How to display error messages for multiple TextField in jetpack compose

When you nave so much in common between two+ views, it's time to move that into a separate composable. You can specify all the differences in the parameters and not repeat same settings for each view.

I suggest you creating state class for your custom text field. I'll store text, error text and validator logic. So you can call validate when you need: on button click or on keyboard done button:

@Composable
fun TestView(
) {
    val nomeState = rememberErrorTextFieldState("", validate = { text ->
        when {
            text.isEmpty() -> {
                "text.isEmpty()"
            }
            else -> null
        }
    })
    val emailState = rememberErrorTextFieldState("", validate = { text ->
        when {
            text.isEmpty() -> {
                "text.isEmpty()"
            }
            !android.util.Patterns.EMAIL_ADDRESS.matcher(text).matches() -> {
                "pattern doesn't match"
            }
            else -> null
        }
    })

    Column {
        ErrorTextField(
            state = nomeState,
            placeholderText = "nome",
            leadingIconVector = Icons.Default.Person,
            modifier = Modifier.align(Alignment.CenterHorizontally),
        )
        ErrorTextField(
            state = emailState,
            placeholderText = "email",
            leadingIconVector = Icons.Default.Email,
            modifier = Modifier.align(Alignment.CenterHorizontally),
        )
        Button(
            onClick = {
                listOf(nomeState, emailState).forEach(ErrorTextFieldState::validate)
            },
        ) {
            Text(text = "stringResource(id = R.string.view_cad)")
        }
    }
}


@Composable
fun ErrorTextField(
    state: ErrorTextFieldState,
    placeholderText: String,
    leadingIconVector: ImageVector,
    modifier: Modifier,
) {
    Column {
        val error = state.error
        TextField(
            value = state.text,
            onValueChange = { state.updateText(it) },
            placeholder = { Text(text = placeholderText) },
            shape = RoundedCornerShape(8.dp),
            colors = TextFieldDefaults.textFieldColors(
                focusedIndicatorColor = Color.Transparent,
                unfocusedIndicatorColor = Color.Transparent,
                disabledIndicatorColor = Color.Transparent,
                errorCursorColor = Color.Red
            ),
            singleLine = true,
            isError = error != null,
            leadingIcon = { Icon(imageVector = leadingIconVector, contentDescription = null) },
            keyboardActions = KeyboardActions {
                state.validate()
            },
            modifier = modifier,
        )
        if (error != null) {
            Text(
                error,
                color = Color.Red,
            )
        }
    }
}

@Composable
fun rememberErrorTextFieldState(
    initialText: String,
    validate: (String) -> String? = { null },
): ErrorTextFieldState {
    return rememberSaveable(saver = ErrorTextFieldState.Saver(validate)) {
        ErrorTextFieldState(initialText, validate)
    }
}

class ErrorTextFieldState(
    initialText: String,
    private val validator: (String) -> String?,
) {
    var text by mutableStateOf(initialText)
        private set

    var error by mutableStateOf<String?>(null)
        private set

    fun updateText(newValue: String) {
        text = newValue
        error = null
    }

    fun validate() {
        error = validator(text)
    }

    companion object {
        fun Saver(
            validate: (String) -> String?,
        ) = androidx.compose.runtime.saveable.Saver<ErrorTextFieldState, String>(
            save = { it.text },
            restore = { ErrorTextFieldState(it, validate) }
        )
    }
}