bool DoValidation(ExpressionValidationContext validationContext, out string errorMessage)
{
errorMessage = null;
//validate
//if the text is empty we clear the error message
if (string.IsNullOrEmpty(validationContext.ExpressionText))
{
errorMessage = null;
return(true);
}
// if the expression text is different from the last time we run the validation we run the validation
else if (!string.Equals(validationContext.ExpressionText, validationContext.ValidatedExpressionText))
{
try
{
//TODO: Add logic to validate expression
}
catch (Exception err)
{
errorMessage = err.Message;
}
return(true);
}
return(false);
}
void StartValidator()
{
if (Validator == null)
{
Validator = new BackgroundWorker();
Validator.WorkerReportsProgress = true;
Validator.WorkerSupportsCancellation = true;
Validator.DoWork += delegate(object obj, DoWorkEventArgs args)
{
BackgroundWorker worker = obj as BackgroundWorker;
if (worker.CancellationPending)
{
args.Cancel = true;
return;
}
ExpressionValidationContext validationContext = args.Argument as ExpressionValidationContext;
if (validationContext != null)
{
string errorMessage;
if (DoValidation(validationContext, out errorMessage))
{
worker.ReportProgress(0, errorMessage);
}
//sleep
if (worker.CancellationPending)
{
args.Cancel = true;
return;
}
Thread.Sleep(ValidationWaitTime);
args.Result = validationContext;
}
};
Validator.RunWorkerCompleted += delegate(object obj, RunWorkerCompletedEventArgs args)
{
if (!args.Cancelled)
{
ExpressionValidationContext validationContext = args.Result as ExpressionValidationContext;
if (validationContext != null)
{
Dispatcher.BeginInvoke(new Action <ExpressionValidationContext>((target) =>
{
//validator could be null by the time we try to validate again or
//if it's already busy
if (Validator != null && !Validator.IsBusy)
{
target.Update(this);
Validator.RunWorkerAsync(target);
}
}), validationContext);
}
}
};
Validator.ProgressChanged += delegate(object obj, ProgressChangedEventArgs args)
{
string error = args.UserState as string;
Dispatcher.BeginInvoke(new Action <string>(UpdateValidationError), error);
};
Validator.RunWorkerAsync(new ExpressionValidationContext(this));
}
}