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See Release Notes

  • Bug fixes for general core bugs in 4.2.x will end 22 April 2024 (12 months).
  • Bug fixes for security issues in 4.2.x will end 7 October 2024 (18 months).
  • PHP version: minimum PHP 8.0.0 Note: minimum PHP version has increased since Moodle 4.1. PHP 8.1.x is supported too.

Differences Between: [Versions 310 and 402] [Versions 311 and 402] [Versions 39 and 402] [Versions 400 and 402] [Versions 401 and 402]

   1  <?php
   2  // This file is part of Moodle - http://moodle.org/
   3  //
   4  // Moodle is free software: you can redistribute it and/or modify
   5  // it under the terms of the GNU General Public License as published by
   6  // the Free Software Foundation, either version 3 of the License, or
   7  // (at your option) any later version.
   8  //
   9  // Moodle is distributed in the hope that it will be useful,
  10  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  // GNU General Public License for more details.
  13  //
  14  // You should have received a copy of the GNU General Public License
  15  // along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
  16  
  17  /**
  18   * This file contains the parent class for moodle blocks, block_base.
  19   *
  20   * @package    core_block
  21   * @license    http://www.gnu.org/copyleft/gpl.html GNU Public License
  22   */
  23  
  24  /// Constants
  25  
  26  /**
  27   * Block type of list. Contents of block should be set as an associative array in the content object as items ($this->content->items). Optionally include footer text in $this->content->footer.
  28   */
  29  define('BLOCK_TYPE_LIST',    1);
  30  
  31  /**
  32   * Block type of text. Contents of block should be set to standard html text in the content object as items ($this->content->text). Optionally include footer text in $this->content->footer.
  33   */
  34  define('BLOCK_TYPE_TEXT',    2);
  35  /**
  36   * Block type of tree. $this->content->items is a list of tree_item objects and $this->content->footer is a string.
  37   */
  38  define('BLOCK_TYPE_TREE',    3);
  39  
  40  /**
  41   * Class for describing a moodle block, all Moodle blocks derive from this class
  42   *
  43   * @author Jon Papaioannou
  44   * @package core_block
  45   */
  46  class block_base {
  47  
  48      /**
  49       * Internal var for storing/caching translated strings
  50       * @var string $str
  51       */
  52      var $str;
  53  
  54      /**
  55       * The title of the block to be displayed in the block title area.
  56       * @var string $title
  57       */
  58      var $title         = NULL;
  59  
  60      /**
  61       * The name of the block to be displayed in the block title area if the title is empty.
  62       * @var string arialabel
  63       */
  64      var $arialabel         = NULL;
  65  
  66      /**
  67       * The type of content that this block creates. Currently support options - BLOCK_TYPE_LIST, BLOCK_TYPE_TEXT
  68       * @var int $content_type
  69       */
  70      var $content_type  = BLOCK_TYPE_TEXT;
  71  
  72      /**
  73       * An object to contain the information to be displayed in the block.
  74       * @var stdClass $content
  75       */
  76      var $content       = NULL;
  77  
  78      /**
  79       * The initialized instance of this block object.
  80       * @var stdClass $instance
  81       */
  82      var $instance      = NULL;
  83  
  84      /**
  85       * The page that this block is appearing on.
  86       * @var moodle_page
  87       */
  88      public $page       = NULL;
  89  
  90      /**
  91       * This blocks's context.
  92       * @var context
  93       */
  94      public $context    = NULL;
  95  
  96      /**
  97       * An object containing the instance configuration information for the current instance of this block.
  98       * @var stdClass $config
  99       */
 100      var $config        = NULL;
 101  
 102      /**
 103       * How often the cronjob should run, 0 if not at all.
 104       * @var int $cron
 105       */
 106  
 107      var $cron          = NULL;
 108  
 109  /// Class Functions
 110  
 111      /**
 112       * Fake constructor to keep PHP5 happy
 113       *
 114       */
 115      function __construct() {
 116          $this->init();
 117      }
 118  
 119      /**
 120       * Function that can be overridden to do extra cleanup before
 121       * the database tables are deleted. (Called once per block, not per instance!)
