updating elements in a repeater?

mzimmers

@kshegunov said in updating elements in a repeater?:

Because I assume that at some later time you/I/whoever are/am/is going to want to tie it with a C++ backend. So, I'd rather not stick to QtQuick items, but either directly expose an array of QObejcts or define a QAbstractItemModel and use that.

Agreed 100%. In this spirit, I'm trying to restructure my application like this:

I have a struct Bottle, based on Q_GADGET. This contains information intrinsic to the bottle (size, dimensions, contents, etc.).
I have a class ReagentManager that contains a private QVector of Bottles. An object of this class is registered as a context property to make it visible to the QML.
One QML view contains a repeater for bottles, containing UI-specific information (size, screen location).

So...while my ReagentManager class is visible to the QML, the QVector of Bottles is not. I can write Q_INVOKABLE access routines for each of them, but I'm curious as to whether there might be a better way of doing it.

Thanks for any input.

My C++ code maintains an instance of the class ReagentManager, so I'm confident that its contents are always current. Now: how best to do something like this:

kshegunov

@mzimmers said in updating elements in a repeater?:

So...while my ReagentManager class is visible to the QML, the QVector of Bottles is not. I can write Q_INVOKABLE access routines for each of them, but I'm curious as to whether there might be a better way of doing it.

Make the bottles QObject instead of them being Q_GADGET and expose their properties (look up the Q_PROPERTY docs and be sure to have the notification signals). After that the QML part remains pretty much the same, the change in the QObject is going to be reflected naturally into the QML scene without anything more than you binding the properties on creation.

mzimmers

@kshegunov thanks. I'm still a little UNclear on the binding details; what would be an example of a bind using your code above?

kshegunov

Bottle {
    cellX: modelData.x //< If modelData is QObject, this is a property binding
    cellY: modelData.y
    cellColor: modelData.color
}

mzimmers

@kshegunov

Trying this:

struct Bottle : public QObject {
  Q_OBJECT
  Q_PROPERTY(quint32 volume MEMBER m_volume NOTIFY volumeChanged)
  Q_PROPERTY(quint32 minVolume MEMBER m_minVolume NOTIFY minVolumeChanged)
  Q_PROPERTY(quint32 amountNeeded MEMBER m_amountNeeded NOTIFY amountNeededChanged)
  Q_PROPERTY(int slotNumber MEMBER m_slotNumber)
  Q_PROPERTY(QString name MEMBER m_name)
  Q_PROPERTY(ReagentBottleType bottleType MEMBER m_bottleType)

 public:
  // needed to represent amounts in int, not float
  // because using floats causes a float-equal error
  // in the generated MOC file.
  quint32 m_volume;                // amount in bottle (in uL)
  quint32 m_minVolume;             // amount in bottle that can't be used (in uL)
  quint32 m_amountNeeded;          // amount needed for synth (in uL)
  int m_slotNumber;                // still figuring this one out
  QString m_name;                  // name of the reagent
  ReagentBottleType m_bottleType;  // bottle type.
signals:
  void volumeChanged();
  void minVolumeChanged();
  void amountNeededChanged();
};

Getting this when I try to build:

/home/mzimmers/git/KOL-UI/src/lib/change_consumables/reagent_manager.h:11: error: use of deleted function ‘QObject::QObject(const QObject&)’
In file included from /home/mzimmers/git/KOL-UI/src/lib/change_consumables/reagent_manager.cpp:7:0:
/home/mzimmers/git/KOL-UI/src/lib/change_consumables/reagent_manager.h:11:8: error: use of deleted function ‘QObject::QObject(const QObject&)’
 struct Bottle : private QObject {
        ^~~~~~

Do I have to convert Bottle from a struct to a C++ class?

eyllanesc

@mzimmers QObject is not copyable so you have to remove the copy constructor from Bottle.

kshegunov

@mzimmers said in updating elements in a repeater?:

Do I have to convert Bottle from a struct to a C++ class?

No, but you can't keep the objects in a QVariantList, because QObjects can't be copied. You need to switch to QList<QObject *>.

PS.
Additional notes:

The notifier signals should report the new value of the property (look up the documentation examples).
If you need to compare floats, then you should probably stick to defining your own setters and getters and registering them with READ/WRITE in the Q_PROPERTY definition instead of relying on MEMBER.

mzimmers

@kshegunov said in updating elements in a repeater?:

No, but you can't keep the objects in a QVariantList, because QObjects can't be copied.

I must be going crazy, but...where in my struct am I using QVariantList?

Thanks for the note about including the new values in the signals.

I'm avoiding floats for the reason you cited, plus a couple more.

kshegunov

@mzimmers said in updating elements in a repeater?:

I must be going crazy, but...where in my struct am I using QVariantList?

Nowhere, but how do you marshal the objects to QML?

mzimmers

@kshegunov said in updating elements in a repeater?:

@mzimmers said in updating elements in a repeater?:

I must be going crazy, but...where in my struct am I using QVariantList?

Nowhere, but how do you marshal the objects to QML?

