I need to extend the grid field list page with a custom button.

Please see attached image, I want to add a "Delete All" records button in my ModelAdmin extension of products, that I can control by VendorID (A product has a vendor). So that when vendors are logged in they can select delete all and upload a new set of products.

I cant use replace data on the import CSV, becuase it will replace all vendors. So i have disabled that and instead want to create a custom button that will only delete their products.

Thanks!

First, you need to create a custom GridFieldComponent for 'Delete All' button - something like below

class GridFieldDeleteAllButton implements GridField_HTMLProvider, GridField_ActionProvider {
	protected $targetFragment;

	public function __construct($targetFragment = "before") {
		$this->targetFragment = $targetFragment;
	}

	public function getHTMLFragments($gridField) {
		$button = new GridField_FormAction(
			$gridField, 
			'deleteall', 
			_t('TableListField.DELETEALL', 'Delete All'),
			'deleteall', 
			null
		);
		$button->setAttribute('data-icon', 'cross-circle');
		$button->addExtraClass('no-ajax');
		return array(
			$this->targetFragment => '<p class="grid-csv-button">' . $button->Field() . '</p>',
		);
	}

	public function getActions($gridField) {
		return array('deleteall');
	}

	public function handleAction(GridField $gridField, $actionName, $arguments, $data) {
		if($actionName == 'deleteall') {
			return $this->handleDeleteAll($gridField);
		}
	}

	public function handleDeleteAll($gridField, $request = null) {
		//Add your own DELETE logic here !
		$items=$gridField->getList();
		foreach ($items as $item) {
			$item->delete();
		}
		Controller::curr()->redirectBack();
	}
}

You then can add this new component to your gridfield under your ModelAdmin extension

    public function updateEditForm(&$form) {
        $gridField = $form->Fields()->fieldByName($this->sanitiseClassName($this->owner->modelClass));
        $gridField->getConfig()->addComponent(new GridFieldDeleteAllButton('before'));        
    }