部署 QML 应用程序

QML documents are loaded and run by the QML runtime. This includes the Declarative UI engine along with the built-in QML types and plugin modules. The QML runtime also provides access to third-party QML types and modules.

Applications that use QML must invoke the QML runtime to run QML documents. You can do this by creating a QQuickView 或 QQmlEngine , as described below. In addition, the Declarative UI package includes the qml tool, which loads .qml files. This tool is useful for developing and testing QML code without having to write a C++ application to load the QML runtime.

采用 Qt Creator 部署应用程序

Qt Creator deploys and packages QML applications to various platforms. For mobile devices, Qt Creator can directly bundle applications to the respective platform package formats, such as APK.

When you run your applications on the target platform, your application needs to access the location of the QML libraries. If you use qmake ， QT_INSTALL_QML environment variable points to the location of the libraries. The Qt 安装程序 install the QML libraries in: <version> / <compiler> /qml 目录。

QML 缓存

The QML runtime loads QML documents by parsing them and generating byte code. Most of the time, the document hasn't changed since the last time it was loaded. To speed up this loading process, the QML runtime maintains a cache file for each QML document. This cache file contains the compiled byte code and a binary representation of the QML document structure. In addition, when multiple applications use the same QML document, the memory needed for the code is shared between application processes. The cache files are loaded via the mmap() system call on POSIX-compliant operating systems or CreateFileMapping() on Windows, resulting in significant memory savings.

Each time you load a changed QML document, the cache is automatically re-created. Cache files are located in a sub-directory of QStandardPaths::CacheLocation with the name "qmlcache". The file extension is .qmlc for QML documents and .jsc for imported JavaScript modules.

提前编译

The automatic caching of compiled QML documents into cache files results in significantly faster application load time. However, the initial creation of cache files can still take time, especially when the application starts for the very first time. To avoid that initial step and provide faster startup times from the very beginning, Qt's build system allows you to perform the compilation step for QML files ahead of time, when compiling the C++ parts of your application.

One benefit of compiling ahead of time is that, in the event of syntax errors in your QML documents, you are notified at application compile-time instead of at run-time, when the file is loaded.

This will happen automatically if you use the CMake QML 模块 API , for qmake see the section below.

qmake

When using qmake, in order to deploy your application with QML files compiled ahead of time, you must organize the files and the build system in a specific way:

• All QML documents (including JavaScript files) must be included as resources via Qt's Resource system .
• Your application must load the QML documents via the qrc:/// URL scheme.
• You can enable Ahead-of-Time compilation using the CONFIG+=qtquickcompiler 指令。

采用 QML 场景进行原型设计

The Declarative UI package includes a QML Runtime Tool, qml , which loads and displays QML documents. This is useful during the application development phase for prototyping QML-based applications without writing your own C++ applications to invoke the QML runtime.

在应用程序中初始化 QML 运行时

To run an application that uses QML, your application must invoke the QML runtime. This is done by writing a Qt C++ application that loads the QQmlEngine by either:

• Loading the QML file through a QQuickView 实例。
• Creating a QQmlEngine instance and loading QML files with QQmlComponent .

采用 QQuickView 初始化

QQuickView 是 QWindow -based class that can load QML files. For example, if there is a QML file, application.qml , it will look like this:

import QtQuick
Rectangle { width: 100; height: 100; color: "red" }
					

It can be loaded in a Qt application's main.cpp 文件像这样：

#include <QGuiApplication>
#include <QQuickView>
int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQuickView view;
    view.setSource(QUrl::fromLocalFile("application.qml"));
    view.show();
    return app.exec();
}
					

This creates a QWindow -based view that displays the contents of application.qml .

Build Files

find_package(Qt6 REQUIRED COMPONENTS Quick)
target_link_libraries(mytarget PRIVATE Qt6::Quick)
						

QT += quick
						

#include <QGuiApplication>
#include <QQmlEngine>
#include <QQmlContext>
#include <QQmlComponent>
int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);
    QQmlEngine engine;
    QQmlContext *objectContext = new QQmlContext(engine.rootContext());
    QQmlComponent component(&engine, "application.qml");
    QObject *object = component.create(objectContext);
    // ... delete object and objectContext when necessary
    return app.exec();
}