Draw simple XY graph ( plot ) with Kotlin without 3rd party library

user_9696274 0
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I want to draw a simple XY chart using my data parsed from JSON, but every answer here is redirecting to using some sort of library. I want to draw it without any library usage, is there is a possible way to do this in Kotlin ?

PS No, it's NOT a homework or smth.

kotlin graph android
1 Answers

There is one simple way to integrate a graph by writing custom view

( original:https://github.com/SupahSoftware/AndroidExampleGraphView )

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

class GraphView(context: Context, attributeSet: AttributeSet) : View(context, attributeSet) {

    private val dataSet = mutableListOf<DataPoint>()
    private var xMin = 0
    private var xMax = 0
    private var yMin = 0
    private var yMax = 0

    private val dataPointPaint = Paint().apply {
        color = Color.BLUE
        strokeWidth = 7f
        style = Paint.Style.STROKE
    }

    private val dataPointFillPaint = Paint().apply {
        color = Color.WHITE
    }

    private val dataPointLinePaint = Paint().apply {
        color = Color.BLUE
        strokeWidth = 7f
        isAntiAlias = true
    }

    private val axisLinePaint = Paint().apply {
        color = Color.RED
        strokeWidth = 10f
    }

    fun setData(newDataSet: List<DataPoint>) {
        xMin = newDataSet.minBy { it.xVal }?.xVal ?: 0
        xMax = newDataSet.maxBy { it.xVal }?.xVal ?: 0
        yMin = newDataSet.minBy { it.yVal }?.yVal ?: 0
        yMax = newDataSet.maxBy { it.yVal }?.yVal ?: 0
        dataSet.clear()
        dataSet.addAll(newDataSet)
        invalidate()
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        dataSet.forEachIndexed { index, currentDataPoint ->
            val realX = currentDataPoint.xVal.toRealX()
            val realY = currentDataPoint.yVal.toRealY()

            if (index < dataSet.size - 1) {
                val nextDataPoint = dataSet[index + 1]
                val startX = currentDataPoint.xVal.toRealX()
                val startY = currentDataPoint.yVal.toRealY()
                val endX = nextDataPoint.xVal.toRealX()
                val endY = nextDataPoint.yVal.toRealY()
                canvas.drawLine(startX, startY, endX, endY, dataPointLinePaint)
            }

            canvas.drawCircle(realX, realY, 7f, dataPointFillPaint)
            canvas.drawCircle(realX, realY, 7f, dataPointPaint)
        }

        canvas.drawLine(0f, 0f, 0f, height.toFloat(), axisLinePaint)
        canvas.drawLine(0f, height.toFloat(), width.toFloat(), height.toFloat(), axisLinePaint)
    }
    private fun Int.toRealX() = toFloat() / xMax * width
    private fun Int.toRealY() = toFloat() / yMax * height

}

data class DataPoint(
    val xVal: Int,
    val yVal: Int
)
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