Step 8: Storing the drawing in a file

Since that you have got a data representation of the drawing, you should be able to transfer that data into a file and read it back. You will also use standard dialog boxes to get file names from the user.

You are going to use class STORABLE from EiffelBase to save and read data of the drawing. But first, you need to create the following abstraction in order to be able to save the linked list of points.

class 
	LINES

inherit LINKED_LIST [LINE] STORABLE

creation make

end -- class LINES

In MAIN_WINDOW you need to change the definition of lines from:

	lines: LINKED_LIST [LINE]

into:

	lines: LINES

The application will show standard dialog boxes in response to the user's selection of Open and Save to get the file name which will be used for the operation. The following attributes need to be added in MAIN_WINDOW:

	open_dialog: WEL_OPEN_FILE_DIALOG
			-- Standard dialog box to open a file.
			
	save_dialog: WEL_SAVE_FILE_DIALOG
			-- Standard dialog box to save a file.

Now, you are ready to implement Open and Save options in on_menu_command. Basically, the file name is retrieved from the standard dialog box and used to save (store_by_name) or read (retrieve_by_name) the data. Extension .DRW is adopted for the files (procedures set_filter and set_default_extension).

	on_menu_command (menu_id: INTEGER) is 
			-- menu_id has been selected.
		do 
			inspect
				menu_id
			...
			when  Cmd_open then  
				if  open_dialog = void then 
					create open_dialog.make
					open_dialog.set_filter (<<"Draw file">>, <<"*.drw">>)
					open_dialog.set_default_extension ("drw")
				end
				open_dialog.activate (Current);
				if  open_dialog.selected then 
					lines ?= lines.retrieve_by_name (open_dialog.file_name)
					invalidate
				end 
			when  Cmd_save then  
				if  save_dialog = void then 
					create save_dialog.make
					save_dialog.set_filter (<<"Draw file">>, <<"*.drw">>)
					save_dialog.set_default_extension ("drw")
				end
				save_dialog.activate (Current)
				if  save_dialog.selected then 
					lines.store_by_name (save_dialog.file_name)
				end 
			...
		end

Figure 15 shows the standard open dialog box as it appears when the user chooses the Open option.

Figure 15

Here is the end of the tutorial, we hope that you have plenty of ideas to improve your application!

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