[Interest] Qml Loader initial property setter

[ekke]

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
> <mailto:shaan7in at gmail.com>> wrote:
>
>     Hi,
>
>     Have you tried using the QML Binding Type?
>     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 <mailto: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
>
>         _______________________________________________
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>         Interest at qt-project.org <mailto:Interest at qt-project.org>
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>
>
>
>
>     -- 
>     Shantanu Tushar    (UTC +0530)
>     shantanu.io <http://shantanu.io>
>
>
>
>
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