If we enable the Japanese language in Samsung Keyboard's configuration and switch to it, we can then input Japanese, with proper conversion and completion.
For instance if we type hi, the input is replaced with
ひ, and kanji replacements and completions appear at the bottom of the screen. This context is maintained as we add more characters. The part of our input under consideration is underlined until we select a replacement.
However, there appears to be no way to type a word which contains a katakana hyphen. Suppose I want to type, ha-to to obtain the conversion ハート. The problem is that when the ordinary hyphen is entered, it immediately cancels the conversion/completion search context and causes the
は, which was converted from
ha to be accepted, followed by an ordinary hyphen.
The desired behavior is to have
はー appear, and stay in the conversion mode. Ideally at that point,
ハート ought to be in the list of completions. If not, then at least after we type to, so that our input is
ハート should be available as the substitution.
Google Japanese Input has a hyphen key in the lower right corner for this. Moreover, if you use a hardware keyboard, the ordinary hyphen key serves in this role. The ordinary hyphen works this way in the Microsoft IME mode on Windows, and in other operating systems' input methods, like Gnome on GNU/Linux and whatnot.
How do we enter katakana words containing the katakana ー using the Japanese mode of Samsung Keyboard?
I'm thinking that perhaps there might exist a pure katakana mode (and a hot key combination to switch to it) in which the - key maps to this character.