It's tricky because we're hopping from one first responder to another.
Specifically, from the CaptionView.textView, which shows the keyboard, to
making the AttachmentApprovalViewController first responder, which shows the
BottomToolbar message text field, so in short order, we're getting multiple
notifications.
User hit's "Done" with caption
- Point A - CaptionView is positioned at the top of the keyboard
- Hide keyboard (frame change details must be calculated by y offset, since willChanage notification doesn't "shrink" the keyboard frame, it just offsets it to be non-visible.
- Point B - caption view is positioned at the bottom of the screen, input accessory view not visible
- Show Keyboard (not actually showing the *keyboard* here, but rather the VC's input accessory view)
- Point C - caption view is positioned atop the input accessory view
We want to animated smoothly from A->C, skipping B. But how do we do that robustly? We could track something like "last known input accessory view height" and never present the captionView below that. But I'm worried it won't be very robust since the input accessory view can change height, e.g. text view grows with text content or dynamic text changes.
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