 122       */
 123      function before_delete() {
 124      }
 125  
 126      /**
 127       * Returns the block name, as present in the class name,
 128       * the database, the block directory, etc etc.
 129       *
 130       * @return string
 131       */
 132      function name() {
 133          // Returns the block name, as present in the class name,
 134          // the database, the block directory, etc etc.
 135          $myname = strtolower(get_class($this));
 136          return substr($myname, strpos($myname, '_') + 1);
 137      }
 138  
 139      /**
 140       * Parent class version of this function simply returns NULL
 141       * This should be implemented by the derived class to return
 142       * the content object.
 143       *
 144       * @return stdObject
 145       */
 146      function get_content() {
 147          // This should be implemented by the derived class.
 148          return NULL;
 149      }
 150  
 151      /**
 152       * Returns the class $title var value.
 153       *
 154       * Intentionally doesn't check if a title is set.
 155       * This is already done in {@link _self_test()}
 156       *
 157       * @return string $this->title
 158       */
 159      function get_title() {
 160          // Intentionally doesn't check if a title is set. This is already done in _self_test()
 161          return $this->title;
 162      }
 163  
 164      /**
 165       * Returns the class $content_type var value.
 166       *
 167       * Intentionally doesn't check if content_type is set.
 168       * This is already done in {@link _self_test()}
 169       *
 170       * @return string $this->content_type
 171       */
 172      function get_content_type() {
 173          // Intentionally doesn't check if a content_type is set. This is already done in _self_test()
 174          return $this->content_type;
 175      }
 176  
 177      /**
 178       * Returns true or false, depending on whether this block has any content to display
 179       * and whether the user has permission to view the block
 180       *
 181       * @return boolean
 182       */
 183      function is_empty() {
 184          if ( !has_capability('moodle/block:view', $this->context) ) {
 185              return true;
 186          }
 187  
 188          $this->get_content();
 189          return(empty($this->content->text) && empty($this->content->footer));
 190      }
 191  
 192      /**
 193       * First sets the current value of $this->content to NULL
 194       * then calls the block's {@link get_content()} function
 195       * to set its value back.
 196       *
 197       * @return stdObject
 198       */
 199      function refresh_content() {
 200          // Nothing special here, depends on content()
 201          $this->content = NULL;
 202          return $this->get_content();
 203      }
 204  
 205      /**
 206       * Return a block_contents object representing the full contents of this block.
 207       *
 208       * This internally calls ->get_content(), and then adds the editing controls etc.
 209       *
 210       * You probably should not override this method, but instead override
 211       * {@link html_attributes()}, {@link formatted_contents()} or {@link get_content()},
 212       * {@link hide_header()}, {@link (get_edit_controls)}, etc.
 213       *
 214       * @return block_contents a representation of the block, for rendering.
 215       * @since Moodle 2.0.
 216       */
 217      public function get_content_for_output($output) {
 218          global $CFG;
 219  
 220          // We can exit early if the current user doesn't have the capability to view the block.
 221          if (!has_capability('moodle/block:view', $this->context)) {
 222              return null;
 223          }
 224  
 225          $bc = new block_contents($this->html_attributes());
 226          $bc->attributes['data-block'] = $this->name();
 227          $bc->blockinstanceid = $this->instance->id;
 228          $bc->blockpositionid = $this->instance->blockpositionid;
 229  
 230          if ($this->instance->visible) {
 231              $bc->content = $this->formatted_contents($output);
 232              if (!empty($this->content->footer)) {
 233                  $bc->footer = $this->content->footer;
 234              }
 235          } else {
 236              $bc->add_class('invisibleblock');
 237          }
 238  
 239          if (!$this->hide_header()) {
 240              $bc->title = $this->title;
 241          }
 242  
 243          if (empty($bc->title)) {
 244              $bc->arialabel = new lang_string('pluginname', get_class($this));
 245              $this->arialabel = $bc->arialabel;
 246          }
 247  
 248          if ($this->page->user_is_editing() && $this->instance_can_be_edited()) {
 249              $bc->controls = $this->page->blocks->edit_controls($this);
 250          } else {
 251              // we must not use is_empty on hidden blocks
 252              if ($this->is_empty() && !$bc->controls) {
 253                  return null;
 254              }
 255          }
 256  
 257          if (empty($CFG->allowuserblockhiding)
 258                  || (empty($bc->content) && empty($bc->footer))
 259                  || !$this->instance_can_be_collapsed()) {
 260              $bc->collapsible = block_contents::NOT_HIDEABLE;
 261          } else if (get_user_preferences('block' . $bc->blockinstanceid . 'hidden', false)) {
 262              $bc->collapsible = block_contents::HIDDEN;
 263          } else {
 264              $bc->collapsible = block_contents::VISIBLE;
 265          }
 266  
 267          if ($this->instance_can_be_docked() && !$this->hide_header()) {
 268              $bc->dockable = true;
 269          }
 270  
 271          $bc->annotation = ''; // TODO MDL-19398 need to work out what to say here.
