error handling in WPF-MVVM / disabled button

I have problem with error handling in view. I use caliburn.micro and MEF.

My VM look like this:

[Export(typeof(IShellViewModel))]
public class ShellViewModel : PropertyChangedBase, IShellViewModel,IDataErrorInfo
{

    #region Private members

    private User _user;
    private Dictionary<string, bool> _validProperties;
    private bool _allPropertiesValid;

    #endregion

    #region Private methods

    private void ValidateProperties()
    {
        if (_validProperties.Values.Any(isValid => !isValid))
        {
            AllPropertiesValid = false;
            return;
        }
        AllPropertiesValid = true;
    }
    #endregion

    #region Constructor

    public ShellViewModel()
    {
        _user = new User();
        _v开发者_开发问答alidProperties = new Dictionary<string, bool> {{"Nick", false}, {"Password", false}};
    }

    #endregion

    #region Properties

    public bool AllPropertiesValid
    {
        get { return _allPropertiesValid; }
        set
        {
            if (_allPropertiesValid != value)
            {
                _allPropertiesValid = value;
                NotifyOfPropertyChange("AllPropertiesValid");
            }
        }
    }

    #endregion

    #region Implementation of IShellViewModel

    public string Nick
    {
        get { return _user.Nick; }
        set
        {
            _user.Nick = value;
            NotifyOfPropertyChange("Nick");
        }
    }

    public string Password
    {
        get { return _user.Password; }
        set
        {
            _user.Password = value;
            NotifyOfPropertyChange("Password");
        }
    }

    public void EmptyLogOn()
    { 
        MessageBox.Show(string.Format("LogOn on server with credential: {0}, {1}", Nick, Password));
    }

    public void LogOn(string nick, string password)
    {

        MessageBox.Show(string.Format("LogOn on server with credential: {0}, {1}", nick, password));
    }

    #endregion

    #region Implementation of IDataErrorInfo

    public string Error
    {
        get { return (_user as IDataErrorInfo).Error; }
    }

    public string this[string propertyName]
    {
        get
        {
            string error = (_user as IDataErrorInfo)[propertyName];
            _validProperties[propertyName] = String.IsNullOrEmpty(error) ? true : false;
            ValidateProperties();
            CommandManager.InvalidateRequerySuggested();
            return error;
        }
    }

    #endregion
}

If I have som error I set properties AllPropertiesValid on false. I bind this properties on Button properties IsEnabled.

So in View I have this:

<Button IsEnabled="{Binding AllPropertiesValid, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}"
        Micro:Message.Attach="EmptyLogOn"
        Content="Prihlás ma"
        Width="100" 
        Height="25" 
        VerticalAlignment="Center"
        Grid.Row="2"
        Grid.ColumnSpan="2"></Button>
<Label Content="{Binding AllPropertiesValid}" Grid.Row="3"/>

But if properties AllPropertiesValid is false Button is still enabled. I check the value of AllPropertiesValid (I bind this properties on label and label content is false) is false.

What’s wrong ? Thank for advance.

EDIT: In designer is button disabled, but when is loaded window button is enable.

If you are doing MVVM then you should be using ICommand (or other higher-level variants such as CommandBase, ...) since you need to do something when button is clicked.

In this case you bind to a command property on the ViewModel, you return false on the CanExecute in the command and button is disabled. Sometimes you have to call CommandManager.InvalidateRequerySuggested().

This does not explain why your code is not working. To be honest, it looks alright to me.