attr.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
<declare-styleable name="VerticalRangeSeekBar">
        <attr name="absoluteMinValue" format="integer|float"/>
        <attr name="absoluteMaxValue" format="integer|float"/>
        <attr name="singleThumb" format="boolean"/>
    </declare-styleable>
    
</resources>

PixelUtil.java

/**
 * Util class for converting between dp, px and other magical pixel units
 */
public class PixelUtil {

    private PixelUtil() {
    }

    public static int dpToPx(Context context, int dp) {
        int px = Math.round(dp * getPixelScaleFactor(context));
        return px;
    }

    public static int pxToDp(Context context, int px) {
        int dp = Math.round(px / getPixelScaleFactor(context));
        return dp;
    }

    private static float getPixelScaleFactor(Context context) {
        DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics();
        return (displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT);
    }

}

VerticalRangeSeekBar.java

public class VerticalRangeSeekBar extends AppCompatImageView {

    public static final Integer DEFAULT_MINIMUM = 0;
    public static final Integer DEFAULT_MAXIMUM = 100;
    public static final int WIDTH_IN_DP = 30;
    public static final int TEXT_LATERAL_PADDING_IN_DP = 3;
    /**
     * Default color of a {@link VerticalRangeSeekBar}, #FF33B5E5. This is also known as "Ice Cream Sandwich" blue.
     */
    public static final int DEFAULT_COLOR = Color.argb(0xFF, 0x33, 0xB5, 0xE5);
    /**
     * An invalid pointer id.
     */
    public static final int INVALID_POINTER_ID = 255;
    // Localized constants from MotionEvent for compatibility
    // with API < 8 "Froyo".
    public static final int ACTION_POINTER_UP = 0x6, ACTION_POINTER_INDEX_MASK = 0x0000ff00, ACTION_POINTER_INDEX_SHIFT = 8;
    private static final int INITIAL_PADDING_IN_DP = 8;
    private static final int DEFAULT_TEXT_SIZE_IN_DP = 14;
    private static final int DEFAULT_TEXT_DISTANCE_TO_BUTTON_IN_DP = 8;
    private static final int DEFAULT_TEXT_DISTANCE_TO_TOP_IN_DP = 8;
    private final int LINE_WIDTH_IN_DP = 2;
    private final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

    //private final Bitmap thumbImage = BitmapFactory.decodeResource(getResources(), R.drawable.seek_thumb_normal);
    private final Bitmap thumbImage = getBitmap(R.drawable.drawable_rounded_accent_thumb);

    private final Bitmap thumbPressedImage = getBitmap(R.drawable.seek_thumb_pressed);
    private final Bitmap thumbDisabledImage = getBitmap(R.drawable.seek_thumb_disabled);

    private final float thumbWidth = thumbImage.getWidth();
    private final float thumbHalfWidth = 0.5f * thumbWidth;
    private final float thumbHalfHeight = 0.5f * thumbImage.getHeight();
    private float INITIAL_PADDING;
    private float padding;
    private int absoluteMinValue, absoluteMaxValue;
    //private NumberType numberType;
    private double absoluteMinValuePrim, absoluteMaxValuePrim;
    private double normalizedMinValue = 0d;
    private double normalizedMaxValue = 1d;
    private Thumb pressedThumb = null;
    private boolean notifyWhileDragging = false;
    private OnRangeSeekBarChangeListener listener;
    private float mDownMotionY;
    private int mActivePointerId = INVALID_POINTER_ID;
    private int mScaledTouchSlop;
    private boolean mIsDragging;
    private int mTextOffset;
    private int mTextSize;
    private int mDistanceToTop;
    private RectF mRect;
    private boolean mSingleThumb;

    public VerticalRangeSeekBar(Context context) {
        super(context);
        init(context, null);
    }

    public VerticalRangeSeekBar(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }

    public VerticalRangeSeekBar(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context, attrs);
    }

    private int extractNumericValueFromAttributes(TypedArray a, int attribute, int defaultValue) {
        TypedValue tv = a.peekValue(attribute);
        if (tv == null) {
            return defaultValue;
        }
        return a.getInteger(attribute, defaultValue);
    }

    private void init(Context context, AttributeSet attrs) {
        if (attrs == null) {
            setRangeToDefaultValues();
        } else {
            TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.VerticalRangeSeekBar, 0, 0);
            setRangeValues(
                    extractNumericValueFromAttributes(a, R.styleable.VerticalRangeSeekBar_absoluteMinValue, DEFAULT_MINIMUM),
                    extractNumericValueFromAttributes(a, R.styleable.VerticalRangeSeekBar_absoluteMaxValue, DEFAULT_MAXIMUM));
            mSingleThumb = a.getBoolean(R.styleable.VerticalRangeSeekBar_singleThumb, false);
            a.recycle();
        }

