therefore, use the class_terminate method to cleanup (close files, destroy helper objects, etc.) before the server is gone for good.
now for the public interface of cprogress: value, show and hide. firstly, the value property is not implemented using an integer variable, but instead is a logical property physically realized by appropriate get and let methods (look closely at the bottom pane of the browser window above). logical properties offer many benefits: validation, the ability to take action when a property changes, read-only data, etc. however, a stronger motivation is that com simply does not allow a class to contain public data properties. in a com-compatible class, the only public members may be methods.
ignoring com for the moment, a logical value property makes sense in this situation since the server needs to update the progress indicator in response to a change in value. the let method is used to capture a write to the logical property, much like the let statement in vba assigns a new value to a variable. note that the new value is passed as a parameter to the method:
| public property let value(byval percentage as integer) | ||
| frm.pbarprogress.value = percentage | '** update progress bar | |
| frm.lblpercentage.caption = _ | ||
| cstr(percentage) & "%" | '** update label | |
| frm.refresh | '** redraw form | |
| end property | ||
the new value is simply assigned to the underlying windows 95 progressbar control on the progress form, as well as written to a label. in order for the client to be able to read the current progress value, a corresponding get method is also provided:
| public property get value() as integer | |
| '** return current state of progress bar | |
| value = frm.pbarprogress.value | |
| end property |
get methods are actually functions which return the current value of the logical property.
the final two members of cprogress are the show and hide methods. these are perhaps the easiest of the bunch, since their function is obvious:
| public sub show() | ||
| frm.show | '** show form and redraw | |
| frm.refresh | ||
| end sub | ||
| public sub hide() | ||
| frm.hide | '** erase form but leave form object in memory | |
| end sub | ||
that's it, the class cprogress is now completely implemented!
| classes vs. instances |
before we begin our discussion of com, let's review the notion of classes, and instances of classes. consider the following client code:
| dim p1 as cprogress, p2 as cprogress, p3 as cprogress | |
| set p1 = new cprogress | ||
| set p2 = new cprogress | ||
| set p3 = new cprogress | ||
| p1.value = 40 | ||
| p2.value = 5 | ||
| p3.value = 99 | ||
| p1.show | ||
| p2.show | ||
| p2.hide | ||
| stop | '** pause client and activate the debugger | |
