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.

<TextBox...

                <TextBox.Text>
                    <Binding Path ="LastName" UpdateSourceTrigger="PropertyChanged">

                        <Binding.ValidationRules>
                            <local:StringRequiredValidationRule />
                        </Binding.ValidationRules>                              
                    </Binding>
                </TextBox.Text>

My rule works, I have a red border around my textbox until I enter a value. I now want to add this validation rule to my other text boxes.

How do I disable the Save button until the page has no validation errors? I'm not sure what to check.

Amp

Answer 1

Here is the complete sample what you need.

http://codeblitz.wordpress.com/2009/05/08/wpf-validation-made-easy-with-idataerrorinfo/

https://skydrive.live.com/?cid=2c6600f1c1d5e3be&id=2C6600F1C1D5E3BE%21203

Abib

Unfortunately the referenced example does not describe the enabling/disabling of the button in detail. – Filial

Would be great to have the key parts here in the answer. If the referred sites go away, this answer gets useless. – Filial

The Question is about how to disable button when using ValidationRules. But the referenced examples is about using IDataErrorInfo - another validation way. – Unmanned

Look this video youtube.com/watch?v=OOHDie8BdGI, it shows a example how to use IDataErrorInfo to disable/enable a button. – Toowoomba

Answer 2

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).

Contrecoup

How to do it if there is no any view and only a Window? – Abib

Who uses code behind any more. How do you do this in a view model? – Shahjahanpur

To be notified of error I had to add NotifyOnValidationError="True" on elements which needed validation : <Binding Path ="LastName" UpdateSourceTrigger="PropertyChanged" NotifyOnValidationError="True"> (default value is false) – Amberjack

Answer 3

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.

Binetta

You didn't answer "how do I disable the Save button". Please provide the code. The sample you referred "Binding to (Validation.Errors)[0] without Creating Debug Spew." Doesn't have any code to disable Save button. – Abib

Answer 4

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;
    }
}

Rhineland

Answer 5

Here is a helper method which tracks validation errors on the dependency objects (and all its children) and calls delegate to notify about the change. It also tracks removal of the children with validation errors.

 public static void AddErrorHandler(DependencyObject element, Action<bool> setHasValidationErrors)
        {
            var errors = new List<Tuple<object, ValidationError>>();

            RoutedEventHandler sourceUnloaded = null;

            sourceUnloaded = (sender, args) =>
                {
                    if (sender is FrameworkElement)
                        ((FrameworkElement) sender).Unloaded -= sourceUnloaded;
                    else
                        ((FrameworkContentElement) sender).Unloaded -= sourceUnloaded;

                    foreach (var error in errors.Where(err => err.Item1 == sender).ToArray())
                        errors.Remove(error);

                    setHasValidationErrors(errors.Any());
                };

            EventHandler<ValidationErrorEventArgs> errorHandler = (_, args) =>
                {
                    if (args.Action == ValidationErrorEventAction.Added)
                    {
                        errors.Add(new Tuple<object, ValidationError>(args.OriginalSource, args.Error));

                        if (args.OriginalSource is FrameworkElement)
                            ((FrameworkElement)args.OriginalSource).Unloaded += sourceUnloaded;
                        else if (args.OriginalSource is FrameworkContentElement)
                            ((FrameworkContentElement)args.OriginalSource).Unloaded += sourceUnloaded;
                    }
                    else
                    {
                        var error = errors
                            .FirstOrDefault(err => err.Item1 == args.OriginalSource && err.Item2 == args.Error);

                        if (error != null) 
                            errors.Remove(error);
                    }

                    setHasValidationErrors(errors.Any());
                };


            System.Windows.Controls.Validation.AddErrorHandler(element, errorHandler);
        } 

Ataxia

Answer 6

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());

Uneventful

Answer 7

Because it's still missing, here is an adaption of Developer's answer in case the link ever goes away:

XAML:

<TextBox.Text Validation.Error="handleValidationError">
    <Binding Path ="LastName" 
             UpdateSourceTrigger="PropertyChanged"
             NotifyOnValidationError="True">
        <Binding.ValidationRules>
            <local:StringRequiredValidationRule />
        </Binding.ValidationRules>                              
    </Binding>
</TextBox.Text>
<Button IsEnabled="{Binding HasNoValidationErrors}"/>

CodeBehind/C#:

private int _numberOfValidationErrors;
public bool HasNoValidationErrors => _numberOfValidationErrors = 0;

private void handleValidationError(object sender, ValidationErrorEventArgs e)
{
    if (e.Action == ValidationErrorEventAction.Added)
        _numberOfValidationErrors++;
    else
        _numberOfValidationErrors--;
}

Goody

Answer 8

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;
            }
        }
}

Jennettejenni

Can you please add all the closing braces in your code? – Quintin

Answer 9

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)));

Fassold

Answer 10

This website has the code you're looking for: https://www.wpfsharp.com/2012/02/03/how-to-disable-a-button-on-textbox-validationerrors-in-wpf/

For posterity the button code should look like this if you are using a ValidationRule override on the input fields:

<Button Content="<NameThisButton>" Click="<MethodToCallOnClick>" >
                <Button.Style>
                    <Style TargetType="{x:Type Button}">
                        <Setter Property="IsEnabled" Value="false" />
                        <Style.Triggers>
                            <MultiDataTrigger>
                                <MultiDataTrigger.Conditions>                                    
                                    <Condition Binding="{Binding ElementName=<TextBoxName>, Path=(Validation.HasError)}" Value="false" />
                                    <Condition Binding="{Binding ElementName=<TextBoxName>, Path=(Validation.HasError)}" Value="false" />
                                </MultiDataTrigger.Conditions>
                                <Setter Property="IsEnabled" Value="true" />
                            </MultiDataTrigger>
                        </Style.Triggers>
                    </Style>
                </Button.Style>
            </Button>

Leek