VerticalTextView that extends AppCompatTextView

VerticalTextView.kt

package uk.co.thewirelessguy.thewirelessguy.widget

import android.content.Context
import android.graphics.Canvas
import android.text.BoringLayout
import android.text.Layout
import android.text.TextUtils
import android.util.AttributeSet
import android.view.Gravity
import androidx.appcompat.widget.AppCompatTextView
import androidx.core.graphics.withSave

/**
 * VerticalTextView that extends AppCompatTextView
 *
 * To use in an XML layout:
 * <com.YOUR_PACKAGE_NAME.VerticalTextView>
 *
 * All standard styles and attributes of a AppCompatTextView can be used. By default, rotated text
 * is from top to bottom. If you set android:gravity="bottom", then it's drawn from bottom to top.
 *
 * Adapted from:
 * @link http://stackoverflow.com/questions/1258275/vertical-rotated-label-in-android
 */

class VerticalTextView(context: Context, attrs: AttributeSet) : AppCompatTextView(context, attrs) {
    private val topDown = gravity.let { g ->
        !(Gravity.isVertical(g) && g.and(Gravity.VERTICAL_GRAVITY_MASK) == Gravity.BOTTOM)
    }
    private var layout1: Layout? = null
    private val metrics = BoringLayout.Metrics()
    private var padLeft = 0
    private var padTop = 0

    /**
     * onMeasure override required if using wrap_content for layout_height.
     * Without onMeasure the text will be truncated to the layout_height with an ellipse.
     */
    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        super.onMeasure(heightMeasureSpec, widthMeasureSpec)
        setMeasuredDimension(measuredHeight, measuredWidth)
    }

    override fun setText(text: CharSequence, type: BufferType) {
        super.setText(text, type)
        layout1 = null
    }

    /**
     * BoringLayout is used to draw text on a view. It is called "boring" because it only handles a
     * single line of left-to-right text without any interesting characters such as emoji.
     * This simplification allows the class to override onDraw with more efficient logic than the
     * default does.
     */
    private fun makeLayout(): Layout? {
        when (layout1) {
            null -> {
                metrics.width = height
                paint.color = currentTextColor
                paint.drawableState = drawableState
                layout1 = BoringLayout.make(text, paint, metrics.width, Layout.Alignment.ALIGN_NORMAL, 2f, 0f, metrics, false, TextUtils.TruncateAt.END, height - compoundPaddingLeft - compoundPaddingRight)
                padLeft = compoundPaddingLeft
                padTop = extendedPaddingTop
            }
        }
        return layout1
    }

    override fun onDraw(canvas: Canvas) {
        when (layout) {
            null -> return
            else -> {
                canvas.withSave {
                    when {
                        topDown -> {
                            val fm = paint.fontMetrics
                            translate(textSize - (fm.bottom + fm.descent), 0f)
                            rotate(90f)
                        }
                        else -> {
                            translate(textSize, height.toFloat())
                            rotate(-90f)
                        }
                    }
                    translate(padLeft.toFloat(), padTop.toFloat())
                    makeLayout()?.draw(this)
                }
            }
        }
    }
}