Switching input method must not drop already-entered content or the caret

What it is

Going from pen to keyboard, or back, must leave already-in-document characters and ink, and the caret’s place, where they were. Switching is changing effector, not opening an empty document, and not treating the uncommitted span as garbage. Loss looks like: handwriting candidates vanish when the soft keyboard rises, focus jumps to the start of the field, an unfinished character is cleared.

Why it happens

The two methods often have two focus and composition systems. A soft keyboard changes the viewport and may rebind the input connection, so the IME composition is committed or dropped. If the handwriting panel is another window, its temporary ink lives only there and is gone if it was not written back. If the caret resets to “new method defaults to end”, a mid-word edit is broken. A correct switch commits or preserves composition, hands the same document offset to the new effector, and scrolls so that place stays visible (especially when the keyboard covers it). Unfinished handwriting should be recognised once or become an explicit ink block before leaving. System-level method switching (globe key) and an in-app pen/keyboard button must share that save path, or one path is safe and the other drops text.

Studying it

Switch mid-sentence, with unfinished composition, and when the soft keyboard is about to cover the caret. Log content diff and caret index.

Independent variables: switch trigger (system / app button / pen proximity), unfinished composition, whether the keyboard changes the viewport. Dependent measures: lost characters/ink, caret jump distance, whether people have to find the place again.

Where it stops holding

A deliberate “new note” control may clear; that is not an input-method switch. Crash recovery is separate. If a password field forbids handwriting, switching to the pen should refuse and keep the masked type, not clear it.

Applying it

• Commit or freeze composition before switching; caret index stays.
• After the soft keyboard rises, scroll the caret into view so people do not think the text vanished.
• Share save logic between system switching and in-app buttons.
• How to check: stop mid-sentence on an unfinished handwritten character, raise the keyboard; the character should appear in place or insert as recognised text, caret after it. Reverse: type half a word, pick up the pen; typed text must not jump to the start of the field. Diff the document automatically before and after.

Related

• Same group: C5.16.1 Mixing ink and type needs explicit join rules · C5.16.3 Handwriting fits drawing and geometric markup; typing fits long prose · C5.16.4 Switching itself has a cost and is not free
• Adjacent: C5.07 Division of Labor Between Pen and Finger · C6.25 IME State and Switching
• Search: caret persistence · IME composition · mode switch loss