Validating Email Addresses in iOS: Ensuring Users Stay Focused on TextFields

Introduction

In iOS app development, it’s common to have UITextFields where users input data. One of the most important aspects of validating user input is ensuring that the cursor remains focused on the text field even after validation fails. In this article, we’ll explore how to achieve this and provide a step-by-step guide on implementing email address validation in iOS.

Understanding `textFieldDidEndEditing` Delegate Method

The textFieldDidEndEditing: delegate method is called when the user taps outside of a UITextField, or presses the “Return” key, effectively ending editing. This method provides an opportunity to validate the input data and take corrective action if necessary.

// Delegate method to check if email address is valid
- (void)textFieldDidEndEditing:(UITextField *)textField {
    // Validate email address here
}

Validating Email Addresses

Email address validation can be complex, as it requires checking for various patterns, such as:

The presence of the “@” symbol
The existence of one or more alphanumeric characters before and after the “@” symbol
The validity of the domain name

Here’s an example implementation of email address validation in Swift:

// Function to validate email addresses
func isValidEmail(email: String) -> Bool {
    let regex = "[A-Z0-9a-z._%+-]+@[A-Z0-9a-z.-]+\.[A-Z|a-z]{2,}"
    
    do {
        // Create a regular expression object
        let regexObject = try NSRegularExpression(pattern: regex)
        
        // Check if the email matches the pattern
        let result = regexObject.firstMatch(in: email, options: .matchingOptions(), range: nil, allowingEmptyStrings: false)
        
        return result == nil
    } catch {
        print("Error: \(error.localizedDescription)")
        return false
    }
}

This implementation uses a regular expression to match the input string against an expected pattern. If the email matches the pattern, it returns true; otherwise, it returns false.

Keeping the Cursor Focused on the Text Field

To keep the cursor focused on the text field after validation fails, you can use the following code snippet:

// Check if the input is valid
if (validEmail) {
    // Not a problem and resignFirstResponder
} else {
    // Show an UIAlertView describing the problem
    
    [textField becomeFirstResponder];
}

In this example, we first check if the email address is valid using the isValidEmail function. If it’s valid, we don’t need to do anything and can resign the first responder (i.e., remove focus from the text field). However, if the input is invalid, we show an error message and immediately become the first responder again, ensuring that the cursor remains focused on the text field.

Handling Validation Failure

When validation fails, you should provide feedback to the user. This can be done using a UIAlertView or by displaying an error message within the app. Here’s how you might implement this in your code:

// Show an error message when validation fails
let errorMessage = "Please enter a valid email address."
let alertController = UIAlertController(title: "Error", message: errorMessage, preferredStyle: .alert)
self.present(alertController, animated: true)

func presentAlertController() {
    let alertController = UIAlertController(
        title: "Email Address",
        message: "Please enter a valid email address.",
        preferredStyle: .alert
    )
    
    let actionOk = UIAlertAction(title: "OK", style: .default) { (action) in }
    
    alertController.addAction(actionOk)
    present(alertController, animated: true)
}

This code snippet creates an alert controller with a default title and message. The user can tap the “OK” button to dismiss the error message.

Best Practices for Email Address Validation

When validating email addresses, consider the following best practices:

Use regular expressions: Regular expressions provide a powerful way to match complex patterns in strings.
Be specific about your requirements: Clearly define what constitutes a valid email address based on your app’s needs.
Handle invalid inputs graciously: Provide feedback to users when their input is invalid, and consider showing suggestions for improvement.

Conclusion

In this article, we explored how to keep the cursor focused on UITextFields even after validation fails. We also provided an example implementation of email address validation using regular expressions and a step-by-step guide on implementing this feature in your iOS app. By following these best practices and guidelines, you can create user-friendly apps that effectively validate user input.