Inline Validation & Error States
Give instant feedback on bad input.
Inline Validation & Error States is a free Jetpack Compose Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Jetpack Compose Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Catch Mistakes Early
Great forms fix problems as the user types, not after they tap submit. Inline validation means instant, gentle feedback. ✅
Compute Validity from State
Derive an isError flag straight from the current value. When the email looks wrong, the flag turns true.
val isError = email.isNotEmpty() && !email.contains("@")The isError Parameter
Pass that flag to the field's isError parameter. Compose then tints the border and label red to signal trouble.
OutlinedTextField(
value = email,
onValueChange = { email = it },
isError = isError
)Explain the Problem
A red border alone is vague. Use supportingText to spell out exactly what went wrong so the user can fix it.
supportingText = {
if (isError) Text("Enter a valid email.")
}Show Errors at the Right Time
Do not shout at an empty field. Validate only after the user has typed, so the error appears when it is actually useful.
Add an Error Icon
A trailingIcon reinforces the message. Swap in a warning icon when the field is in an error state.
trailingIcon = {
if (isError) Icon(Icons.Default.Warning, "Error")
}Validate Many Fields
Each field gets its own flag. Combine them to know whether the whole form is valid and ready to submit.
val formValid = emailValid && passwordValidGate the Submit Button
Tie the button's enabled flag to form validity. Users cannot submit until every field passes its check.
Button(onClick = ::submit, enabled = formValid) {
Text("Sign Up")
}Keep Messages Kind
Write error text that helps, not blames. Password too short beats Invalid input every single time.
Validation Is Just State
Notice the pattern: errors are plain values derived from state. No magic, just the same Compose model you already know.
Real Forms Feel Trustworthy
Clear, timely feedback builds trust. Users feel guided rather than tested, and they finish your forms with ease.
Quick Check
How do you turn a text field's border red to signal a problem?
Recap
You built inline validation: derive an error flag, set isError, explain it with supporting text, and gate submit on validity. Forms that feel great. 🌟
Frequently asked questions
Is the “Inline Validation & Error States” lesson free?
Yes — the full text of “Inline Validation & Error States” is free to read here on the web, and the Jetpack Compose Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Jetpack Compose Academy course, upgrade to CoddyKit PRO.
What will I learn in “Inline Validation & Error States”?
Give instant feedback on bad input. You practise Jetpack Compose Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Jetpack Compose Academy?
No prior experience is required. Jetpack Compose Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Inline Validation & Error States” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Jetpack Compose Academy lesson?
Yes. Every Jetpack Compose Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- TextField & OutlinedTextField
- Labels, Placeholders & Leading Icons
- Keyboard Types & IME Actions
- Inline Validation & Error States