Demo for real-time time series graph

gistfile1.txt

package com.demo.demo;

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

import androidx.annotation.Nullable;

import java.util.Locale;
import java.util.Timer;
import java.util.TimerTask;

public class CustomView extends View {
    private final Paint paint = new Paint();
    private final Timer timer = new Timer();
    private long start = 0;

    public CustomView(Context context) {
        super(context);
        init();
    }

    public CustomView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    public CustomView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init();
    }

    public CustomView(Context context, @Nullable AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init();
    }

    private void init() {
        paint.setColor(Color.BLACK);
        paint.setTextSize(36);
        paint.setTextAlign(Paint.Align.CENTER);

        timer.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                invalidate();
            }
        }, 0, 10);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        final long currentTimeMillis = System.currentTimeMillis();
        if (start == 0) {
            start = currentTimeMillis;
        }

        draw(canvas, currentTimeMillis - start);
    }

    private void draw(Canvas canvas, long duration) {
        final long durationInSecond = duration / 1000L;

        final long durationWithoutMillisecond = durationInSecond * 1000L;

        final int localOffsetFromCenter = millisecondToPixel(
                durationWithoutMillisecond - duration
        );

        assert(localOffsetFromCenter <= 0);

        final int width = canvas.getWidth();
        final int height = canvas.getHeight();
        final int centerX = width / 2;
        final int centerY = height / 2;

        final int textLocationY = centerY;
        final int pixelForOneSecond = millisecondToPixel(1000);
        final int textLocationX = centerX + localOffsetFromCenter;

        int lowerTextLocationX = textLocationX - pixelForOneSecond;
        int upperTextLocationX = textLocationX + pixelForOneSecond;
        long lowerDurationWithoutMillisecond = durationWithoutMillisecond - 1000;
        long upperDurationWithoutMillisecond = durationWithoutMillisecond + 1000;

        canvas.drawLine(centerX, 0, centerX, height, paint);

        // Lower
        while (lowerTextLocationX >= -pixelForOneSecond && lowerDurationWithoutMillisecond >= 0) {
            final String s = getDurationAsString(lowerDurationWithoutMillisecond);
            canvas.drawText(s, (float)lowerTextLocationX, (float)textLocationY, paint);
            lowerTextLocationX = lowerTextLocationX - pixelForOneSecond;
            lowerDurationWithoutMillisecond = lowerDurationWithoutMillisecond - 1000;
        }

        // Center
        final String string = getDurationAsString(durationWithoutMillisecond);
        canvas.drawText(string, (float)textLocationX, (float)textLocationY, paint);

        // Upper
        while (upperTextLocationX <= (pixelForOneSecond+width) && upperDurationWithoutMillisecond >= 0) {
            final String s = getDurationAsString(upperDurationWithoutMillisecond);
            canvas.drawText(s, (float)upperTextLocationX, (float)textLocationY, paint);
            upperTextLocationX = upperTextLocationX + pixelForOneSecond;
            upperDurationWithoutMillisecond = upperDurationWithoutMillisecond + 1000;
        }
    }

    public static int millisecondToPixel(long millisecond) {
        return (int)(0.125 * (double)millisecond);
    }

    public static String getDurationAsString(long duration) {
        duration = duration / 1000L;
        return String.format(Locale.ENGLISH, "%01d:%02d", (duration / 60), (duration % 60));
    }
}