Advanced Plugin Development for the Windows Live Writer SDKWindows Live Writer (WLW) was once a popular desktop blog editor that allowed authors to compose posts offline and publish to many blogging platforms. Although development on WLW slowed after Microsoft’s original project, the Windows Live Writer SDK enables developers to extend the editor with custom plugins — tool windows, publish actions, effects, and content providers — that enhance authoring workflows. This article delves into advanced plugin development for the Windows Live Writer SDK: architecture, extension points, best practices, practical patterns, and troubleshooting tips for building robust, maintainable plugins.
Background and architecture
Windows Live Writer exposes extension points through an SDK built primarily around .NET and COM-style interfaces. Plugins run inside the WLW process and interact with the editor via a set of contracts: post content models, the document object model for the editing surface (HTML/CSS), publishing pipelines, and UI integration hooks. Understanding the runtime context and lifecycle of a WLW plugin is essential:
- Plugins are loaded at startup (or on demand) by WLW.
- Plugins must be mindful of thread affinity — WLW’s UI runs on a single STA thread.
- Plugins interact with the editor’s content model and publish pipeline; changes should be transactional and respect the editor’s undo stack where possible.
- Performance and stability are critical: a misbehaving plugin can crash the whole application.
Extension points and plugin types
Advanced WLW plugin development focuses on a few common extension types:
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Provider plugins
- Content providers supply or transform content (e.g., image hosts, video embed providers).
- They integrate with dialogs that insert media or generate markup.
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Publish plugins
- These hook into the publishing pipeline, augmenting or replacing parts of the process (e.g., pre-publish validation, remote processing, post-publish notifications).
- Often used to implement custom deployment flows or analytics.
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UI integration (tool windows, ribbons, menus)
- Add commands, toolbars, menu items, or dockable panels.
- Provide interactive controls that manipulate the post, templates, or metadata.
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Effects and formatting plugins
- Transform post HTML: apply styles, generate shortcodes, or sanitize content.
- Should preserve semantic content and be reversible whenever possible.
Development environment and project setup
- Use Visual Studio (2012–2015 recommended for compatibility with older WLW SDK assemblies) or a recent VS with appropriate project settings targeting .NET Framework versions supported by WLW (typically .NET 3.5 or .NET 4.0 depending on SDK).
- Reference the WLW SDK assemblies and any COM interop assemblies provided by the SDK.
- Plugins typically build as class libraries (.dll) and are installed to the WLW plugin folder or registered via the user’s configuration so WLW can discover them.
- Use strong naming and an installer (MSI or ClickOnce) for production deployment, ensuring files are placed in correct extension directories and any registry keys are set if required by the SDK.
Key APIs and patterns
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Initialization and registration
- Implement the plugin entry interface and register your plugin with metadata (name, version, author, supported features).
- Use attribute-based or manifest-based registration patterns provided by the SDK.
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Command pattern for UI actions
- Expose commands that WLW binds to menus or toolbars.
- Implement ICommand-like interfaces so actions can be enabled/disabled according to context (e.g., only enabled when a post is open).
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Content model interaction
- Work with the editor’s post object rather than raw document text where possible. This often provides higher-level access to paragraphs, images, and metadata.
- When manipulating HTML directly, use robust HTML parsers (e.g., Html Agility Pack) to avoid brittle string operations.
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Asynchronous operations
- Offload network or disk I/O to background threads; marshal results back to the UI thread.
- Maintain responsiveness: use progress reporting and allow cancellation.
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Error handling and resilience
- Catch exceptions at boundaries between plugin and host. Surface only actionable errors to users and log full details for diagnostics.
- Use retry/backoff strategies for transient network failures.
Example plugin scenarios
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Remote image hosting plugin
- Intercepts inserted local images, uploads them to a remote CDN, replaces src attributes with CDN URLs, and updates post content.
- Needs to show progress, allow image selection options (quality, resize), and preserve alt text and captions.
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Pre-publish linter and formatter
- Analyzes post HTML for accessibility, SEO, and style issues; optionally auto-fixes certain issues (alt text, heading order).
- Hooks into publish pipeline to block publishing if critical issues exist, and offers interactive fixes.
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Shortcode expansion and templating
- Provides a UI to insert complex widgets as shortcodes and expands them to HTML at publish time (or stores both forms to allow editing).
- Maintains round-trip fidelity: users should be able to see and edit the shortcode representation after insertion.
Practical code patterns (conceptual)
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Registering a command:
- Create a class that implements the provided plugin command interface.
- Return metadata (label, icon) and implement Execute(context) to perform the action.
- Use context objects to access the current post, selection, and editor services.
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Safe HTML manipulation:
- Parse HTML into a DOM, locate nodes of interest, modify nodes, and then serialize back.
- Preserve unknown attributes and custom elements to avoid data loss.
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Background uploading with UI progress:
- Start upload on thread-pool thread or Task.Run.
- Report progress via synchronization context to update a progress bar in the tool window.
- On completion, update post content on the UI thread and add an undo action to revert the change.
Security and privacy considerations
- Avoid storing user credentials insecurely. Use the platform’s protected storage APIs (Windows DPAPI) or OAuth flows where possible.
- Be explicit about network calls and obtain user consent when uploading private content.
- Sanitize any content fetched from external sources before inserting into the post to prevent script injection or malformed markup.
Testing and debugging
- Unit-test pure logic (HTML transformations, validators) with sample HTML fixtures.
- Use integration testing with a local WLW instance: attach a debugger to WLW.exe, set breakpoints in your plugin assembly, and step through initialization and UI actions.
- Log to a file with configurable verbosity so users can produce diagnostic logs without exposing sensitive content.
Packaging, deployment, and updates
- Provide an installer that registers the plugin and places files in WLW’s expected extension folder.
- Offer an update mechanism: check a versioned manifest on your server, download new DLLs, and atomically replace them with appropriate locking and restart instructions.
- Ensure backward compatibility with older versions of WLW where feasible; check host capabilities at runtime and degrade features gracefully.
Performance optimization
- Minimize startup work; defer expensive initialization until the plugin is used.
- Cache remote metadata and use conditional requests (ETags/If-Modified-Since) to reduce network overhead.
- Avoid large in-memory copies of post content; operate on incremental changes when possible.
Troubleshooting common issues
- Plugin not loaded: verify DLL is in correct folder, manifest metadata is valid, and assembly targets a compatible .NET version.
- UI freeze or crash: check for long-running work on the UI thread and unhandled exceptions. Use try/catch at plugin boundaries.
- Broken publish pipeline: ensure your plugin respects the host’s publish contracts and properly calls continuation/completion callbacks.
Future-proofing and migration tips
- Abstract host-specific APIs behind interfaces in your plugin to make it easier to port to forks or successors of WLW (e.g., Open Live Writer).
- Keep transformations reversible where possible so users can edit content later.
- Track usage telemetry (respecting privacy) to understand feature adoption and pain points.
Conclusion
Advanced plugin development for the Windows Live Writer SDK requires solid understanding of the host’s extension model, careful UI/threading practices, robust content manipulation, and attention to security and performance. By following best practices — using background operations, safe HTML parsing, clean command patterns, and thorough testing — you can deliver plugins that significantly extend WLW’s capabilities while remaining stable and user-friendly.
If you want, I can provide a small sample plugin scaffold (C#) that demonstrates command registration, a tool window, and safe HTML modification.
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