Unable to change bools in C++ struct

[mzimmers]

@JoeCFD no problem. But it's weird, isn't it?

[JonB]

@mzimmers said in Unable to change bools in C++ struct:

I also tried reducing this to a minimal example, but that worked (ugh).

This really means you need to start from such a good situation, or from a bad situation, and work towards the other. Till you can produce a "this works, and with this tiny change that does not work".

[GrecKo]

@mzimmers
Do a copy of your schedule before modifying it and assign it back when you are done.

[mzimmers]

@GrecKo this:

    Component.onCompleted: {
        var tempSchedule = newSchedule
        console.log("ScheduleScreen.qml: newSchedule is " + newSchedule)
        tempSchedule.name = "xxx"
        tempSchedule.m_maintenance = true
        tempSchedule.timeOffset = 55
        tempSchedule.timeFrame = ScheduleEnums.TIMEFRAME_DAILY;
        newSchedule = tempSchedule
        console.log("ScheduleScreen.qml: tempSchedule is " + tempSchedule)
        console.log("ScheduleScreen.qml: newSchedule is " + newSchedule)
    }

Produces this:

qml: ScheduleScreen.qml: newSchedule is Schedule({00000000-0000-0000-0000-000000000000}, , {00000000-0000-0000-0000-000000000000}, false, false, , START_ACTION_TURN_ON, END_ACTION_TURN_OFF, START_WHEN_TIME_OF_DAY, END_WHEN_TIME_OF_DAY, 09:00:00.000, 17:00:00.000, TIMEFRAME_WEEKLY, REPEAT_EVERY_WEEK, , , , 0, )
qml: ScheduleScreen.qml: tempSchedule is Schedule({00000000-0000-0000-0000-000000000000}, xxx, {00000000-0000-0000-0000-000000000000}, false, false, , START_ACTION_TURN_ON, END_ACTION_TURN_OFF, START_WHEN_TIME_OF_DAY, END_WHEN_TIME_OF_DAY, 09:00:00.000, 17:00:00.000, TIMEFRAME_DAILY, REPEAT_EVERY_WEEK, , , , 55, )
qml: ScheduleScreen.qml: newSchedule is Schedule({00000000-0000-0000-0000-000000000000}, xxx, {00000000-0000-0000-0000-000000000000}, false, false, , START_ACTION_TURN_ON, END_ACTION_TURN_OFF, START_WHEN_TIME_OF_DAY, END_WHEN_TIME_OF_DAY, 09:00:00.000, 17:00:00.000, TIMEFRAME_DAILY, REPEAT_EVERY_WEEK, , , , 55, )

So...no change. Really odd, isn't it?

[mzimmers]

@JonB agree completely, though I'm not sure what the next step is, given how "close to the top" this code is. It probably has something to do with how I coded my struct, but I sure can't see what might be doing this.

[fcarney]

@mzimmers when I get strange stuff not working I do a clean, run qmake, build. Sometimes it is just a moc issue. Not sure how that works with cmake though.

[mzimmers]

@fcarney tried that -- same results. Good suggestion, though.

[mzimmers]

OK, so I discovered something, but I don't understand it. I stepped through this in the debugger, and confirmed the problem is in the C++ side:

Then, for lack of anything else to try, I removed the initializer in my struct:

// bool m_maintenance = false; // before
bool m_maintenance; // now

and...

For another test, I added this line to my c'tor:

bool m_maintenance = false;

And got the original (bad) result.

I also "changed polarity" (initialize to true; try to set to false) with the same (bad) result.

So...this problem just got a little bigger. I'm not willing to release code to the field that creates structs with uninitialized values; I need to figure out what's going on here.

EDIT: this occurs on 6.6 as well as 6.5.3.

ANY ideas, no matter how far-fetched, are welcome. Thanks...

[JoeCFD]

Check this out.
https://stackoverflow.com/questions/1069621/are-members-of-a-c-struct-initialized-to-0-by-default
It may not be a C++ problem. Instead it is a C problem. Struct is very C style. I even avoid using it.

[mzimmers]

@JoeCFD interesting article, though my issue is with modification, not initialization.

Regarding the use of structs: I suppose I could use a class, but I'd be astonished if that made a difference. I'm deliberately avoiding using QObject here, too.

[JoeCFD]

@mzimmers bool m_maintenance; // now
is undefined.

can you try:
bool m_maintenance{ false };
I do not know if it will make a difference.

[mzimmers]

@JoeCFD said in Unable to change bools in C++ struct:

@mzimmers bool m_maintenance; // now
is undefined.

I realize that, and that's not acceptable. But currently I have the options of leaving it undefined, or initializing it and (somehow) making it QML-immutable in the process.

I can't even modify it if I initialize it in QML, like this:

    property schedule newSchedule: ({ "maintenance": false })

[mzimmers]

@JoeCFD said in Unable to change bools in C++ struct:

can you try:
bool m_maintenance{ false };

Same (bad) result. Thanks for the suggestion, though.

[JoeCFD]

@mzimmers
try
class Schedule

not struct Schedule
.

[mzimmers]

@JoeCFD no change in behavior.

[GrecKo]

@JoeCFD struct is just a class where everything is public by default.

[GrecKo]

@mzimmers what's the issue on this output? We don't know which field is which. Also why are you using m_maintenance in QML? That's not the name of your property.

[mzimmers]

@GrecKo I don't know how that got in there, but that wasn't how it was originally, and it's not how it is now. My screenshots above are correct.

[mzimmers]

OK, guys - here's a minimal repeatable example:

// schedule.h
#pragma once

#include <QObject>
#include <QMetaType>
#include <QtQml/qqmlregistration.h>
#include <QtQmlIntegration/QtQmlIntegration>

struct Schedule
{
    Q_GADGET
    QML_VALUE_TYPE(schedule)
    QML_STRUCTURED_VALUE
    Q_PROPERTY(bool maintenance MEMBER m_maintenance)
public:
    bool m_maintenance;
    Q_INVOKABLE Schedule() {}
    bool operator ==(const Schedule &rhs) const {return true;}
};

// Main.qml
import QtQuick
import QtQuick.Controls
import QtQuick.Layouts
import QtQuick.Window

Window {
    id: mainWindow
    width: 640
    height: 480
    visible: true

    property schedule newSchedule: ({  })

    Switch {
        onClicked: {
            console.log("switch is " + checked)
            newSchedule.maintenance = checked
            console.log("newSchedule.maintenance is " + newSchedule.maintenance)
        }
    }
}

Output:

qml: switch is true
qml: newSchedule.maintenance is false
qml: switch is false
qml: newSchedule.maintenance is false
qml: switch is true
qml: newSchedule.maintenance is false
qml: switch is false
qml: newSchedule.maintenance is false

I can provide the cmake file as well if desired, but it doesn't contain anything unusual.

[GrecKo]

@mzimmers said in Unable to change bools in C++ struct:

bool operator ==(const Schedule &rhs) const {return true;}

If you remove this non-sensical operator== your code works as expected.

My guess is that the engine modifies a temp Schedule internally, checks the equality and assign it only if it's different. As it's always equal it won't modify it.