Re: [xmlvm-users] Optional Methods in C-Backend

[Panayotis K. <pan...@pa...>]

On 05 Μαϊ 2011, at 11:35 π.μ., Markus Heberling wrote:

> Hi,
> 
> I'd like to use a UITableViewDelegate with the C Backend. Some methods in that class are optional. XMLVM generates stubs for the, that throw the XMLVM_NOT_IMPLEMENTED Error:
> 
> JAVA_FLOAT org_xmlvm_iphone_UITableViewDelegate_heightForRowAtIndexPath___org_xmlvm_iphone_UITableView_org_xmlvm_iphone_NSIndexPath(JAVA_OBJECT me, JAVA_OBJECT n1, JAVA_OBJECT n2)
> {
>     //XMLVM_BEGIN_WRAPPER[org_xmlvm_iphone_UITableViewDelegate_heightForRowAtIndexPath___org_xmlvm_iphone_UITableView_org_xmlvm_iphone_NSIndexPath]
>     XMLVM_NOT_IMPLEMENTED();
>     //XMLVM_END_WRAPPER
> }
> 
> I can override all of the methods, of course, but I rather would leave them out. What would be the correct way to handle optional methods?
> 
> Markus

I can't help you with the C backend, but I'll describe a bit what I did in the same case with the ObjC backend, so that the C Gurus here could advise the correct answer.

The problem is, there is no "default" value for these (and all similar) methods. Moreover, the iOS would behave different, when these methods are present, and do something else, when these methods are missing. 

What I did on the ObjC backend was to do something similar to what (I believe) Apple does.
First of all, *all* ObjC delegate methods exist and all point to their Java counterpart.
Then the method that answers to the ObjC runtime if this method exists (i.e. respondsToSelector) is overridden. If an actual Java-based implementation exists, then respondsToSelector responds that the actual ObjC delegate selector exists (although the ObjC selector *always* exist). If it doesn't then it replies that this method does not exist.

WIth such a trick it is possible to properly inform the UITableView that an optional *Java* method exist, and have the desired/correct behavior.