Qt Quick 怎么做

This page aims to provide an easily discoverable, useful reference that shows the simplest and best way of performing specific tasks in Qt Quick. Each solution provides QML and/or C++ code snippets where applicable, and every snippet is automatically tested by Qt to ensure they remain functional.

How do I:

从 QML 调用 C++ 函数，当点击按钮时

Assuming that the C++ type should be globally available to the QML files in the application, the simplest way is to make it a QML singleton with QML_SINGLETON . For example, in the header file, backend.h :

#include <QObject>
#include <QQmlEngine>
class Backend : public QObject
{
    Q_OBJECT
    QML_ELEMENT
    QML_SINGLETON
public:
    Q_INVOKABLE void doStuff();
};

backend.cpp :

#include "backend.h"
#include <QDebug>
void Backend::doStuff()
{
    qDebug() << "Did stuff!";
}

You can then call that function from any QML file:

import QtQuick.Controls
import MyModule
ApplicationWindow {
    width: 400
    height: 400
    title: qsTr("C++ Button example")
    Button {
        text: qsTr("Click me")
        onClicked: Backend.doStuff()
    }
}

If the C++ type only needs to be available to a small set of QML files, consider using QML_ELEMENT . For more ways of exposing C++ types to QML, see Choosing the Correct Integration Method Between C++ and QML .

This example assumes that the Backend type is available in a QML module. With CMake, this is done via qt_add_qml_module . For an example that demonstrates this in detail, see 构建 QML 应用程序 .

See which item has active focus

Write a property change signal handler for the window's activeFocusItem 特性：

import QtQuick
import QtQuick.Controls
ApplicationWindow {
    width: 400
    height: 400
    visible: true
    title: qsTr("Active focus debugging example")
    onActiveFocusItemChanged: print("activeFocusItem: " + activeFocusItem)
    Row {
        TextField {
            objectName: "textField1"
        }
        TextField {
            objectName: "textField2"
        }
    }
}

This will print the item which currently has active focus to the console. To ensure that the output is useful, give each item a descriptive objectName .