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

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

    \title Debugging a Qt Quick Example Application

    This section uses the
    \l{QML Advanced Tutorial}{Same Game}
    example application to illustrate how to debug Qt Quick applications in the
    \gui Debug mode.

    For more information about all the options you have, see
    \l{Debugging Qt Quick Projects}.

    The Same Game demo shows how to write a game in QML, using JavaScript for
    all the game logic. Open the demo project in \QC to debug it:

    \list 1

        \li To look at the code that starts a new game, place a breakpoint in
            samegame.qml by clicking between the line number and the window
            border on the line where where the \c startNewGame() function is
            called (1).

            \image qtquick-example-setting-breakpoint1.png

            The red circle indicates that a breakpoint is now set on that line
            number.

        \li Select \gui {Debug > Start Debugging > Start Debugging} or press
            \key{F5}.

        \li Once the Same Game application starts, click the \gui {New Game}
            button to start a new game.

        \li When the debugger hits the breakpoint, it interrupts the
            application. \QC displays the nested function calls leading to the
            current position as a call stack trace (1).

            \image qtquick-example-setting-breakpoint2.png

        \li Click the
            \inlineimage qtcreator-debug-button-step-into.png
            (\gui {Step Into}) button on the toolbar or press \key F11 to step
            into the code in the stack. The samegame.js file opens in the code
            editor at the function that starts a new game.

            \image qtquick-example-stack.png

        \li Examine the local variables in the \gui {Locals and Expressions}
            view. Step through the code to see how the information changes in
            the view.

        \li Add a breakpoint at the end of the \c {startNewGame()} function, and
            click \inlineimage qtcreator-debugging-continue.png
            (\gui Continue) to hit the breakpoint.

            \image qtquick-example-setting-breakpoint3.png

        \li To execute JavaScript commands in the current context, open the
            \gui {QML/JS Console} output pane.

        \li To change the score to 1000, enter \c{gameCanvas.score = 1000}
            in the console.

            \image qtquick-example-script-console.png

        \li To remove a breakpoint, right-click it and select
            \gui {Delete Breakpoint}.

        \li Select the \gui {Locals and Expressions} tab to explore the object
            structure at runtime:

            \image qtquick-example-qml-inspector.png

        \li Click
            \inlineimage qml-inspector-app-on-top.png
            (\gui {Show Application on Top}) to keep the application visible
            while you interact with the debugger.

        \li Click
            \inlineimage qml-inspector-select-button.png
            (\gui Select) to activate selection mode and then click the
            \gui {Quit} button to move into the \gui ButtonLabel component
            in the \gui {QML/JS Console} and the code editor.

        \li In the \gui {Locals and Expressions} view, double-click the value of
            the \c text property to change it temporarily from \gui {Quit} to
            \gui {End Game}.

            \image qtquick-example-property-values.png

            When you select an element, the cursor moves to it in the code
            editor, where you can change the value permanently.

    \endlist

*/