Helps work with vvvv gamma's Channel system from C# — IChannelHub, public channels, [CanBePublished] attributes, hierarchical data propagation, channel subscriptions, bang channels, and spread sub-channels. Use when reading or writing public channels from C# nodes, publishing .NET types as channels, working with IChannelHub, subscribing to channel changes, managing hierarchical channel state, or implementing reactive/observable data flow. Trigger for any mention of IChannel, IChannelHub, reactiv
Channels are named, typed, observable value containers — the central reactive data flow mechanism in vvvv gamma. Any code (patches, C# nodes, external bindings) can read and write channels by their string path.
Key properties:
- Each channel has a path (string), a type, and a current value
Setting a value fires all subscribers (reactive push)
vvvv provides built-in channel bindings for MIDI, OSC, Redis, and UI
Channels persist state across sessions
Public Channels and IChannelHub
Public channels are channels registered in the app-wide channel hub — accessible by any code via string path lookup.
Core API (VL.Core.Reactive)
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CRITICAL: NEVER use hub.TryAddChannel() — it creates channels with null values, which causes NullReferenceException in vvvv's SubChannelsBinding.EnsureMutatingPropertiesAreReflectedInChannels. The SubChannel system tries to walk properties of the null value and crashes. Always use TryGetChannel (lookup only).
[CanBePublished] Attribute
For vvvv to expose .NET type properties as public channels, the type must be decorated with [CanBePublished(true)] from VL.Core.EditorAttributes.
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Rules:
- [CanBePublished(true)] on a class/struct → all properties are published as channels
INLINECODE9 on an individual property → hides it from the channel system
.NET types are NOT published by default — the attribute is required
Available from VL.Core version 2025.7.1-0163+
Channel Path Conventions
Channels use dot-separated hierarchical paths. Spread elements use bracket notation:
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Sub-channels are created automatically by vvvv's SubChannel system when a type with [CanBePublished(true)] is published. You don't create them manually.
Use const string path constants to avoid typos:
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Retry-Bind Pattern
Channels may not exist when your node starts — vvvv publishes them after model initialization. You must retry each frame until the channel appears:
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Once bound, the cached reference is valid for the node's lifetime — no need to re-lookup.
PublicChannelHelper — Reusable Utility
A helper class that encapsulates the retry-bind + optional subscription pattern. Reusable in any project:
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Usage in a ProcessNode:
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Channel Accessor Node Patterns
Three patterns for ProcessNodes that wrap channel access:
Hierarchy Node (reads a model object)
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Leaf Parameter Node (reads a typed value)
Same pattern as hierarchy node, but the output type is a standard leaf value like float, bool, or string.
Indexed Spread Element Node (takes int index)
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Reactive Subscriptions
Subscribe to channel value changes using the standard IObservable pattern:
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Bang Channels
For trigger/event properties (delete, insert, move operations), use System.Reactive.Unit — NOT float:
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The event IS the bang — the value is irrelevant. Subscribe and act on the callback:
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INLINECODE20 channels show as "Unit" type in vvvv's node browser, not "Float".
Hierarchical Data Propagation
vvvv's channel system automatically propagates changes through the hierarchy:
- Write a root record to its channel → all child channels auto-update
Write a leaf channel → parent channels auto-update
This is built into vvvv's SubChannel system — no manual propagation needed
This enables efficient bulk operations:
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Spread Channels and Sub-Channels
When a Spread<T> property is published (where T has [CanBePublished(true)]), vvvv automatically creates sub-channels for each element:
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Setting the spread channel propagates to all sub-channels automatically. No need to update individual sub-channels.
When modifying a spread (add/remove/reorder elements):
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Warning: Spread.AsSpreadUnsafe(array) wraps without copying — the array must NOT be mutated after.
Feedback loop prevention: When writing to a channel you're also subscribed to, use a suppression flag:
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Critical Rules
1. NEVER TryAddChannel — only use TryGetChannel (lookup-only)
Always retry-bind — channels appear after model initialization, not immediately
[CanBePublished(true)] required on .NET types for channel publication
Always dispose subscriptions — in the node's Dispose() method
System.Reactive.Unit for bangs — not float or INLINECODE31
Spread.AsSpreadUnsafe — array must not be mutated after wrapping
Suppression flags — prevent feedback loops when writing to subscribed channels
csharp
public static class ChannelPaths
{
public const string Volume = Settings.Audio.Volume;
public const string Brightness = App.Scene.Display.Brightness;
}
重试绑定模式
当您的节点启动时，通道可能不存在——vvvv 在模型初始化后发布它们。您必须每帧重试直到通道出现：
csharp
[ProcessNode]
public class MyChannelReader : IDisposable
{
private IChannel
public void Update(out float value)
{
// 重试直到通道存在
if (_channel == null)
{
var hub = IChannelHub.HubForApp;
if (hub != null)
_channel = hub.TryGetChannel(Settings.Audio.Volume);
}
// 读取值（带安全转换）
value = _channel?.Object is float f ? f : 0f;
}
public void Dispose() { _channel = null; }
}
一旦绑定，缓存的引用在节点的生命周期内有效——无需重新查找。
PublicChannelHelper——可复用工具类
一个封装了重试绑定 + 可选订阅模式的辅助类。可在任何项目中复用：
csharp
public class PublicChannelHelper : IDisposable
{
private IChannel
public PublicChannelHelper(Action? onNext = null)
{
_onNext = onNext;
}
public IChannel
public bool TryBind(IChannelHub hub, string path)
{
if (_channel != null) return true;
var ch = hub.TryGetChannel(path);
if (ch == null) return false;
