Modifying the Android seekbar widget to operate vertically

I’ve created a solution which works (at least for me, anyway) and creates a vertical SeekBar.
http://hackskrieg.wordpress.com/2012/04/20/working-vertical-seekbar-for-android/

This code will correctly select/deselect the thumb, move correctly, update the listener correctly (only when the progress changes!), update/draw the progress correctly, etc. I hope it helps you.

public class VerticalSeekBar extends SeekBar {

public VerticalSeekBar(Context context) {
    super(context);
}

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

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

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

@Override
protected synchronized void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(heightMeasureSpec, widthMeasureSpec);
    setMeasuredDimension(getMeasuredHeight(), getMeasuredWidth());
}

protected void onDraw(Canvas c) {
    c.rotate(-90);
    c.translate(-getHeight(), 0);

    super.onDraw(c);
}

private OnSeekBarChangeListener onChangeListener;
@Override
public void setOnSeekBarChangeListener(OnSeekBarChangeListener onChangeListener){
    this.onChangeListener = onChangeListener;
}

private int lastProgress = 0;
@Override
public boolean onTouchEvent(MotionEvent event) {
    if (!isEnabled()) {
        return false;
    }

    switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
        onChangeListener.onStartTrackingTouch(this);
        setPressed(true);
        setSelected(true);
        break;
    case MotionEvent.ACTION_MOVE:
        // Calling the super seems to help fix drawing problems
        super.onTouchEvent(event);
        int progress = getMax() - (int) (getMax() * event.getY() / getHeight());

        // Ensure progress stays within boundaries of the seekbar
        if(progress < 0) {progress = 0;}
        if(progress > getMax()) {progress = getMax();}

        // Draw progress
        setProgress(progress);

        // Only enact listener if the progress has actually changed
        // Otherwise the listener gets called ~5 times per change
        if(progress != lastProgress) {
            lastProgress = progress;
            onChangeListener.onProgressChanged(this, progress, true);
        }

        onSizeChanged(getWidth(), getHeight() , 0, 0);
        onChangeListener.onProgressChanged(this, getMax() - (int) (getMax() * event.getY() / getHeight()), true);
        setPressed(true);
        setSelected(true);
        break;
    case MotionEvent.ACTION_UP:
        onChangeListener.onStopTrackingTouch(this);
        setPressed(false);
        setSelected(false);
        break;
    case MotionEvent.ACTION_CANCEL:
        super.onTouchEvent(event);
        setPressed(false);
        setSelected(false);
        break;
    }
    return true;
}

public synchronized void setProgressAndThumb(int progress) {
    setProgress(getMax() - (getMax()- progress));
    onSizeChanged(getWidth(), getHeight() , 0, 0);
}

public synchronized void setMaximum(int maximum) {
    setMax(maximum);
}

public synchronized int getMaximum() {
    return getMax();
}
}

I just placed this vertical SeekBar inside a LinearLayout with layout_height set to FILL_PARENT and layout_width set to WRAP_CONTENT.

<LinearLayout
    android:layout_width="wrap_content"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <com.safetyculture.jsadroidtablet.VerticalSeekBar
        android:id="@+id/calculatorVerticalSeekBar"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_gravity="bottom"
        android:max="4"
        android:progress="2" />

</LinearLayout>

NOTE: You must set an OnSeekBarChangeListener, otherwise interacting with the SeekBar will produce NullPointerException.