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Application Profiler Tool

While metrics primarily contain a single dimension of information, suitable for displaying as a chart, profilers capture richer data. After a recording is completed, Developer Tools aggregates the results and displays them as a table.

Recording a Profile​

  1. Click the Record button to start a profiling session.
  2. The application continues running normally while data is collected in the background.
  3. Click Record again to stop.
  4. Results are aggregated and displayed across separate tabs, one for each profiler type.

For best results, try to isolate the interaction you want to measure. For example, open a specific view or trigger a UI action while recording, so the data isn't diluted by unrelated activity.

Style Matching​

When a control is created or added to the visual tree, Avalonia evaluates all active style selectors to determine which ones apply. The Style Matching profiler aggregates match attempts.

Columns:

  • Selector — the style selector being evaluated (e.g., TextBlock.h1, Button:pointerover > ContentPresenter)
  • Elapsed — total time spent evaluating this selector across all match attempts
  • Fast Reject Count — how many times the selector was quickly ruled out without full evaluation. A fast reject occurs when a control can be excluded by a simple static check, such as a mismatched type or control name. Importantly, a fast-rejected control will not be re-evaluated later when activators change — for example, a TextBox will never be re-evaluated for Button:pointerover, because it was already rejected on type
  • Match Attempts — total number of times this selector was tested against a control
  • Matches — how many attempts resulted in a successful match

A high number of match attempts with very few matches can indicate an overly broad selector. Consider targeting a concrete control type rather than a base class to reduce unnecessary matching during control creation.

Style Activators​

Unlike Style Matching (which measures initial selector resolution), this profiler measures how often selectors are re-evaluated at runtime. This happens when conditional selectors — those with activators like :pointerover, :focus, :pressed — toggle on and off as the user interacts with the application.

Columns:

  • Selector — the style selector being re-evaluated
  • Elapsed — total time spent on re-evaluations
  • Evaluations — total number of times the selector's activator was re-evaluated
  • Active Evaluations — how many evaluations resulted in the style becoming active
  • Activator — type of activator responsible (e.g., pseudo-class, property match)

If a selector shows a very high number of evaluations, it may be toggling more often than expected. Narrowing the scope of such selectors can help.

Resource Lookup​

Every time a control, style, or binding resolves a resource by key (e.g., a brush, thickness, or template), Avalonia walks the resource hierarchy until it finds a match. This profiler aggregates those lookups by key.

Columns:

  • Key — the resource key being looked up
  • Elapsed — total time spent resolving this key across all lookups
  • Total Lookups — how many times this key was requested
  • Successful — how many lookups found a matching resource
  • Theme Variant — the theme variant (Light/Dark) active during the lookup

A key with many total lookups but few successful ones likely indicates a missing or misspelled resource definition. You can use the Resources Tool to inspect available resources at each scope.