如何调用组件内部定义的函数？

Question

设置

我的系统是 KUbuntu 17.10，Qt 5.9。

我有一个 stackview，它实际上包含更多组件，但为了简洁起见，我将它们删掉了。基本上，当 "Return the Item" 按钮被按下时， submitReturnButton 信号在 C++ 端被捕获。捕捉端没有任何状态，它只是尝试发送文本以在标签上设置。

代码

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QObject>
#include <QQuickWindow>

#include "returnserver.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QLatin1String("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty())
        return -1;

    //boilerplate ends here

    QObject *topLevel = engine.rootObjects().value(0);
    QQuickWindow *window = qobject_cast<QQuickWindow *>(topLevel);
    QObject* returnStatusLabel = engine.findChild<QObject*>("returnStatusLabel");

    ReturnServer returner(returnStatusLabel);

    QObject::connect(window, SIGNAL(submitReturnForm(QString)), &returner, SLOT(returnPressed(QString)));
    return app.exec();
}

returnserver.h

#ifndef RETURNSERVER_H
#define RETURNSERVER_H

#include <QObject>
#include <QVariant>
#include <QString>
#include <QQuickWindow>

class ReturnServer : public QObject
{
    Q_OBJECT

    QObject* target;
public:
    ReturnServer(QObject* target, QObject* parent = nullptr);

public slots:
    void returnPressed(const QString& str);
};

#endif // RETURNSERVER_H

returnserver.cpp

#include "returnserver.h"
#include <QString>
#include <QVariant>

ReturnServer::ReturnServer(QObject* target, QObject *parent) :
    target(target),
    QObject(parent)
{

}

void ReturnServer::returnPressed(const QString& str)
{
    //qDebug() << "the signal got to slot correctly";
    QVariant status = "Returned";

//    emit statusReady(QVariant::fromValue(status));
    QMetaObject::invokeMethod(target, "setReturnStatus", Q_ARG(QVariant, status));
}

QML

main.qml 不太相关，只是为了表明该应用程序具有堆栈视图并分解为组件

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.3

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: qsTr("Borrowment terminal")

    signal submitReturnForm(string itemID)

    property int lineEditLength: 120
    background: Rectangle
    {
        id: mainBackground
        color: "gray"
    }

    StackView
    {
        id: stack
        initialItem: returnPageComponent
    }

    Component
    {
        id: returnPageComponent
        ReturnPage{}
    }
}

ReturnPage.qml:

import QtQuick 2.0
import QtQuick.Layouts 1.3
import QtQuick.Controls 2.2

Item {
    id: returnPageView

    ColumnLayout {
        id: returnPageMenu
        x: 213
        y: 99
        width: 200
        height: 282
        Layout.margins: 20

        //redundant, just to make it compile
        Rectangle {
            width: lineEditLength
            height: 40
            color: "white"
            Layout.alignment: Qt.AlignHCenter | Qt.AlignVCenter
            TextInput {
                id: itemIDEdit
                width: parent.width
                height: parent.height
                font.pixelSize: 20
                maximumLength: 8
            }


        }

        //this label I want to set
        Label
        {
            id: returnStatusLabel
            objectName: "returnStatusLabel"
            function setReturnStatus(status) {
                console.log("set return status to " + status)
                ReturnPage.returnStatus = status
            }
            text: "empty"
            width: 100
            height: 20
            Layout.alignment: Qt.AlignHCenter | Qt.AlignVCenter
            font.pointSize: 14

        }

        Button {
            id: returnItemButton
            width: 75
            height: 30
            text: "Return the Item"
            Layout.alignment: Qt.AlignHCenter | Qt.AlignVCenter
            onClicked:  submitReturnForm(itemIDEdit.text)
        }    
    }
}

截图

问题

我怎样才能 invoke/set 将 returnStatusLabel 发送到从 C++ 端发送的某些文本，因为它在不同的组件中？

我试过的

创建 main.qml 中的函数并从 C++ 调用它，并将根对象作为目标。

这确实调用了函数，但未设置文本。我怀疑这是关于没有使用正确的对象，所以关于生命周期。
在标签本身中创建函数，在 C++ 中找到对象并以对象作为参数调用函数

在这种情况下，函数根本没有被调用，尽管调试器没有抱怨连接设置不正确。

Answer 1

代码太多了...解释你的想法的文字很少，因此回答起来很复杂，我可能会完全错过重点。

How can I invoke/set the returnStatusLabel to some text sent from C++ end, given that it is in a different component?

你不能。组件只不过是一个声明，或者更好：一个配置好的工厂来生产某种类型的实例。但是，没有您可以调用函数的此类对象的实例。

但我在另一个组件中没有看到任何蜂鸣声。我只能看到，您犯了从 C++ 端与 QML 端混合的错误。

引用文档：

Warning: While it is possible to use C++ to access and manipulate QML objects deep into the object tree, we recommend that you do not take this approach outside of application testing and prototyping. One strength of QML and C++ integration is the ability to implement the QML user interface separately from the C++ logic and dataset backend, and this strategy breaks if the C++ side reaches deep into the QML components to manipulate them directly. This would make it difficult to, for example, swap a QML view component for another view, if the new component was missing a required objectName. It is better for the C++ implementation to know as little as possible about the QML user interface implementation and the composition of the QML object tree.

正确的方法是在 QML 中创建 ResponseServer 的实例，以便您可以轻松地在此处执行 wireing，或者公开 C++ 生成的实例ResponseServer 作为上下文属性或 QML 的单例实例。
基线是：在 QML 中连接信号。以 properties 的形式提供您可以轻松绑定的值。

如何调用组件内部定义的函数？

How to invoke a function defined inside of a component?

c++

qt

qml

qt5

qtquick2

设置

代码

截图

问题

我试过的