Profile QML code

With QML Profiler, you can find causes for typical performance problems in Qt Quick applications, such as slowness and unresponsive, stuttering user interfaces.

You can launch QML Profiler from Qt Extension for VS Code to profile a running QML application and to analyze profiling data.

Install QML profiler

To profile QML applications, you need to install QML Profile. Go to Command Palette and select Qt: Install the most recent QML trace viewer.

If you do not install QML Profiler, Qt Extension for VS Code offers to install it the first time you start profiling a application.

To use a particular QML Profiler executable, set the path to it in the QML Profiler settings.

Collect profiling data

To collect profiling data about the currently open application:

1. Go to Command Palette and select Qt: Profile QML application or (Profile QML application) on the toolbar.
2. Use the application to collect profiling data.
3. Close the application or select (Stop QML profiler) on the toolbar.

Use the QML Profiler to collect data and analyze the results.

For more information, see Profiling QML applications in the Qt Creator documentation.

You can set arguments to pass to the application when you start QML Profiler in the QML Profiler settings.

Attach QML Profiler to running applications

To attach the QML Profiler to a running application for collecting profiling data:

1. In the Terminal, start the application with the following arguments:

   <your_executable_path> -qmljsdebugger=host:<IP_address>,port:<port_number>,block,services:QmlProfiler,CanvasFrameRate

   Where IP_address is the IP address of the host where the application is running, port_number is the debugging port, and block prevents the application from running until the debug client connects to the server. This enables profiling from the start.

2. When the application is running, go to Command Palette, and select Qt: Attach to running QML application for profiling.
3. Enter the IP address of the host, and then select Enter.
4. Enter the port number, and then select Enter.