Cake PHP Update single fields in View - Undefined Variable - variables

Question

i search a long time, but i dont find a solution for my problem.
The case is, that i have a few buttons integrated in my view and clicking on them affected updating single input fields. The problem is that i have warnings, that variables are undefined in view. I understand why and how i suppress them, but i`m not sure, if this is a good solution. Is there a better way to solve this? What is best practice?
Here is my code from the view file:
<?php
echo $this->Form->create('Excel', array('type' => 'file'));
echo $this->Form->file('File');
echo $this->Form->submit('Upload xls File');
echo $this->Form->end();
echo $this->Form->create('Config');
//echo $this->Form->input('Name');
echo $this->Form->input('vlanNumber');
echo $this->Form->input('description', array('value' => $description));
echo $this->Form->input('preSharedKey', array('value' => $preSharedKey));
echo $this->Form->button('generate', array('name'=>'generateButton'));
echo $this->Form->input('customerPeerIp', array('default' => 'id_of_default_val','value' => $cusPeerIp));
The generate button affect a new preSharedKey. And the upload of the csv affected an update of the other fields.
The relevant code of the controller is this:
public function inputData() {
if ($this->request->is('post')) {
$post_data = $this->request->data;
if (isset($this->request->data['show'])) { //Submit Button was clicked
$this->Session->write('Configuration',$post_data); //Store the input fields in the session
return $this->redirect(array('action' => 'showPreview'));
} else if (isset($this->request->data['cancel'])) { // Cancel button was clicked: Go back to index site
return $this->redirect(array('action' => 'index'));
} else if (isset($this->request->data['generateButton'])) {
return $this->set('preSharedKey', $this->getRandomString(20)); //Set a Pre Shared Key with 30 signs
}
if (!empty($this->data) && is_uploaded_file($this->data['Excel']['File']['tmp_name'])) {
$this->importData($this->data['Excel']['File']['tmp_name']);
$excel=new Excel();
$values=$excel->getParams($this->data['Excel']['File']['tmp_name']);
$this->set('description',$values['description']);
$this->set('cusPeerIp',$values['cust_peer']);
return;
//this calls the Excel Class function
}
//print_r($post_data);
//echo $post_data['Config']['Name'];
//echo $this->request['Config']['task_1'];
}
$this->set('description','');
$this->set('cusPeerIp','');
$this->set('preSharedKey', '');
}
Can you please help me?