        //setValuePrimAndNumberType();

        INITIAL_PADDING = PixelUtil.dpToPx(context, INITIAL_PADDING_IN_DP);

        mTextSize = PixelUtil.dpToPx(context, DEFAULT_TEXT_SIZE_IN_DP);
        mDistanceToTop = PixelUtil.dpToPx(context, DEFAULT_TEXT_DISTANCE_TO_TOP_IN_DP);
        mTextOffset = this.mTextSize + PixelUtil.dpToPx(context,
                DEFAULT_TEXT_DISTANCE_TO_BUTTON_IN_DP) + this.mDistanceToTop;

        float lineWidth = PixelUtil.dpToPx(context, LINE_WIDTH_IN_DP);
        mRect = new RectF(
                mTextOffset / 2 + thumbHalfHeight - lineWidth / 2,
                padding,
                mTextOffset / 2 + thumbHalfHeight + lineWidth / 2,
                getWidth() - padding);

        // make RangeSeekBar focusable. This solves focus handling issues in case EditText widgets are being used along with the RangeSeekBar within ScollViews.
        setFocusable(true);
        setFocusableInTouchMode(true);
        mScaledTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
    }

    private Bitmap getBitmap(int drawableRes) {
        Drawable drawable = getResources().getDrawable(drawableRes);
        Canvas canvas = new Canvas();
        Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
        canvas.setBitmap(bitmap);
        drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
        drawable.draw(canvas);

        return bitmap;
    }

    public void setRangeValues(int minValue, int maxValue) {
        this.absoluteMinValue = minValue;
        this.absoluteMaxValue = maxValue;
        setValuePrimAndNumberType();
    }

    @SuppressWarnings("unchecked")
    // only used to set default values when initialised from XML without any values specified
    private void setRangeToDefaultValues() {
        this.absoluteMinValue = DEFAULT_MINIMUM;
        this.absoluteMaxValue = DEFAULT_MAXIMUM;
        setValuePrimAndNumberType();
    }

    private void setValuePrimAndNumberType() {
        absoluteMinValuePrim = absoluteMinValue;
        absoluteMaxValuePrim = absoluteMaxValue;
    }

    public void resetSelectedValues() {
        setSelectedMinValue(absoluteMinValue);
        setSelectedMaxValue(absoluteMaxValue);
    }

    public boolean isNotifyWhileDragging() {
        return notifyWhileDragging;
    }

    /**
     * Should the widget notify the listener callback while the user is still dragging a thumb? Default is false.
     *
     * @param flag
     */
    public void setNotifyWhileDragging(boolean flag) {
        this.notifyWhileDragging = flag;
    }

    /**
     * Returns the absolute minimum value of the range that has been set at construction time.
     *
     * @return The absolute minimum value of the range.
     */
    public int getAbsoluteMinValue() {
        return absoluteMinValue;
    }

    /**
     * Returns the absolute maximum value of the range that has been set at construction time.
     *
     * @return The absolute maximum value of the range.
     */
    public int getAbsoluteMaxValue() {
        return absoluteMaxValue;
    }

    /**
     * Returns the currently selected min value.
     *
     * @return The currently selected min value.
     */
    public int getSelectedMinValue() {
        return normalizedToValue(normalizedMinValue);
    }

    /**
     * Sets the currently selected minimum value. The widget will be invalidated and redrawn.
     *
     * @param value The Number value to set the minimum value to. Will be clamped to given absolute minimum/maximum range.
     */
    public void setSelectedMinValue(int value) {
        // in case absoluteMinValue == absoluteMaxValue, avoid division by zero when normalizing.
        if (0 == (absoluteMaxValuePrim - absoluteMinValuePrim)) {
            setNormalizedMinValue(0d);
        } else {
            setNormalizedMinValue(valueToNormalized(value));
        }
    }

    /**
     * Returns the currently selected max value.
     *
     * @return The currently selected max value.
     */
    public int getSelectedMaxValue() {
        return normalizedToValue(normalizedMaxValue);
    }

