Hi.
I'm porting one piece of software from <QtDeclarative> to Qt5's native
<QtQml> module. One obstacle which I've hit so far is the lack of access to
the raw, unprocessed "script text" from QQmlScriptString which was formerly
possible via QDeclarativeScriptString::script. Here is how I use this.
At one side of an application, there's a module which reads description of
"supported objects". These files are written in QML, using custom objects
(so that you cannot instantiate e.g. a Rectangle) -- this is how a sample
file might look like:
frobzinator.qml:
Device {
width: 120
height: 10
name: "Frobzinator"
Property {
name: "price"
type: int
}
Property {
name: "procured"
type: QDateTime
}
validator: price < 666 && procured >= 2012
}
When our application reads this file, it registers the "Frobzinator"
component to be available to the users. They can add new "Frobzinators" to
some canvas, and our app knows that it should let them edit two custom
properties, the "price" and "procured". When users have finished editing,
the app should check that the price is less than 666 units and that the
item was not "procured" before 2012.
As it is right now, the application is using QtDeclarative for parsing the
definitions of the allowed data types. An internal data structure is
created and the actual string "price < 666 && procured >= 2012" is stored
for later use. The GUI of this application is based on QGraphicsScene, and
when it is time to validate the object properties, a throwaway
QDeclarativeExpression is created, we feed its context object actual data
via setContextProperty() calls, and in the end evaluate the expression.
Now, this specific case describes a pretty trivial concept which is
expressible by simple boundary checking, but we want to support more
complicated expressions including function calls to some utility JS
library.
The important feature of this design is that the actual validator script is
passed as plaintext, not as an already compiled JS, and that the
user-created objects have nothing to do with QML. I suspect that this
desing might even be required (the original context objects from
frobzinator.qml are long gone when we get around to calling these
validators) and it's also, IMHO, a good practice to introduce a clear
separation between the "let's parse the supported data formats" and "let's
work with the user-provided data" phases without introducing
interdependencies in there. In Qt4 and Qt5's QtDeclarative compatibility
module, this was easy to do thanks to QDeclarativeScriptString::script().
However, this has moved into the PIMPL in Qt5's QtQml.
Can I somehow access (and reuse in an QQmlExpression later) the raw,
unprocessed script value in Qt5's QtQML? Why was the script() method
removed in Qt5, and would you object to a patch adding it back? Is that
feasible, technically?
With kind regards,
Jan
--
Trojitá, a fast Qt IMAP e-mail client -- http://trojita.flaska.net/
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