Fatal error: Uncaught Error: Call to a member function setSaveParametersInSession() on boolean in

Question

I'm new in magento so I don't know why this is wrong. Please help. Thanks!

Config.xml

  <?xml version="1.0"?>
  <config>
       <modules>
         <Mymodule_MemberShip>
             <version>1.0.0</version>
         </Mymodule_MemberShip>
     </modules>
     <admin>
         <routers>
             <adminhtml>
                 <args>
                     <modules>
                         <mymodule_membership before="Mage_Adminhtml">Mymodule_MemberShip_Adminhtml</mymodule_membership>
                     </modules>
                 </args>
             </adminhtml>
         </routers>
     </admin>
     <adminhtml>
         <layout>
             <updates>
                 <membership>
                      <file>membership.xml</file>
                 </membership>
             </updates>
         </layout>
     </adminhtml>
     <global>
         <blocks>
             <membership>
                 <class>Mymodule_MemberShip_Block</class>
             </membership>
         </blocks>
         <models>
             <membership>
                 <class>Mymodule_MemberShip_Model</class>
                 <resourceModel>membership_resource</resourceModel>
             </membership>
             <membership_resource>
                 <class>Mymodule_MemberShip_Model_Resource</class>
                 <entities>
                     <package>
                         <table>membership_package</table>
                     </package>
                 </entities>
             </membership_resource>
         </models>
         <resources>
             <membership_setup>
                 <setup>
                     <module>Mymodule_MemberShip</module>
                 </setup>
             </membership_setup>

             <membership_write>
                 <connection>
                     <use>core_write</use>
                 </connection>
             </membership_write>

             <membership_read>
                 <connection>
                     <use>core_read</use>
                 </connection>
             </membership_read>
         </resources>
         <helpers>
             <membership>
                 <class>Mymodule_MemberShip_Helper</class>
             </membership>
         </helpers>
     </global>
 </config>

Mymodule/MemberShip/Block/Adminhtml/Package.php

<?php
class Mymodule_MemberShip_Block_Adminhtml_Package extends 
Mage_Adminhtml_Block_Widget_Grid_Container {
    public function __construct()
    {
        $this->_blockGroup = 'membership';
        $this->_controller = 'adminhtml_package';
        $this->_headerText = $this->__('Package');

        parent::__construct();
    }
}

package.xml

<?xml version="1.0"?>
<layout version="0.1.0">
    <adminhtml_package_index>
        <reference name="content">
            <block type="membership/adminhtml_package" name="package"/>
        </reference>
    </adminhtml_package_index>
</layout>

Package.php

<?php
class Mymodule_MemberShip_Block_Adminhtml_Package_Package extends 
Mage_Adminhtml_Block_Widget_Grid
{
    public function __construct()
    {
        parent::__construct();
        $this->setDefaultSort('id');
        $this->setId('mymodule_package_package');
        $this->setDefaultDir('asc');
        $this->setSaveParametersInSession(true);
    }
    protected function _getCollectionClass()
    {
        return 'mymodule/package_collection';
    }
    protected function _prepareCollection()
    {
        $collection = Mage::getResourceModel($this->_getCollectionClass());
        $this->setCollection($collection);
        return parent::_prepareCollection();
    }
    protected function _prepareColumns()
    {
        $this->addColumn('id',
            array(
                'header'=> $this->__('ID'),
                'width' => '50px',
                'index' => 'id'
            )
        );
        $this->addColumn('discount_type',
            array(
                'header'=> $this->__('Discount Type'),
                'index' => 'discount_type'
            )
        );
        $this->addColumn('discount_value',
            array(
                'header'=> $this->__('Discount Value'),
                'index' => 'discount_value'
            )
        );
        return parent::_prepareColumns();
     }
    protected function _prepareMassaction()
    {
        $this->setMassactionIdField('id');
        $this->getMassactionBlock()->setFormFieldName('id');
        $this->getMassactionBlock()->addItem('delete', array(
            'label'    => Mage::helper('core')->__('Delete'),
            'url'      => $this->getUrl('*/*/massDelete'),
            'confirm'  => Mage::helper('core')->__('Are you sure?')
        ));

        return $this;
    }
    public function getRowUrl($row)
    {
        return $this->getUrl('*/*/edit', array('id' => $row->getId()));
    }
}

Answer 1

Change your grid file class to Mymodule_MemberShip_Block_Adminhtml_Package_Grid and Package.php to Grid.php it will fix your issue. Because in Mage_Adminhtml_Block_Widget_Grid_Container class of core searching for the Grid.php file under Adminhtml/Package folder. Here is the code of core file.

protected function _prepareLayout()
{
    $this->setChild( 'grid',
        $this->getLayout()->createBlock( $this->_blockGroup.'/' . $this->_controller . '_grid',
        $this->_controller . '.grid')->setSaveParametersInSession(true) );
    return parent::_prepareLayout();
}