    /**
     * Sets the currently selected maximum value. The widget will be invalidated and redrawn.
     *
     * @param value The Number value to set the maximum value to. Will be clamped to given absolute minimum/maximum range.
     */
    public void setSelectedMaxValue(int value) {
        // in case absoluteMinValue == absoluteMaxValue, avoid division by zero when normalizing.
        if (0 == (absoluteMaxValuePrim - absoluteMinValuePrim)) {
            setNormalizedMaxValue(1d);
        } else {
            setNormalizedMaxValue(valueToNormalized(value));
        }
    }

    /**
     * Registers given listener callback to notify about changed selected values.
     *
     * @param listener The listener to notify about changed selected values.
     */
    public void setOnRangeSeekBarChangeListener(OnRangeSeekBarChangeListener listener) {
        this.listener = listener;
    }

    /**
     * Handles thumb selection and movement. Notifies listener callback on certain events.
     */
    @SuppressLint("ClickableViewAccessibility")
    @Override
    public boolean onTouchEvent(MotionEvent event) {

        if (!isEnabled()) {
            return false;
        }

        int pointerIndex;

        final int action = event.getAction();
        switch (action & MotionEvent.ACTION_MASK) {

            case MotionEvent.ACTION_DOWN:
                // Remember where the motion event started
                mActivePointerId = event.getPointerId(event.getPointerCount() - 1);
                pointerIndex = event.findPointerIndex(mActivePointerId);
                mDownMotionY = event.getY(pointerIndex);

                pressedThumb = evalPressedThumb(mDownMotionY);

                // Only handle thumb presses.
                if (pressedThumb == null) {
                    return super.onTouchEvent(event);
                }

                setPressed(true);
                invalidate();
                onStartTrackingTouch();
                trackTouchEvent(event);
                attemptClaimDrag();

                break;
            case MotionEvent.ACTION_MOVE:
                if (pressedThumb != null) {

                    if (mIsDragging) {
                        trackTouchEvent(event);
                    } else {
                        // Scroll to follow the motion event
                        pointerIndex = event.findPointerIndex(mActivePointerId);
                        final float y = event.getY(pointerIndex);

                        if (Math.abs(y - mDownMotionY) > mScaledTouchSlop) {
                            setPressed(true);
                            invalidate();
                            onStartTrackingTouch();
                            trackTouchEvent(event);
                            attemptClaimDrag();
                        }
                    }

                    if (notifyWhileDragging && listener != null) {
                        listener.onRangeSeekBarValuesChanged(this, getSelectedMinValue(), getSelectedMaxValue());
                    }
                }
                break;
            case MotionEvent.ACTION_UP:
                if (mIsDragging) {
                    trackTouchEvent(event);
                    onStopTrackingTouch();
                    setPressed(false);
                } else {
                    // Touch up when we never crossed the touch slop threshold
                    // should be interpreted as a tap-seek to that location.
                    onStartTrackingTouch();
                    trackTouchEvent(event);
                    onStopTrackingTouch();
                }

                pressedThumb = null;
                invalidate();
                if (listener != null) {
                    listener.onRangeSeekBarValuesChanged(this, getSelectedMinValue(), getSelectedMaxValue());
                }
                break;
            case MotionEvent.ACTION_POINTER_DOWN: {
                final int index = event.getPointerCount() - 1;
                // final int index = ev.getActionIndex();
                mDownMotionY = event.getY(index);
                mActivePointerId = event.getPointerId(index);
                invalidate();
                break;
            }
            case MotionEvent.ACTION_POINTER_UP:
                onSecondaryPointerUp(event);
                invalidate();
                break;
            case MotionEvent.ACTION_CANCEL:
                if (mIsDragging) {
                    onStopTrackingTouch();
                    setPressed(false);
                }
                invalidate(); // see above explanation
                break;
        }
        return true;
    }

    private final void onSecondaryPointerUp(MotionEvent ev) {
        final int pointerIndex = (ev.getAction() & ACTION_POINTER_INDEX_MASK) >> ACTION_POINTER_INDEX_SHIFT;

        final int pointerId = ev.getPointerId(pointerIndex);
        if (pointerId == mActivePointerId) {
            // This was our active pointer going up. Choose
            // a new active pointer and adjust accordingly.
            // TODO: Make this decision more intelligent.
            final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
            mDownMotionY = ev.getY(newPointerIndex);
            mActivePointerId = ev.getPointerId(newPointerIndex);
        }
    }

    private final void trackTouchEvent(MotionEvent event) {
        final int pointerIndex = event.findPointerIndex(mActivePointerId);
        final float y = event.getY(pointerIndex);

        if (Thumb.MIN.equals(pressedThumb) && !mSingleThumb) {
            setNormalizedMinValue(screenToNormalized(y));
        } else if (Thumb.MAX.equals(pressedThumb)) {
            setNormalizedMaxValue(screenToNormalized(y));
        }
    }

