我无法完美地将 Java 转换为 Kotlin

Question

I'm new to Kotlin and Java.

I've been building GPA grade calculator and showing them with graph on Android Studio with Kotlin.

I use hellochart lib.

I can't convert the example from java to kotlin.

this is the link of example I tried to use https://www.codingdemos.com/draw-android-line-chart/ ?

    package com.codingdemos.codingdemos;
    import android.graphics.Color;
    import android.os.Bundle;
    import android.support.v7.app.AppCompatActivity;
    import java.util.ArrayList;
    import java.util.List;
    import lecho.lib.hellocharts.model.Axis;
    import lecho.lib.hellocharts.model.AxisValue;
    import lecho.lib.hellocharts.model.Line;
    import lecho.lib.hellocharts.model.LineChartData;
    import lecho.lib.hellocharts.model.PointValue;
    import lecho.lib.hellocharts.model.Viewport;
    import lecho.lib.hellocharts.view.LineChartView;
    public class MainActivity extends AppCompatActivity {
        LineChartView lineChartView;
    String[] axisData = {"Jan", "Feb", "Mar", "Apr", "May", "June", "July",
    "Aug", "Sept","Oct", "Nov", "Dec"};
    int[] yAxisData = {50, 20, 15, 30, 20, 60, 15, 40, 45, 10, 90, 18};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            lineChartView = findViewById(R.id.chart);
            List yAxisValues = new ArrayList();
            List axisValues = new ArrayList();

            Line line = new Line(yAxisValues).setColor(Color.parseColor("#9C27B0"));
    for (int i = 0; i < axisData.length; i++) {
            axisValues.add(i, new AxisValue(i).setLabel(axisData[i]));
        }

        for (int i = 0; i < yAxisData.length; i++) {
            yAxisValues.add(new PointValue(i, yAxisData[i]));
        }

        List lines = new ArrayList();
        lines.add(line);

        LineChartData data = new LineChartData();
        data.setLines(lines);

        Axis axis = new Axis();
        axis.setValues(axisValues);
        axis.setTextSize(16);
        axis.setTextColor(Color.parseColor("#03A9F4"));
        data.setAxisXBottom(axis);

        Axis yAxis = new Axis();
        yAxis.setName("Sales in millions");
        yAxis.setTextColor(Color.parseColor("#03A9F4"));
        yAxis.setTextSize(16);
        data.setAxisYLeft(yAxis);

        lineChartView.setLineChartData(data);
        Viewport viewport = new Viewport(lineChartView.getMaximumViewport());
        viewport.top = 110;
        lineChartView.setMaximumViewport(viewport);
        lineChartView.setCurrentViewport(viewport);
    }

}

Please help me to convert it to Kotlin without no error:(. Thankyou

Answer 1

Try this code.. Hope it works for you

class MainActivity : AppCompatActivity() {
 private var axisData: Array<String> = arrayOf(
    "Jan",
    "Feb",
    "Mar",
    "Apr",
    "May",
    "June",
    "July",
    "Aug",
    "Sept",
    "Oct",
    "Nov",
    "Dec"
)
 private var yAxisData: IntArray = intArrayOf(50, 20, 15, 30, 20, 60, 15, 40, 45, 10, 90, 18)
override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    val yAxisValues:ArrayList<PointValue> = ArrayList()
    val axisValues:ArrayList<AxisValue> = ArrayList()

    val line = Line(yAxisValues).setColor(Color.parseColor("#9C27B0"))
    for (i in axisData.indices) {
        axisValues.add(i, AxisValue(i.toFloat()).setLabel(axisData[i]))
    }

    for (i in yAxisData.indices) {
        yAxisValues.add(PointValue(i.toFloat(), yAxisData[i].toFloat()))
    }

    val lines:ArrayList<Line> = ArrayList()
    lines.add(line)

    val data = LineChartData()
    data.lines = lines

    val axis = Axis()
    axis.values = axisValues
    axis.textSize = 16
    axis.textColor = Color.parseColor("#03A9F4")
    data.axisXBottom = axis

    val yAxis = Axis()
    yAxis.name = "Sales in millions"
    yAxis.textColor = Color.parseColor("#03A9F4")
    yAxis.textSize = 16
    data.axisYLeft = yAxis

    chart.lineChartData = data
    val viewport = Viewport(chart.maximumViewport)
    viewport.top = 110f
    chart.maximumViewport = viewport
    chart.currentViewport = viewport
}
}

