HighlightView.kt

HighlightView.kt

package com.linecorp.highlightview

import android.annotation.SuppressLint
import android.content.Context
import android.content.res.TypedArray
import android.graphics.Canvas
import android.graphics.Color
import android.graphics.Paint
import android.graphics.PorterDuff
import android.graphics.PorterDuffXfermode
import android.support.annotation.AttrRes
import android.support.constraint.ConstraintLayout
import android.util.AttributeSet
import android.view.LayoutInflater
import android.view.View

class HighlightView : ConstraintLayout {
    private lateinit var view: View
    private lateinit var styledAttrs: TypedArray

    private val paint: Paint
        get() = Paint().apply {
            flags = Paint.ANTI_ALIAS_FLAG
            xfermode = PorterDuffXfermode(PorterDuff.Mode.CLEAR)
        }

    private val layoutInflater: LayoutInflater
        get() = context.getSystemService(Context.LAYOUT_INFLATER_SERVICE) as LayoutInflater
    private val highlightPadding: Int
        get() = if (::styledAttrs.isInitialized) {
            styledAttrs.getDimensionPixelSize(
                R.styleable.HighlightView_highlight_padding,
                DEFAULT_HIGHLIGHT_PADDING
            )
        } else {
            DEFAULT_HIGHLIGHT_PADDING
        }

    private var target: HighlightTarget? = null

    constructor(context: Context) : super(context) {
        initView()
    }

    constructor(
        context: Context,
        attrs: AttributeSet
    ) : super(context, attrs) {
        initView(attrs)
    }

    constructor(
        context: Context,
        attrs: AttributeSet,
        @AttrRes defStyleAttr: Int
    ) : super(
        context,
        attrs,
        defStyleAttr
    ) {
        initView(attrs, defStyleAttr)
    }

    override fun onDraw(canvas: Canvas?) {
        canvas?.apply {
            drawBackgroundColor()
            maybeDrawHighlightCircle()
        }
    }

    private fun initView(
        attrs: AttributeSet? = null,
        @AttrRes defStyleAttr: Int = UNSET_ATTRIBUTE_RESOURCE
    ) {
        setWillNotDraw(false)
        setLayerType(LAYER_TYPE_HARDWARE, null /* paint */)
        view = layoutInflater
            .inflate(
                R.layout.highlight_view,
                this /* root */,
                false /* attachToRoot */
            )
            .maybeApplyStyledAttributes(attrs, defStyleAttr)
            .also(::addView)
    }

    fun highlight(target: HighlightTarget) {
        this.target = target
        invalidate()
    }

    @SuppressLint(value = ["Recycle"])
    private fun View.maybeApplyStyledAttributes(
        attrs: AttributeSet? = null,
        @AttrRes defStyleAttr: Int
    ): View {
        if (attrs == null) {
            return this
        }
        styledAttrs = if (defStyleAttr == UNSET_ATTRIBUTE_RESOURCE) {
            context.obtainStyledAttributes(
                attrs,
                R.styleable.HighlightView
            )
        } else {
            context.obtainStyledAttributes(
                attrs,
                R.styleable.HighlightView,
                defStyleAttr,
                0 /* defStyleRes */
            )
        }
        return this
    }

    private fun Canvas.drawBackgroundColor() =
        background?.draw(this /* canvas */)
            ?: drawColor(DEFAULT_BACKGROUND_COLOR)

    private fun Canvas.maybeDrawHighlightCircle() =
        target?.viewReference?.get()?.let { targetView: View ->
            drawCircle(
                targetView.x,
                targetView.y,
                highlightPadding.toFloat(),
                paint
            )
        }

    companion object {
        private const val UNSET_ATTRIBUTE_RESOURCE = -1
        private const val DEFAULT_HIGHLIGHT_PADDING = 0
        private val DEFAULT_BACKGROUND_COLOR =
            Color.parseColor("#66000000" /* colorString */)
    }
}