Display cursor pointed line in textbox and hide other lines

Question

Is there any method to display only single line of textfile which is loaded in textbox when cursor/key up&down is done and hide other lines while current line is highlighted.

 

Example:

Two lines of textfile in textbox are:

 

abcdef

1234

 

when cursor is pointed on line containing "abcdef" then line containing "1234" which is second line of textfile should be hide and when cursor is on second line then first and other lines of textbox should be hide

 

above image shows the one line of image and only one line of textfile which is browsed in textbox.

 

need to do same.

 

is there any solution for this?