CircleGraphView.java

public class CircleGraphView extends View {

    static class Data {
        int value;
        int color;

        Data(int value, int color) {
            this.value = value;
            this.color = color;
        }
    }

    static final int DIVIDER_SPACE = 2;
    static final int GRAPH_WIDTH = 24;
    static final int STROKE_WIDTH = 2;

    private int centerX;
    private int centerY;
    private float outerRadius;
    private float innerRadius;

    private RectF outerBounds;
    private RectF innerBounds;

    Path path;
    Paint fillPaint;
    Paint strokePaint;

    private List<Data> dataList = new ArrayList<Data>();

    public CircleGraphView(Context context) {
        this(context, null);
    }

    public CircleGraphView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CircleGraphView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        centerX = w / 2;
        centerY = h / 2;

        outerRadius = w > h ? centerY : centerX;
        innerRadius = outerRadius - Utils.convertDpToPixel(GRAPH_WIDTH);

        outerBounds = new RectF(
                centerX - outerRadius, centerY - outerRadius,
                centerX + outerRadius, centerY + outerRadius
        );

        innerBounds = new RectF(
                centerX - innerRadius, centerY - innerRadius,
                centerX + innerRadius, centerY + innerRadius
        );
    }

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

        int total = 0;
        for (Data data : dataList) {
            total += data.value;
        }

        if (0 >= total) {
            return;
        }

        float offset = 0;
        for (Data data : dataList) {
            float angle = 360f * data.value / total;
            drawPie(canvas, offset, angle, data.color);
            offset += angle;
        }
    }

    public void setData() {
        List<Data> dataList = new ArrayList<>();
        dataList.add(new Data(500, Color.BLUE));
        dataList.add(new Data(300, Color.RED));
        dataList.add(new Data(300, Color.YELLOW));
        dataList.add(new Data(200, Color.GREEN));
        this.dataList.addAll(dataList);
    }

    private void init(Context context) {
        Utils.init(context.getResources());

        path = new Path();
        fillPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        strokePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
    }

    private void drawPie(Canvas canvas, float startAngle, float sweepAngle, int color) {
        int x, y;

        float adjustedStartAngle = startAngle - 90 + DIVIDER_SPACE;
        float adjustedSweepAngle = sweepAngle - (2 * DIVIDER_SPACE);
        float deltaTheta = adjustedStartAngle + adjustedSweepAngle;

        path.reset();

        // inner arc
        path.arcTo(innerBounds, adjustedStartAngle, adjustedSweepAngle);

        // divider (inner -> outer)
        x = (int) (Math.cos(deltaTheta * Math.PI / 180) * outerRadius);
        y = (int) (Math.sin(deltaTheta * Math.PI / 180) * outerRadius);
        path.lineTo(centerX + x, centerY + y);

        // outer arc
        path.arcTo(outerBounds, deltaTheta, -adjustedSweepAngle);

        // divider (outer -> inner)
        x = (int) (Math.cos(adjustedStartAngle * Math.PI / 180) * innerRadius);
        y = (int) (Math.sin(adjustedStartAngle * Math.PI / 180) * innerRadius);
        path.lineTo(centerX + x, centerY + y);

        fillPaint.setColor(color);
        fillPaint.setAlpha(160);
        canvas.drawPath(path, fillPaint);

        strokePaint.setColor(color);
        strokePaint.setStrokeWidth(Utils.convertDpToPixel(STROKE_WIDTH));
        strokePaint.setStyle(Paint.Style.STROKE);
        canvas.drawPath(path, strokePaint);
    }
}