Answer 2

We can easily Convert java project to Kotlin Follow these steps

Convert Single java file to kotlin

open java class / select from project > Go to tool Bar > click on Code > select Convert java file to kotlin file

Convert java project into kotlin

Select app form side menu (see in screen shot) >Go to tool bar > Click on Code > Select Convert java file to kotlin file

Short cut key is: Ctrl + Alt + Shift+K

Some time in kotlin file show some error, to resolve these error click on error line and press Alt + Enter to display error message with resolve hints

Answer 3

Usually, I habited to convert JAVA code to kotlin using this

Select convert from java (from the top right side)

using this your MainActivity looks like this.

package com.codingdemos.codingdemos
import android.graphics.Color
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import java.util.ArrayList
import lecho.lib.hellocharts.model.Axis
import lecho.lib.hellocharts.model.AxisValue
import lecho.lib.hellocharts.model.Line
import lecho.lib.hellocharts.model.LineChartData
import lecho.lib.hellocharts.model.PointValue
import lecho.lib.hellocharts.model.Viewport
import lecho.lib.hellocharts.view.LineChartView
class MainActivity:AppCompatActivity() {
  internal var lineChartView:LineChartView
  internal var axisData = arrayOf<String>("Jan", "Feb", "Mar", "Apr", "May", "June", "July", "Aug", "Sept", "Oct", "Nov", "Dec")
  internal var yAxisData = intArrayOf(50, 20, 15, 30, 20, 60, 15, 40, 45, 10, 90, 18)
  protected fun onCreate(savedInstanceState:Bundle) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    lineChartView = findViewById(R.id.chart)
    val yAxisValues = ArrayList()
    val axisValues = ArrayList()
    val line = Line(yAxisValues).setColor(Color.parseColor("#9C27B0"))
    for (i in axisData.indices)
    {
      axisValues.add(i, AxisValue(i).setLabel(axisData[i]))
    }
    for (i in yAxisData.indices)
    {
      yAxisValues.add(PointValue(i, yAxisData[i]))
    }
    val lines = ArrayList()
    lines.add(line)
    val data = LineChartData()
    data.setLines(lines)
    val axis = Axis()
    axis.setValues(axisValues)
    axis.setTextSize(16)
    axis.setTextColor(Color.parseColor("#03A9F4"))
    data.setAxisXBottom(axis)
    val yAxis = Axis()
    yAxis.setName("Sales in millions")
    yAxis.setTextColor(Color.parseColor("#03A9F4"))
    yAxis.setTextSize(16)
    data.setAxisYLeft(yAxis)
    lineChartView.setLineChartData(data)
    val viewport = Viewport(lineChartView.getMaximumViewport())
    viewport.top = 110
    lineChartView.setMaximumViewport(viewport)
    lineChartView.setCurrentViewport(viewport)
  }
}

Answer 4

I've tried to convert to idiomatic Kotlin here-

class MainActivity : AppCompatActivity() {
    private val axisData = listOf(
        "Jan", "Feb", "Mar", "Apr", "May", "June", "July", "Aug", "Sept", "Oct", "Nov", "Dec"
    )
    private val yAxisData = listOf(50, 20, 15, 30, 20, 60, 15, 40, 45, 10, 90, 18)

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val lineChartView = findViewById(R.id.chart)

        val axisValues = axisData.mapIndexed { i, data -> AxisValue(i).setLabel(data) }
        val yAxisValues = yAxisData.mapIndexed { i, data -> PointValue(i, data) }

        val line = Line(yAxisValues).setColor(Color.parseColor("#9C27B0"))
        val lines = listOf(line)

        val data = LineChartData()
        data.setLines(lines)

        val axis = Axis().apply {
            setValues(axisValues)
            setTextSize(16)
            setTextColor(Color.parseColor("#03A9F4"))
        }
        data.setAxisXBottom(axis)

        val yAxis = Axis().apply {
            setName("Sales in millions")
            setTextColor(Color.parseColor("#03A9F4"))
            setTextSize(16)
        }
        data.setAxisYLeft(yAxis)

        lineChartView.setLineChartData(data)
        val viewport = Viewport(lineChartView.getMaximumViewport())
        viewport.top = 110
        lineChartView.setMaximumViewport(viewport)
        lineChartView.setCurrentViewport(viewport)
    }
}