 272  
 273          return $bc;
 274      }
 275  
 276  
 277      /**
 278       * Return an object containing all the block content to be returned by external functions.
 279       *
 280       * If your block is returning formatted content or provide files for download, you should override this method to use the
 281       * \core_external\util::format_text, \core_external\util::format_string functions for formatting or external_util::get_area_files for files.
 282       *
 283       * @param  core_renderer $output the rendered used for output
 284       * @return stdClass      object containing the block title, central content, footer and linked files (if any).
 285       * @since  Moodle 3.6
 286       */
 287      public function get_content_for_external($output) {
 288          $bc = new stdClass;
 289          $bc->title = null;
 290          $bc->content = null;
 291          $bc->contentformat = FORMAT_HTML;
 292          $bc->footer = null;
 293          $bc->files = [];
 294  
 295          if ($this->instance->visible) {
 296              $bc->content = $this->formatted_contents($output);
 297              if (!empty($this->content->footer)) {
 298                  $bc->footer = $this->content->footer;
 299              }
 300          }
 301  
 302          if (!$this->hide_header()) {
 303              $bc->title = $this->title;
 304          }
 305  
 306          return $bc;
 307      }
 308  
 309      /**
 310       * Return the plugin config settings for external functions.
 311       *
 312       * In some cases the configs will need formatting or be returned only if the current user has some capabilities enabled.
 313       *
 314       * @return stdClass the configs for both the block instance and plugin (as object with name -> value)
 315       * @since Moodle 3.8
 316       */
 317      public function get_config_for_external() {
 318          return (object) [
 319              'instance' => new stdClass(),
 320              'plugin' => new stdClass(),
 321          ];
 322      }
 323  
 324      /**
 325       * Convert the contents of the block to HTML.
 326       *
 327       * This is used by block base classes like block_list to convert the structured
 328       * $this->content->list and $this->content->icons arrays to HTML. So, in most
 329       * blocks, you probaby want to override the {@link get_contents()} method,
 330       * which generates that structured representation of the contents.
 331       *
 332       * @param $output The core_renderer to use when generating the output.
 333       * @return string the HTML that should appearn in the body of the block.
 334       * @since Moodle 2.0.
 335       */
 336      protected function formatted_contents($output) {
 337          $this->get_content();
 338          $this->get_required_javascript();
 339          if (!empty($this->content->text)) {
 340              return $this->content->text;
 341          } else {
 342              return '';
 343          }
 344      }
 345  
 346      /**
 347       * Tests if this block has been implemented correctly.
 348       * Also, $errors isn't used right now
 349       *
 350       * @return boolean
 351       */
 352  
 353      function _self_test() {
 354          // Tests if this block has been implemented correctly.
 355          // Also, $errors isn't used right now
 356          $errors = array();
 357  
 358          $correct = true;
 359          if ($this->get_title() === NULL) {
 360              $errors[] = 'title_not_set';
 361              $correct = false;
 362          }
 363          if (!in_array($this->get_content_type(), array(BLOCK_TYPE_LIST, BLOCK_TYPE_TEXT, BLOCK_TYPE_TREE))) {
 364              $errors[] = 'invalid_content_type';
 365              $correct = false;
 366          }
 367          //following selftest was not working when roles&capabilities were used from block
 368  /*        if ($this->get_content() === NULL) {
 369              $errors[] = 'content_not_set';
 370              $correct = false;
 371          }*/
 372          $formats = $this->applicable_formats();
 373          if (empty($formats) || array_sum($formats) === 0) {
 374              $errors[] = 'no_formats';
 375              $correct = false;
 376          }
 377  
 378          return $correct;
 379      }
 380  
 381      /**
 382       * Subclasses should override this and return true if the
 383       * subclass block has a settings.php file.
