Runtime property bindings

Select a component in Designer and choose ƒx beside a runtime property. General, Layout and Appearance come first, followed by component-specific settings, shared configuration, and finally Custom properties. Bound rows show their expression or query and disable the saved literal editor. Remove the binding to restore the authored literal. Apply and Undo use Designer history.

This feature requires preview.11 or a later compatible build. Preview.10 predates it.

Supported values

The browser and gateway share apps/web/src/runtimeProperties.json, which declares applicable component types, value types, enums and limits. It covers common properties plus chart axes/type/series/legend, process and gauge limits, drawing points and symbols, image presentation, choice options and indicator states, table data/columns/page size, input validation and format, history range/paths, alarm priority, repeater columns/gap, and container layout and pane presentation. Pane paths address existing authored pane indexes.

Custom Number, Text and Boolean values also have ƒx. Expressions can read bound custom values on this component or a sibling in the same form. Dependencies resolve before consumers regardless of definition order. Cycles, missing sources, wrong types and unavailable query/tag values produce diagnostics rather than silently reading the saved custom value. Template placements and repeated forms keep independent scopes.

Expressions retain the bounded scalar grammar. Structured properties such as options, points, chart series and datasets accept JSON text, then validate and decode it to the required structure. For example, a text custom property containing [{"label":"Running","value":"run"}] can supply an Options binding. The expression choices references that custom property. Structured text is limited to 4,096 characters; literal expression source is limited to 2,048. Larger chart data should use the existing named-query dataset binding. Invalid JSON and unknown fields are rejected.

An explicit Data expression/query-property binding takes precedence over a chart's named-query dataset source. Remove that Data binding to restore the dataset source; a failed binding does not silently fall back to old data.

An expression or named-query result can supply a property, but not both at once. Scalar query bindings still require exactly one row and one chosen column; use a JSON text column for a structured target. Query parameters may read custom properties and their dependencies, but cannot indirectly introduce tag or password-input sources. The gateway reconstructs permitted custom sources when executing published parameterized actions.

Runtime behavior

The engine resolves nested properties without modifying saved definitions. Related fields, such as chart axis bounds, are checked together. A failed binding displays its error and prevents interaction with the affected control. Bindings do not grant tag, query, command or script permissions.

Input validation bindings control browser presentation and validation. Published gateway input constraints remain authoritative and cannot be loosened by a browser binding. Input Value source continues to use its existing typed two-way state binding; expression bindings do not add reverse writes.

Tables can display an authored or bound dataset. Supplied data takes precedence over a configured query while present. These tables support presentation, filtering, paging and selection; database cell/batch editing requires a named-query source and is not allowed with supplied data.

A bound split ratio or dock size is controlled by its source, so its resize handle is disabled until the binding is removed. Unrelated pane label updates do not reset the selected tab or local sizing. Repeater gap and column changes retain the normal per-row form scopes.

IDs, field names, template/query/command declarations, scripts, event definitions, permissions, initial form defaults and resource catalogs remain configuration. Template parameters, input state and chart query datasets retain their dedicated binding editors. Property-change handlers retain their existing scalar watch contract; adding a runtime binding does not add arbitrary structured event payloads or Python assignment targets.

Bound image asset IDs must refer to assets already available on the gateway. Project packages include authored static asset references; assets referenced only by a dynamic expression must be transferred separately.

Workshop

The independently authored Runtime property bindings workshop is described in examples/runtime-property-bindings.json. Its distributable package is maintained at artifacts/sparkproj/runtime-property-bindings.sparkproj.

1. Import the package, review it and explicitly publish the application.
2. Change Chart maximum. The chart axis reads a custom property that is itself bound to session state.
3. Toggle Show chart legend. The legend, table row count and repeater columns change together.
4. Change Repeater gap and Split position. Write different notes in the embedded forms and confirm their independent values remain.
5. Open a second operator tab. Its state starts from independent defaults.
6. In Designer, inspect the corresponding ƒx rows and the custom property at the bottom. Remove a binding, Undo, and verify the original binding returns.

No gateway connections, tags, credentials, scripts or equipment writes are included in this portable example.