INotifyDataErrorInfo how to force the view to getErrors()?-CodePudding

I have a desktop app developed with WPF in .net framework 4 and trying to set up my field validation with MVVM. I have implemented INotifyDataErrorInfo interface on my EntryClass which is being used inside MainWindowViewModel.

The interface implementation is done so my properties are not validated on propertychange inside set{} but rather after a user click 'Save' button.

 public bool IsFormValid()
        {
            bool valid = true;
            _errorHandler.ClearAllErrors();
            if (BrojTransakcije==null || BrojTransakcije.Length<4)
            {
                _errorHandler.AddError(nameof(BrojTransakcije), "Invalid chars");
                valid = false;
            }
            return valid;
        }

And it works, after clicking'save' I first clear all of the properties ( and raise ErrorsChanged() ) check the property and if it is invalid the error is shown on the view.

 private void RaiseErrorChanged(string propertyName)
        {
            ErrorsChanged?.Invoke(this, new DataErrorsChangedEventArgs(propertyName));
        }
        public void ClearAllErrors()
        {
            _formGreske.Clear();
            RaiseErrorChanged(string.Empty); //reset everything
        }

The problem I am having is: after the user inputs the correct value, the validation passes but the error info still stays on the screen, its not updating. If a user appends something on that input and clicks 'Save' again the error dissapears.

I have narrowed it down that the view (the binding engine I suppose) is not calling the GetErrors() method of the interface and it does not understand that the errors are cleared. Is there a way to force the view(binding engine) to forcely GetErrors() because obviously is not doing that?

<StackPanel>
                        <Label Style="{StaticResource LabelTitles}" 
                           Content="Broj transakcije"></Label>
                        <TextBox Style="{StaticResource InputBox}" 
                                 Text="{Binding NoviUnos.BrojTransakcije,
                            ValidatesOnNotifyDataErrors=True}">
                        </TextBox>
                    </StackPanel>

CodePudding user response：

If you are triggering the validation on Save (eg not in your set{}) then the only time it knows to validate is when you click save again.

I would add some logic to your set; to so it validates on LostFocus personally

Also just as a general note in case you haven't heard of it the 'mvvm community toolkit' is amazing for this stuff. Using the ObservableValidator class does a lot of the hard work for you https://learn.microsoft.com/en-us/windows/communitytoolkit/mvvm/observablevalidator

CodePudding user response：

Is there a way to force the view(binding engine) to forcely GetErrors() ...?

Implement INotifyPropertyChanged and raise the PropertyChanged event for the data-bound source property (BrojTransakcije). See this answer for more information.