Debugging QML with Qt creator

Question

I have a Qt (5.8.0) project using QML files. I would like to set breakpoints in the QML file using Qt creator (4.2.1) so I can follow the flow. However I cannot get it to work. I have enabled "Enable QML debugging and profiling" in the qmake build step and "Enable C++" and "Enable QML" in the run step.

The breakpoints in the C++ code are hit, but the QML are ignored. When starting I get the following message:

QDeclarativeDebugServer: Ignoring 
\"-qmljsdebugger=port:42715,block,services:DebugMessages,QmlDebugger,V8Debugger,QmlInspector\". 
Debugging has not been enabled.

When I try to debug QML files in demo projects like "Calendar" with the same kit it does work and breakpoints are hit.

Any ideas?

I found myself here and then figured out my problem: QML debugging works by a collaboration between the QApplication and the debugger, with the -qmljsdebugger flag, which magically gets consumed by the QApplication c'tor. I had made a "dummy" QAppliation in order to parse the command-line args before launching my app. As a result, the first QApplication consumed the arg, and so the "real" QApplication never saw it. — Ben
– Ben, Commented May 30, 2023 at 14:01

Jens · Accepted Answer · 2018-04-11 07:35:23Z

4

Did you enable the QML Debugger in your code? I remember putting something like this into my code:

For Qt4:

#include <QtDeclarative/qdeclarativedebug.h>
QDeclarativeDebuggingEnabler qmldbg;

or in case of Qt5:

#include <QQmlDebuggingEnabler>
QQmlDebuggingEnabler enabler;

Also QML debugging needs to be activated in the Execution Settings:

edited Apr 11, 2018 at 7:35

answered Apr 10, 2018 at 8:18

Jens

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4 Comments

Frank Over a year ago

That does seem to fix the "QDeclarativeDebugServer ignoring" message. Now it says "Qml debugging is enabled. Only use this in a safe environment!" However the breakpoints are still not being hit in the QML.

Jens Over a year ago

Can you see a message like "QDeclarativeDebugServer: Waiting for connection on port 3768..." on the console?

Frank Over a year ago

When I use your "Qt4" solution I do get the message: "Qml debugging is enabled. Only use this in a safe environment! QDeclarativeDebugServer: Waiting for connection on port 40393... QDeclarativeDebugServer: Connection established"

Frank Over a year ago

However when I try the Qt5 solution (and adding Qt+=quick to my project) I get some confusing messages: "QML debugging is enabled. Only use this in a safe environment. "QDeclarativeDebugServer: Ignoring \"-qmljsdebugger=port:36014,block,services:DebugMessages,QmlDebugger,V8Debugger,QmlInspector\". Debugging has not been enabled.""

Frank · Accepted Answer · 2018-04-12 06:23:48Z

2

I found a way to make it work. Looks like I am using the combination of Qt5, while using the Declarative package and Qt Quick 1.1. When I removed the Declarative package and instead use the qml and quick packages (Qt+=qml quick) and updated my software to use Qt Quick 2.2, the breakpoints were hit (also using the #include as suggested by the answer of Jens)

edited Apr 12, 2018 at 6:23

answered Apr 12, 2018 at 6:18

Frank

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Luke Dupin · Accepted Answer · 2018-09-10 07:13:33Z

2

I had to remove a package from my .pro file:

#CONFIG += qtquickcompiler

With this line commented out and confirming my project's build steps: "Enable QML debugging and profiling" was checked, the breakpoints worked.

answered Sep 10, 2018 at 7:13

Luke Dupin

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