Binding does not work for TemplateSelector - wpf

Question

I have one part of the view is dynamic based on a TemplateSelector. However, the binding does not work for the controls in the DataTemplate.(The controls do show on screen, just the conetent/texts are empty). I suspect it's a DataContext issue, but couldn't figure out after a lot of searching on line. Here is my XAML:
<Grid>
<Grid.DataContext>
<local:MyViewModel/>
</Grid.DataContext>
<Grid.Resources>
<DataTemplate x:Key="T1">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="40" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="120" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0"
Grid.Row="0"
Text="Music"
Style="{StaticResource ResourceKey=textBlockStyle}" />
<TextBox Grid.Column="1"
Grid.Row="0"
Style="{StaticResource ResourceKey=textBoxStyle}"
Text="{Binding Path=MusicName}" />
</Grid>
</DataTemplate>
<DataTemplate x:Key="T2">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="40" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="120" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0"
Grid.Row="0"
Text="Currency"
Style="{StaticResource ResourceKey=textBlockStyle}" />
<ComboBox Grid.Column="1"
Grid.Row="0"
Style="{StaticResource ResourceKey=comboBoxStyle}"
ItemsSource="{Binding Path=Currency_List}"
SelectedItem="{Binding Path=Currency}" />
</Grid>
</DataTemplate>
<local:ProductTypeTemplateSelector T1="{StaticResource ResourceKey=T1}"
T2="{StaticResource ResourceKey=T2}"
x:Key="myTemplateSelector" />
<Grid.Resources>
<Grid.RowDefinitions>
<RowDefinition Height="30" />
<RowDefinition Height="*" />
<RowDefinition Height="40"/>
<RowDefinition Height="20" />
</Grid.RowDefinitions>
<!-- This biding works -->
<TextBlock Grid.Row="0"
Text="{Binding Path=MusicName}"/>
<!-- This biding does not work -->
<ContentControl Grid.Row="1"
Name="ccc"
Content="{Binding Path=Product_Type}"
ContentTemplateSelector="{StaticResource myTemplateSelector}">
</ContentControl>
</Grid>
This is my View Model (Technically, it is View Model and Model mixed together. I am not really implementing a full MVVM pattern)
public class MyViewModel: INotifyPropertyChanged
{
public MyViewModel()
{
SetLists();
}
protected void SetLists()
{
SetList_Product_Type();
SetList_Currency();
}
protected void SearchAndPopulate()
{
string query = string.Format("select * from dbo.vehicle_attributes where ticker like '%{0}%'", Search_Text);
DataView dv = DAL.ExecuteQuery(query);
if (dv.Count > 0)
{
DataRowView dvr = dv[0];
Vehicle_Id = int.Parse(dvr["vehicle_id"].ToString());
Product_Type = dvr["product_type_name"].ToString();
Vehicle_Name = dvr["vehicle_name"].ToString();
Is_Onshore = dvr["domicile_name"].ToString() == "Onshore";
Currency = dvr["currency"].ToString();
CUSIP = dvr["CUSIP"].ToString();
ISIN = dvr["isin"].ToString();
Ticker = dvr["ticker"].ToString();
Valoren = dvr["valoren"].ToString();
PC_Class = PC_Class_List.Find(x => x.Class_Name == dvr["class_name"].ToString());
Implementation_Type = Implementation_Type_List.Find ( x => x.Implementation_Type_Name == dvr["implementation_type_name"].ToString());
Price_Frequency = Price_Frequency_List.Find( x => x.Price_Frequency_Name == dvr["price_freq_name"].ToString());
Status = Status_List.Find( x => x.Status_Name == dvr["status_name"].ToString());
if (!string.IsNullOrEmpty(dvr["last_status_update"].ToString()))
{
Status_Date = DateTime.Parse(dvr["last_status_update"].ToString());
}
else
{
Status_Date = DateTime.MinValue;
}
switch (Product_Type)
{
case "Mutual Fund":
query = string.Format("select lf.dividend_currency, i.ticker from dbo.liquid_funds lf " +
"left join dbo.vehicles i on i.vehicle_id = lf.index_id " +
"where lf.vehicle_id ='{0}'",Vehicle_Id);
DataView dv_mutual_fund = DAL.ExecuteQuery(query);
if(dv_mutual_fund.Count > 0)
{
DataRowView dvr_mutual_fund = dv_mutual_fund[0];
Dividend_Currency = dvr_mutual_fund["dividend_currency"].ToString();
Benchmark_Ticker = dvr_mutual_fund["ticker"].ToString();
}
break;
default:
break;
}
}
}
public ICommand SearchVehicleCommand
{
get
{
return new Command.DelegateCommand(SearchAndPopulate);
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string name)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(name));
}
}
//ProductType
protected List<string> _product_Type_List = new List<string>();
public List<string> Product_Type_List
{
get
{
return _product_Type_List;
}
set
{
_product_Type_List = value;
OnPropertyChanged("Product_Type_List");
}
}
protected void SetList_Product_Type()
{
string query = "SELECT * FROM dbo.product_types WHERE is_enabled = 1";
DataView dv = DAL.ExecuteQuery(query);
List<string> l = new List<string>();
for (int i = 0; i < dv.Count; i++)
{
l.Add(dv[i]["product_type_name"].ToString());
}
Product_Type_List = l;
}
protected string _product_type;
public string Product_Type
{
get
{
return _product_type;
}
set
{
_product_type = value;
OnPropertyChanged("Product_Type");
SetList_Implementation_Type();
}
}
//Currency
protected List<string> _currency_List = new List<string>();
public List<string> Currency_List
{
get
{
return _currency_List;
}
set
{
_currency_List = value;
OnPropertyChanged("Currency_List");
}
}
protected void SetList_Currency()
{
string query = "SELECT currency FROM dbo.currencies";
DataView dv = DAL.ExecuteQuery(query);
List<string> l = new List<string>();
for (int i = 0; i < dv.Count; i++)
{
l.Add(dv[i]["currency"].ToString());
}
Currency_List = l;
}
protected string _currency;
public string Currency
{
get
{
return _currency;
}
set
{
_currency = value;
OnPropertyChanged("Currency");
}
}
// Music Name
protected string _musicName;
public string MusicName
{
get
{
return _musicName;
}
set
{
_musicName = value;
OnPropertyChanged("MusicName");
}
}
}
This is the class interface (sorry for the formatting above, but somehow I can't get it right):
And this is my DelegateCommand class:
public class DelegateCommand : ICommand
{
private readonly Action _action;
public DelegateCommand(Action action)
{
_action = action;
}
public void Execute(object parameter)
{
_action();
}
public bool CanExecute(object parameter)
{
return true;
}
}
This is the DataTemplateSelector:
public class MyTemplateSelector : DataTemplateSelector
{
public DataTemplate T1 { get; set; }
public DataTemplate T2 { get; set; }
public override DataTemplate SelectTemplate(object item,
DependencyObject container)
{
string product_type = (string)item;
if (product_type == "Type1")
return T1;
else
return T2;
}
}

