MPAndroidChart - why line not showing?

问题

I want to create a small application with a schedule. But for some reason, when I add a lot of points to the chart, it simply does not appear, although with a small number of points everything works.

   void f() {
 ArrayList<Entry> values = new ArrayList<>();

    for (int i = x1, index = 0, j = y; i < x2; ++i, ++index)
    {
        float waveLength = (float) calib_a * i +  (float) calib_b;
        int pixel = rotated.getPixel(i, j);
        float I = (Color.red(pixel) + Color.blue(pixel) + Color.green(pixel)) / 765.0f;
        values.add(new Entry((int) waveLength, I));
        Log.d("[SPECTRAl]", " WAVE:  " +waveLength + "  I: " + I);
       // i += 4;
    }



    LineDataSet lineValues = new LineDataSet(values, "");

    lineValues.setColor(Color.BLACK);
    lineValues.setLineWidth(2f);
    LineData line = new LineData(lineValues);
    chart.getXAxis().setGranularity(100f);
    chart.setData(line);
    chart.invalidate();
}

But work with:

   void f() {
 ArrayList<Entry> values = new ArrayList<>();

 values.add(new Entry(100, 6));
 values.add(new Entry(200, 3));
 values.add(new Entry(300, 2));
 values.add(new Entry(400, 4));



    LineDataSet lineValues = new LineDataSet(values, "");

    lineValues.setColor(Color.BLACK);
    lineValues.setLineWidth(2f);
    LineData line = new LineData(lineValues);
    chart.getXAxis().setGranularity(100f);
    chart.setData(line);
    chart.invalidate();
}

回答1:

Following code creating issues:

 for (int i = x1, index = 0, j = y; i < x2; ++i, ++index)
{
    float waveLength = (float) calib_a * i +  (float) calib_b;
    int pixel = rotated.getPixel(i, j);
    float I = (Color.red(pixel) + Color.blue(pixel) + Color.green(pixel)) / 765.0f;
    values.add(new Entry((int) waveLength, I));
    Log.d("[SPECTRAl]", " WAVE:  " +waveLength + "  I: " + I);
   // i += 4;
}

First you need to change casting of int into float into following line as this library get float values as input:

values.add(new Entry((float) waveLength, I));

Instead you can remove casting as your wavelength is already a float:

values.add(new Entry(waveLength, I));

Secondly:values.add(new Entry(100, 6)); this line work as values.add(new Entry(x, y));

So you need to give chart proper x values and corresponding y values to generate a graph. x values should be in proper sequence to create a chart if the value of x at n (here n is index of entry) is equals or less than value of x at n-1 at any point then you will not be able to generate a chart. So fixing the code of for loop above as I described your chart will work properly. Best of luck :)

来源：https://stackoverflow.com/questions/58173935/mpandroidchart-why-line-not-showing

标签

java

android

mpandroidchart