如何从其他QML文件及C++页面修改Label的文本内容？

Alright, let's tackle your two requirements step by step: modifying the labelname text from main.qml, and updating it via a C++ signal. Here's how you can do both:

1. Update labelname Text from main.qml #

First, you need to expose the labelname's text property so it's accessible from outside text.qml. We'll add a top-level property to the Item in text.qml and bind the label's text to it:

Modified text.qml: #

import QtQuick 2.0
import QtQuick.Controls 2.3

Item {
    // Expose a property for external access
    property string userName: qsTr("John")

    Rectangle {
        id: rectangle
        x: 0
        y: 0
        width: 672
        height: 480
        color: "#ffffff"
        GroupBox {
            id: groupBox
            x: 56
            y: 155
            width: 537
            height: 285
            title: qsTr("Group box")
            Label {
                id: labelname
                x: 54
                y: 27
                // Bind the label's text to our exposed property
                text: userName
            }
            Label {
                id: labelsname2
                x: 54
                y: 62
                text: qsTr("devid")
            }
        }
    }
}

Now, in main.qml, instantiate the text.qml component, give it an ID, and modify the userName property directly in the button's onClicked handler:

Modified main.qml: #

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.3

Window {
    visible: true
    width: 672 // Match the rectangle width in text.qml for full visibility
    height: 480
    title: qsTr("Hello World")

    // Instantiate the text.qml component with an ID
    Item {
        id: textComponentInstance
        anchors.fill: parent
        source: "text.qml"
    }

    Button {
        id: button
        x: 190
        y: 127
        text: qsTr("change name")
        onClicked: {
            // Update the exposed property to change labelname's text
            textComponentInstance.userName = "Alice"
        }
    }
}

2. Update labelname Text via C++ Signal #

Next, let's set up a C++ class that emits a signal carrying the username, then connect that signal to our QML property.

Step 1: Create the C++ Signal Class #

Create a NameSender class that inherits from QObject and defines a signal for sending names:

#include <QObject>

class NameSender : public QObject
{
    Q_OBJECT
public:
    explicit NameSender(QObject *parent = nullptr) : QObject(parent) {}

signals:
    // Signal to send the new username to QML
    void sendName(const QString &newName);

public slots:
    // A test slot to trigger the signal (you can call this from your C++ logic)
    void triggerNameUpdate() {
        emit sendName("Bob from C++");
    }
};

Step 2: Register the Class with QML #

In your main.cpp, register the NameSender class so it's accessible in QML, and create an instance to expose as a context property:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "namesender.h" // Include your header file

int main(int argc, char *argv[])
{
#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#endif
    QGuiApplication app(argc, argv);

    // Register the NameSender class with QML
    qmlRegisterType<NameSender>("com.example", 1, 0, "NameSender");

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);

    // Create a NameSender instance and expose it to QML
    NameSender *nameSender = new NameSender();
    engine.rootContext()->setContextProperty("nameSender", nameSender);

    engine.load(url);

    return app.exec();
}

#include "main.moc" // Required for Qt's meta-object system

Step 3: Connect the C++ Signal in QML #

Update main.qml to connect the C++ signal to the textComponentInstance's userName property. We'll also add a button to trigger the C++ slot for testing:

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.3
import com.example 1.0 // Import our registered C++ class

Window {
    visible: true
    width: 672
    height: 480
    title: qsTr("Hello World")

    Item {
        id: textComponentInstance
        anchors.fill: parent
        source: "text.qml"
    }

    Button {
        id: qmlButton
        x: 190
        y: 127
        text: qsTr("change name from QML")
        onClicked: {
            textComponentInstance.userName = "Alice"
        }
    }

    Button {
        id: cppButton
        x: 190
        y: 180
        text: qsTr("change name from C++")
        onClicked: {
            // Trigger the C++ slot to emit the signal
            nameSender.triggerNameUpdate()
        }
    }

    // Connect the C++ signal to update our QML property
    Connections {
        target: nameSender
        function onSendName(newName) {
            textComponentInstance.userName = newName
        }
    }
}

That's it! Now you can update the labelname text either from QML directly or via a signal emitted from C++.

内容的提问来源于stack exchange，提问作者sagar bade