Is it possible to transmit pointer to model from C

问题:

I have class with QSqlDatabase and with pointer to QSqlTableModel in one class. I use pointer to QSqlTableModel, because initialization of database is going on in constructor and after that I create QSqlTableModel using this database (also in constructor but in heap already).
This class is registered type in qml and so I create it in QML. How is it better to point out TableView to the QSqlTableModel pointer of this class? If it is possible.

回答1:

It is not entirely clear what you're asking. I'm going to assume you want to share a pointer to your model with QML.

1. Have a Q_PROPERTY for it. All Q_PROPERTYs are automatically visible to QML.

   • When returning QSqlTableModel* you need to register that type, too. E.g.

     qmlRegisterUncreatableType<QSqlTableModel>(
         "NameOfModuleInQML", 1, 0, "QSqlTableModel",
         "Cannot instanciate QSqlTableModel from QML");
     

   • Note that you cannot do this then:

     property QSqlTableModel mytabmodel
     

     do this instead if you need to:

     property QtObject mytabmodel
     

2. Return it from a method of a class registered with QML (note that you must return QObject*). This is very likely what you want. E.g.

    class SomeClass : public QObject {
         // ...
    public:
        Q_INVOKABLE QObject *model() {
             return tableModel;
        }
        // ...
    };
   

   Then you can do this in QML:

   TableView {
       model: instanceOfYourclass.model()
       // other bindings
   
       TableViewColumn {
           title: qsTr("Name")
           role: "Name"
           width: 150
       }
   
       // and so on
   }
   

3. You can create a singleton

   QObject *tableModelProvider(QQmlEngine *engine, QJSEngine *scriptEngine)
   {
       (void)engine;
       (void)scriptEngine;
   
       return new QSqlTableModel(...);
   }
   
   qmlRegisterSingletonType<QSqlTableModel>("NameOfModule", 1, 0, "NameInQML", tableModelProvider);
   

   This is a suitable approach if there is and ever will be only one instance of your model and if you don't need much to initialize it.

4. Set your model as a context property

    QQmlEngine engine;
   
    // ..
    engine.rootContext()->setContextProperty("nameInQml", yourTableModelInstance);