Dynamic categories

Dynamic categories are categories that are dynamically repopulated based on a function each time they are opened.

Blockly supports this by allowing you to associate a category with a function via a registered string key. The function should return a definition of a category's contents (including blocks, buttons, labels, etc). The contents can be specified as JSON or XML, although JSON is recommended.

Also note that the function is provided the target workspace as a parameter, so the blocks in your dynamic category can be based on the state of the workspace.

JSON

// Returns an array of objects.
var coloursFlyoutCallback = function(workspace) {
  // Returns an array of hex colours, e.g. ['#4286f4', '#ef0447']
  var colourList = getPalette();
  var blockList = [];
  for (var i = 0; i < colourList.length; i++) {
    blockList.push({
      'kind': 'block',
      'type': 'colour_picker',
      'fields': {
        'COLOUR': colourList[i]
      }
    });
  }
  return blockList;
};

// Associates the function with the string 'COLOUR_PALETTE'
myWorkspace.registerToolboxCategoryCallback(
    'COLOUR_PALETTE', coloursFlyoutCallback);

XML

// Returns an array of XML nodes.
var coloursFlyoutCallback = function(workspace) {
  // Returns an array of hex colours, e.g. ['#4286f4', '#ef0447']
  var colourList = getPalette();
  var blockList = [];
  for (var i = 0; i < colourList.length; i++) {
    var block = document.createElement('block');
    block.setAttribute('type', 'colour_picker');
    var field = document.createElement('field');
    field.setAttribute('name', 'COLOUR');
    field.innerText = colourList[i];
    block.appendChild(field);
    blockList.push(block);
  }
  return blockList;
};

// Associates the function with the string 'COLOUR_PALETTE'
myWorkspace.registerToolboxCategoryCallback(
    'COLOUR_PALETTE', coloursFlyoutCallback);

After the dynamic category functions are associated with a string key (aka registered) you can assign this string key to the custom property of your category definition to make the category dynamic.

JSON

{
  "kind": "category",
  "name": "Colours",
  "custom": "COLOUR_PALETTE"
}

XML

<category name="Colours" custom="COLOUR_PALETTE"></category>

Built-in dynamic categories

Blockly provides three built-in dynamic categories.

• 'VARIABLE' creates a category for untyped variables.
• 'VARIABLE_DYNAMIC' creates a category for typed variables. It has buttons to create strings, numbers, and colours.

• 'PROCEDURE' creates a category for function blocks.

JSON

{
  "kind": "category",
  "name": "Variables",
  "custom": "VARIABLE"
},
{
  "kind": "category",
  "name": "Variables",
  "custom": "VARIABLE_DYNAMIC"
},
{
  "kind": "category",
  "name": "Functions",
  "custom": "PROCEDURE"
}

XML

<category name="Variables" custom="VARIABLE"></category>
<category name="Variables" custom="VARIABLE_DYNAMIC"></category>
<category name="Functions" custom="PROCEDURE"></category>

Note: The word 'procedure' is used throughout the Blockly codebase, but the word 'function' has found to be more understandable by students. Sorry for the mismatch.