Debugging Qt Quick Projects
Note: You need Qt 4.7.1 or later to debug Qt Quick projects.
Setting Up QML Debugging
The process of setting up debugging for Qt Quick projects depends on the type of the project: Qt Quick UI or Qt Quick Application.
To debug Qt Quick UI projects:
- Select Projects, and then select the QML check box in the Run Settings, to enable QML debugging.
- Compile the QML Observer debugging helper. For more information, see Debugging Helpers for QML.
To debug Qt Quick Applications:
- Select Projects, and then select the Link QML debugging library check box in Build Steps.
You might have to compile the library first, by selecting the Compile link.
Note: Debugging requires opening a socket at a well-known port, which presents a security risk. Anyone on the Internet could connect to the application that you are debugging and execute any JavaScript functions. Therefore, you must make sure that the port is properly protected by a firewall.
- In the Run Settings, select the QML check box to enable QML debugging.
- Select Build > Rebuild Project to clean and rebuild the project.
Starting QML Debugging
To start the application, choose Debug > Start Debugging > Start Debugging or press F5. Once the application starts running, it behaves and performs as usual. You can then perform the following tasks:
- Debug JavaScript functions
- Preview QML changes at runtime
- Inspect QML at runtime
Debugging JavaScript Functions
You can use the Qt Creator Debug mode to inspect the state of your application while debugging. You can interact with the debugger in several ways, as described in the following sections:
Executing JavaScript Expressions
When the application is interrupted by a breakpoint, you can use the QML Script Console to execute JavaScript expressions in the current context. To open it, choose Window > View > QML Script Console.
You can type JavaScript expressions and use them to get information about the state or your application. For example, property values.
You can see the current value of a property by hovering over it in the code editor.
Previewing QML Changes at Runtime
If you change property values or add properties in the code editor, the changes are updated in the running application when you save them. If live preview is not supported for an element, a message appears. Click Reload to preview the changes.
Reloading is enabled by default. To disable it, click 
on the toolbar.
Inspecting QML at Runtime
While the application is running, you can use the QML Observer view to explore the object structure, debug animations, and inspect colors. To open the QML Observer view, choose Window > View > QML Observer. The view shows the properties of the currently selected QML element.
When you debug complex applications, you can use the observe mode to jump to the position in code where an element is defined. To switch to the observe mode, click 
on the toolbar.
Click elements in the running application to jump to their definitions in the code. Double-click elements to browse the element hierarchy. The hierarchy is displayed as bread crumbs in the QML Observer view.
To move the application running in Qt QML Viewer to the front, select the Show Application on Top button.
You can also right-click an element in the running application to view the element hierarchy as a context menu. Select an element to jump to its definition in code.
To zoom in and out of the application, click the Zoom button.
To inspect colors, click the Color Picker button. You can also click 
to copy the color definition to the clipboard.
Debugging Animations
To play and pause animations in the running application, select the Play/Pause Animations button on the toolbar or Debugging > Animations > Pause, or press Ctrl+..
To change the speed at which animations are played, select a value in Debugging > Animations or click and hold down the Play/Pause Animations button to select a value.