UnigramDev/Unigram/composer-typing-performance • f094679 • 4 files, +371/-38
Show SendFilesPopup before the files have been typed

Dropping a lot of files left the user staring at nothing. Every file was
probed before the popup was constructed, one after another, and a probe is a
file open plus a header decode for photos or a whole ffmpeg open for video and
audio. Nothing was on screen until the last one finished.

StorageMedia.ProbeAsync types files concurrently, capped so a large drop cannot
open hundreds of decoders at once, and reports each result with its original
index as it lands. Every await in the chain captures the caller's context, so
the callback arrives on the UI thread.

SendFileExecute no longer probes. Both overloads funnel into SendFilesAsync,
which takes either already-typed items or raw files; with files it builds the
popup empty and starts probing from the Loaded handler. That hook is load
bearing: OpenAsync queues behind any other dialog and only creates its closing
task once it reaches the front, so a Hide from a result that resolved earlier
would have had nothing to close.

Results are buffered and flushed on a low priority dispatch, so everything
resolving within one UI turn is appended by a single AddRange -- one
CollectionChanged, one UpdateView, one UpdatePanel. Each batch is sorted by
original index, so the picked order survives whenever probing is fast enough to
land in one flush, which is the common case.

The permission and size guard moved rather than disappeared. One Validating
function holds the original messages: a loop up front for already-typed items,
a callback for probed ones. The first failure cancels probing and closes the
popup, and the error is raised after OpenAsync returns, which is already where
the caption is restored.

Three consequences. The title counts what is still coming rather than what has
landed, so it shows the drop's real size instead of ticking up, and stays on
the Files declension until types are known. The requested media/files mode
cannot be resolved against an empty list, so UpdateView settles it as the first
items arrive, until the user picks a mode themselves. Send is disabled while
probing and Accept returns early, since Enter bypasses the button and sending
half a drop would silently discard the rest.

The batch CreateAsync overload keeps its serial loop for the callers that still
need it, but its try-catch moved inside the loop: one unreadable file used to
discard every file after it.

Known edge: if every file fails to probe the popup appears briefly and then
closes itself, where before it never appeared. The alternative is waiting for
the first result, which is the stall this removes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

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