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CenterAlignedTextView
package me.rajin.centeralignedtextview
import android.content.Context
import android.graphics.Rect
import android.graphics.Typeface
import android.text.SpannableStringBuilder
import android.text.Spanned
import android.text.TextPaint
import android.text.style.CharacterStyle
import android.text.style.UpdateAppearance
import android.util.AttributeSet
import androidx.appcompat.widget.AppCompatTextView
import androidx.core.text.getSpans
import java.util.WeakHashMap
class CenterAlignedTextView : AppCompatTextView {
companion object {
/**
* ratio is offset / fontHeight
* fontHeight = ascent - descent
* offset = (capHeight - ascent - descent) / 2 (in iOS)
* Note that in android, ascent and descent is multiplied by -1 (because yAxis is downward)
*/
val typeface2fontHeightOffsetRatio = mutableMapOf<Typeface, Float>()
/**
* This map is for calculated offset ratio.
*/
val weakTypeface2fontHeightOffsetRatio = WeakHashMap<Typeface, Float>()
}
var realText: CharSequence? = null
constructor(context: Context) : super(context) {
init(context, null)
}
constructor(context: Context, attrs: AttributeSet?) : super(context, attrs) {
init(context, attrs)
}
constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr) {
init(context, attrs)
}
private fun init(context: Context, attrs: AttributeSet?) {
// refresh span
this.text = text
}
/**
* overriding setText(text: CharSequence?, type: BufferType?) is not complete solution.
* There is one setText method in AppCompatTextView that does not use this method.
* Because there is one setText method that does not call this overridable method.
* setText(char[] text, int start, int len)
* link : https://github.com/aosp-mirror/platform_frameworks_base/blob/e0dd9516b516bc9042ad5d6f4b7fef053ce07d0e/core/java/android/widget/TextView.java#L4063-L4070
*/
override fun setText(text: CharSequence?, type: BufferType?) {
realText = text
val spannedText = text?.let {
SpannableStringBuilder(it).apply {
val spanList = getSpans<VerticalCenterAlignSpan>()
spanList.forEach { span ->
removeSpan(span)
}
setSpan(
VerticalCenterAlignSpan(),
0, it.length, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE
)
}
} ?: text
super.setText(spannedText, type)
}
private class VerticalCenterAlignSpan : CharacterStyle(), UpdateAppearance {
override fun updateDrawState(paint: TextPaint?) {
if (paint != null) {
val ratio = typeface2fontHeightOffsetRatio[paint.typeface] ?: {
// as fallback, calculate offset using "X"'s text bounds
// note that this is not accurate because
// 1. text bounds of "X" can be different from typeface's meta data.
// 2. getTextBounds returns in pixel(int).
// to improve accuracy, we measure ratio with large text size.
weakTypeface2fontHeightOffsetRatio[paint.typeface] ?: {
val oldTextSize = paint.textSize
paint.textSize = 30f
val newFontMetric = paint.fontMetrics
val bounds = Rect()
paint.getTextBounds("X", 0, 1, bounds)
val capHeight = -bounds.top
val calculatedOffset =
(capHeight + newFontMetric.ascent + newFontMetric.descent) / 2f
val ratio =
calculatedOffset / (newFontMetric.descent - newFontMetric.ascent)
weakTypeface2fontHeightOffsetRatio[paint.typeface] = ratio
paint.textSize = oldTextSize
ratio
}()
}()
val fontMetric = paint.fontMetrics
val offsetY = (fontMetric.descent - fontMetric.ascent) * ratio
paint.baselineShift = offsetY.toInt()
}
}
}
}
// Before using CenterAlignedTextView, set font-ratio map.
val spoqaHansRatio = -0.036148648648648626f
val spoqaFonts = listOf(
ResourcesCompat.getFont(this, R.font.spoqa_han_sans_thin),
ResourcesCompat.getFont(this, R.font.spoqa_han_sans_light),
ResourcesCompat.getFont(this, R.font.spoqa_han_sans_bold),
ResourcesCompat.getFont(this, R.font.spoqa_han_sans_regular)
)
spoqaFonts.forEach {
if (it != null) {
typeface2fontHeightOffsetRatio[it] = spoqaHansRatio
}
}
// You may need to do this...
spoqaFonts.map { Typeface.create(it, Typeface.NORMAL) }.forEach {
if (it != null) {
typeface2fontHeightOffsetRatio[it] = spoqaHansRatio
}
}
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