WPF MVVM Update source property only after user confirmation

Question

I am new to wpf and I have this situation. Let's say that I have a Customer model with FirstName, LastName, Telephone and so on. If the details of an existing customer needs to be edited, the CustomerEdit viewmodel is opened where it has a property of type Customer. The view has some textboxes bounded to CurrentCustomer.FirstName , CurrentCustomer.LastName and so on. Now whenever the user provided an input in those textboxes, the bounded property gets updated. There is a button for saving the changes done. Can there be some way to update source properties only when the save button is pressed, and if possible, in an MVVM way?

Answer 1

By default Text DP's, UpdateSourceTrigger value is LostFocus. Change it to Explicit and from save button click manually update the source by getting binding expression and calling UpdateSource() on it.

XAML:

<TextBox x:Name="myTextBox"
         Text="{Binding PropertyName, UpdateSourceTrigger=Explicit}"/>
<Button Click="btnSave_Click"/>

Code behind:

private void btnSave_Click(object sender, RoutedEventArgs e)
{
    myTextBox.GetBindingExpression(TextBox.TextProperty).UpdateSource();
}

---

Having this logic in code behind is not violating any MVVM rule but still if you don't want it in code behind. You can achieve this way:

Create an ICommand in your view model and bind to button command and in command parameter pass the text value of textBox. You can either use RelayCommand or DelegateCommand whichever suits your needs. For DelegateCommand refer to this here.

<TextBox x:Name="myTextBox"
         Text="{Binding PropertyName, UpdateSourceTrigger=Explicit}"/>
<Button Command="{Binding SaveCommand}"
        CommandParameter="{Binding Text, ElementName=myTextBox}"/>

and in ViewModel command method set the actual value to which your textBox text is binded with.

private void SaveMethod(object parameter)
{
   this.PropertyName = parameter.ToString();
}

Answer 2

Apply UpdateSourceTrigger Explicit like

<TextBox Name="itemNameTextBox"
         Text="{Binding Path=ItemName, UpdateSourceTrigger=Explicit}" />

MSDN:

"If you have a dialog or a user-editable form and you want to defer source updates until the user is finished editing the fields and clicks "OK", you can set the UpdateSourceTrigger value of your bindings to Explicit"

MVVM Style:

If you want to do it in MVVM Style and if you have multiple textboxes then I suggest you to use a converter and create "Customer" object at there, which you can cast back easily in your VM. Handle the ICommand in your VM (Which will raised from your Button) and create CommandParameter by using Converter (textboxes values you can pass as an input to your converter).

Answer 3

In MVVM scenario implement IEditableObject interface in View-model as explained and recommend in this SO Answer

IEditableObject is a good interface anytime you want to be able to roll back changes.