Validate input as the user types

You can validate input as the user types in a text field, such as entering a name, email, address, or other contact information. This validation reduces errors and saves your users time.

Version compatibility

This implementation requires that your project minSDK be set to API level 21 or higher.

Dependencies

Validate input as the user types

Use the following code to display the field input and validate the text while the user types. If the information is not validated, an error message helps the user correct the input.

class EmailViewModel : ViewModel() {
    var email by mutableStateOf("")
        private set

    val emailHasErrors by derivedStateOf {
        if (email.isNotEmpty()) {
            // Email is considered erroneous until it completely matches EMAIL_ADDRESS.
            !android.util.Patterns.EMAIL_ADDRESS.matcher(email).matches()
        } else {
            false
        }
    }

    fun updateEmail(input: String) {
        email = input
    }
}

@Composable
fun ValidatingInputTextField(
    email: String,
    updateState: (String) -> Unit,
    validatorHasErrors: Boolean
) {
    OutlinedTextField(
        modifier = Modifier
            .fillMaxWidth()
            .padding(10.dp),
        value = email,
        onValueChange = updateState,
        label = { Text("Email") },
        isError = validatorHasErrors,
        supportingText = {
            if (validatorHasErrors) {
                Text("Incorrect email format.")
            }
        }
    )
}

@Preview
@Composable
fun ValidateInput() {
    val emailViewModel: EmailViewModel = viewModel<EmailViewModel>()
    ValidatingInputTextField(
        email = emailViewModel.email,
        updateState = { input -> emailViewModel.updateEmail(input) },
        validatorHasErrors = emailViewModel.emailHasErrors
    )
}
TextSnippets.kt

Key points about the code

  • Defines a composable that reuses the OutlinedTextField component, adding the required parameters to display validator error messages as user types.
  • EmailViewModel is used to maintain state and provide the email validation logic.
  • if isError is true, the UI provides a visual indicator of a validation error state.
  • The component will display "Incorrect email format." until a complete, correct email is input.

Results

A valid text input
Figure 1. A text input field with email validators displaying no error messages for a valid email address.
An invalid text input with errors
Figure 2. A text input field displaying an error message when an invalid email address is entered.

Collections that contain this guide

This guide is part of these curated Quick Guide collections that cover broader Android development goals:

Display text

Text is a central piece of any UI. Find out different ways you can present text in your app to provide a delightful user experience.
Quick guide collection
Learn how to implement ways for users to interact with your app by entering text and using other means of input.
Quick guide collection

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