The ZoneChange command can be used to great effect with the ZonePosition function, to link the positions of various items in the dialogue box. For example, if a slider bar has been assigned to zone 1, and an active list to zone 2, you would be able to scroll through the list with the slider using a line like this:
X> VSlide 1,16,16,8,64,0,1,12,1; create a twelve position slider [ZChange 2,ZPosition;] set zone two to position of changed slider
The commands inside the square brackets are executed automatically whenever the slider is moved on the screen, and they copy the new slider position straight into the active list command and move the list through the selector window.
Here is a step by step procedure for generating a selection box on screen:
Firstly, create a list of components needed for the selector. This could begin with a vertical scroll bar, where 0 VA holds the address of the item array already set up in the main program, and AS returning the number of items:
X> VSlider 1,x,y,width,height,0,8,0 VA AS,1;[]
Next an ActiveList is defined for the selection window, using a line like this:
X> AList 2,x+width,y,20,8,0 VA,0,0,0,4; set up the item list
Finally, a text edit zone is created to hold the current item on screen, like this;
X> EDit 3,x,y+height,width/8,width/8,0,0,2;
Now the scroll bar can be linked to the item display in the ActiveList window, as already explained.
X> VSlider 1,x,y,width,height,0,1,0 VA AS,1; create a twelve position slider [ZChange 2,ZPosition;] set zone two to slider position
Lastly, the ActiveList is linked with the EDit command, so that it loads the selected item into the editing zone, as follows:
X> AList 2,x+width,y,20,8,0 VA,0,0,0,4; set up the item list [ZChange 3,0 VA ZPosition ARray;] load the edit zone with selected item
Remember that 0 VA stores the address of the array, ZPosition holds the item number and ARray is used to get the item. This will return the value of the selected item straight to the EDit zone. If you need to transfer the edited version back to the selector, the appropriate array item needs to be loaded directly from the main AMOS Professional program. Please see the DIALOG UPDATE command for a detailed explanation.
It is sometimes necessary to link up a number of zones in sequence, and relative values instead of absolute zone numbers can be used for this purpose.