 384       *
 385       * @return boolean
 386       */
 387      function has_config() {
 388          return false;
 389      }
 390  
 391      /**
 392       * Default behavior: save all variables as $CFG properties
 393       * You don't need to override this if you 're satisfied with the above
 394       *
 395       * @deprecated since Moodle 2.9 MDL-49385 - Please use Admin Settings functionality to save block configuration.
 396       */
 397      function config_save($data) {
 398          throw new coding_exception('config_save() can not be used any more, use Admin Settings functionality to save block configuration.');
 399      }
 400  
 401      /**
 402       * Which page types this block may appear on.
 403       *
 404       * The information returned here is processed by the
 405       * {@link blocks_name_allowed_in_format()} function. Look there if you need
 406       * to know exactly how this works.
 407       *
 408       * Default case: everything except mod and tag.
 409       *
 410       * @return array page-type prefix => true/false.
 411       */
 412      function applicable_formats() {
 413          // Default case: the block can be used in courses and site index, but not in activities
 414          return array('all' => true, 'mod' => false, 'tag' => false);
 415      }
 416  
 417  
 418      /**
 419       * Default return is false - header will be shown
 420       * @return boolean
 421       */
 422      function hide_header() {
 423          return false;
 424      }
 425  
 426      /**
 427       * Return any HTML attributes that you want added to the outer <div> that
 428       * of the block when it is output.
 429       *
 430       * Because of the way certain JS events are wired it is a good idea to ensure
 431       * that the default values here still get set.
 432       * I found the easiest way to do this and still set anything you want is to
 433       * override it within your block in the following way
 434       *
 435       * <code php>
 436       * function html_attributes() {
 437       *    $attributes = parent::html_attributes();
 438       *    $attributes['class'] .= ' mynewclass';
 439       *    return $attributes;
 440       * }
 441       * </code>
 442       *
 443       * @return array attribute name => value.
 444       */
 445      function html_attributes() {
 446          $attributes = array(
 447              'id' => 'inst' . $this->instance->id,
 448              'class' => 'block_' . $this->name() . ' block',
 449              'role' => $this->get_aria_role()
 450          );
 451          if ($this->hide_header()) {
 452              $attributes['class'] .= ' no-header';
 453          }
 454          if ($this->instance_can_be_docked() && get_user_preferences('docked_block_instance_' . $this->instance->id, 0)) {
 455              $attributes['class'] .= ' dock_on_load';
 456          }
 457          return $attributes;
 458      }
 459  
 460      /**
 461       * Set up a particular instance of this class given data from the block_insances
 462       * table and the current page. (See {@link block_manager::load_blocks()}.)
 463       *
 464       * @param stdClass $instance data from block_insances, block_positions, etc.
 465       * @param moodle_page $page the page this block is on.
 466       */
 467      function _load_instance($instance, $page) {
 468          if (!empty($instance->configdata)) {
 469              $this->config = unserialize_object(base64_decode($instance->configdata));
 470          }
 471          $this->instance = $instance;
 472          $this->context = context_block::instance($instance->id);
 473          $this->page = $page;
 474          $this->specialization();
 475      }
 476  
 477      /**
 478       * Allows the block to load any JS it requires into the page.
 479       *
 480       * By default this function simply permits the user to dock the block if it is dockable.
 481       *
 482       * Left null as of MDL-64506.
 483       */
 484      function get_required_javascript() {
 485      }
 486  
 487      /**
 488       * This function is called on your subclass right after an instance is loaded
 489       * Use this function to act on instance data just after it's loaded and before anything else is done
 490       * For instance: if your block will have different title's depending on location (site, course, blog, etc)
 491       */
 492      function specialization() {
 493          // Just to make sure that this method exists.
