blocks/moodleblock.class.php

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