Finding a better way to disable the add to cart button if customer is not logged in

Question

If the customer is not logged in , customer shouldn't be able to add the product in cart and simultaneously it should redirect to login page with an error message.

Answer 1

Try this,

I created this Module on this. I hope you are asking Magento 1

app/etc/modules/MPS_Addtocartredirect.xml

<?xml version="1.0"?>
<config>
  <modules>
    <MPS_Addtocartredirect>
      <active>true</active>
      <codePool>local</codePool>
      <version>0.1.0</version>
    </MPS_Addtocartredirect>
  </modules>
</config>

app\code\local\MPS\Addtocartredirect\etc

<?xml version="1.0"?>
<config>
  <modules>
    <MPS_Addtocartredirect>
      <version>0.1.0</version>
    </MPS_Addtocartredirect>
  </modules>
  <frontend>
    <routers>
      <addtocartredirect>
        <use>standard</use>
          <args>
            <module>MPS_Addtocartredirect</module>
            <frontName>addtocartredirect</frontName>
          </args>
      </addtocartredirect>
    </routers>
        <layout>
          <updates>
            <addtocartredirect>
              <file>addtocartredirect.xml</file>
            </addtocartredirect>
          </updates>
        </layout>
  </frontend>
  <global>
    <helpers>
      <addtocartredirect>
        <class>MPS_Addtocartredirect_Helper</class>
      </addtocartredirect>
    </helpers>
    <blocks>
      <addtocartredirect>
        <class>MPS_Addtocartredirect_Block</class>
      </addtocartredirect>
    </blocks>
  </global>
</config> 

app\code\local\MPS\Addtocartredirect\controllers\IndexController.php

<?php
class MPS_Addtocartredirect_IndexController extends Mage_Core_Controller_Front_Action{
    public function IndexAction() {

      $this->loadLayout();   
      $this->renderLayout(); 

    }


    public function redirectmeAction(){
      $redirect_url = Mage::getUrl('customer/account/login/');
      Mage::app()->getFrontController()->getResponse()->setRedirect($redirect_url)->sendResponse();
      //$this->_redirectReferer($redirect_url);
      Mage::getSingleton('core/session')->addError('Please login First'); // Add your Error Message
    }
}

app\code\local\MPS\Addtocartredirect\Helper\Data.php

<?php
class MPS_Addtocartredirect_Helper_Data extends Mage_Core_Helper_Abstract
{
}

app\code\local\MPS\Addtocartredirect\Block\Index.php

<?php   
class MPS_Addtocartredirect_Block_Index extends Mage_Core_Block_Template{  
}

app\design\frontend\base\default\layout\addtocartredirect.xml

<?xml version="1.0"?>   
<layout version="0.1.0">  
  <catalog_product_view>
    <reference name="content">
        <action method="setTemplate">
            <template>addtocartredirect/view.phtml</template>
        </action>
    </reference>
</catalog_product_view>
</layout>   

app\design\frontend\base\default\template\addtocartredirect\view.phtml

    <?php
/**
 * Magento
 *
 * NOTICE OF LICENSE
 *
 * This source file is subject to the Academic Free License (AFL 3.0)
 * that is bundled with this package in the file LICENSE_AFL.txt.
 * It is also available through the world-wide-web at this URL:
 * http://opensource.org/licenses/afl-3.0.php
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@magentocommerce.com so we can send you a copy immediately.
 *
 * DISCLAIMER
 *
 * Do not edit or add to this file if you wish to upgrade Magento to newer
 * versions in the future. If you wish to customize Magento for your
 * needs please refer to http://www.magentocommerce.com for more information.
 *
 * @category    design
 * @package     rwd_default
 * @copyright   Copyright (c) 2014 Magento Inc. (http://www.magentocommerce.com)
 * @license     http://opensource.org/licenses/afl-3.0.php  Academic Free License (AFL 3.0)
 */

/**
 * Product view template
 *
 * @see Mage_Catalog_Block_Product_View
 * @see Mage_Review_Block_Product_View
 */
?>
<?php $_helper = $this->helper('catalog/output'); ?>
<?php $_product = $this->getProduct(); ?>
<script type="text/javascript">
    var optionsPrice = new Product.OptionsPrice(<?php echo $this->getJsonConfig() ?>);
</script>
<div id="messages_product_view"><?php echo $this->getMessagesBlock()->getGroupedHtml() ?></div>
<div class="product-view">
    <div class="product-essential">
    <?php $Islogin = Mage::getSingleton('customer/session')->isLoggedIn(); ?>
        <form action="<?php if($Islogin){ echo $this->getSubmitUrl($_product); } else{ echo $this->getUrl('addtocartredirect/index/redirectme');} ?>" method="post" id="product_addtocart_form"<?php if($_product->getOptions()): ?> enctype="multipart/form-data"<?php endif; ?>>
            <?php echo $this->getBlockHtml('formkey') ?>
            <div class="no-display">
                <input type="hidden" name="product" value="<?php echo $_product->getId() ?>" />
                <input type="hidden" name="related_product" id="related-products-field" value="" />
            </div>

            <div class="product-img-box">
                <div class="product-name">
                    <h1><?php echo $_helper->productAttribute($_product, $_product->getName(), 'name') ?></h1>
                </div>
                <?php echo $this->getChildHtml('media') ?>
            </div>

