C++/QML : How to define and handle multiple contexts for dynamically created components?

Question

基本上我的情况是这样的:

我有一个扩展 QQuickView 的类，它通过设置上下文属性将某些对象从 C++ 公开到 QML。显示的 View 是从 QML 创建的，并且都是同一定制组件的不同实例；当某些事件发生时会创建新 View ，当这种情况发生时，现有 View 应显示最初在 C++ 端分配给它们的对象，而新 View 应显示分配给它们的对象。

所以，在 C++ 方面，我有这样的东西:

WindowManager::WindowManager(QQuickView *parent) :
QQuickView(parent)
{
      // Setting the source file to use
      this->setSource(QUrl("qrc:/qml/main.qml"));

      // Exposing the istance of this class to QML for later use
      this->rootContext()->setContextProperty("qquickView", this);

      // Calling the method that will create dynamically a new view that will be child of main.qml; the parameter is not important, just a random number to start with
      this->prepareNewView(3)

      this->showFullScreen();
}

WindowManager::prepareNewView(int stuffId)
{
      MyDatabase db;

      // Getting something to show in QML from somewhere based on the parameter received
      SomeStuff stuff = db.getStuff(stuffId)

      // Exposing the object I need to show in QML
      this->rootContext()->setContextProperty("someStuff", stuff);



      QObject *object = this->rootObject();

      // Here I'm invoking a function from main.qml that will add a new view dynamically
      QMetaObject::invokeMethod(object, "addView");
}

现在，在 QML 端我有一个像这样的主文件:

// main.qml
Rectangle {
    id: mainWindow
    width: 1000
    height: 1000

    // This function adds a component to mainWindow
    function addView()
    {
        // Creating the component from my custom made component
        var component = Qt.createComponent("MyComponent.qml");

        // Creating an istance of that component as a child of mainWindow
        var newView = component.createObject(mainWindow);


        // ... Now I would be doing something with this new view, like connecting signals to slots and such
    }
}

然后我得到了我的自定义组件，这是将动态创建的 View :

// MyComponent.qml
Rectangle {
    id: customComponent

    // Here I would be using the object I exposed from the C++ side
    x: someStuff.x
    y: someStuff.y
    width: someStuff.width
    height: someStuff.height

    // Here I'm creating a MouseArea so that clicking this component will cause the creation of another view, that will have to show diffrent things since the parameter I'm passing should be different from the starting parameter passed in the constructor of WindowManager
    MouseArea {
        anchors.fill: parent
        onClicked: qquickView.prepareNewView(Math.random())
    }
}

现在，一切照原样，一开始它会显示 id 为 3 的“东西”，这是作为主上下文的上下文属性公开的。

但是，如果我单击 MouseArea，假设将传递 3 以外的 id，将公开一个具有相同名称的新上下文属性，从而导致覆盖旧属性。这意味着第一个 View 现在将显示刚刚暴露的“东西”，而不是基于 stuffId 等于 3 的“东西”，而我需要的是第一个 View 继续显示它应该显示的内容(“东西” "with id = 3), 以及以后出现的任何其他 View 对应于它们的 id 的东西。

发生这种情况是因为我在每个组件共有的上下文中定义了一个属性，而我应该定义一个仅对动态创建的组件的新实例可见的属性。但我该怎么做呢？

在文档中我读到可以直接从 C++ 创建一个组件并定义它应该使用的上下文...像这样(摘自 here 的片段):

QQmlEngine engine;
QStringListModel modelData;
QQmlContext *context = new QQmlContext(engine.rootContext());
context->setContextProperty("myModel", &modelData);

QQmlComponent component(&engine);
component.setData("import QtQuick 2.0\nListView { model: myModel }", QUrl());
QObject *window = component.create(context);

我认为这对我打算做的事情有用。每当我从 C++ 创建一个新 View (由单击 MouseArea 引起)时，我都会创建一个以“someStuff”作为其属性的新上下文，以便每个 View 都有自己的“东西”......但我需要访问从 QML 新创建的 View ，因为在我在 main.qml 中的 addView() 函数中创建它之后，我访问该 View 以执行某些操作(不重要的是)，如果我从 C++ 创建组件的 istance我不知道如何从 QML 访问它...有没有办法将组件从 C++ 传递到 QML 以便访问它？

我不知道如何解决这个问题或找到另一种方法来动态创建具有自定义内容的 View ，同时所有内容都可见...欢迎任何建议。

Answer 1

我实际上发现直接将用 C++ 创建的组件传递给 QML 是可能的(而且很容易)。

所以现在，我几乎像这样修改了代码:

WindowManager::prepareNewView(int stuffId)
{
    MyDatabase db;

    // Getting something to show in QML from somewhere based on the parameter received
    SomeStuff stuff = db.getStuff(stuffId)


    // Creating the new context, based on the global one
    QQmlContext *context = new QQmlContext(this->rootContext());


    // Exposing the object I need to show in QML to the new context
    context ->setContextProperty("someStuff", stuff);

    // Creating the component
    QQmlComponent component(this->engine(), QUrl("qrc:/qml/MyComponent.qml"));

    // Creating the istance of the new component using the new context
    QQuickItem *newView = qobject_cast<QQuickItem*>(component.create(context));


    // Getting the root component (the Rectangle with it mainWindow)
    QObject *object = this->rootObject();

    // Manually setting the new component as a child of mainWIndow
    newView->setParentItem(qobject_cast<QQuickItem*>(object));

    // Invoking the QML that will connect the events of the new window, while passing the component created above as QVariant
    QMetaObject::invokeMethod(object, "addView", Q_ARG(QVariant, QVariant::fromValue(newView)));
 }

在 QML 中，main.qml 中的函数现在是这样的:

// Function called from C++; the param "newView" is the last component added
function addView(newView)
{
    // ... Here I would use the new view to connect signals to slots and such as if I created "newView" directly in QML
}

所以我毕竟没有对代码进行过多更改。