Hi James,
Well, I've got the Factory approach pretty much working. My only problem
comes from the newly-created subclass instances. So, I have (on a class
HIDDeviceMouseFactory, which implements interface HIDDeviceFactory):
Function CreateInstance() as HIDDevice
return new HIDDeviceMouse()
End Function
This is registered with a list of factories known to the plugin, as you
described. The CreateInstance function is then called from my plugin via
something like...
REALobject(*CreateInstanceFuncPtr)(REALobject instance) = NULL;
CreateInstanceFuncPtr = (REALobject(*)(REALobject
instance))REALInterfaceRoutine(me->RegisteredDeviceFactories[i],
"HIDDeviceFactory", "CreateInstance");
REALobject UserCreatedDevice = NULL;
// Call the function
if(CreateInstanceFuncPtr) {
UserCreatedDevice =
CreateInstanceFuncPtr(me->RegisteredDeviceFactories[i]);
if (UserCreatedDevice) {
REALLockObject(UserCreatedDevice);
return UserCreatedDevice;
}
}
This correctly calls the factory¹s CreateInstance function in RB, and I do
get a non-NULL UserCreatedDevice back in the plugin (sometimes).
What (I think) I'm finding, however, is that the new HIDDeviceMouse is
created in the RB code in the factory, but it is destroyed before I get
chance to lock it when it is returned to the plugin. The object needs to go
³back in² to the plugin before it is returned from GetNextDevice as a
HIDDevice. Is there some way I can ensure it is not destroyed, so that I
can lock it?
Thank for the help!
Dave.
> From: James Milne <[EMAIL PROTECTED]>
> Reply-To: REALbasic NUG <[email protected]>
> Date: Mon, 24 Apr 2006 10:28:42 +0100
> To: REALbasic NUG <[email protected]>
> Cc: REALbasic NUG <[email protected]>
> Subject: Re: How do I subclass a class with an event?
>
> Dave Addey wrote:
>> Hi NUG,
>>
>> I have an RB plugin, which has a GetNextDevice function that returns a new
>> instance of a class, called HIDDevice. A HIDDevice has one event,
>> DataAvailable. The HIDDevice class is defined in the plugin too.
>>
>> What I need to do in RB code is to subclass the HIDDevice class, so that I
>> can enter some custom code in the subclass DataAvailable event. This is
>> easy enough. What I also need to do is to assign the output of
>> GetNextDevice to an instance of my subclass, and this is causing problems.
>>
>> For example:
>>
>> Dim myHIDDevice as HIDDevice_Mouse // a subclass of HIDDevice
>>
>> myHIDDevice_Mouse = GetNextDevice
>>
>>
>> This second line fails on compilation, with the following error:
>>
>> Type mismatch error. Expected HIDDevice_Mouse, but got HIDDevice.
>>
>> Now, surely, HIDDevice_Mouse is a HIDDevice. So, shouldn¹t this work?
>>
>>
>> I also tried casting the output of GetNextDevice, like this:
>>
>> myHIDDevice = HIDDevice_Mouse(GetNextDevice)
>>
>> This compiles, but causes an IllegalCastException when this code executes in
>> the application. I¹m not sure why.
>>
>> How should I do this?
>
> You can't convert one instance of a HIDDevice into a HIDDevice_Mouse. They are
> different types, even though HIDDevice_Mouse inherits from HIDDevice.
>
> You need to separate your design into two parts. You can, for instance, use a
> Factory pattern approach. Your plugin defines a HIDDeviceFactory interface.
> You can implement that interface in classes in your REALbasic code, so that
> you have a HIDDeviceMouseFactory, HIDDeviceKeyboardFactory, etc. You create
> instances of these factories and register the instances with your plugin. The
> interface would have one method, "CreateInstance() as HIDDevice". In the case
> of the HIDDeviceMouseFactory, you would implement it like so:
>
> Function CreateInstance() as HIDDevice
> return new HIDDeviceMouse()
> End Function
>
> Your plugin would expose a method for registering factories with it, ie
>
> RegisterFactory( deviceType as String, factory as HIDDeviceFactory )
>
> When the REALbasic calls the RegisterFactory function, the plugin would add
> the factory object to an internal list of factories, along with the device
> type. When the plugin came across a HID device that matched that type, it
> would call the factory object to create an instance of the appropriate HID
> Device subtype.
>
> Alternatively, you could split the HIDDevice class into two parts. All
> instances of HIDDevice would have a device handle property which represented
> the actual HID device. You would create instances of HIDDeviceMouse, etc on
> the app side, then attach them to the physical HID device return from the
> plugin.
>
> Created on the REALbasic side: Created on the plugin side:
> HIDDevice --------------------------> HIDPhysicalDevice
> ^
> / \
> HIDDeviceMouse HIDDeviceKeyboard
>
> Imagine you had a HIDDeviceManager class in the plugin which has a
> DeviceAttached() event. You create a subclass of this in REALbasic. You would
> implement this DeviceAttached() event like so:
>
> Class MyHIDDeviceManager
> Sub DeviceAttached( theDevice as HIDPhysicalDevice )
> select case theDevice.type
> case "Mouse"
> Dim mouse as HIDDeviceMouse(theDevice)
> ' Save mouse object somewhere
>
> case "Keyboard"
> Dim keyboard as HIDDeviceKeyboard(theDevice)
> ' Save keyboard object somewhere
> end select
> End Sub
>
> Hope this helps.
>
> --
> Kind regards,
> James Milne
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