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Debugging QMLConsole APILogconsole.log, console.debug, console.info, console.warn and console.error can be used to print debugging information to the console. For example: function f(a, b) { console.log("a is ", a, "b is ", b); } The output is generated using the qDebug, qWarning, qCritical methods in C++ (see also http://doc.qt.nokia.com/latest/debug.html#warning-and-debugging-messages). Setting the environment variable QML_CONSOLE_EXTENDED also prints the source code location of the call. Assertconsole.assert tests that an expression is true. If not, it will write an optional message to the console and print the stack trace. function f() {
var x = 12
console.assert(x == 12, "This will pass");
console.assert(x > 12, "This will fail");
}
Timerconsole.time and console.timeEnd log the time (in milliseconds) that was spent between the calls. Both take a string argument that identifies the measurement. For example: function f() {
console.time("wholeFunction");
console.time("firstPart");
// first part
console.timeEnd("firstPart");
// second part
console.timeEnd("wholeFunction");
}
Traceconsole.trace prints the stack trace of JavaScript execution at the point where it was called. The stack trace info contains function name, file name, line number and column number. The stack trace is limited to last 10 stack frames. Countconsole.count prints the current number of times a particular piece of code has been executed, along with a message. That is, function f() {
console.count("f called");
}
will print f called: 1, f called: 2 ... whenever f() is executed. Profileconsole.profile turns on the QML and JavaScript profilers. Nested calls are not supported and a warning will be printed to the console. console.profileEnd turns off the QML and JavaScript profilers. Calling this function without a previous call to console.profile will print a warning to the console. A profiling client should have been attached before this call to receive and store the profiling data. For example: function f() {
console.profile();
//Call some function that needs to be profiled.
//Ensure that a client is attached before ending
//the profiling session.
console.profileEnd();
}
Exceptionconsole.exception prints an error message together with the stack trace of JavaScript execution at the point where it is called. Debugging TransitionsWhen a transition doesn't look quite right, it can be helpful to view it in slow motion to see what is happening more clearly. This functionality is supported in the QML Viewer tool: to enable this, click on the "Debugging" menu, then "Slow Down Animations". Debugging module importsThe QML_IMPORT_TRACE environment variable can be set to enable debug output from QML's import loading mechanisms. For example, for a simple QML file like this: import QtQuick 2.0 Rectangle { width: 100; height: 100 } If you set QML_IMPORT_TRACE=1 before running the QML Viewer (or your QML C++ application), you will see output similar to this: QQmlImportDatabase::addImportPath "/qt-sdk/imports" QQmlImportDatabase::addImportPath "/qt-sdk/bin/QMLViewer.app/Contents/MacOS" QQmlImportDatabase::addToImport 0x106237370 "." -1.-1 File as "" QQmlImportDatabase::addToImport 0x106237370 "Qt" 4.7 Library as "" QQmlImportDatabase::resolveType "Rectangle" = "QDeclarativeRectangle" Debugging with Qt CreatorQt Creator provides built-in support for QML debugging. QML projects and standalone C++ applications that utilize QML can be debugged on desktops as well as on remote devices. For more information, see the Qt Creator Manual. |
