Dynamic Form Validation in Kotlin: Enhancing User Experience
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Chapter 1: Introduction to Dynamic Forms
In this blog post, we explore an expertly crafted Kotlin code example that showcases the development of a dynamic form using Jetpack Compose within an Android application. This code reflects the developer's expertise in Kotlin and their grasp of contemporary Android development methodologies.
Let's take a closer look at some code:
Understanding the FormFieldState Data Class
The FormFieldState data class serves as an efficient representation of each form field's state. It encompasses a label, a mutable value state, a validation function, an error message, and a boolean to indicate user interaction.
data class FormFieldState(
val label: String,
var value: MutableState<String>,
val validator: (String) -> Boolean,
val errorMessage: String,
var hasInteracted: Boolean = false
)
This design promotes code reusability and manageability. Utilizing a lambda function for validation provides significant flexibility, enabling any validation logic to be integrated.
DynamicForm Composable Function
The DynamicForm function is crafted to construct a form dynamically based on a provided list of form fields. Each field incorporates its own validation logic and state.
@Composable
fun DynamicForm(fields: List<FormFieldState>, onSubmit: () -> Unit) {
Column {
fields.forEach { field ->
ValidatedTextField(field)}
val isFormValid = fields.all { it.validator(it.value.value) }
Button(onClick = onSubmit, enabled = isFormValid) {
Text("Submit")}
}
}
- Column Layout: The function initiates by establishing a vertical layout using Column.
- Iterating Through Fields: The loop fields.forEach { field -> ValidatedTextField(field) } generates a text field for each FormFieldState in the list.
- Form Validation: The line val isFormValid = fields.all { it.validator(it.value.value) } determines if every field in the form passes validation.
- Submit Button: The Button composable creates a submission button that is only active when all fields are validated. The button’s color dynamically adjusts based on the form’s validity.
ValidatedTextField Composable Function
The ValidatedTextField function establishes a text field equipped with validation features.
@Composable
fun ValidatedTextField(formFieldState: FormFieldState, modifier: Modifier = Modifier) {
val isError = formFieldState.hasInteracted && !formFieldState.validator(formFieldState.value.value)
OutlinedTextField(
value = formFieldState.value.value,
onValueChange = { formFieldState.value.value = it },
label = { Text(formFieldState.label) },
isError = isError,
modifier = modifier
.onFocusChanged { focusState ->
if (!focusState.isFocused && !formFieldState.hasInteracted) {
formFieldState.hasInteracted = true}
}
)
if (isError) {
Text(formFieldState.errorMessage, color = Color.Red)}
}
- Error State Management: The variable isError determines if the field should display an error, which occurs only after user interaction and if validation fails.
- OutlinedTextField: This component collects user input. The current value is displayed, and onValueChange updates this value dynamically.
- Focus Handling: The onFocusChanged modifier tracks focus changes, updating hasInteracted accordingly.
- Error Message Display: If an error exists, the appropriate error message is shown below the text field.
Initialization of Form Fields
val formFields = remember {
listOf(
FormFieldState("Name", mutableStateOf(""), { it.length >= 4 }, "Name must be at least 4 characters")
// Other fields can be added here
)
}
DynamicForm(fields = formFields) {
// Form submission handling
}
- Using remember: The remember composable maintains the state of formFields during UI recompositions, ensuring that user input and validation states remain intact.
- FormFieldState Objects: Each FormFieldState object signifies a unique field in the form with its specific properties and validation rules.
Conclusion
This code effectively illustrates how to develop a dynamic and interactive form using Jetpack Compose in Kotlin. Every form field is validated, and the overall validity of the form dictates the submission process. The ValidatedTextField component ensures users are appropriately guided with relevant error messages, significantly improving the user experience.
The first video, titled "How to Validate Forms with Clean Architecture (You're Doing it Wrong)," provides insights into form validation best practices and common pitfalls.
The second video, "HTMX - Dynamic HTML without Javascript," explores dynamic HTML generation techniques without relying on JavaScript.