    /**
     * Tries to claim the user's drag motion, and requests disallowing any ancestors from stealing events in the drag.
     */
    private void attemptClaimDrag() {
        if (getParent() != null) {
            getParent().requestDisallowInterceptTouchEvent(true);
        }
    }

    /**
     * This is called when the user has started touching this widget.
     */
    void onStartTrackingTouch() {
        mIsDragging = true;
    }

    /**
     * This is called when the user either releases his touch or the touch is canceled.
     */
    void onStopTrackingTouch() {
        mIsDragging = false;
    }

    /**
     * Ensures correct size of the widget.
     */
    @Override
    protected synchronized void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int width = thumbImage.getWidth() + PixelUtil.dpToPx(getContext(), WIDTH_IN_DP);
        if (MeasureSpec.UNSPECIFIED != MeasureSpec.getMode(widthMeasureSpec)) {
            width = Math.min(width, MeasureSpec.getSize(widthMeasureSpec));
        }

        int height = 200;
        if (MeasureSpec.UNSPECIFIED != MeasureSpec.getMode(heightMeasureSpec)) {
            height = MeasureSpec.getSize(heightMeasureSpec);
        }
        setMeasuredDimension(width, height);
    }

    /**
     * Draws the widget on the given canvas.
     */
    @Override
    protected synchronized void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        paint.setTextSize(mTextSize);
        paint.setStyle(Style.FILL);
        paint.setColor(Color.GRAY);
        paint.setAntiAlias(true);

        // draw min and max labels
        padding = INITIAL_PADDING + thumbHalfHeight;

        // draw seek bar background line
        mRect.top = padding;
        mRect.bottom = getHeight() - padding;
        canvas.drawRect(mRect, paint);

        // draw seek bar active range line
        mRect.top = normalizedToScreen(normalizedMinValue);
        mRect.bottom = normalizedToScreen(normalizedMaxValue);

        paint.setColor(DEFAULT_COLOR);
        canvas.drawRect(mRect, paint);

        // draw minimum thumb if not a single thumb control
        if (!mSingleThumb) {
            drawThumb(normalizedToScreen(normalizedMinValue), Thumb.MIN.equals(pressedThumb), canvas);
        }

        // draw maximum thumb
        drawThumb(normalizedToScreen(normalizedMaxValue), Thumb.MAX.equals(pressedThumb), canvas);

    }

    /**
     * Overridden to save instance state when device orientation changes. This method is called automatically if you assign an id to the RangeSeekBar widget using the {@link #setId(int)} method. Other members of this class than the normalized min and max values don't need to be saved.
     */
    @Override
    protected Parcelable onSaveInstanceState() {
        final Bundle bundle = new Bundle();
        bundle.putParcelable("SUPER", super.onSaveInstanceState());
        bundle.putDouble("MIN", normalizedMinValue);
        bundle.putDouble("MAX", normalizedMaxValue);
        return bundle;
    }

    /**
     * Overridden to restore instance state when device orientation changes. This method is called automatically if you assign an id to the RangeSeekBar widget using the {@link #setId(int)} method.
     */
    @Override
    protected void onRestoreInstanceState(Parcelable parcel) {
        final Bundle bundle = (Bundle) parcel;
        super.onRestoreInstanceState(bundle.getParcelable("SUPER"));
        normalizedMinValue = bundle.getDouble("MIN");
        normalizedMaxValue = bundle.getDouble("MAX");
    }

    /**
     * Draws the "normal" resp. "pressed" thumb image on specified x-coordinate.
     *
     * @param screenCoord The x-coordinate in screen space where to draw the image.
     * @param pressed     Is the thumb currently in "pressed" state?
     * @param canvas      The canvas to draw upon.
     */
    private void drawThumb(float screenCoord, boolean pressed, Canvas canvas) {
        Bitmap buttonToDraw;
        buttonToDraw = pressed ? thumbPressedImage : thumbImage;
        canvas.drawBitmap(buttonToDraw, mTextOffset / 2, screenCoord - thumbHalfWidth,
                paint);
    }

