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Form Data Validation in .NET MAUI PDF Viewer (SfPdfViewer)

25 Mar 20267 minutes to read

Before saving a filled PDF form, you may want to validate that all required fields contain acceptable values. Validation is performed by iterating the FormFields collection, checking each field’s value against your rules, and only proceeding with save if all criteria are met.

Validation example

The following example validates a registration form before saving. It checks the criteria listed in the table below. If all criteria pass, the document is saved. Otherwise, an error dialog is shown.

Field Validation Rules
Name Required. 3–30 characters. No numbers or special characters.
Email Required. Must match standard email format.
Date of birth Required. Must be in dd/MM/yyyy format.
Course At least one item must be selected.
Signature Must not be empty. 
async void ValidateAndSaveForm()
{
    ReadOnlyObservableCollection<FormField> _formFields = PdfViewer.FormFields;

    if (_formFields == null || _formFields.Count == 0)
        return;

    List<string> errors = new List<string>();

    foreach (FormField formField in _formFields)
    {
        if (formField is TextFormField textFormField)
        {
            if (textFormField.Name == "Name")
            {
                if (string.IsNullOrEmpty(textFormField.Text))
                    errors.Add("Name is required.");
                else if (textFormField.Text.Length < 3)
                    errors.Add("Name should have at least 3 characters.");
                else if (textFormField.Text.Length > 30)
                    errors.Add("Name should not exceed 30 characters.");
                else if (Regex.IsMatch(textFormField.Text, @"[0-9]"))
                    errors.Add("Name should not contain numbers.");
                else if (Regex.IsMatch(textFormField.Text, @"[!@#$%^&*(),.?""{|}|<>]"))
                    errors.Add("Name should not contain special characters.");
            }
            else if (textFormField.Name == "dob")
            {
                if (string.IsNullOrEmpty(textFormField.Text))
                    errors.Add("Date of birth is required.");
                else if (!DateTime.TryParseExact(textFormField.Text, "dd/MM/yyyy",
                         CultureInfo.InvariantCulture, DateTimeStyles.None, out _))
                    errors.Add("Date of birth should be in dd/MM/yyyy format.");
            }
            else if (textFormField.Name == "email")
            {
                if (string.IsNullOrEmpty(textFormField.Text))
                    errors.Add("Email is required.");
                else if (!Regex.IsMatch(textFormField.Text, @"^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$"))
                    errors.Add("Email should be in the correct format.");
            }
        }
        else if (formField is ListBoxFormField listBoxFormField)
        {
            if (listBoxFormField.SelectedItems.Count == 0)
                errors.Add("Please select at least one course from the list.");
        }
        else if (formField is SignatureFormField signatureFormField)
        {
            if (signatureFormField.Signature == null)
                errors.Add("Please sign in the signature field.");
        }
    }

    if (errors.Count > 0)
    {
        await DisplayAlert("Validation Errors", string.Join("\n", errors), "Try Again");
    }
    else
    {
        string fileName = Path.Combine(FileSystem.Current.AppDataDirectory, "FilledForm.pdf");
        using FileStream fileStream = File.Create(fileName);
        PdfViewer.SaveDocument(fileStream);
        await DisplayAlert("Success", "Form submitted successfully.", "OK");
    }
}

See Also