            <div class="product-shop">
                <div class="product-name">
                    <span class="h1"><?php echo $_helper->productAttribute($_product, $_product->getName(), 'name') ?></span>
                </div>

                <div class="price-info">
                    <?php echo $this->getPriceHtml($_product); ?>
                    <?php echo $this->getChildHtml('bundle_prices') ?>
                    <?php echo $this->getTierPriceHtml() ?>
                </div>

                <div class="extra-info">
                    <?php echo $this->getReviewsSummaryHtml($_product, 'default', false)?>
                    <?php echo $this->getChildHtml('product_type_availability'); ?>
                </div>

                <?php echo $this->getChildHtml('alert_urls') ?>

                <?php if ($_product->getShortDescription()):?>
                    <div class="short-description">
                        <div class="std"><?php echo $_helper->productAttribute($_product, nl2br($_product->getShortDescription()), 'short_description') ?></div>
                    </div>
                <?php endif;?>




                <?php echo $this->getChildHtml('other');?>

                <?php if ($_product->isSaleable() && $this->hasOptions()):?>
                    <?php echo $this->getChildChildHtml('container1', '', true, true) ?>
                <?php endif;?>

            </div>

            <div class="add-to-cart-wrapper">
                <?php echo $this->getChildHtml('product_type_data') ?>
                <?php echo $this->getChildHtml('extrahint') ?>

                <?php if (!$this->hasOptions()):?>
                    <div class="add-to-box">
                        <?php if($_product->isSaleable()): ?>
                            <?php echo $this->getChildHtml('addtocart') ?>
                            <?php if( $this->helper('wishlist')->isAllow() || $_compareUrl=$this->helper('catalog/product_compare')->getAddUrl($_product)): ?>
                                <span class="or"><?php echo $this->__('OR') ?></span>
                            <?php endif; ?>
                        <?php endif; ?>
                        <?php echo $this->getChildHtml('addto') ?>
                        <?php echo $this->getChildHtml('sharing') ?>
                    </div>
                    <?php echo $this->getChildHtml('extra_buttons') ?>
                <?php elseif (!$_product->isSaleable()): ?>
                    <div class="add-to-box">
                        <?php echo $this->getChildHtml('addto') ?>
                        <?php echo $this->getChildHtml('sharing') ?>
                    </div>
                <?php endif; ?>
            </div>

            <?php echo $this->getChildHtml('related_products') ?>

            <div class="clearer"></div>
            <?php if ($_product->isSaleable() && $this->hasOptions()):?>
                <?php echo $this->getChildChildHtml('container2', '', true, true) ?>
            <?php endif;?>
        </form>
        <script type="text/javascript">
        //<![CDATA[
            var productAddToCartForm = new VarienForm('product_addtocart_form');
            productAddToCartForm.submit = function(button, url) {
                if (this.validator.validate()) {
                    var form = this.form;
                    var oldUrl = form.action;

                    if (url) {
                       form.action = url;
                    }
                    var e = null;
                    try {
                        this.form.submit();
                    } catch (e) {
                    }
                    this.form.action = oldUrl;
                    if (e) {
                        throw e;
                    }

                    if (button && button != 'undefined') {
                        button.disabled = true;
                    }
                }
            }.bind(productAddToCartForm);

            productAddToCartForm.submitLight = function(button, url){
                if(this.validator) {
                    var nv = Validation.methods;
                    delete Validation.methods['required-entry'];
                    delete Validation.methods['validate-one-required'];
                    delete Validation.methods['validate-one-required-by-name'];
                    // Remove custom datetime validators
                    for (var methodName in Validation.methods) {
                        if (methodName.match(/^validate-datetime-.*/i)) {
                            delete Validation.methods[methodName];
                        }
                    }

                    if (this.validator.validate()) {
                        if (url) {
                            this.form.action = url;
                        }
                        this.form.submit();
                    }
                    Object.extend(Validation.methods, nv);
                }
            }.bind(productAddToCartForm);
        //]]>
        </script>
    </div>

    <div class="product-collateral toggle-content tabs">
        <?php if ($detailedInfoGroup = $this->getChildGroup('detailed_info', 'getChildHtml')):?>
            <dl id="collateral-tabs" class="collateral-tabs">
                <?php foreach ($detailedInfoGroup as $alias => $html):?>
                    <dt class="tab"><span><?php echo $this->escapeHtml($this->getChildData($alias, 'title')) ?></span></dt>
                    <dd class="tab-container">
                        <div class="tab-content"><?php echo $html ?></div>
                    </dd>
                <?php endforeach;?>
            </dl>
        <?php endif; ?>
    </div>

    <?php echo $this->getChildHtml('upsell_products') ?>
    <?php echo $this->getChildHtml('product_additional_data') ?>

</div>

if you already have some customization in view.phtml then change only this code

<?php $Islogin = Mage::getSingleton('customer/session')->isLoggedIn(); ?>
        <form action="<?php if($Islogin){ echo $this->getSubmitUrl($_product); } else{ echo $this->getUrl('addtocartredirect/index/redirectme');} ?>" method="post" id="product_addtocart_form"<?php if($_product->getOptions()): ?> enctype="multipart/form-data"<?php endif; ?>>

This code only for individual page