The following save button code works well on mobile xpage:
var checkBox31:com.ibm.xsp.component.xp.XspInputCheckbox = getComponent(\"checkBox31\");
var customerI
A checkbox has a value of either 'false' or 'true' (indicating it is 'deselected' & 'selected'), it shouldn't return a value of "" or null. Therefore, the first if statement is never true, and your dialog will never appear.
I believe what you want is that if the checkbox is unselected, there must be a customer ID entered in the input. If so, I think this is the code you want:
var checkBox31:com.ibm.xsp.component.xp.XspInputCheckbox = getComponent("checkBox31");
var customerID1:com.ibm.xsp.component.xp.XspInputText = getComponent("customerID1");
var a = checkBox31.getValue();
var b = customerID1.getValue();
if (a == "false") {
if (b == "") {
sessionScope.put("ITDialog","You must enter Customer ID");
var dialog1:com.ibm.xsp.extlib.component.dialog.UIDialog = getComponent("dialog1");
dialog1.show();
}
}