    /**
     * Decides which (if any) thumb is touched by the given x-coordinate.
     *
     * @param touchY The x-coordinate of a touch event in screen space.
     * @return The pressed thumb or null if none has been touched.
     */
    private Thumb evalPressedThumb(float touchY) {
        Thumb result = null;
        boolean minThumbPressed = isInThumbRange(touchY, normalizedMinValue);
        boolean maxThumbPressed = isInThumbRange(touchY, normalizedMaxValue);
        if (minThumbPressed && maxThumbPressed) {
            // if both thumbs are pressed (they lie on top of each other), choose the one with more room to drag. this avoids "stalling" the thumbs in a corner, not being able to drag them apart anymore.
            result = (touchY / getHeight() > 0.5f) ? Thumb.MIN : Thumb.MAX;
        } else if (minThumbPressed) {
            result = Thumb.MIN;
        } else if (maxThumbPressed) {
            result = Thumb.MAX;
        }
        return result;
    }

    /**
     * Decides if given x-coordinate in screen space needs to be interpreted as "within" the normalized thumb x-coordinate.
     *
     * @param touchY               The x-coordinate in screen space to check.
     * @param normalizedThumbValue The normalized x-coordinate of the thumb to check.
     * @return true if x-coordinate is in thumb range, false otherwise.
     */
    private boolean isInThumbRange(float touchY, double normalizedThumbValue) {
        return Math.abs(touchY - normalizedToScreen(normalizedThumbValue)) <= thumbHalfHeight;
    }

    /**
     * Sets normalized min value to value so that 0 <= value <= normalized max value <= 1. The View will get invalidated when calling this method.
     *
     * @param value The new normalized min value to set.
     */
    private void setNormalizedMinValue(double value) {
        normalizedMinValue = Math.max(0d, Math.min(1d, Math.min(value, normalizedMaxValue)));
        invalidate();
    }

    /**
     * Sets normalized max value to value so that 0 <= normalized min value <= value <= 1. The View will get invalidated when calling this method.
     *
     * @param value The new normalized max value to set.
     */
    private void setNormalizedMaxValue(double value) {
        normalizedMaxValue = Math.max(0d, Math.min(1d, Math.max(value, normalizedMinValue)));
        invalidate();
    }

    /**
     * Converts a normalized value to a Number object in the value space between absolute minimum and maximum.
     *
     * @param normalized
     * @return
     */
    @SuppressWarnings("unchecked")
    private int normalizedToValue(double normalized) {
        double v = absoluteMinValuePrim + normalized * (absoluteMaxValuePrim - absoluteMinValuePrim);
        // TODO parameterize this rounding to allow variable decimal points
        return (int) (Math.round(v * 100) / 100);
    }

    /**
     * Converts the given Number value to a normalized double.
     *
     * @param value The Number value to normalize.
     * @return The normalized double.
     */
    private double valueToNormalized(int value) {
        if (0 == absoluteMaxValuePrim - absoluteMinValuePrim) {
            // prevent division by zero, simply return 0.
            return 0d;
        }
        return (value - absoluteMinValuePrim) / (absoluteMaxValuePrim - absoluteMinValuePrim);
    }

    /**
     * Converts a normalized value into screen space.
     *
     * @param normalizedCoord The normalized value to convert.
     * @return The converted value in screen space.
     */
    private float normalizedToScreen(double normalizedCoord) {
        return (float) (padding + normalizedCoord * (getHeight() - 2 * padding));
    }

    /**
     * Converts screen space x-coordinates into normalized values.
     *
     * @param screenCoord The x-coordinate in screen space to convert.
     * @return The normalized value.
     */
    private double screenToNormalized(float screenCoord) {
        int height = getHeight();
        if (height <= 2 * padding) {
            // prevent division by zero, simply return 0.
            return 0d;
        } else {
            double result = (screenCoord - padding) / (height - 2 * padding);
            return Math.min(1d, Math.max(0d, result));
        }
    }

    /**
     * Thumb constants (min and max).
     */
    private static enum Thumb {
        MIN, MAX
    }

    /**
     * Callback listener interface to notify about changed range values.
     *
     * @author Stephan Tittel (stephan.tittel@kom.tu-darmstadt.de)
     */
    public interface OnRangeSeekBarChangeListener {

        public void onRangeSeekBarValuesChanged(VerticalRangeSeekBar bar, int minValue, int maxValue);
    }

}