Answer 1

The DataContext of a DataTemplate is set to the object that it is bound to. So in your case the DataContext for your Templates are Product_Type and you are expecting it to be MyViewModel.
There is a workaround for what you need. It uses a RelativeSource binding and FindAncester to access the DataContext of the Parent object.
Your DataTemplate bindings should look like this:
XAML
<DataTemplate x:Key="T1">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="40" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="120" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0"
Grid.Row="0"
Text="Music"
Style="{StaticResource ResourceKey=textBlockStyle}" />
<TextBox Grid.Column="1"
Grid.Row="0"
Style="{StaticResource ResourceKey=textBoxStyle}"
Text="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentControl}}, Path=DataContext.MusicName}" />
</Grid>
</DataTemplate>
<DataTemplate x:Key="T2">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="40" />
<RowDefinition Height="40" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="120" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0"
Grid.Row="0"
Text="Currency"
Style="{StaticResource ResourceKey=textBlockStyle}" />
<ComboBox Grid.Column="1"
Grid.Row="0"
Style="{StaticResource ResourceKey=comboBoxStyle}"
ItemsSource="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentControl}}, Path=DataContext.Currency_List}"
SelectedItem="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ContentControl}}, Path=DataContext.Currency}" />
</Grid>
</DataTemplate>
From MSDN
Find Ancestor - Refers to the ancestor in the parent chain of the data-bound element. You can use this to bind to an ancestor of a specific type or its subclasses.
The AncestorType attribute goes up the visual tree and finds the first Ancestor of the given type, in this case it's looking for ContentControl the path to the required property can then be set relative to this.
Update
Think of a template as a guide on how to display an object. The DataContext of the DataTemplate is going to be whatever object it is asked it to display.
In this case the ContentControl is told to display Product_Type and, depending on the value of Product_Type, to use a particular Template. Product_Type is given to the DataTemplate and becomes the DataContext.
WPFTutorials has some good examples.