Improved Android HTML escaping

[sebastianludwig]

Previously discussed in #212.

The original issue was that Twine escaped all < with &lt. This made it impossible to use references to styled strings directly in a layout file. #216 changed this behaviour to always leave styling tags alone and never escape <b> and friends. This however made it very cumbersome to combine placeholders with styling. Previous to #216 it was possible to write

String text = getString(R.string.styledPlaceholder, "Twine");
styledPlaceholderGetStringTextView.setText(Html.fromHtml(text));

as suggested by the documentation.

Currently (after #216) users have to write

SpannedString text = new SpannedString(getText(R.string.styledPlaceholder));
String html = Html.toHtml(text);
String formatted = String.format(html, "Twine");
styledPlaceholderGetStringTextView.setText(Html.fromHtml(formatted));

This PR tries to fix the introduced regression and offer the best of both worlds:

• Styling tags in strings not containing placeholders won't be escaped, so it's possible to use them directly in layouts or retrieve them programatically with styling intact with getText()
• Styling tags in strings that do contain placeholders will be escaped, so it's possible to use the old, official getText()+fromHtml way

TL;DR: We made it worse, this makes it better.

As you were involved in the previous discussion @Aqua-Ye, @jpm-polymorph, any thoughts about this?

[jpm-polymorph]

👍

I'm happy with this solution. It's unfortunate that we have to handle the two cases in two separate ways, but we can blame Android for that as they handle strings in two different ways.

[scelis]

This looks great! Thanks so much for all of the investigations and the fix for this complicated issue. One minor suggestion for how to improve the README. If you have time to fix that up, great! Otherwise I'll merge this in the next day or two and update it myself.

[scelis]

Actually, I'll get this merged now.