 494      }
 495  
 496      /**
 497       * Is each block of this type going to have instance-specific configuration?
 498       * Normally, this setting is controlled by {@link instance_allow_multiple()}: if multiple
 499       * instances are allowed, then each will surely need its own configuration. However, in some
 500       * cases it may be necessary to provide instance configuration to blocks that do not want to
 501       * allow multiple instances. In that case, make this function return true.
 502       * I stress again that this makes a difference ONLY if {@link instance_allow_multiple()} returns false.
 503       * @return boolean
 504       */
 505      function instance_allow_config() {
 506          return false;
 507      }
 508  
 509      /**
 510       * Are you going to allow multiple instances of each block?
 511       * If yes, then it is assumed that the block WILL USE per-instance configuration
 512       * @return boolean
 513       */
 514      function instance_allow_multiple() {
 515          // Are you going to allow multiple instances of each block?
 516          // If yes, then it is assumed that the block WILL USE per-instance configuration
 517          return false;
 518      }
 519  
 520      /**
 521       * Serialize and store config data
 522       */
 523      function instance_config_save($data, $nolongerused = false) {
 524          global $DB;
 525          $DB->update_record('block_instances', ['id' => $this->instance->id,
 526                  'configdata' => base64_encode(serialize($data)), 'timemodified' => time()]);
 527      }
 528  
 529      /**
 530       * Replace the instance's configuration data with those currently in $this->config;
 531       */
 532      function instance_config_commit($nolongerused = false) {
 533          global $DB;
 534          $this->instance_config_save($this->config);
 535      }
 536  
 537      /**
 538       * Do any additional initialization you may need at the time a new block instance is created
 539       * @return boolean
 540       */
 541      function instance_create() {
 542          return true;
 543      }
 544  
 545      /**
 546       * Copy any block-specific data when copying to a new block instance.
 547       * @param int $fromid the id number of the block instance to copy from
 548       * @return boolean
 549       */
 550      public function instance_copy($fromid) {
 551          return true;
 552      }
 553  
 554      /**
 555       * Delete everything related to this instance if you have been using persistent storage other than the configdata field.
 556       * @return boolean
 557       */
 558      function instance_delete() {
 559          return true;
 560      }
 561  
 562      /**
 563       * Allows the block class to have a say in the user's ability to edit (i.e., configure) blocks of this type.
 564       * The framework has first say in whether this will be allowed (e.g., no editing allowed unless in edit mode)
 565       * but if the framework does allow it, the block can still decide to refuse.
 566       * @return boolean
 567       */
 568      function user_can_edit() {
 569          global $USER;
 570  
 571          if (has_capability('moodle/block:edit', $this->context)) {
 572              return true;
 573          }
 574  
 575          // The blocks in My Moodle are a special case.  We want them to inherit from the user context.
 576          if (!empty($USER->id)
 577              && $this->instance->parentcontextid == $this->page->context->id   // Block belongs to this page
 578              && $this->page->context->contextlevel == CONTEXT_USER             // Page belongs to a user
 579              && $this->page->context->instanceid == $USER->id) {               // Page belongs to this user
 580              return has_capability('moodle/my:manageblocks', $this->page->context);
 581          }
 582  
 583          return false;
 584      }
 585  
 586      /**
 587       * Allows the block class to have a say in the user's ability to create new instances of this block.
 588       * The framework has first say in whether this will be allowed (e.g., no adding allowed unless in edit mode)
 589       * but if the framework does allow it, the block can still decide to refuse.
 590       * This function has access to the complete page object, the creation related to which is being determined.
 591       *
 592       * @param moodle_page $page
 593       * @return boolean
 594       */
 595      function user_can_addto($page) {
 596          global $CFG;
 597          require_once($CFG->dirroot . '/user/lib.php');
 598  
 599          // List of formats this block supports.
 600          $formats = $this->applicable_formats();
 601  
 602          // Check if user is trying to add blocks to their profile page.
 603          $userpagetypes = user_page_type_list($page->pagetype, null, null);
 604          if (array_key_exists($page->pagetype, $userpagetypes)) {
 605              $capability = 'block/' . $this->name() . ':addinstance';
 606              return $this->has_add_block_capability($page, $capability)
 607                  && has_capability('moodle/user:manageownblocks', $page->context);
 608          }
 609  
 610          // The blocks in My Moodle are a special case and use a different capability.
