Send events to JavaScript

An event contract lets C# push typed notifications to JavaScript without waiting for a response.

Declare the event

using Vidra.Bridge;

namespace MyApp;

public record SyncStatus(string State, int Completed);

[BridgeEventContract("sync")]
public interface ISyncEvents
{
    [BridgeEvent("statusChanged")]
    void StatusChanged(SyncStatus payload);
}

The source generator creates a typed SyncEvents.StatusChanged token in C#. vidra-codegen creates the matching TypeScript subscription method.

Register the event

Register the generated event name with the bridge:

.UseVidra(dispatcher =>
{
    dispatcher.RegisterEvents(
        SyncEvents.StatusChanged.Contract,
        SyncEvents.StatusChanged.Member);
})

Registration advertises the event in the app contract manifest.

Emit from C#

From a VidraPage, send the generated token and payload:

await Bridge.SendEventAsync(
    SyncEvents.StatusChanged,
    new SyncStatus("uploading", 42));

Code outside the page can receive an IJsCallbackChannel and call the same typed API.

Subscribe from JavaScript

The generated proxy follows the on<EventName> convention:

import { sync } from "./generated/index.js";

const unsubscribe = sync.onStatusChanged((status) => {
  console.log(status.state, status.completed);
});

// Later:
unsubscribe();

The handler receives a generated SyncStatus type. Returning the unsubscribe function from a component cleanup prevents duplicate subscriptions.

Built-in events

Built-in modules expose events through the same generated API:

import { appWindow, connectivity } from "@vidra-dev/sdk";

const stopConnectivity = connectivity.onChanged((status) => {
  console.log(status.access, status.profiles);
});

const stopResize = appWindow.onResized((windowInfo) => {
  console.log(windowInfo.width, windowInfo.height);
});

See MAUI Essentials and Runtime events for available built-in events.