Saves all the images and documents in DcsBuffer to a folder named dirName.
String The name for the folder to save files.
The data in Buffer is temporarily stored in buffer. Once the app is closed, it will be cleared. Using this function will make the data persisted in the buffer. Users can recover it to Buffer using load function.
If dirName folder doesn't exist, a folder will be created automatically. If dirName folder exists and there are image and document data stored in it, all the data will be cleared and the new data will be loaded.
If dirName is nil or '', exception DcsValueNotValidException will be thrown.