 611          $mypagetypes = my_page_type_list($page->pagetype); // Get list of possible my page types.
 612  
 613          if (array_key_exists($page->pagetype, $mypagetypes)) { // Ensure we are on a page with a my page type.
 614              // If the block cannot be displayed on /my it is ok if the myaddinstance capability is not defined.
 615              // Is 'my' explicitly forbidden?
 616              // If 'all' has not been allowed, has 'my' been explicitly allowed?
 617              if ((isset($formats['my']) && $formats['my'] == false)
 618                  || (empty($formats['all']) && empty($formats['my']))) {
 619  
 620                  // Block cannot be added to /my regardless of capabilities.
 621                  return false;
 622              } else {
 623                  $capability = 'block/' . $this->name() . ':myaddinstance';
 624                  return $this->has_add_block_capability($page, $capability)
 625                         && has_capability('moodle/my:manageblocks', $page->context);
 626              }
 627          }
 628          // Check if this is a block only used on /my.
 629          unset($formats['my']);
 630          if (empty($formats)) {
 631              // Block can only be added to /my - return false.
 632              return false;
 633          }
 634  
 635          $capability = 'block/' . $this->name() . ':addinstance';
 636          if ($this->has_add_block_capability($page, $capability)
 637                  && has_capability('moodle/block:edit', $page->context)) {
 638              return true;
 639          }
 640  
 641          return false;
 642      }
 643  
 644      /**
 645       * Returns true if the user can add a block to a page.
 646       *
 647       * @param moodle_page $page
 648       * @param string $capability the capability to check
 649       * @return boolean true if user can add a block, false otherwise.
 650       */
 651      private function has_add_block_capability($page, $capability) {
 652          // Check if the capability exists.
 653          if (!get_capability_info($capability)) {
 654              // Debug warning that the capability does not exist, but no more than once per page.
 655              static $warned = array();
 656              if (!isset($warned[$this->name()])) {
 657                  debugging('The block ' .$this->name() . ' does not define the standard capability ' .
 658                          $capability , DEBUG_DEVELOPER);
 659                  $warned[$this->name()] = 1;
 660              }
 661              // If the capability does not exist, the block can always be added.
 662              return true;
 663          } else {
 664              return has_capability($capability, $page->context);
 665          }
 666      }
 667  
 668      static function get_extra_capabilities() {
 669          return array('moodle/block:view', 'moodle/block:edit');
 670      }
 671  
 672      /**
 673       * Can be overridden by the block to prevent the block from being dockable.
 674       *
 675       * @return bool
 676       *
 677       * Return false as per MDL-64506
 678       */
 679      public function instance_can_be_docked() {
 680          return false;
 681      }
 682  
 683      /**
 684       * If overridden and set to false by the block it will not be hidable when
 685       * editing is turned on.
 686       *
 687       * @return bool
 688       */
 689      public function instance_can_be_hidden() {
 690          return true;
 691      }
 692  
 693      /**
 694       * If overridden and set to false by the block it will not be collapsible.
 695       *
 696       * @return bool
 697       */
 698      public function instance_can_be_collapsed() {
 699          return true;
 700      }
 701  
 702      /**
 703       * If overridden and set to false by the block it will not be editable.
 704       *
 705       * @return bool
 706       */
 707      public function instance_can_be_edited() {
 708          return true;
 709      }
 710  
 711      /** @callback callback functions for comments api */
 712      public static function comment_template($options) {
 713          $ret = <<<EOD
 714  <div class="comment-userpicture">___picture___</div>
 715  <div class="comment-content">
 716      ___name___ - <span>___time___</span>
 717      <div>___content___</div>
 718  </div>
 719  EOD;
 720          return $ret;
 721      }
 722      public static function comment_permissions($options) {
 723          return array('view'=>true, 'post'=>true);
 724      }
 725      public static function comment_url($options) {
 726          return null;
 727      }
 728      public static function comment_display($comments, $options) {
 729          return $comments;
 730      }
 731      public static function comment_add(&$comments, $options) {
 732          return true;
 733      }
 734  
 735      /**
 736       * Returns the aria role attribute that best describes this block.
