Using WPF Validation rules and disabling a 'Save' button

问题

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. So now I want to add this validation rule to my other text boxes.

Now, how do I disable the Save button until the page has no errors? I do not know what to check to see if there are any validation errors.

回答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

回答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).

回答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.

回答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;
    }
}

回答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);
        } 

回答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());

回答7:

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;
            }
        }
}

回答8:

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)));

回答9:

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--;
}

来源：https://stackoverflow.com/questions/231052/using-wpf-validation-rules-and-disabling-a-save-button