Well, like this (I think this is what you're asking):

    Column {
      id: myColumn
      Repeater {
        id: bottleRepeater
        model: bottleModel
        Bottle {
          cellX: model.x
          cellY: model.y
          cellHeight: model.height
          cellWidth: model.width
          volume: model.volume
          bottleScaleFactor: scaleFactor
        }

But if I'm doing something wrong in QML, why is the compiler giving me an error pointed at my struct?

kshegunov

@mzimmers said in updating elements in a repeater?:

Well, like this (I think this is what you're asking):

I mean from the C++ side. What is bottleModel and where does it come from?

mzimmers

From the same QML file:

  ListModel {
    id: bottleModel

    ListElement {
      // position 1
      x: 400
      y: 17
      height: 75
      width: 75
    }
    ...

kshegunov

This is confusing, I thought the data is supposed to come from C++.

mzimmers

I know, I'm doing a lousy job of explaining this. in C++:

typedef QVector<Bottle> Bottles;
class ReagentManager : public QObject {
  Q_OBJECT
 private:
  Bottles m_bottleList;
}
<in another file>
  ReagentManager m_reagentManager;
  engine->rootContext()->setContextProperty("reagentManager", &m_reagentManager);

In QML:

    onVisibleChanged: {
      if (visible) {
        reagentManager.updateBottleList()
        rack.updateBottles()
      }
    }

    // update our QML array based on the C++ model.
    function updateBottles() {
      var modelSize = bottleModel.count
      var i
      var l_color
      var volume
      var minVolume
      var amountNeeded
      var name

      for (i = 0; i < modelSize; ++i) {
        name = reagentManager.getName(i)
        bottleRepeater.itemAt(i).cellText = name

        volume = reagentManager.m_volume
        minVolume = reagentManager.getMinVolume(i)
        amountNeeded = reagentManager.getAmountNeeded(i)
        l_color = ((volume - minVolume) >= amountNeeded) ? "green" : "red"
        bottleRepeater.itemAt(i).cellColor = l_color
      }
    }

So, my QML function calls C++ routines to obtain the needed data. I'm trying to convert this to the approach you suggested; this is where I ran into the problem with the struct.

I still don't see where the QVariantList comes into play, though.

kshegunov

typedef QVector<Bottle> Bottles;

If Bottle is derived from QObject you can't keep it directly in a vector (can't copy the objects). You need to keep Bottle * there.

mzimmers

@kshegunov ah. OK, thanks for that. I'll look into making that change, and will report back.

mzimmers

I've changed my QVector to pointers (seems to be working).

I think I see why my example is so confusing -- in my Bottle Repeater, I'm using a QML ListModel. This ListModel only contains UI-specific information (position, size). Additional informationmust come from an object (ReagentManager) that is exposed via a call to setContextProperty().

So: do I need to change my model to the instance of ReagentManager, and find another way to access the information currently in my ListModel? Or is there a more clever way to do this?

Thanks...

kshegunov

@mzimmers said in updating elements in a repeater?:

So: do I need to change my model to the instance of ReagentManager, and find another way to access the information currently in my ListModel? Or is there a more clever way to do this?

Why do you need the ListModel is the question now. Pass the objects vector from the context property (i.e the bottleManager object) directly to the repeater.

mzimmers

@kshegunov said in updating elements in a repeater?:

Why do you need the ListModel is the question now. Pass the objects vector from the context property (i.e the bottleManager object) directly to the repeater.

I'm using the list model for UI-specific information:

  ListModel {
    id: bottleModel

    ListElement {
      // position 1
      x: 400
      y: 17
      height: 75
      width: 75
    }
    ...

I could probably put this data in arrays in QML. As I mentioned, I'd prefer not to put it into my C++ as it's purely UI data.

From my definition of the ReagentManager class:

class ReagentManager : public QObject {
  Q_OBJECT
 public:
  explicit ReagentManager(QObject *parent = nullptr);
  Bottles m_bottleList;
  Q_PROPERTY(Bottles bottleList MEMBER m_bottleList)
  ...

And in my QML:

    function updateBottles() {
      var modelSize = bottleModel.count
      var i
      var volume

      for (i = 0; i < modelSize; ++i) {
        volume = reagentManager.bottleList[i].volume
    ...

I'm getting an error "TypeError: Cannot read property '0' of undefined." Is my syntax wrong, or am I still not understanding how to access the property?

Thanks...

EDIT: looking at the QML Debugger Console, I see this message:

QMetaProperty::read: Unable to handle unregistered datatype 'Bottles' for property 'ReagentManager::bottleList'

kshegunov

@mzimmers said in updating elements in a repeater?:

I could probably put this data in arrays in QML. As I mentioned, I'd prefer not to put it into my C++ as it's purely UI data.

You already have this data in the c++, you feed it to the JS engine as far as I can see. I'd just tie the cpp backend to the UI stuff and not mess with any intermediate stuff, much less using explicit JS code.

Basically like this:

Column {
      Repeater {
        model: reagentManager.bottleList //< This being a property that holds the list of bottles
        Bottle {
          cellX: modelData.x
          cellY: modelData.y //< Or use some other value, or nothing, however you decide to do it
          ...
          volume: modelData.volume //< This binds to the property of the QObject, so when the C++ changes value this updates
          ...
        }
     ...
}

@mzimmers said in updating elements in a repeater?:

I'm getting an error "TypeError: Cannot read property '0' of undefined." Is my syntax wrong, or am I still not understanding how to access the property?
Thanks...
EDIT: looking at the QML Debugger Console, I see this message:

From the method:

https://doc.qt.io/qt-5/qqmllistproperty.html
or
you return QList<QObject *>
or
you return a QVariantList() << bottle1 << bottle2

... different possibilities.