This module defines a Prism-based event (CheckDataToDownloadEvent) used to signal and coordinate a check for data that needs to be downloaded in the DTS system. It enables decoupled communication between components: a producer (e.g., a service or UI module) raises the event to request validation or assessment of download requirements, optionally bypassing the check (e.g., for forced updates or initialization scenarios). The event carries context via CheckDataToDownloadEventArgs, including whether the check should be skipped and a reference to the originating component.
2. Public Interface
CheckDataToDownloadEvent Type:class inheriting from CompositePresentationEvent<CheckDataToDownloadEventArgs> Behavior: A Prism event used for publishing and subscribing to download-check requests across modules. As a CompositePresentationEvent, it supports thread marshaling (via ThreadOption) and event subscription management (e.g., weak references, multiple subscribers).
bool BypassCheck { get; } — Indicates whether the download check logic should be skipped. true means the check is bypassed (e.g., proceed directly to download or skip validation).
object Producer { get; } — A reference to the component that raised the event (e.g., a view model, service, or controller). Used for tracing or context-aware handling. Constructor:
CheckDataToDownloadEventArgs(bool bypassCheck, object o) — Initializes the args with the bypass flag and producer reference. Both parameters are required and immutable after construction.
3. Invariants
BypassCheck is set at construction and never modified (read-only via private set).
Producer is set at construction and never modified (read-only via private set).
Producer may be null (no validation is enforced in the constructor), but callers are expected to provide a meaningful reference when possible.
The event is intended for one-time publication per request; repeated publications require new event instances.
No ordering guarantees exist for subscribers (Prism’s CompositePresentationEvent delivers events to all subscribers concurrently or in undefined order depending on configuration).
4. Dependencies
Depends on:
Microsoft.Practices.Prism.Events (Prism library for event aggregation).
DTS.Common.Events.Diagnostics namespace (module-scoped grouping; no external cross-module dependencies implied by the file alone).
Used by:
Any module/component needing to trigger or respond to download-check requests (e.g., a data synchronization service, update manager, or UI component).
Subscribers would typically be in modules that handle data download logic (e.g., DTS.DownloadService), though not explicitly stated in this file.
5. Gotchas
Producer is typed as object, not a specific interface or base type (e.g., IProducer), which may lead to runtime type-casting assumptions in subscribers.
No validation on bypassCheck values (e.g., true/false are both accepted without constraint).
The event name CheckDataToDownloadEvent implies a request for a check, but subscribers may misinterpret it as a notification of completed checks—clear documentation of intent is critical.
CompositePresentationEvent implies thread-safety via event aggregation, but subscribers must still handle cross-thread access if Producer is UI-bound (e.g., marshaling to the UI thread).
