Only open one same dialog at a time

[conanjou]

hi , 
I see some examples which can open the same dialog at a time, but I don't know how to do.
Can give me one simple hint, thanks.

[Gintaras]

It depends on how the dialog now can be opened multiple times. Need an example code.

[conanjou]

if the dialog can open multiple times, can any easy method be used to transfer from multiple times to one time? 
thanks.