Crazy Fancy Android Text

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Crazy Fancy Android Text DevFest MN (2019) @danlew42

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The Trouble with Trello (Markdown) • Basic nesting of elements would fail • Image loading was iﬀy at best • Endless URL parsing issues • Code blocks would fail to render due to cool wind breezes • HTML-escaped entities would scramble text • Russian text crashes the app

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Text -> Abstract Syntax Tree -> Fancy TextView

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Simple Styles

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Styling an Entire TextView

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Styling an Entire TextView

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Spannable Span Span Span Span Span Span

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Deﬁnitions Span - markup objects that can style text Spannable - text with mutable spans Spanned - text with spans

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Constructing Spannables

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Easy Mode: HTML ^Whoa this _is wild! \n\n How did you do that? \n\n I cheated Spans! ==

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Easy Mode: HTML ^Whoa this _is wild! \n\n How did you do that? \n\n I cheated Spans!

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Easy Mode: HTML textView.text = HtmlCompat.fromHtml( "^Whoa this _is wild!" + "\n\n" + "How did you do that?" + "\n\n" + "I cheated Spans!”, 0 )

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Easy Mode: HTML == textView.text = HtmlCompat.fromHtml( "^Whoa this _is wild!" + "\n\n" + "How did you do that?" + "\n\n" + "I cheated Spans!”, 0 )

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Easy Mode: HTML !=

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Easy Mode: HTML != ^Whoa this _is wild! \n\n How did you do that? \n\n I cheated Spans! textView.text = HtmlCompat.fromHtml( "^Whoa this _is wild!" + "\n\n" + "How did you do that?" + "\n\n" + "I cheated Spans!”, 0 )

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HTML Drawbacks • Limited tag support • Strings support diﬀerent tags than Html.fromHtml() • Details: https://blog.danlew.net/2011/04/13/html_in_text_views/

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Hard Mode: Build Your Own • Code only • Verbose • Flexible & powerful

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Hard Mode: Build Your Own == val text = SpannableString("Whoa this is wild!\n\nHow did you do that?\n\nI cheated Spans!") text.setSpan(SuperscriptSpan(), 0, 4, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(StyleSpan(Typeface.ITALIC), 5, 9, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(SubscriptSpan(), 10, 12, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(StyleSpan(Typeface.BOLD), 13, 17, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(ForegroundColorSpan(Color.RED), 20, 40, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(StrikethroughSpan(), 42, 51, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE)

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Hard Mode: Build Your Own val text = SpannableString("Whoa this is wild!\n\nHow did you do that?\n\nI cheated Spans!") text.setSpan(SuperscriptSpan(), 0, 4, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(StyleSpan(Typeface.ITALIC), 5, 9, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(SubscriptSpan(), 10, 12, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(StyleSpan(Typeface.BOLD), 13, 17, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(ForegroundColorSpan(Color.RED), 20, 40, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(StrikethroughSpan(), 42, 51, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE)

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Hard Mode: Build Your Own Class Mutable Text Mutable Markup SpannedString No No SpannableString No Yes SpannableStringBuilder Yes Yes

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Hard Mode: Build Your Own text.setSpan( SuperscriptSpan(), 0, 4, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE ) Span Start End WTF?

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Span Flags • Flags deﬁne behavior • Can control precise behavior… • …But just use 0 or SPAN_EXCLUSIVE_EXCLUSIVE

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Multiple Spans

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Built-In Spans N

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Span Types • Appearance-only spans • Metric-aﬀecting spans • Paragraph-aﬀecting spans

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Appearance-only Spans • StyleSpan • UnderlineSpan • ForegroundColorSpan • BackgroundColorSpan • URLSpan

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Metric-affecting Spans • SuperscriptSpan • RelativeSizeSpan • ImageSpan

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Paragraph-affecting Spans • LeadingMarginSpan • DrawableMarginSpan • BulletSpan • QuoteSpan

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Bad Spans • BulletSpan - Sucks until API 28! • QuoteSpan - Sucks until API 28! • URLSpan - Crashes when there’s no intent handler!

