POST无法在CodeIgniter中工作，而GET工作正常

I'm facing this issue with POST in CodeIgniter which is not working while if I switch to GET, that works fine.

Login Controller

public function login_check(){
    print_r($this->input->post());
    if($this->input->post('email')!=NULL){
        echo '1';
    }
    else{
        header('Content-Type: application/json');
        echo json_encode( array('a' => $this->input->post('email')));
}

CSRF is set to false in config file, while base url is set to http://localhost/xyz/

.htaccess

<IfModule mod_rewrite.c>
    RewriteEngine on
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)$ index.php/$1 [L]
</IfModule>

Routes

$route['api/login-check'] = 'login/login_check';

If I set $this->input->get('email') while setting method GET in postman, that works absolutely okay.

What's something that I'm missing? Any help in this will be appreciated.

EDIT:

Response from postman:

Array() {"a":null}

The code is doing exactly as you are asking it to do.

A break down of your code goes like...

If I get something from $this->input->post('email') then 
     echo '1';
else if $this->input->post('email') is NULL
     then assign NULL to a and return it in a json_encoded array.

Going by your code it might meant to be something like...

public function login_check(){
    print_r($this->input->post());
    if($this->input->post('email') == NULL){ // This was != 
        echo '1';
    }
    else{
        header('Content-Type: application/json');
        echo json_encode( array('a' => $this->input->post('email')));
}

The Only change being to alter != to == in your if statement.

One of those "stare at it too long and never see it" simple Logic Error :)

A better recommendation is to use something like...

public function login_check(){
    print_r($this->input->post());

    if($this->input->post('email')){
        header('Content-Type: application/json');
        echo json_encode( array('a' => $this->input->post('email')));
        exit();
    }
    else {
        // Handle the case where no email was entered.
        echo '1';
    }
}

That should get you back on track.

Update: I have tried this in postman (just installed it ) and for a POST you need to set the key/value under Body and not Headers as you do with GET, if that's something you were also missing.