[Interest] Issues with QML binding

[Nibedit Dey]

Thank you for your inputs.
The values are fetched only once and assigned to the *Text *element.
This doesn't require any notification later as the data doesn't change in
the app's lifetime.
Hence, I haven't used Q_PROPERTY and notification signals. However, the
*getStringData()* has some logic inside it before returning the string.

This issue is sometimes seen in low-end embedded hardware and does
not appear at all in desktop and high-end embedded devices. I know the
issue can be fixed by using Q_PROPERTY and notification signals,
but I am trying to understand what might be going wrong in low-end embedded
hardware. Debugging is not helping much here as it is not repeatedly
reproducible.
It seems like there is some sync issue with Q_INVOKABLE method execution
time and QML creation in some low-end hardware.

For example, if I want to show the version number of an application by
invoking a C++ function like below:
text: "Version:" + *backendCPP.getVersion()*
Do you see any problem with the above line?

Thanks & Regards,
Nibedit

On Thu, Jul 29, 2021 at 11:18 PM Alexander Dyagilev <alervdvcw at gmail.com>
wrote:

> *backendCPP.getStringData() is  a method. You can't bind it. You should
> use propery (Q_PROPERTY) and bind to it *
> *instead. *
> On 7/27/2021 6:50 PM, Nibedit Dey wrote:
>
> Dear All,
>
> I recently came across a strange issue related to QML binding.
> The issue is not reproducible often which makes it difficult to find the
> root cause.
>
> Sample QML code:
> Case 1: *text : "Retrieved details"+ backendCPP.getStringData()
>  //Sometimes, the complete string is empty*
> *Case 2: property string someString : backendCPP.getStringData()*
> *text: **"Retrieved details:"+** someString // Displays **Retrieved details:
> value remains empty*
>
> 99% time, the value is fetched and displayed properly in Text element.
> Rarely, it remains empty.
> Here backendCPP is a C++ instance exposed through context property and
> an invokable method is used to fetch data. Notify signal is not used in
> this case.
> I believe during failure cases the data is not retrieved from backendCPP,
> when binding happened due to delay in the invokable method. Is my
> assumption correct?
> Although we can handle the issue in multiple ways including using a NOTIFY
> signal or using Qt.binding, I am curious if anyone has observed this issue.
> Please share your inputs.
>
> Thanks & Regards,
> Nibedit
>
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