[Interest] Qml Loader initial property setter

[Jérôme Godbout]

Thanks for pointing this out, but I was aware of that. Sometime a default
value is impossible (null) making bad behavior or bad binding, primitive
type can always have default value that make sense that way but complex
object don't.
It's sad that the imperative setSource() function can set those property
and the declarative way is not.

On Sun, Apr 3, 2016 at 11:10 AM, ekke <ekke at ekkes-corner.org> wrote:

> if you want to refer to a property as 'model.i' and there are situations
> where 'model' doesn't exist always,
> it's easy to avoid error messages:
>
> model? model.i : 42
>
> this way you can set a default value while model is null
> (haven't tried this yet with Qt 5.6 but I'm doing it this way in
> BlackBerry 10 Cascades)
>
> ekke
>
> Am 01.04.16 um 16:05 schrieb Jérôme Godbout:
>
> Yes, but the binding loaded object internal binding are printing error,
> since the object is created without the input, then the external binding
> are created. They will get eventually correct, but the console will be
> filled with error message and I try to avoid that at all cost. Here's a
> simple example that will complain about unable to access i and j of
> undefined / assign undefined to width and height (this example is a bit
> stupid but just a demo to show the problems with more complex model and
> object):
>
> // MyComponent.qml
> Item
> {
>  property var model
>  width: model.i
>  height: model.j
> }
>
> // Main.qml
> MyModel
> {
>   id: myModel_
>   property int i: 24
>   property int j: 12
> }
>
> Loader
> {
>   id: loader_
>   source: "MyComponent.qml"
> }
>
> Binding
> {
>   target: loader_.item
>   property: 'model'
>   value: myModel_
>   when: loader_.status == Loader.Ready
> }
>
> What I would like is the Loader call QQmlComponent::beginCreate(), then
> having a hook to init some property then the Loader can finish the
> component QQmlComponent::completeCreate(). This way I was able to make it
> work, but having a custom component for that is a bit annoying.
>
> Loader
> {
>   source: "MyComponent.qml"
>   onInitProperty:  // signal emit with component object returned by
> beginCreate(),
>   {
>     object.model = Qt.binding(function(){ return myModel_; });
>     ...
>   }
> }
>
> That seem clean and would avoid the problems to have object into bad state
> for a brief moment.
>
> Jerome
>
> On Fri, Apr 1, 2016 at 12:04 AM, Shantanu Tushar <shaan7in at gmail.com>
> wrote:
>
>> Hi,
>>
>> Have you tried using the QML Binding Type?
>> <http://doc.qt.io/qt-5/qml-qtqml-binding.html>
>> http://doc.qt.io/qt-5/qml-qtqml-binding.html
>>
>> On Thu, Mar 24, 2016 at 11:11 PM, Jérôme Godbout < <jerome at bodycad.com>
>> jerome at bodycad.com> wrote:
>>
>>> Hi,
>>>
>>> I was wondering if I am the only one who found the initial property of a
>>> source based Loader Item a bit annoying. inline sourceComponent with
>>> Component {} declaration are well ok on the other hand. I'm explaining
>>> myself, when using a loader you have 2 choice to set the initial binding on
>>> created item:
>>>
>>> 1- On item changed set the binding
>>>
>>> *Loader*
>>> *{*
>>> *  source: externalObj.getSrc() // return something like "myItem.qml"*
>>> *  onItemChanged:*
>>> *  {*
>>> *    if(!item) return;*
>>> *    item.myprop = Qt.binding(function(){ return myExternalProperty; })*
>>> *  }*
>>> *}*
>>>
>>> 2- use the setSource() function instead of the source directly
>>>
>>> *Loader*
>>> *{*
>>> *  property url myDummySrc: externalObj.getSrc()*
>>> *  onMyDummySrcChanged:*
>>> *  {*
>>> *     setSource(myDummySrc, { 'myprop': Qt.binding(function(){ return
>>> myExternalProperty; }) });*
>>> *  }*
>>> *}*
>>>
>>> This is rather annoying and ugly. Number 1 is also having the problem
>>> where *myItem.qml* must be able to handle *myprop *to have a default
>>> value or being empty without output a lots of console error. Number 2 work
>>> well and is the solution I find myself writing often. I was wondering if a
>>> Loader that support a dictionary of initial property when source changed
>>> would be nice:
>>>
>>> *Loader*
>>> *{*
>>> *  source: externalObj.getSrc()*
>>> *  initialProperties: { 'myprop': Qt.binding(function(){ return
>>> myExternalProperty; })  }*
>>> *}*
>>>
>>> What do you think?
>>> Jerome
>>>
>>> _______________________________________________
>>> Interest mailing list
>>> Interest at qt-project.org
>>> http://lists.qt-project.org/mailman/listinfo/interest
>>>
>>>
>>
>>
>> --
>> Shantanu Tushar    (UTC +0530)
>> shantanu.io
>>
>
>
>
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