Limiting Check Boxes by User

Question

How can I limit the number of check boxes a user can select?  I created the form in Acrobat XI, there are 20 check boxes and are named "chkBox0 thru chkBox20."

Answer 1

Here's a sample form that demonstrates one way to do this: https://workspaces.acrobat.com/?d=j-aUbc3YTz1uu8Jx0LvzHg
Each check box calls the same function that's defined in a document-level JavaScript. You'll have to study it a bit to see how it works.
Here's the document-level function:
function limitCheckNumber(prefix, lower, upper, max) {
    // Initialize the selected check box count
    var count = 0;
    // Loop through the check boxes to see if the limit has been exceeded
    for (var i = lower; i < upper + 1; i += 1) {
        // Increment the counter if the current check box is selected
        if (getField(prefix + "." + i).value !== "Off") count += 1;
        // If the count exceeds the limit, deselect the check box that was just selected
        // and alert the user
        if (count > max) {
            event.target.value = "Off";
            app.alert("A maximum of " + max + " check boxes can be selected", 3);
            break;
And here is the Mouse Up script for each check box:
limitCheckNumber("check", 0, 9, 4);
The check boxes are named: check.0, check.1,...,check.9, and it's limited to 4 check boxes max selected at one time.