IDataErrorInfo error message triggers, but no message is shown

Question

Hello fellow programmers. I have this strange issue on Silverlight MVVM pattern using IDataErrorInfo. It's my first question made here in StackOverflow, so I hope I manage to explain it correctly. Here's the deal:

I Have this huge Job Register ChildWindow that has some controls that should only be enabled if a checkbox called HasPrevision is checked. The idea is: if the job has a Prevision, then all the controls related to the prevision are Enabled, otherwise, they are Disabled. Now, if there is a prevision, the user MUST choose a Prevision Type in the PrevisionType ComboBox. So, if the HasPrevision checkbox is CHECKED, the PrevisionType must be selected, but if the HasPrevision checkbox is NOT CHECKED, the PrevisionType comboBox can be left unselected.

Here are the XAML for those controls (I won't show all the xaml here because it's rather big, but I believe that the problem can be solved just by showing those lines):

<!-- The HasPrevision CheckBox -->
<CheckBox Grid.Column="1"
  Grid.Row="3"
  x:Name="cbxHasPrevision"
  IsChecked="{Binding SelectedJob.HasPrevision, Mode=TwoWay}"
  Margin="0,20,2,0" />

<!-- The PrevisionType ComboBox -->
<telerik:RadComboBox Grid.Column="1"
  Grid.Row="4"
  x:Name="cmbPrevisionType"
  IsEnabled="{Binding HasPrevision, Converter={StaticResource ControlesCadastroProcessoConverter}, ConverterParameter=IsEnabled}"
  ItemsSource="{Binding PrevisionTypeList, Mode=OneWay}"                             
  SelectedItem="{Binding SelectedJob.PrevisionType , Mode=TwoWay, NotifyOnValidationError=True, ValidatesOnDataErrors=True, ValidatesOnExceptions=True, ValidatesOnNotifyDataErrors=True}"
  Margin="0,4,48,4"
  Height="22"
  DisplayMemberPath="DsPrevisionType"/>

So, as you can see, the HasPrevision and the PrevisionType properties are binded to a property in my ViewModel called SelectedJob. SelectedJob is a Job object. All I want to do is use the IDataErrorInfo interface in my Job Class to identify if the PrevisionType is selected. Now, I can only require a PrevisionType if the HasPrevision property is "true", so my job class has this code for the IDataErrorInfo:

public string this[string columnName]
    {
        get
        {
            switch (columnName)
            {
                case "PrevisionType":                      
                    if (HasPrevision && (PrevisionType== null))
                        return "Select a PrevisionType";
                    break;
            }
            return null;
        }

}

This sounds very logical to me. When I debug the code, it actually works: the switch identifies the columnName, it enters the case "PrevisionType" and it actually runs the return code inside the If statement returning the error message, not the default "return null" clause. But the error message don't show the error! Even worse: the combo box wont event validate automatically. When the "Save" button is clicked, I check for errors and set the PrevisionType comboBox to the InvalidFocused state. The comboBox DOES get the red border around it indicating that it is in an error state, but the error message is blank. When I hover my mouse of the control, an empty small red box appears, with nothing on it.

Even more weird than that: if I REMOVE the "HasPrevision" check from the IF statement, leaving the code as follow, the message is shown and the control is validated automatically!!!

public string this[string columnName]
    {
        get
        {
            switch (columnName)
            {
                case "PrevisionType":                      
                    if (PrevisionType== null)
                        return "Select a PrevisionType";
                    break;
            }
            return null;
        }
    }

Everything I can think of is that since I'm trying to validate a property based on another property value, somewhere in the middle of the set's and get's the Silverlight environment gets "confused"? I don't know, I've been trying to find a solution for this for 2 days with no success. Here are some of the other codes that I believe that are relevant.

The properties in my Job Class:

    private bool _HasPrevision;
    [DataMember]
    public bool HasPrevision
    {
        get { return _HasPrevision; }
        set
        {
            _HasPrevision= value;
            RaisePropertyChanged("HasPrevision");
        }
    }


    private PrevisionType.PrevisionType _PrevisionType { get; set; }
    [DataMember]
    public PrevisionType.PrevisionType PrevisionType
    {
        get { return _PrevisionType; }
        set
        {
            _PrevisionType = value;
            RaisePropertyChanged("PrevisionType");
        }
    }

My SelectedJob property in my ViewModel is:

public const string SelectedJobPropertyName = "SelectedJob";
    private Objects.Register.Job.Job _SelectedJob = null;
    public Objects.Register.Job.Job SelectedJob
    {
        get
        {
            return _SelectedJob;
        }

        set
        {
            if (_SelectedJob == value)
                return;

            var oldValue = _SelectedJob;
            _SelectedJob = value;
            RaisePropertyChanged(SelectedJobPropertyName , oldValue, value, true);
        }
    }

And my code for the Save Button is:

[...]

if(SelectedJob["PrevisionType"] != null)
{
    VisualStateManager.GoToState(cmbPrevisionTypeControl, "InvalidFocused", true);
    return;
}

[...]

Thanks in advance and I'm sorry if I got a little bit confused on explaining this.

EDIT 1: I had already read on those questions here, but they don't quite help me:

IDataErrorInfo - not seeing any error message even though one gets picked up

Silverlight IDataErrorInfo message does not show in custom control's textbox

Pliskin Pliskin · Accepted Answer · 2012-09-26T22:11:52

I'm using the Telerik RadComboBox in similar fashion and I have no issues getting the error message displayed. Here's my XAML for your reference, hope this helps...

 <TextBlock Text="Select a User to Assign the Current Step To:" Grid.Row="3" Visibility="{Binding ShowAssigneeUser}"/>
            <telerik:RadComboBox x:Name="cmbAllActiveCrmUsers" 
                                 IsEditable="True" 
                                 Grid.Row="4"                   
                                 telerik:TextSearch.TextPath="FullName" 
                                 Text="{Binding FullName, Mode=TwoWay, ValidatesOnDataErrors=True, NotifyOnValidationError=True}"
                                 VerticalAlignment="Center"
                                 Visibility="{Binding ShowAssigneeUser}"
                                 ItemsSource="{Binding AllActiveCrmUsersExceptCurrentUser}" 
                                 SelectedIndex="{Binding DefaultAssigneeUserIndex, Mode=TwoWay}"
                                 ItemTemplate="{StaticResource ComboBoxMultilineTemplate}" 
                                 Style="{StaticResource ComboBoxStyle}"
                                 Command="{Binding AssignUserChangeCommand}"
                                 CommandParameter="{Binding SelectedIndex, ElementName=cmbAllActiveCrmUsers}"
                                  >
                <telerik:RadComboBox.ItemsPanel>
                    <ItemsPanelTemplate>
                        <VirtualizingStackPanel />
                    </ItemsPanelTemplate>
                </telerik:RadComboBox.ItemsPanel>
            </telerik:RadComboBox>

IDataErrorInfo error message triggers, but no message is shown

}

1 Answers