SwiftUI TextField Validation: Real-Time Input Formatting

This approach encapsulates validation styling and error display logic into a reusable ViewModifier, keeping your view code clean while providing consistent validation UI across your app.

struct ValidationModifier: ViewModifier {
    let isValid: Bool
    let errorMessage: String
    
    func body(content: Content) -> some View {
        VStack(alignment: .leading, spacing: 4) {
            content
                .textFieldStyle(.roundedBorder)
                .overlay(
                    RoundedRectangle(cornerRadius: 8)
                        .stroke(isValid ? Color.clear : Color.red, lineWidth: 1)
                )
            
            if !isValid {
                Text(errorMessage)
                    .font(.caption)
                    .foregroundColor(.red)
                    .transition(.opacity)
            }
        }
        .animation(.easeInOut(duration: 0.2), value: isValid)
    }
}

extension View {
    func validation(isValid: Bool, error: String) -> some View {
        modifier(ValidationModifier(isValid: isValid, errorMessage: error))
    }
}

Why This is a Best Practice

Separating validation presentation from business logic improves code maintainability, enables consistent UI patterns, and makes testing easier by isolating concerns. The modifier can be applied to any input field with different validation rules.

This approach encapsulates validation styling and error display logic into a reusable ViewModifier, keeping your view code clean while providing consistent validation UI across your app.

struct ValidationModifier: ViewModifier {
    let isValid: Bool
    let errorMessage: String
    
    func body(content: Content) -> some View {
        VStack(alignment: .leading, spacing: 4) {
            content
                .textFieldStyle(.roundedBorder)
                .overlay(
                    RoundedRectangle(cornerRadius: 8)
                        .stroke(isValid ? Color.clear : Color.red, lineWidth: 1)
                )
            
            if !isValid {
                Text(errorMessage)
                    .font(.caption)
                    .foregroundColor(.red)
                    .transition(.opacity)
            }
        }
        .animation(.easeInOut(duration: 0.2), value: isValid)
    }
}

extension View {
    func validation(isValid: Bool, error: String) -> some View {
        modifier(ValidationModifier(isValid: isValid, errorMessage: error))
    }
}

Why This is a Best Practice

History

SwiftUI TextField Validation: Real-Time Input Formatting

Why This is a Best Practice