A common way to set(get) the state of an item is setItemValue(). The method sets value for an item and checks it (if appropriate).
Applied to all items.
dhxForm.setItemValue(name, value);
For checkbox and radio items you can also use 3 more methods:
// checking items dhxForm.checkItem(name, value); // for radio buttons 2nd argument value should be passed // unchecking items dhxForm.uncheckItem(name, value); // getting current state var isChecked = dhxForm.isItemChecked(name, value); // returns true/false