DrawRectView.kt

package jp.tsur.android

import android.content.Context
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Paint
import android.graphics.RectF
import android.util.AttributeSet
import android.view.View

class DrawRectView(context: Context?, attrs: AttributeSet?) : View(context, attrs) {

    private val paint: Paint = Paint(Paint.ANTI_ALIAS_FLAG)
    private var rect: RectF? = null

    init {
        paint.color = Color.GREEN
        paint.strokeWidth = 10f
    }

    override fun onDraw(canvas: Canvas?) {
        super.onDraw(canvas)
        val rect1 = rect
        rect1 ?: return

        canvas?.drawRect(rect1.left, rect1.top, rect1.right, rect1.bottom, paint)
    }

    fun draw(rect: RectF) {
        this.rect = rect
        postInvalidate()
    }
}