Qt Application Fails to Load QML Modules in Docker Container

Rakesh U

Hello Qt Community,

I’m encountering several issues while running a Qt QML application inside a Docker container. The application starts but fails to load QML modules and the required Qt platform plugin. I’m looking for guidance on how to resolve these issues.
Issue Description
When running my Qt QML application in a Docker container, I get the following errors:

Application starting...
qt.qpa.xcb: could not connect to display :0
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, xcb.

Dockerfile Configuration
Here’s the Dockerfile I’m using to build the Docker image:

# Use an Ubuntu base image
FROM ubuntu:22.04

# Install required dependencies
RUN apt-get update && \
    apt-get install -y \
    build-essential \
    cmake \
    qtbase5-dev \
    qtdeclarative5-dev \
    qtquickcontrols2-5-dev \
    libgl1-mesa-dev \
    libxcb1 \
    libxcb-xinerama0 \
    libxcb-xkb1 \
    libxkbcommon-x11-0 \
    libxkbcommon0 \
    libgl1-mesa-glx \
    libgl1-mesa-dri \
    && rm -rf /var/lib/apt/lists/*

# Set environment variables for Qt
ENV QT_QPA_PLATFORM_PLUGIN_PATH=/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms

# Create an application directory
WORKDIR /usr/src/app

# Copy your Qt QML application to the container
COPY . /usr/src/app

# Build the QML application using CMake
RUN mkdir build && cd build && cmake .. && make

# Command to run the QML application
CMD ["./build/Qml_App"]

CPP main

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QDebug>

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

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    qDebug() << "Loading QML file from" << url.toString();
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreated,
        &app,
        [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl) {
                qDebug() << "Failed to load QML file";
                QCoreApplication::exit(-1);
            }
        },
        Qt::QueuedConnection);
    engine.load(url);

    qDebug() << "Application loaded";
    return app.exec();
}

Troubleshooting Steps Taken

Verified Installation of Qt Modules: Ensured the Dockerfile installs all necessary Qt packages.
Checked Qt Plugin Path: Set QT_QPA_PLATFORM_PLUGIN_PATH in the Dockerfile.
Verified QML Imports: Confirmed that the QML modules should be present in the container.
Verified Plugin Path: Ensured the Qt platform plugin path is correctly set.

Request for Assistance

Ensuring the required QML modules are correctly installed in the Docker container.
Why Window is not opening(QML)
Diagnosing why the Qt platform plugin "xcb" cannot be initialized.

Thank you in advance for your help!

Best regards,
Rakesh U

JonB

@Rakesh-U said in Qt Application Fails to Load QML Modules in Docker Container:

qt.qpa.xcb: could not connect to display :0

This is the only message which matters. However you invoke your application with the Docker Container you do not have an Xorg display available to it. Are you running an X server? Try to run some other Xorg application, such as xterm, and you should be seeing the same error.

Rakesh U

running on ubuntu 20.04

JonB

@Rakesh-U said in Qt Application Fails to Load QML Modules in Docker Container:

running on ubuntu 20.04

Whatever, it's still as per my answer above.

Rakesh U

@JonB still getting same error

JonB

@Rakesh-U Did you/could you try running xterm in exactly same environment?