Yes/No and Tristate

[dsigner1]

Hello Everyone,
I have been away from Access for about two years. Now I have offered to help a friend with a program he has. He uses quite a lot of tick boxes for Yes/No questions. he asked me if it was possible to show the difference between entering an actual NO and never ever visiting the box in the first place. I replied "that's easy you need tri-state".

Now I am trying to do it I have run into trouble. I can switch tri-state on all right but the table field is still Yes/No so it does not save the third state.

Second attempt is to replace the tick box with an option group showing yes/No/Not clicked. Now I find that I am trying to use the "improved" version 7 interface and I can't get the option group wizard to work at all.

Can any one spare a minute or two to get me back on track please?

I see there are still some names on the forum that I remember.

Thanks all

 

[jdraw]

I did a google search and found this link
http://stackoverflow.com/questions/10922853/ms-access-checkbox-based-on-value-of-textbox

As I understand things, if the checkbox has never been assigned a value and has no default, it will be Null (uninitialized variable which equates to intrinsic constant vbEmpty)
If the checkbox is checked it will be True (-1), if the box is unchecked, but has been assigned a default or once was checked, it will be False (0).

My understanding is far from definitive. Most users/developers consider a checkbox as 2 state.

You may find more technical( read that as definitive/correct) discussions, examples via google or forums.

 

[dsigner1]

Thank you Jdraw. I thought there was some reason that I had steered clear of the "facility" before. It just seemed to fit the requirement because i got a bit rusty. I'll just create my own 3 state.

What a fantastic forum this is. Someone always knows the answer and gives the time up to tell you

 

[Pat Hartman]

Option groups require numeric values and so you can't assign null using an option group, You also can't assign null using the checkbox. In both cases the underlying value might be null, you can go from nothing to something but not something to nothing.

If you really want three states, use an integer rather than a boolean data type (tristate booleans are not supported in SQL server so the integer is more flexible.)

Once you switch to an integer, you can use a combo with options of Yes and No. Null will just be "empty". Using an integer, you can change the value from something (yes or no) to nothing by tabbing into the control and pressing the delete key.