfApplication1="clr-namespace:WpfApplication1"
Title="MainWindow"
Width="525"
Height="350">
<Window.Resources>
<wpfApplication1:MyConverter x:Key="MyConverter" />
</Window.Resources>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<ListBox ItemsSource="{Binding Tags}">
<ListBox.ItemTemplate>
<DataTemplate>
<Border Margin="1"
BorderBrush="Black"
BorderThickness="1"
CornerRadius="2">
<StackPanel Orientation="Vertical">
<TextBlock Text="{Binding Name}" />
<TextBlock Text="{Binding Value}" />
</StackPanel>
</Border>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
<StackPanel Grid.Column="1" Orientation="Vertical">
<Button x:Name="buttonChangeRandomTag"
Click="ButtonChangeRandomTag_OnClick"
Content="Change Random Tag Value" />
<TextBlock Text="{Binding Tags, Converter={StaticResource MyConverter}, ConverterParameter=Tag1}" />
<TextBlock Text="{Binding Tags, Converter={StaticResource MyConverter}, ConverterParameter=Tag2}" />
<TextBlock Text="{Binding Tags, Converter={StaticResource MyConverter}, ConverterParameter=Tag3}" />
<TextBlock Text="{Binding Tags, Converter={StaticResource MyConverter}, ConverterParameter=Tag4}" />
</StackPanel>
</Grid>
View Code behind:
public partial class MainWindow : Window
{
public MainWindow()
{
DataContext = new MainWindowViewModel();
InitializeComponent();
}
private void ButtonChangeRandomTag_OnClick(object sender, RoutedEventArgs e)
{
(DataContext as MainWindowViewModel).ChangeRandomTag();
}
}
Converter:
[ValueConversion(typeof(ObservableCollection<Tag>), typeof(int))]
public class MyConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
var collection = value as ObservableCollection<Tag>;
var key = parameter as string;
if (collection == null || parameter == null)
return 0;
var result = collection.FirstOrDefault(item => item.Name.Equals(key));
if (result == null)
return 0;
return result.Value;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
throw new NotImplementedException();
}
}
Tag Class:
public class Tag : INotifyPropertyChanged
{
private string name;
private int value;
public string Name
{
get { return name; }
set
{
if (value == name) return;
name = value;
OnPropertyChanged("Name");
}
}
public int Value
{
get { return value; }
set
{
if (value == this.value) return;
this.value = value;
OnPropertyChanged("Value");
}
}
public Tag(string name, int value)
{
Value = value;
Name = name;
}
public event PropertyChangedEventHandler PropertyChanged;
[NotifyPropertyChangedInvocator]
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
}
}

Answer 2

You could use a ValueConverter to do that for you:
[ValueConversion(typeof(string), typeof(string))]
public class StringToTagPropertyConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null || value != typeof(ObservableCollection<Tag>)) return
DependencyProperty.UnsetValue;
if (parameter as string == null) return DependencyProperty.UnsetValue;
ObservableCollection<Tag> tagObject = (ObservableCollection<Tag>)value;
string returnValue = tagObject.Where(t => t.Name.ToLower() ==
parameter.ToString().ToLower()).FirstOrDefault();
return returnValue ?? DependencyProperty.UnsetValue;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return DependencyProperty.UnsetValue;
}
}
You would use it like this:
<my:UserControl1 x:Name="control1" Margin="12,89,0,0" HorizontalAlignment="Left"
Width="257" Height="249" VerticalAlignment="Top" STCode="{Binding Tags,
Converter={StaticResource StringToTagPropertyConverter},
ConverterParameter="Name"}" />
By changing the value of the ConverterParameter, you can get the ValueConverter to return different properties of your 'tag object'. I am assuming that you know how to add a value converter in XAML.