SwiftUI Binding Validation: Real-Time Form Feedback

Use didSet property observers with @State to trigger validation instantly as users type. Combine this with computed properties to show real-time feedback without blocking input.

This approach uses computed properties for validation logic and a separate state flag to control when validation feedback appears. The validation runs on every change but only displays feedback after the user starts interacting with the field.

struct ValidatedTextField: View {
    @State private var email = ""
    @State private var hasStartedEditing = false
    
    private var isValidEmail: Bool {
        email.contains("@") && email.contains(".")
    }
    
    private var showValidation: Bool {
        hasStartedEditing && !email.isEmpty
    }
    
    var body: some View {
        VStack(alignment: .leading, spacing: 8) {
            TextField("Email", text: $email)
                .textFieldStyle(.roundedBorder)
                .onTapGesture {
                    hasStartedEditing = true
                }
            
            if showValidation {
                HStack {
                    Image(systemName: isValidEmail ? "checkmark.circle.fill" : "xmark.circle.fill")
                        .foregroundColor(isValidEmail ? .green : .red)
                    Text(isValidEmail ? "Valid email" : "Please enter a valid email")
                        .font(.caption)
                        .foregroundColor(isValidEmail ? .green : .red)
                }
                .animation(.easeInOut(duration: 0.2), value: isValidEmail)
            }
        }
    }
}

Why This is a Best Practice

Computed properties automatically update when their dependencies change, providing real-time feedback without manual state management. The `hasStartedEditing` flag prevents premature validation messages, creating a better user experience by not showing errors before users have a chance to input valid data.

Use didSet property observers with @State to trigger validation instantly as users type. Combine this with computed properties to show real-time feedback without blocking input.

struct ValidatedTextField: View {
    @State private var email = ""
    @State private var hasStartedEditing = false
    
    private var isValidEmail: Bool {
        email.contains("@") && email.contains(".")
    }
    
    private var showValidation: Bool {
        hasStartedEditing && !email.isEmpty
    }
    
    var body: some View {
        VStack(alignment: .leading, spacing: 8) {
            TextField("Email", text: $email)
                .textFieldStyle(.roundedBorder)
                .onTapGesture {
                    hasStartedEditing = true
                }
            
            if showValidation {
                HStack {
                    Image(systemName: isValidEmail ? "checkmark.circle.fill" : "xmark.circle.fill")
                        .foregroundColor(isValidEmail ? .green : .red)
                    Text(isValidEmail ? "Valid email" : "Please enter a valid email")
                        .font(.caption)
                        .foregroundColor(isValidEmail ? .green : .red)
                }
                .animation(.easeInOut(duration: 0.2), value: isValidEmail)
            }
        }
    }
}

Why This is a Best Practice

History

SwiftUI Binding Validation: Real-Time Form Feedback

Why This is a Best Practice