Getting changed data using binding in WPF/C#

Question

I have a basic project in WPF.
All it does it retrieve / update products.

As shown in the image below, the user enters an ID, the data is then displayed according to it, and the user is able to change the data and click 'Save Product' to save it to the database.

The GetProduct(int id) function retrieves a product by the ID provided.
The SaveProduct() function saves the changed fields.

Also, there are two DataTemplates:
1) For the ProductModel - includes 3 textboxes: ProductId, ProductName, UnitPrice.
2) For the ProductViewModel - includes the save/get buttons + a textbox for the user to enter the id of the desired product.

What I'm trying to do is get the changed data when a user clicks the 'Save Product' button.

The most ideal way in my opinion, is to use Binding.
Each textbox is already binded, but I have no idea how to get the binded data.

Here is an example of a binded textbox in the FIRST DataType (ProductModel):
<TextBox Grid.Row="0" Grid.Column="1" Text="{Binding ProductId}" Margin="5" Width="150" />

There is one for each of the following properties: ProductId, ProductName and UnitPrice.

IMPORTANT!: The Get/SaveProduct() functions are in the ProductViewModel class, while the actual product class is - you guessed it - ProductModel. The ProductViewModel class holds a variable that contains the current product displayed.

This is the button that's used to save the info - it is written in the SECOND DataType (ProductViewModel):
<Button Content="Save Product" DockPanel.Dock="Right" Margin="10,2" VerticalAlignment="Center" Command="{Binding Path=SaveProductCommand}" Width="100" />

The SaveProductCommand command simply fires the SaveProduct() function.

I have a few questions regarding this whole subject:

1. What does it mean when a binding is used like this : {Binding ProductId} ?

2. The default binding mode for textboxes is TwoWay as far as I remember. But in this case, ProductId/Name + UnitPrice are not dependency properties, therefore is it right that the binded values do not update/sent back when the text in the textboxes is changed? (Since there isn't an event attached to it...)

3. A data context was never configured in my project, but all of the "binding tags" in my XAML pages don't seem to have a defined source. Could it be that the source is actually the DataType in the DataTemplate that includes the binded objects?

4. The SECOND DataTemplate (the ProductViewModel one) has this ContentControl tag: <ContentControl Margin="10" Content="{Binding Path=CurrentProduct}" />.
   What is it's purpose?

5. If a TwoWay binding were/does occur, how do I get the values from within the SaveProduct() function? Do I just refer to, say CurrentProduct.ProductName to get the changed name?

Much thanks to everyone who takes their time to answer - I appreciate it so much!

Answer 1

What does it mean when a binding is used like this : {Binding ProductId} ?

The specific control property you have this binding set on is going to look for the ProductId property on the object set as the DataContext and set the propertys value in the control accordingly.

The default binding mode for textboxes is TwoWay as far as I remember. But in this case, ProductId/Name + UnitPrice are not dependency properties, therefore is it right that the binded values do not update/sent back when the text in the textboxes is changed? (Since there isn't an event attached to it...)

You do not need to make the properties within your object a DependencyProperty for TwoWay binding to occur.

A data context was never configured in my project, but all of the "binding tags" in my XAML pages don't seem to have a defined source. Could it be that the source is actually the DataType in the DataTemplate that includes the binded objects?

The bindings being set within your XAML will use the object stored within the DataContext, thus if you do not explicitly set the DataContext of the view, it will be null. You should note however that the DataContext is inherited from its parent. If you are in fact setting the content by using say, CurrentProduct, then all the properties will be available to bind to per your Product type.

The SECOND DataTemplate (the ProductViewModel one) has this ContentControl tag:

<ContentControl Margin="10" Content="{Binding Path=CurrentProduct}" />

What is it's purpose?

It is acting as the container of your CurrentProduct, which can contain one and only one item.

If a TwoWay binding were/does occur, how do I get the values from within the SaveProduct() function? Do I just refer to, say CurrentProduct.ProductName to get the changed name?

Without seeing the entire application, my guess is that the ContentControl is being set to the CurrentProduct and your TextBox, etc.. are all bound to the respective properties, such as CurrentProduct.ProductId, etc... The product which you want to save is in fact the CurrentProduct. When you call save within your ViewModel, you simply access the CurrentProduct and persist it as needed, where CurrentProduct.PropertyName will contain the changes which were propagated from the UI.