silverstripe-gridfieldextensions/code/GridFieldExternalLink.php

<?php
/**
 * Displays a link to an external source referenced 'external link'
 */
class GridFieldExternalLink extends GridFieldDataColumns {

	/**
	 * Add a column for the actions
	 *
	 * @param type $gridField
	 * @param array $columns
	 */
	public function augmentColumns($gridField, &$columns) {
		if(!in_array('Actions', $columns)) $columns[] = 'Actions';
	}

	/**
	 * Return any special attributes that will be used for FormField::create_tag()
	 *
	 * @param GridField $gridField
	 * @param DataObject $record
	 * @param string $columnName
	 * @return array
	 */
	public function getColumnAttributes($gridField, $record, $columnName) {
		return array('class' => 'col-buttons');
	}

	/**
	 * Add the title
	 *
	 * @param GridField $gridField
	 * @param string $columnName
	 * @return array
	 */
	public function getColumnMetadata($gridField, $columnName) {
		if($columnName == 'Actions') {
			return array('title' => '');
		}
		return array();
	}

	/**
	 * Which columns are handled by this component
	 *
	 * @param type $gridField
	 * @return type
	 */
	public function getColumnsHandled($gridField) {
		return array('Actions');
	}

	/**
	 * @param GridField $gridField
	 * @param DataObject $record
	 * @param string $columnName
	 *
	 * @return string - the HTML for the column
	 */
	public function getColumnContent($gridField, $record, $columnName) {
		$data = new ArrayData(array(
			'Link' => $record->hasMethod('getExternalLink') ? $record->getExternalLink() : $record->ExternalLink,
			'Text' => $record->hasMethod('getExternalLinkText') ? $record->getExternalLinkText() : 'External Link'
		));

		return $data->renderWith('GridFieldExternalLink');
	}
}