runtime error: module is not installed when using qt_add_qml_module()

timjquetee

I'm following various examples and documentation trying to learn how to use qt_add_qml_module() to create a simple module mymodule using cmake and have my windows QML application import and use that module.

I get the following error message at run-time:

qrc:/main.qml:4:1: module "modules.mymodule" is not installed

I think I am missing some fundamental understanding or step.
The file modules/mymodule/CMakeLists.txt is:

cmake_minimum_required(VERSION 3.16)
qt_add_qml_module(mymodule
    URI modules.mymodule
    VERSION 1.0
    QML_FILES MyRect.qml
    SHARED)

The file modules/mymodule/MyRect.qml is:

import QtQuick
import QtQuick.Controls.Basic
import QtQuick.Layouts

Item {
    id: root
    implicitWidth: 50
    implicitHeight: 50
    Rectangle {
        color: "blue"
        anchors.fill: parent
    }
}

The main.qml file imports this module and tries to display a MyRect:

import QtQuick
import modules.mymodule

ApplicationWindow {
    id: root
    visible: true

    width: 1000
    height: 800

    MyRect {

    }
   ...

The CMakeLists.txt for the main application includes the following:

qt_add_executable(mytestapp main.cpp)
set_target_properties(mytestapp PROPERTIES WIN32_EXECUTABLE ON)
target_link_libraries(mytestapp PRIVATE Qt6::Core Qt6::Gui Qt6::Qml Qt6::Quick)
qt_add_qml_module(mytestapp URI main VERSION 1.0 QML_FILES main.qml NO_RESOURCE_TARGET_PATH NO_PLUGIN IMPORTS modules.mymodules)

find_program(WINDEPLOYQT_EXE windeployqt.exe)
add_custom_command(
    TARGET mytestapp POST_BUILD
    COMMAND ${WINDEPLOYQT_EXE} --no-translations $<TARGET_FILE:mytestapp > --qmldir ${CMAKE_CURRENT_SOURCE_DIR}
    COMMENT "Running windeployqt for target mytestapp "
)

And the main.cpp is:

int main(int argc, char **argv)
{
    QGuiApplication app(argc, argv);
    app.setApplicationName(QFileInfo(app.applicationFilePath()).baseName());
    QQmlApplicationEngine engine;
    engine.load(QUrl("qrc:/main.qml"));
    return app.exec(); 
}

I have been able to work-around the error if I change mymodule to be built as a STATIC library instead of SHARED, and also explicitly add mymodule to the target_link_libraries() of the main applicaiton. I don't understand why using STATIC works, but using SHARED doesn't. When using a SHARED library for mymodule, I can see the .dll file mymodule.dll being copied to the application build directory, but the error says "module "modules.mymodule" is not installed". What does 'installed' mean in this context?

kaixoo

For future readers: you need to set the extra module as static in order for it to link with the main executable. I don't know why this is. It's very hidden in the Qt guide

qt_add_library(UiComponents STATIC)
qt_add_qml_module(UiComponents
    URI "Muse.UiComponents"
    VERSION 1.0
    NO_PLUGIN
    QML_FILES
        ....