How to use the value of a CheckBox which is not a field in a table from X++

To do this you have to use the overrided method "modified" of this field.

Then you can write your code like following: 

public boolean modified()
{
    boolean                   ret;
    PayrollEmplrate           PayrollEmplrate;
    ;

    ret = super();

    element.design().controlName("Heade_family");

    if ( Heade_family.value() == 0)
    {
        // write your  instructions here
    }
    else
    {
        // write your  instructions here
    } 
    return ret;
}

Happy Daxing!