How to bind a variable with a textblock - wpf

Question

I was wondering how I would be able to bind a text block to a variable within my C# class.
Basically I have a "cart" variable in my .cs file. Within that Cart class I have access to the different totals.
The following is what I have for binding, but it does not seem to bind to the variable...
<StackPanel
Width="Auto"
Height="Auto"
Grid.ColumnSpan="2"
Grid.Row="5"
HorizontalAlignment="Right">
<TextBlock
Name="Subtotal"
FontFamily="Resources/#Charlemagne Std"
FontSize="20"
Text="{Binding ElementName=cart, Path=SubTotal}">
</TextBlock>
<TextBlock
Name="Tax"
FontFamily="Resources/#Charlemagne Std"
FontSize="20"
Text="{Binding ElementName=cart, Path=Tax}">
</TextBlock>
<TextBlock
Name="Total"
FontFamily="Resources/#Charlemagne Std"
FontSize="20"
Text="{Binding ElementName=cart, Path=Total}">
</TextBlock>
</StackPanel>
What is the correct way of doing it? Thanks again for the help!

Answer 1

If you further want the TextBoxes to update automatically when your cart class changes, your class must implement the INotifyPropertyChanged interface:
class Cart : INotifyPropertyChanged
{
// property changed event
public event PropertyChangedEventHandler PropertyChanged;
private int _subTotal;
private int _total;
private int _tax;
private void OnPropertyChanged(String property)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(property));
}
}
public int SubTotal
{
get
{
return _subTotal;
}
set
{
_subTotal = value;
OnPropertyChanged("SubTotal");
}
}
public int Total
{
get
{
return _total;
}
set
{
_total = value;
OnPropertyChanged("Total");
}
}
public int Tax
{
get
{
return _tax;
}
set
{
_tax = value;
OnPropertyChanged("Tax");
}
}
}

Answer 2

ElementName in binding is used to reference other controls, not variables in code behind. To reference variables in code behind, you need to assign that variable to a Control's DataContext property.
Replace every occurrence of following line of code :
<TextBlock Name="Subtotal" FontFamily="Resources/#Charlemagne Std" FontSize="20" Text="{Binding ElementName=cart, Path=SubTotal}"></TextBlock>
with :
<TextBlock Name="Subtotal" FontFamily="Resources/#Charlemagne Std" FontSize="20" Text="{Binding Path=SubTotal}"></TextBlock>
And in your Window's constructor or Load event, write following code :
this.DataContext = cart;

Answer 3

Two solutions..
First solution:
Put the cart as DataSource in your code behind:
DataSource = cart;
And bind to it as follows:
{Binding Path=PropertyOfCart}
Second solution:
Bind to your root control with an ElementName binding, and get the cart through a property on this control:
Name your root/parent control where cart is a propery:
<UserControl .....snip..... x:Name="Root">
Bind to it like this:
{Binding ElementName=Root, Path=Cart.PropertyOfCart}
Please note that Cart must be a property of your UserControl, and not a field

Answer 4

You need to set your class as the data source for your form. See also this question.