qtquick-debugging.qdoc

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/*!
    \contentspage {Qt Creator Manual}
    \previouspage creator-debugging-helpers.html
    \page creator-debugging-qml.html
    \nextpage creator-debugging-example.html

    \title Debugging Qt Quick Projects

    \note You need Qt 5.0 or later to debug Qt Quick projects.

    For an example of how to debug Qt Quick Projects, see
    \l{Debugging a Qt Quick Example Application}.

    \section1 Setting Up QML Debugging

    The process of setting up debugging for Qt Quick projects depends on the
    \l{Creating Qt Quick Projects}{type of the project}: Qt Quick UI or Qt Quick
    Application, and the Qt version used.

    To debug Qt Quick UI projects, select the \uicontrol {Enable QML} check box in the
    \uicontrol {Debugger Settings} in \uicontrol Projects mode \uicontrol {Run Settings}.

    To debug Qt Quick Applications:

        \list 1

        \li Debugging is enabled by default for Qt 5.0, or later.

            You might have to compile the library first, by selecting the
            \uicontrol Compile link.

            \image qml-link-debugging-library.png "Build Steps"

            \note Debugging requires opening a socket at a TCP port,
            which presents a security risk. Anyone on the Internet could connect
            to the application that you are debugging and execute any JavaScript
            functions. Therefore, you must make sure that the port is properly
            protected by a firewall.

        \li In the \uicontrol {Run Settings}, \uicontrol {Debugger Settings} section, select
            the \uicontrol {Enable QML} check box to enable
            QML debugging.

        \li Select \uicontrol {Build > Rebuild Project} to clean and rebuild the
            project.

        \li To debug applications on devices, check that Qt 5.0, or later,
            libraries are installed on the device and
            \l{Running on Multiple Platforms}{select the corresponding kit for the device}
            before you start debugging.

    \endlist

    \section1 Mixed C++/QML Debugging

    To debug both the C++ and QML parts of your application at the same time,
    select the \uicontrol {Enable C++} and \uicontrol {Enable QML} checkboxes for both
    languages in the \uicontrol {Debugger Settings} section in the project
    \uicontrol{Run Settings}.

    \image qtquick-debugging-settings.png

    \section1 Starting QML Debugging

    To start the application, choose \uicontrol {Debug > Start Debugging >
    Start Debugging} or press \key F5. Once the application starts running, it
    behaves and performs as usual. You can then perform the following tasks:

    \list

        \li Debug JavaScript functions

        \li Execute JavaScript expressions to get information about the state of
            the application

        \li Inspect QML properties and JavaScript variables and change them
            temporarily at runtime

    \endlist

    To debug already running applications:

    \list 1

        \li Build the application by using the appropriate configuration
            parameters (if you build the application with \QC, it automatically
            uses the correct configuration):

            \c {CONFIG+=qml_debug}


        \li Start the application with the following arguments:

            \c {qmljsdebugger=port:<port>[,host:<ip address>][,block]}

            Where \c port (mandatory) specifies the debugging port,
            \c {ip address} (optional) specifies the IP address of the host
            where the application is running, and \c block (optional) prevents
            the application from running until the debug client connects to the
            server. This enables debugging from the start.

        \li Select \uicontrol {Debug > Start Debugging > Attach to QML Port}.

            Choose the kit configured for the device where the application to
            be debugged is running. The port number to use is displayed in the
            standard output when the application starts.

    \endlist

    \section1 Debugging JavaScript Functions

    You can use the \QC \uicontrol Debug mode to inspect the state of your
    application while debugging. You can interact with the debugger by:

    \list

        \li \l{Setting Breakpoints}{Setting breakpoints}

        \li \l{Viewing Call Stack Trace}{Viewing call stack trace}

        \li \l{Locals and Expressions}{Viewing locals and expressions}

    \endlist

    \section1 Executing JavaScript Expressions

    When the application is interrupted by a breakpoint, you can use the
    \uicontrol {Debugger Console} to execute JavaScript expressions in the current
    context. To open it, choose \uicontrol Window > \uicontrol {Output Panes}
    > \uicontrol {Debugger Console}.

    \image qml-script-console.png "Debugger Console"

    For more information about using the console, see \l{Debugger Console}.

    \section1 Applying QML Changes at Runtime

    When you change property values in the \uicontrol {Debugger Console} or in the
    \uicontrol {Locals and Expressions} view, they are immediately updated in the running
    application, but not in the source code.

    \section1 Inspecting Items

    While the application is running, you can use the
    \uicontrol {Locals and Expressions} view to explore the QML item structure.

    \image qml-observer-view.png "QML item tree"

    To keep the application visible while you interact with the debugger, select
    \uicontrol Debug > \uicontrol {Show Application on Top}.

    You can view a QML item in \uicontrol {Locals and Expressions} in the following
    ways:

    \list

        \li Expand the item in the object tree.

        \li Select the item in the code editor.

        \li Select \uicontrol Debug > \uicontrol Select to activate selection
            mode and then click an item in the running application.

    \endlist

    To change property values temporarily, without editing the source,
    double-click them and enter the new values. You can view the results in the
    running application.

    \section1 Inspecting User Interfaces

    When you debug complex applications, you can jump to the position in code
    where an item is defined.

    In the selection mode, you can click items in the running
    application to jump to their definitions in the code. The properties of the
    selected item are displayed in the \uicontrol {Locals and Expressions} view.

    The \uicontrol Select tool will be enabled either if your application is
    using Qt 5.7 or later, or if your application is using an earlier version
    of Qt and is based on the \c QQuickView class.

    You can also view the item hierarchy in the running application:

    Double-click an item in the running application to cycle through the item
    stack at the cursor position.

    To switch out of the selection mode, toggle the \uicontrol Select menu item.

    To move the application running in \QQV to the front, select
    \uicontrol Debug > \uicontrol {Show Application on Top}.

*/