React native How to validate username and password

Question

I want to validate username and password,then I want to display error below input field.

I have given already in alert form,but I need to display error below input field.

If anyone knows please let me know.

 if( uname == '' && pwd == '' || uname == '' || pwd =='' || uname =="true" && pwd == '') {
       if(uname == ''){
        alert('Username is required');
       } 
      else
        {
        alert('Password is required');
        }

      // alert('This value is required');  
    }
    else{
      alert('Invalid username/password');
    }

Answer 1

i have given code to reach that question functionality

this.state ={
error : ''
}

 const { username, password } = this.state;
      if(username == ''){
        this.setState({error:'Username is required'});
        }
        else if(password == ''){
          this.setState({error:'Password is required'});
        }
        else{     
        this.setState({error: null}) 
 }

<Text style={styles.error}>
            {this.state.error}
 </Text>

Answer 2

put one <Text> element below <TextInput>

take one state errorMessage and use it in <Text>

when you want to display error set the message in errorMessage

ane when not set it null