How to set a Column list box to required.

[#1]

My application should allow the users to select the required columns to proceed with further evaluation of the data. And I want to set the column list box status to required. But it is still displaying optional in the modal. How to set them to required.

Button box("X Column", colListX<<Append(colListData<<GetSelected)),
colListX = ColListBox(<<set required(1),nLines(1)),
Button box("Y Column", colListY<<Append(colListData<<GetSelected) ),
colListY = Col List Box(<<set required(1),nLines(1)),
Button box("BY Column", colListBy<<Append(colListData<<GetSelected)),
colListBy = Col List Box(nLines(1))

And I even wanted to display an error msg when the required fields are not selected. Can "Isempty" function used to check whether column list box is empty or not.

Error = expr(New Window("JMP ALERT" , <<Modal, Textbox("Please select the required fields."),ButtonBox("OK")));
If(Isempty(colListX) == 1,
Error
);

[#2]

You need to use

    << set Min Items()

to set how many items are required for a given list

Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
New Window( "Col List Box Example",
	Col List Box( all, width( 250 ), maxSelected( 1 ) ),
	fontobj = lb = Col List Box()
);
lb << set Min Items(1);

Use the Scripting Index to find what messages can be passed to the Platforms, along with examples 

[#3]

Yeah, that worked. Thank you so much.

I have another doubt, how can we check whether ColListBox is empty? Can we use "IsEmpty" ? Could you help me with this.

Error = expr(New Window("JMP ALERT" , <<Modal, Textbox("Please select the required fields."),ButtonBox("OK")));
If(Isempty(colListX) == 1,
Error
);

[#4 · Accepted solution]

I typically check to see how many items are found after using the messsage

     << Get Items()

Here is an example from the Scripting Index that I did a slight modification to, to find the number of items returned from the Get Items message

Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );
New Window( "Col List Box Example",
	Col List Box( all, width( 250 ), maxSelected( 1 ) ),
	fontobj = lb = Col List Box()
);
lb << Append( "height" );
nitems(lb << Get Items());

[#5]

Yeah, that worked. Thank you so much.