 737       *
 738       * Region is the default, but this should be overridden by a block is there is a region child, or even better
 739       * a landmark child.
 740       *
 741       * Options are as follows:
 742       *    - landmark
 743       *      - application
 744       *      - banner
 745       *      - complementary
 746       *      - contentinfo
 747       *      - form
 748       *      - main
 749       *      - navigation
 750       *      - search
 751       *
 752       * @return string
 753       */
 754      public function get_aria_role() {
 755          return 'complementary';
 756      }
 757  
 758      /**
 759       * This method can be overriden to add some extra checks to decide whether the block can be added or not to a page.
 760       * It doesn't need to do the standard capability checks as they will be performed by has_add_block_capability().
 761       * This method is user agnostic. If you want to check if a user can add a block or not, you should use user_can_addto().
 762       *
 763       * @param moodle_page $page The page where this block will be added.
 764       * @return bool Whether the block can be added or not to the given page.
 765       */
 766      public function can_block_be_added(moodle_page $page): bool {
 767          return true;
 768      }
 769  }
 770  
 771  /**
 772   * Specialized class for displaying a block with a list of icons/text labels
 773   *
 774   * The get_content method should set $this->content->items and (optionally)
 775   * $this->content->icons, instead of $this->content->text.
 776   *
 777   * @author Jon Papaioannou
 778   * @package core_block
 779   */
 780  
 781  class block_list extends block_base {
 782      var $content_type  = BLOCK_TYPE_LIST;
 783  
 784      function is_empty() {
 785          if ( !has_capability('moodle/block:view', $this->context) ) {
 786              return true;
 787          }
 788  
 789          $this->get_content();
 790          return (empty($this->content->items) && empty($this->content->footer));
 791      }
 792  
 793      protected function formatted_contents($output) {
 794          $this->get_content();
 795          $this->get_required_javascript();
 796          if (!empty($this->content->items)) {
 797              return $output->list_block_contents($this->content->icons, $this->content->items);
 798          } else {
 799              return '';
 800          }
 801      }
 802  
 803      function html_attributes() {
 804          $attributes = parent::html_attributes();
 805          $attributes['class'] .= ' list_block';
 806          return $attributes;
 807      }
 808  
 809  }
 810  
 811  /**
 812   * Specialized class for displaying a tree menu.
 813   *
 814   * The {@link get_content()} method involves setting the content of
 815   * <code>$this->content->items</code> with an array of {@link tree_item}
 816   * objects (these are the top-level nodes). The {@link tree_item::children}
 817   * property may contain more tree_item objects, and so on. The tree_item class
 818   * itself is abstract and not intended for use, use one of it's subclasses.
 819   *
 820   * Unlike {@link block_list}, the icons are specified as part of the items,
 821   * not in a separate array.
 822   *
 823   * @author Alan Trick
 824   * @package core_block
 825   * @internal this extends block_list so we get is_empty() for free
 826   */
 827  class block_tree extends block_list {
 828  
 829      /**
 830       * @var int specifies the manner in which contents should be added to this
 831       * block type. In this case <code>$this->content->items</code> is used with
 832       * {@link tree_item}s.
 833       */
 834      public $content_type = BLOCK_TYPE_TREE;
 835  
 836      /**
 837       * Make the formatted HTML ouput.
 838       *
 839       * Also adds the required javascript call to the page output.
 840       *
 841       * @param core_renderer $output
 842       * @return string HTML
 843       */
 844      protected function formatted_contents($output) {
 845          // based of code in admin_tree
 846          global $PAGE; // TODO change this when there is a proper way for blocks to get stuff into head.
 847          static $eventattached;
 848          if ($eventattached===null) {
 849              $eventattached = true;
 850          }
 851          if (!$this->content) {
 852              $this->content = new stdClass;
 853              $this->content->items = array();
 854          }
 855          $this->get_required_javascript();
 856          $this->get_content();
 857          $content = $output->tree_block_contents($this->content->items,array('class'=>'block_tree list'));
 858          return $content;
 859      }
 860  }