How do I check if no instances of an object are on screen?

Could someone tell me how to check if all instances of an object are not on screen?

Thanks

If you need to keep track of the number of objects :

System pick all Object1

--- Object1 is on screen > Set Global Var to Object1.PickedCount

Now Global Var is the number of Object1 on screen. Whenever Global Var is 0 then none of them are on screen.

If you don't need to keep track of the number of objects :

Object1 is on screen > Set a variable to true

else

Set false

This would mean whenever any Object1 is on screen then the variable would set to true, if set to false then this means no Object1 are on screen.

Sprite is on screen

Else

.................actions

Thanks