[Development] Another method of registering QML types

[Alan Alpert]

On Thu, Nov 8, 2012 at 3:58 PM, BRM <bm_witness at yahoo.com> wrote:
> ----- Original Message -----
>
>> From: Alan Alpert <416365416c at gmail.com>
>> On Thu, Nov 8, 2012 at 12:49 PM, BRM <bm_witness at yahoo.com> wrote:
>>>>  From: Alan Alpert <416365416c at gmail.com>
>>>
>>>>  To: development <development at qt-project.org>
>>>>  Cc:
>>>>  Sent: Thursday, November 8, 2012 12:57 PM
>>>>  Subject: [Development] Another method of registering QML types
>>>>
>>>>  Currently, there is no way to register QML files as types from C++.
>>>>  This is the exact same functionality that qmldir provides, but I think
>>>>  there are situations where you'll want to do this progamatically
>>>>  instead of with a qmldir file. There is a very specific example I have
>>>>  in mind: Platform Components.
>>>>
>>>>  I'm suggesting another qmlRegisterTypes function, one that takes a
>> URL
>>>>  instead of a C++ type:
>>>>
>>>>  qmlRegisterType(const char* url, const char *uri, int versionMajor,
>>>>  int versionMinor, const char *qmlName).
>>>>
>>>>  https://codereview.qt-project.org/#change,39135 is a proof of concept
>>>>  implementation.
>>>>
>>>>  This would allow for a platform component import which looks like this:
>>>>  if(platform=="desktoplinux")
>>>>
>> qmlRegisterType("/usr/share/desktop/components/Button.qml", uri,
>>>>  2, 0, "Button");
>>>>  else if (platform=="meego")
>>>>      qmlRegisterType("/usr/share/meego/components/Button.qml",
>> uri, 2,
>>>>  0, "Button");
>>>>  ...
>>>>
>>>>  Except that the strings would also be generated procedurally, instead
>>>>  of having a dozen lines of code per component type.
>>>>
>>>>  The function isn't strictly for that usecase, there are other cases
>>>>  where you might want dynamically directed types. The other case that
>>>>  comes to mind is if you have an application with built-in types and
>>>>  you want to add a file from qrc as a type to outside files (or
>>>>  vice-versa). It would be nice to hear other usecases if anyone has
>>>>  them, to ensure this API can meet those requirements.
>>>>
>>>>  Any comments on this suggested addition to the QtDeclarative public
>> API?
>>>
>>>  Sounds interesting. Here's another potential use case: server-side
>> interface definitions.
>>>
>>>  I have a system now where QML (actually its predecessor QtScript) was of
>> interest to me (haven't gotten to using it yet) so that I could put
>> interfaces for the system in a (trusted) server component.
>>>  The generic (multi-system, multi-customer) user interface would have
>> theoretically downloaded the interface descriptions (e.g. QML files) and then
>> loaded them.
>>>  I never did it at the time as I hadn't figured out the storage side,
>> and got into doing some custom widgets for some of the functionality.
>>>
>>>  >From this perspective it would be useful to be able to hand it a
>> QByteArray containing a QML file, or http/ftp/custom URLs for remote QML file
>> access.[1]
>>>
>>>  One thought - it would probably be good to have a function that could
>> return other URLs that would also need to be loaded for successful use, perhaps
>> as an error condition, or qmlRegisterType() would need to be able to read the
>> embedded URLs and recurse to do the same.
>>>
>>>  As I haven't gotten into using QML yet, I don't know how well QML
>> would meet that kind of use. It'd be a really cool one to support though.
>>>
>> I think this is already supported, in that the URL transparency of QML
>> means that if you have local assets with a remote file, it should
>> automatically load the assets remotely to go with it. I might need a
>> more specific example of what you mean if you're talking about
>> something not already supported, but I know the following is
>> supported:
>> If you have a http://remote/Image.qml with code like Image { source:
>> "graphic.png" } the png will be fetched transparently.
>
> As I said, i have not had the chance to play with QML. So if what I said is already supported great!
>
> Now, in my hypothetical case, I was planning on storing the dialog description probably as text within the server somehow. I never got to those details;
> but the server I have does not present a normal URL style interface - that is, it's not an http server but a specific application server with a proprietary XML protocol;
> so a client application would have to request the data and receive a big XML blob with the QML-based dialog and then somehow load it - thus it would be nice to be able to detect any imports not loaded so that it would be able to retrieve and load them.
>
> Any how...that is just a hypothetical, but one that may be very useful to consider if people are not doing that already. If I had the time, I'd probably invest more into QML and do just I described; but I'd still have to figure out the server-side storage and transport issues for my server. (A web server is not an option; though if sftp is support, that would be.) Any how...enough dreaming...

I think for that usecase you'd be adding a custom network access
manager that processes your special application protocol. But so long
as the URLs can be parsed like file paths (don't know how it would
handle ? parameters) I think that should work already.

--
Alan Alpert