CODEWITHSUNDEEP
c#wpfmvvmuser-controls
GrayDS
GrayDS

Reputation: 363

wpf usercontrol with exposed commands in more than one place within application

I obviously don't get this somewhere.

I have created a UserControl, the bare bones of which is:

private readonly DependencyProperty SaveCommandProperty =
      DependencyProperty.Register("SaveCommand", typeof(ICommand),
                                  typeof(ctlToolbarEdit));

private readonly DependencyProperty IsSaveEnabledProperty = 
      DependencyProperty.Register("IsSaveEnabled", typeof(bool), 
        typeof(ctlToolbarEdit), new PropertyMetadata(
           new PropertyChangedCallback(OnIsSaveEnabledChanged)));

public ctlToolbarEdit()
{
   InitializeComponent();
}

public bool IsSaveEnabled
{
   get { return (bool)GetValue(IsSaveEnabledProperty); }
   set { SetValue(IsSaveEnabledProperty, value); }
}

public static void OnIsSaveEnabledChanged(DependencyObject d,
   DependencyPropertyChangedEventArgs e)
{
   ((ctlToolbarEdit)d).cmdSave.IsEnabled = (bool)e.NewValue;
}

#region Command Handlers
public ICommand SaveCommand
{
   get { return (ICommand)GetValue(SaveCommandProperty); }
   set { SetValue(SaveCommandProperty, value); }
}

private void cmdSave_Click(object sender, RoutedEventArgs e)
{
   if (SaveCommand != null) 
      SaveCommand.Execute(null);
}

#endregion

Excellent. You can see what I am doing ... handling the click event of the button, and basically firing up the command.

The form (lets call that Form1 for the time being ... but note that this is actually a UserControl: common practice, I believe, in MVVM) that is hosting the control has the following line:

<ctl:ctlToolbarEdit HorizontalAlignment="Right" Grid.Row="1" 
   SaveCommand="{Binding Save}" IsSaveEnabled="{Binding IsValid}" />

This works great. I have an ICommand in my ViewModel called 'Save' and the ViewModel is correctly presenting the IsValid property.

So far so very good.

Now I want to have my new usercontrol also on Form2 (which is also a usercontrol - common practice, I believe, on MVVM). As it happens, Form1 and Form2 are on the screen at the same time.

It compiles, but I get a runtime exception:

'SaveCommand' property was already registered by 'ctlToolbarEdit'."

... leading me to believe that I don't get 'commands' at all.

Why can I not use my usercontrol in more than one place?

If I cannot, what would you suggest is another way to do this?

Very frustrating!

Thanks for any help.

Upvotes: 2

Views: 2182

Answers (1)

jkriddle
jkriddle

Reputation: 708

Try making your dependency properties static. Otherwise it is getting re-registered every time you instantiate a new control. Your usage of the MVVM commands looks good otherwise and sounds like you have a good grasp on it.

Upvotes: 4

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