---
name: maui-hybridwebview
description: >
  Guidance for embedding web content in .NET MAUI apps using HybridWebView,
  including JavaScript–C# interop, bidirectional communication, raw messaging,
  and trimming/NativeAOT considerations.
  USE FOR: "HybridWebView", "JavaScript interop", "embed web content", "JS to C# interop",
  "C# to JavaScript", "web view interop", "raw message", "InvokeJavaScriptAsync",
  "web content MAUI".
  DO NOT USE FOR: deep linking from external URLs (use maui-deep-linking),
  REST API calls (use maui-rest-api), or Blazor Hybrid apps (different from HybridWebView).
---

# HybridWebView in .NET MAUI

`HybridWebView` hosts HTML/JS/CSS content inside a .NET MAUI app with bidirectional C#↔JS communication. It is **not** a general browser control — it is designed for local web content shipped with the app.

## Common gotchas

| Issue | Fix |
|---|---|
| Blank white screen | Web assets missing from `Resources/Raw/wwwroot` or `DefaultFile` not set |
| JS interop silently fails | Missing `<script src="_hwv/HybridWebView.js"></script>` in HTML |
| `InvokeJavaScriptAsync` returns null | Return type missing `[JsonSerializable]` attribute in `JsonSerializerContext` |
| JS → C# calls do nothing | `SetInvokeJavaScriptTarget` not called before JS invokes C# methods |
| Serialization crash with trimming | Not using source-generated `JsonSerializerContext` |

## ⚠️ Bridge script is mandatory

The HTML page **must** include the bridge script **before** any app scripts:

```html
<!-- ✅ Correct order -->
<script src="_hwv/HybridWebView.js"></script>
<script src="scripts/app.js"></script>

<!-- ❌ Wrong — app.js loads before bridge, interop calls fail silently -->
<script src="scripts/app.js"></script>
<script src="_hwv/HybridWebView.js"></script>
```

## JSON serialization — every type must be registered

Every parameter type **and** return type used in `InvokeJavaScriptAsync` must have a `[JsonSerializable]` entry:

```csharp
// ✅ Correct — all interop types registered
[JsonSerializable(typeof(int))]
[JsonSerializable(typeof(string))]
[JsonSerializable(typeof(Person))]
internal partial class MyJsonContext : JsonSerializerContext { }

// ❌ Wrong — adding a new type to interop without registering it
// This causes silent null returns or runtime exceptions
```

> **Rule**: When you add a new type to the interop surface, you **must** add a `[JsonSerializable(typeof(T))]` attribute to the context. Forgetting this is the #1 cause of mysterious interop failures.

## SetInvokeJavaScriptTarget — timing matters

```csharp
// ✅ Set target BEFORE the web page loads and JS calls C#
myHybridWebView.SetInvokeJavaScriptTarget(new MyJsBridge());

// ❌ Setting it after JS already tried to call — calls are lost
```

⚠️ Call `SetInvokeJavaScriptTarget` during page construction or `OnAppearing`, not lazily.

## Exception handling (.NET 9+)

JS exceptions thrown during `InvokeJavaScriptAsync` are forwarded to .NET. Always wrap interop calls:

```csharp
// ✅ Catches JS errors
try
{
    var result = await myHybridWebView.InvokeJavaScriptAsync<string>(
        "riskyFunction", MyJsonContext.Default.String);
}
catch (Exception ex)
{
    Debug.WriteLine($"JS error: {ex.Message}");
}

// ❌ Unhandled JS exception crashes the interop pipeline
var result = await myHybridWebView.InvokeJavaScriptAsync<string>(
    "riskyFunction", MyJsonContext.Default.String);
```

## Trimming / NativeAOT pitfalls

Trimming is **disabled by default** in MAUI projects. If you enable it:

- ⚠️ You **must** use source-generated `JsonSerializerContext` (not reflection-based serialization)
- ⚠️ Set `JsonSerializerIsReflectionEnabledByDefault` to `false`
- Using `JsonSerializerContext` as shown above is recommended **regardless** of trimming settings

```xml
<PropertyGroup>
  <PublishTrimmed>true</PublishTrimmed>
  <JsonSerializerIsReflectionEnabledByDefault>false</JsonSerializerIsReflectionEnabledByDefault>
</PropertyGroup>
```

## Decision framework — typed interop vs raw messages

| Need | Use |
|---|---|
| Structured data exchange with type safety | `InvokeJavaScriptAsync` / `InvokeDotNet` with `JsonSerializerContext` |
| Simple string payloads, fire-and-forget | `SendRawMessage` / `RawMessageReceived` |
| Calling C# from JS with return values | `InvokeDotNet` (target must be set first) |
| Multiple JS functions to call | Typed interop — one `InvokeJavaScriptAsync` per function |

## Quick checklist

- [ ] Web content is under `Resources/Raw/wwwroot`
- [ ] `index.html` includes `<script src="_hwv/HybridWebView.js"></script>` **before** app scripts
- [ ] `DefaultFile` is set (or defaults to `index.html`)
- [ ] Every interop type has a `[JsonSerializable]` entry in a `JsonSerializerContext`
- [ ] `SetInvokeJavaScriptTarget` is called before JS invokes C# methods
- [ ] `InvokeJavaScriptAsync` calls are wrapped in try/catch (.NET 9+)
- [ ] If trimming enabled: source-generated JSON serialization configured


---
Source attribution: davidortinau
Original project: https://github.com/davidortinau/maui-skills/blob/79bb4bfd8f671ed0dd97bdf92a36430928e8d984/plugins/maui-skills/skills/maui-hybridwebview/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 David Ortinau

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: davidortinau
Original project: https://github.com/davidortinau/maui-skills/blob/79bb4bfd8f671ed0dd97bdf92a36430928e8d984/plugins/maui-skills/skills/maui-hybridwebview/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Frontend Developer, Mobile Developer, Product Manager
Specialties: API, Design, Frontend
Tools: .Net Maui
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: d6bc4cf135acd2f8d51370b57e89402d881265229085f747a99710292c2ee17d