block_example.module

<?php

/**
 * @file
 * This is an example outlining how a module can define blocks to be
 * displayed on each page.
 */

/**
 * Implementation of hook_block().
 *
 * This hook both declares to Drupal what blocks are provided by the module, and
 * generates the contents of the blocks themselves.
 */
function block_example_block($op = 'list', $delta = 0, $edit = array()) {
  // The $op parameter determines what piece of information is being requested.
  switch ($op) {
    case 'list':
      // If $op is "list", we just need to return a list of block descriptions.
      // This is used to provide a list of possible blocks to the administrator,
      // end users will not see these descriptions.
      $blocks[0]['info'] = t('Example: configurable text string');
      $blocks[1]['info'] = t('Example: empty block');
      return $blocks;
    case 'configure':
      // If $op is "configure", we need to provide the administrator with a
      // configuration form. The $delta parameter tells us which block is being
      // configured. In this example, we'll allow the administrator to customize
      // the text of the first block.
      $form = array();
      if ($delta == 0) {
        // All we need to provide is a text field, Drupal will take care of
        // the other block configuration options and the save button.
        $form['block_example_string'] = array(
          '#type' => 'textfield',
          '#title' => t('Block contents'),
          '#size' => 60,
          '#description' => t('This string will appear in the example block.'),
          '#default_value' =>
            variable_get('block_example_string',  t('Some example content.')),
        );
      }
      return $form;
    case 'save':
      // If $op is "save", we need to save settings from the configuration form.
      // Since the first block is the only one that allows configuration, we
      // need to check $delta to make sure we only save it.
      if ($delta == 0) {
        // Have Drupal save the string to the database.
        variable_set('block_example_string', $edit['block_example_string']);
      }
      return;
    case 'view': default:
      // If $op is "view", then we need to generate the block for display
      // purposes. The $delta parameter tells us which block is being requested.
      switch ($delta) {
        case 0:
          // The subject is displayed at the top of the block. Note that it
          // should be passed through t() for translation.
          $block['subject'] = t('Title of block #1');
          // The content of the block is typically generated by calling a custom
          // function.
          $block['content'] = block_example_contents(1);
          break;
        case 1:
          $block['subject'] = t('Title of block #2');
          $block['content'] = block_example_contents(2);
          break;
      }
      return $block;
  }
}

/**
 * A block content function.
 */
function block_example_contents($which_block) {
  if ($which_block == 1) {
    // Modules would typically perform some database queries to fetch the
    // content for their blocks. Here, we'll just use the variable set in the
    // block configuration or, if none has set, a default value.
    return variable_get('block_example_string',  t('A default value.'));
  }

  if ($which_block == 2) {
    // It is possible that your block will not have any content, since it is
    // probably dynamically constructed. In this case, Drupal will not display
    // the block at all.
    return;
  }
}