qt-creator/doc/src/debugger/qtquick-debugging.qdoc

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/*!
    \contentspage index.html
    \previouspage creator-debugging-helpers.html
    \page creator-debugging-qml.html
    \nextpage creator-debugging-example.html

    \title Debugging Qt Quick Projects

    \note You need Qt 4.7.1 or later to debug Qt Quick projects. Debugging
    projects not created with the Qt Quick wizards is only supported with
    Qt 4.8, or later.

    To debug Qt Quick applications running on devices, you must install
    Qt 4.7.4, or later, libraries on devices.

    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:

    \list 1

        \li In \gui Projects mode \gui {Run Settings}, select the
            \gui {Enable QML} check box in the \gui {Debugger Settings} to
            enable QML debugging.

        \li For Qt 4.7, compile the QML Inspector debugging helper. For more information,
            see \l{Debugging Helpers for QML}.

    \endlist

    To debug Qt Quick Applications:

        \list 1

        \li Debugging is enabled by default for Qt 4.8, or later. For Qt 4.7,
            select \gui Projects, and then select the
            \gui {Enable QML debugging} check box in the \gui qmake section
            in \gui {Build Steps}.

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

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

            \note Debugging requires opening a socket at a well-known 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 \gui {Run Settings}, \gui {Debugger Settings} section, select
            the \gui {Enable QML} check box to enable
            QML debugging.

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

        \li To debug applications on devices, check that Qt 4.7.4, 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 \gui {Enable C++} and \gui {Enable QML} checkboxes for both
    languages in the \gui {Debugger Settings} section in the project
    \gui{Run Settings}.

    \image qtquick-debugging-settings.png

    \section1 Starting QML Debugging

    To start the application, choose \gui {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 Change QML code and immediately see the changes at runtime

        \li Inspect QML code and change it 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):

            \list

                \li Qt Quick 1: \c {CONFIG+=declarative_debug}

                \li Qt Quick 2: \c {CONFIG+=qml_debug}

            \endlist

        \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 \gui {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 \gui 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
    \gui {QML/JS Console} to execute JavaScript expressions in the current
    context. To open it, choose \gui Window > \gui {Output Panes} > \gui {QML/JS Console}.

    \image qml-script-console.png "QML/JS Console"

    For more information about using the console, see \l{QML/JS Console}.

    \section1 Applying QML Changes at Runtime

    If you change property values or add properties in the code editor, the
    debugger can update the properties in the running application when you save
    the file. This is enabled by default. To disable it, click the
    \inlineimage qml-observer-bar-reload.png "Apply Changes on Save button"
    (\gui {Apply Changes on Save}) button on the toolbar.

    When you change property values in the \gui {QML/JS Console} or in the
    \gui {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
    \gui {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, click
    \inlineimage qml-inspector-app-on-top.png
    (\gui {Show Application on Top}).

    You can view a QML item in \gui {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 Click
            \inlineimage qml-inspector-select-button.png
            (\gui 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 or you can zoom into the user interface.

    When the \gui Select tool is enabled, 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 \gui {Locals and Expressions} view.

    You can also right-click an item in the running application to view the
    item hierarchy as a context menu.

    \image qml-observer-context-menu.png "QML item hierarchy"

    To switch to the zoom mode, click the \gui Zoom button. Click in the
    running application to zoom in. Right-click to open a context menu that
    contains zoom controls.

    To switch out of the selection or zoom mode, deselect the \gui Select or
    \gui Zoom button.

    To move the application running in \QQV to the front, select the
    \gui {Show Application on Top} button.

*/