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Custom Spans

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Custom Span Process • Pick a Span to extend • Decipher how it works • Get frustrated by limited Span API

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Thematic Break Span

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Thematic Break Span ≈ ≈ ReplacementSpan

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Thematic Break Span ReplacementSpan

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Thematic Break Span ReplacementSpan

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Thematic Break Span ReplacementSpan

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Thematic Break Span ReplacementSpan

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Thematic Break Span class ThematicBreakSpan(val lineColor: Int, val lineHeight: Int, val verticalPadding: Int) : ReplacementSpan() { override fun getSize(paint: Paint, text: CharSequence?, start: Int, end: Int, fm: Paint.FontMetricsInt?): Int { if (fm != null) { fm.ascent = -lineHeight - (2 * verticalPadding) fm.descent = 0 fm.top = fm.ascent fm.bottom = 0 } return 1 } ... }

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Thematic Break Span class ThematicBreakSpan(val lineColor: Int, val lineHeight: Int, val verticalPadding: Int) : ReplacementSpan() { override fun draw(canvas: Canvas, text: CharSequence?, start: Int, end: Int, x: Float, top: Int, y: Int, bottom: Int, paint: Paint) { val color = paint.color val style = paint.style paint.color = lineColor paint.style = Paint.Style.FILL canvas.drawRect(etc etc etc) paint.color = color paint.style = style } }

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Custom Span Limitations • Bound by API limitations • Cannot Parcelable custom spans • Cannot copy/paste your custom span • Choose wisely what you extend

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Example Custom Spans • BetterURLSpan : URLSpan • BulletSpanCompat : BulletSpan • QuoteSpanCompat : QuoteSpan • CodeBackgroundSpan : LineBackgroundSpan • ListItemSpan : BulletSpan • ThematicBreakSpan : ReplacementSpan

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Odds & Ends

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Reusing Spans? val boldSpan = StyleSpan(Typeface.BOLD) val text = SpannableString("Alice threw the ball to Bob") text.setSpan(boldSpan, 0, 5, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE) text.setSpan(boldSpan, 24, 27, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE)

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Spacing Newlines Newlines Newlines w/ RelativeSizeSpan

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Construction Optimization Class Mutable Text Mutable Markup SpannableString No Yes SpannableStringBuilder Yes Yes

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Construction Optimization • SpannableStringBuilder was taking 98% of construction time • Faster method: val sb = StringBuilder() val spans = mutableListOf() data class SpanInfo(val what: Any, val start: Int, val end: Int, val flags: Int)

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Construction Optimization Construction Layout SpannableStringBuilder 51.3ms 9.4ms StringBuilder + SpannableString 1.5ms 16.4ms https://blog.danlew.net/2018/08/30/exploring-spannable-performance/

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Replacement Spans • Cannot attach to empty space • Options • Invisible character • Fallback text if replacement span fails • Space character

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Testing Spans • Comparing two Spannables is diﬃcult because… • Span API is weird • Spans do not implement equals() • Not all Span attributes are public

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Testing Spans val spanObjects = spanned.getSpans(0, spanned.length, Any::class.java) spanObjects.forEach { span -> val start = expected.getSpanStart(span) val end = expected.getSpanEnd(span) val flags = expected.getSpanFlags(span) }

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Testing Spans val spanObjects = spanned.getSpans(0, spanned.length, Any::class.java) spanObjects.forEach { span -> val start = spanned.getSpanStart(span) val end = spanned.getSpanEnd(span) val flags = spanned.getSpanFlags(span) }

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Testing Spans fun assertSpanEquals(expected: RelativeSizeSpan, actual: RelativeSizeSpan) { assertEquals(expected.sizeChange, actual.sizeChange) } fun assertSpanEquals(expected: LeadingMarginSpan.Standard, actual:LeadingMarginSpan.Standard) { assertEquals(expected.getLeadingMargin(true), actual.getLeadingMargin(true)) assertEquals(expected.getLeadingMargin(false), actual.getLeadingMargin(false)) }

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Resources • Florina Muntenescu: https://medium.com/@ﬂorina.muntenescu • Optimizing spans • Styling internationalized text • …And more! • Google IO Talk: https://youtu.be/x-FcOX6ErdI

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Questions? @danlew42