How to check data when using binding in WPF

Question

Maybe this is easy, but I didn't find a solution for my problem yet.

When I use binding and a user changes for example the text in a textbox, how can I perform some backround checks like:

• Is this name already in my database
• Does the name fit to my allowed character set

Without binding this is easy i just call the functions that do the trick.

Example:

<TextBox x:Name="textbox_Name" Height="23" Margin="108,37,20,0" TextWrapping="Wrap" Text="{Binding Name,UpdateSourceTrigger=LostFocus}" VerticalAlignment="Top"/>

• The datacontext is ObjectXYZ.
• ObjectXYZ has a Name and a Description property.
• I also have a Database with a ObservableCollection of type "ObjectXYZ" called "list"

Normaly I woud do something like: if(!Database.isExistingObject(textbox_Name.Text) { ObjectXYZ.Name=textbox_Name.Text; }

With binding the name gets directly changed(Two way binding)...how can I check it before its changed?

Answer 1

You can still call your background checks if you call them right after the user has updated the textbox content.

private string name;

public string Name 
{
    get
    {
        return name;
    }

    set
    {           
        CheckName(value); // Or whatever are you check functions

        name = value;

        PropertyChanged("Name");
    }
}

I hope this helps.