React Native - How to validate Textinput correclty? - forms

Question

How to validate Textinput correclty? I want to validate my form correctly with custom form validation and after validation display errors in Text component, but how? Please, guys show me example!

Answer 1

install react-native-snackbar to show error messages.
import React, { Component } from 'react';
import { View, Text, TextInput } from 'react-native';
import Snackbar from 'react-native-snackbar';
export default class LoginPasswordScreen extends Component {
constructor(props) {
super(props);
this.state = {
password: ''
}
}
validate = () => {
//include your validation inside if condition
if (this.state.password == "") {
() => {
setTimeout(() => {
Snackbar.show({
title: 'Invalid Credintials',
backgroundColor: red,
})
}, 1000);
}
}
else {
Keyboard.dismiss();
// navigate to next screen
}
}
render() {
return (
<View>
<TextInput
returnKeyType="go"
secureTextEntry
autoCapitalize="none"
autoCorrect={false}
autoFocus={true}
onChangeText={(password) => this.setState({ password })}
/>
<TouchableOpacity>
<Text onPress={this.validate}>Next</Text>
</TouchableOpacity>
</View>
);
}
}

Answer 2

Every field, you have to do a comparison and show the error message and as I see there is no direct form validation even though there is form component available in react native.
In One of my react native project, I added a form and later on click of Submit, I had written one validate function to check all my inputs.
For this, I used one nice javascript library-
npm library- validator
And for showing error message, you can use, Toast, ALert or Snackbar

Answer 3

Would be nice if you provide some thoughts or code on how you would think it can be approached. But the way i did it was pretty simple, on my component state i got the following object:
this.state = {
loading: false,
username: {
text: '',
valid: false
},
password: {
text: '',
valid: false
},
isLoginValid: false
};
Then on the TextInput for username, i would first, bind its value to this.state.username.text, also, during onChangeText I just do a simple validation of the field, if the form is quite big, you may have a switch(fieldtype) where you have for each field, what treatment you want to apply a.k.a validation.
onChangeText={ (text) => { this.validateInput(text, 'username')}} (username would be the form input on the state object)
For instance, for username you want only to be length != 0 and length <= 8 characters, for email you may run a RegExp() with the email validation and also its length, for password a different logic, etc... after that i just simply save the state for that field input and if it's valid or not. Like this:
validateInput(text, fieldname) {
let stateObject = {
text: text,
valid: text.length !== 0
}
this.setState({ [fieldname]: stateObject }, () => {
this.checkValidation();
});
}
In checkValidation I check for all the input fields and if every one is valid, i set formValid to true.
This formValid would for example, allow the user to tap on the "Login" button otherwise it applies an opacity of 0.5 to it and disables it.
The rest you may guess, is just playing around with the valid variables of each field to what you want to display and what not.
In a Register form I also added an X or a "Tick" icon if the input text field is ok or not. Let your imagination guide you.
Hope it helps.