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29 \page qdeclarativedebugging.html
30 \inqmlmodule QtQuick 2
37 \c console.log, console.debug, console.info, console.warn and console.error can be used to print
38 debugging information to the console. For example:
42 console.log("a is ", a, "b is ", b);
46 The output is generated using the qDebug, qWarning, qCritical methods in C++
47 (see also http://doc.qt.nokia.com/latest/debug.html#warning-and-debugging-messages).
49 \hint Setting the environment variable QML_CONSOLE_EXTENDED also prints the source
50 code location of the call.
54 \c console.time and console.timeEnd log the time (in milliseconds) that was spent between
55 the calls. Both take a string argument that identifies the measurement. For example:
59 console.time("wholeFunction");
60 console.time("firstPart");
62 console.timeEnd("firstPart");
64 console.timeEnd("wholeFunction");
70 \c console.trace prints the stack trace of JavaScript execution at the point where
71 it was called. The stack trace info contains function name, file name, line number
72 and column number. The stack trace is limited to last 10 stack frames.
76 \c console.count prints the current number of times a particular piece of code has been executed,
77 along with a message. That is,
81 console.count("f called");
85 will print \c{f called: 1}, \c{f called: 2} ... whenever \c{f()} is executed.
89 \c console.profile turns on the QML and JavaScript profilers. Nested calls are not
90 supported and a warning will be printed to the console.
92 \c console.profileEnd turns off the QML and JavaScript profilers. Calling this function
93 without a previous call to console.profile will print a warning to the console. A
94 profiling client should have been attached before this call to receive and store the
95 profiling data. For example:
100 //Call some function that needs to be profiled.
101 //Ensure that a client is attached before ending
102 //the profiling session.
103 console.profileEnd();
107 \section1 Debugging Transitions
109 When a transition doesn't look quite right, it can be helpful to view it in slow
110 motion to see what is happening more clearly. This functionality is supported
111 in the \l {QML Viewer} tool: to enable this,
112 click on the "Debugging" menu, then "Slow Down Animations".
115 \section1 Debugging module imports
117 The \c QML_IMPORT_TRACE environment variable can be set to enable debug output
118 from QML's import loading mechanisms.
120 For example, for a simple QML file like this:
125 Rectangle { width: 100; height: 100 }
128 If you set \c {QML_IMPORT_TRACE=1} before running the \l {QML Viewer}
129 (or your QML C++ application), you will see output similar to this:
132 QDeclarativeImportDatabase::addImportPath "/qt-sdk/imports"
133 QDeclarativeImportDatabase::addImportPath "/qt-sdk/bin/QMLViewer.app/Contents/MacOS"
134 QDeclarativeImportDatabase::addToImport 0x106237370 "." -1.-1 File as ""
135 QDeclarativeImportDatabase::addToImport 0x106237370 "Qt" 4.7 Library as ""
136 QDeclarativeImportDatabase::resolveType "Rectangle" = "QDeclarativeRectangle"
140 \section1 Debugging with Qt Creator
142 \l{http://qt.nokia.com/products/developer-tools}{Qt Creator} provides built-in
143 support for QML debugging. QML projects and standalone C++ applications that
144 utilize QML can be debugged on desktops as well as on remote devices.
145 For more information, see the Qt Creator Manual.