source/php/Entity/CustomPostType.php
public function addTableColumn($key, $title, $sortable = false, $contentCallback = false)
    {
        $this->tableColumns[$key] = $title;

        if ($sortable === true) {
            $this->tableSortableColumns[$key] = $key;
        }

        if ($contentCallback !== false) {
            $this->tableColumnsContentCallback[$key] = $contentCallback;
        }
    }
public function addTableColumn($key, $title, $sortable = false, $contentCallback = false)
    {
        $this->tableColumns[$key] = $title;

        if ($sortable === true) {
            $this->tableSortableColumns[$key] = $key;
        }

        if ($contentCallback !== false) {
            $this->tableColumnsContentCallback[$key] = $contentCallback;
        }
    }
Adds a column to the admin list table
@param string   $key             Column key
@param string   $title           Column title
@param boolean  $sortable        Sortable or not
@param callback $contentCallback Callback function for displaying
column content (params: $columnKey, $postId)