Using WPF Validation rules and the disabling of a 'Save' button

Question

I have a page where a few textboxes cannot be empty before clicking a Save button.

Answer 1

this is it you need to check the HasError control property from the code behaind

and do this code in the save button click

 BindingExpression bexp = this.TextBox1.GetBindingExpression(TextBox.TextProperty);
bexp.UpdateSource(); // this to refresh the binding and see if any error exist 
bool hasError = bexp.HasError;  // this is boolean property indique if there is error 

MessageBox.Show(hasError.ToString());

Answer 2

just inhert your ViewModel from System.ComponentModel.IDataErrorInfo for Validate and from INotifyPropertyChanged to notify button

make property:

    public bool IsValid
    {
        get
        {
            if (this.FloorPlanName.IsEmpty())
                return false;
            return true;
        }
    }

in xaml, connect it to button

<Button Margin="4,0,0,0" Style="{StaticResource McVMStdButton_Ok}" Click="btnDialogOk_Click" IsEnabled="{Binding IsValid}"/>

in the IDataErrorInfo overrides, notify btutton

public string this[string columnName]{
        get
        {
            switch (columnName)
            {
                case "FloorPlanName":
                    if (this.FloorPlanName.IsEmpty())
                    {
                        OnPropertyChanged("IsValid");
                        return "Floor plan name cant be empty";
                    }
                    break;
            }
        }
}

Answer 3

I've tried several of the solutions stated above; however, none of them worked for me.

My Simple Problem

I have a simple input window that request a URI from the user, if the TextBox value isn't a valid Uri then the Okay button should be disabled.

My Simple Solution

Here is what worked for me:

CommandBindings.Add(new CommandBinding(AppCommands.Okay,
            (sender, args) => DialogResult = true,
            (sender, args) => args.CanExecute = !(bool) _uriTextBoxControl.GetValue(Validation.HasErrorProperty)));

Answer 4

You want to use Validation.HasError attached property.

Along the same lines Josh Smith has an interesting read on Binding to (Validation.Errors)[0] without Creating Debug Spew.

Answer 5

On the codebehind for the view you could wireup the Validation.ErrorEvent like so;

this.AddHandler(Validation.ErrorEvent,new RoutedEventHandler(OnErrorEvent)); 

And then

private int errorCount;
private void OnErrorEvent(object sender, RoutedEventArgs e)
{
    var validationEventArgs = e as ValidationErrorEventArgs;
    if (validationEventArgs  == null)
        throw new Exception("Unexpected event args");
    switch(validationEventArgs.Action)
    {
        case ValidationErrorEventAction.Added:
            {
                errorCount++; break;
            }
        case ValidationErrorEventAction.Removed:
            {
                errorCount--; break;
            }
        default:
            {
                throw new Exception("Unknown action");
            }
    }
    Save.IsEnabled = errorCount == 0;
}

This makes the assumption that you will get notified of the removal (which won't happen if you remove the offending element while it is invalid).

Answer 6

int count = 0;

private void LayoutRoot_BindingValidationError(object sender, ValidationErrorEventArgs e)
{
    if (e.Action == ValidationErrorEventAction.Added)
    {
        button1.IsEnabled = false;
        count++;
    }
    if (e.Action == ValidationErrorEventAction.Removed)
    {                
        count--;
        if (count == 0) button1.IsEnabled = true;
    }
}