Validation and NotififyOnValidation Error don't work

Question

I have a property Name which is required in the model. Then in the VM I have a Name property that access the one of the model. And in my view I bind a textbox with the Name property of the VM. But the textbox does not get in red when it is empty. I do get the error : Field Name is required. But once again the textbox does not turn red. Please help

here is the model :

public class Task : BasicAuditTrail
{

    [Required]
    [MaxLength(256)]
    public string Name { get; set; }
}

Here is the VM :

public class TaskManagerViewModel : ViewModelBase, ITaskManagerViewModel
{
    public Task CurrentTask => taskManager.CurrentTask;

    public string Name
    {
        get
        {
            return CurrentTask.Name;
        }
        set
        {
            CurrentTask.Name = value;
            IsDirty = true;
            RaisePropertyChanged();
        }
    }

The View :

<TextBox Grid.Row="0" Grid.Column="3" Name="Name" Text="{Binding Name, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, NotifyOnValidationError=True}" />

@ShivaniKatukota I could and it works that way. But the issue is that I need to change the value of the property IsDirty when Name changes. And I should not access IsDirty from the model — raihane, May 17 '18 at 12:04
You could subscribe the PropertyChanged event of CurrentTask and change the IsDirty property there — Shivani Katukota, May 17 '18 at 12:24
@ShivaniKatukota How do I subscribe the PropertyChange event ? — raihane, May 17 '18 at 14:43
I tried it but it's not working **public TaskManagerViewModel(ITaskManager taskManager) { CurrentTask.PropertyChanged += MyViewModel_PropertyChanged; }** **private void MyViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e) { IsDirty = true; }** — raihane, May 17 '18 at 15:02
Yes I tried the one by Rached. I removed the switch case because I want to set IsDirty for all the properties of CurrentTask. But it is not working — raihane, May 17 '18 at 15:07
What is the problem? Isn’t the method called on property change? — Shivani Katukota, May 17 '18 at 15:08
Excatly. the method is never called with I change the field name. So IsDirty does not change — raihane, May 17 '18 at 15:10
Do you raise property change event after changing the name on the model? — Shivani Katukota, May 17 '18 at 15:11
Yes. **[Required] [MaxLength(256)] public string Name { get { return name; } set { name = value; OnPropertyChanged(); } }** — raihane, May 17 '18 at 15:14
You are subscribing to the property change event in the constructor of the viewmodel.. the CurrentTask is never set after that?? — Shivani Katukota, May 17 '18 at 15:24
@ShivaniKatukota Yes exactly you're right. CurrentTask was never set after that. So I moved the subscription from the constructor to another method where CurrentTask is changing and it's working perfectly. Thank you for your help and patience :) — raihane, May 17 '18 at 15:34

score 1 · Accepted Answer · answered May 17 '18 at 15:38

As mentioned in comments, the Name property of CurrentTask should be directly bind to the Textbox. This makes the error to work correctly.

To set the IsDirty property on the viemwodel, subscribe to the PropertyChanged event of the CurrentTask and set IsDirty there!

PS: make sure to remove the event when the CurrentTask is changing so as to not have any memory leaks

Validation and NotififyOnValidation Error don't work

1 Answers1