set IsEnabled = false a button in silverlight

Question

I have the following code in the ViewModel class, in the constructor where I define that the buttons are always Enabled = false when starting the form ...

 public partial class EditarConceptoWindow : ChildWindow
 {
  public EditarConceptoWindow(string documentoId)
  {
     InitializeComponent();
     viewModel.Saved += new EventHandler<Microsoft.Practices.Prism.Events.DataEventArgs<bool>>(ViewModel_Saved);
    viewModel.Calculation += new EventHandler<Microsoft.Practices.Prism.Events.DataEventArgs<bool>>(ViewModel_Calculation);
    this.DataContext = viewModel;

    BtnCalcular.IsEnabled = false;
    BtnObtenerTCRM.IsEnabled = false;
    ....... rest of code 

In a checked event of a check box when placing the Selected check box, it must be enabled to be set to true, depending on whether a particular element of a combobox has been selected as well;

   private void cbAgregarManual_Checked(object sender, RoutedEventArgs e)
     {
      if (this.ComboConcepto.SelectedValue.ToString() == "DPI")
        {
            BtnCalcular.IsEnabled = true;
            BtnObtenerTCRM.IsEnabled= true;
        }

    }

This must be done if and only if the checkbox is clicked and the DPI value is selected in the combobox.

But the behavior of the buttons is that when starting the form they are always IsEnabled = true and if the checkbox control is clicked if it works but I can't find a reason because only until I click the checkbox it works, there are some controls (such as TextBoxes, and also the buttons) with this directive in the XAML.

IsEnabled="{Binding ElementName=cbAgregarManual, Path=IsChecked }"

Answer 1

I suggest that you centralize the logic of the enabling into one property to avoid this mismatch of logic setting confusion.

In this new property it will use INotifyPropertyChanged for the notification of that change, but called in from other properties. So to sum up, when any of the associated values change, they do the notify call on the logic property; that process ensures that the control is properly en/dis-abled.

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Example

Such as this pseudo code where I check three different other properties:

public bool IsEnabledCombo { get { return ClickStatus 
                                       && OtherStatus 
                                       && !string.IsNullOrEmpty( UserText); }

public bool ClickStatus { get { return _clickStatus; } 
                         set { _clickStatus = value; 
                               NotifyPropertyChanged("ClickStatus");
                               NotifyPropertyChanged("IsEnabledCombo");
                             }}

 public bool OtherStatus { get { return _otherStatus; } 
                         set { _clickStatus = value; 
                               NotifyPropertyChanged("OtherStatus");
                               NotifyPropertyChanged("IsEnabledCombo");
                             }}   
  public string UserText { ... 
                          set { _userText = value;                            
                               NotifyPropertyChanged("UserText");
                               NotifyPropertyChanged("IsEnabledCombo");

Bind your control as such

  IsEnabled="{Binding IsEnabledCombo }"

So wherever one of the related values can change they also call NotifyPropertyChanged("IsEnabledCombo"); and the control status is updated automatically.

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I provide a another notify chained example doing similar on my blog:

Xaml: ViewModel Main Page Instantiation and Loading Strategy for Easier Binding