Coding – r3dux.org

I needed to convert the day number, that is, what day it is between 1 and 365, into a month and day without using Calendar / DateTime classes and such today, so I knocked up a few simple functions that work assuming it’s not a leap year (i.e. that February has 28 days).

Here they are if they’re of any use to you:

int dateToDayNumber(int month, int day)
{
	// Catch invalid input and return early
	if (month < 1 || month > 12 || day < 1 || day > 31) return 0;

	if (month == 1 ) return       day;
	if (month == 2 ) return 31  + day;
	if (month == 3 ) return 59  + day;
	if (month == 4 ) return 90  + day;
	if (month == 5 ) return 120 + day;
	if (month == 6 ) return 151 + day;
	if (month == 7 ) return 181 + day;
	if (month == 8 ) return 212 + day;
	if (month == 9 ) return 243 + day;
	if (month == 10) return 273 + day;
	if (month == 11) return 304 + day;
	return 334 + day;
}

int dayNumberToMonth(int dayNumber)
{
	// Catch invalid input and return early
	if (dayNumber < 1 || dayNumber > 365) return 0;

	if (dayNumber <= 31 ) return 1;  // Jan
	if (dayNumber <= 59 ) return 2;  // Feb
	if (dayNumber <= 90 ) return 3;  // Mar
	if (dayNumber <= 120) return 4;  // Apr
	if (dayNumber <= 151) return 5;  // May
	if (dayNumber <= 181) return 6;  // Jun
	if (dayNumber <= 212) return 7;  // Jul
	if (dayNumber <= 243) return 8;  // Aug
	if (dayNumber <= 273) return 9;  // Sep
	if (dayNumber <= 304) return 10; // Oct
	if (dayNumber <= 334) return 11; // Nov
	return 12;                       // Dec
}

int dayNumberToDayOfMonth(int dayNumber)
{
	// Catch invalid input and return early
	if (dayNumber < 1 || dayNumber > 365) return 0;

	if (dayNumber <= 31 ) return dayNumber;       // Jan
	if (dayNumber <= 59 ) return dayNumber - 31;  // Feb
	if (dayNumber <= 90 ) return dayNumber - 59;  // Mar
	if (dayNumber <= 120) return dayNumber - 90;  // Apr
	if (dayNumber <= 151) return dayNumber - 120; // May
	if (dayNumber <= 181) return dayNumber - 151; // Jun
	if (dayNumber <= 212) return dayNumber - 181; // Jul
	if (dayNumber <= 243) return dayNumber - 212; // Aug
	if (dayNumber <= 273) return dayNumber - 243; // Sep
	if (dayNumber <= 304) return dayNumber - 273; // Oct
	if (dayNumber <= 334) return dayNumber - 304; // Nov
	return dayNumber - 334;                       // Dec
}

int dateToDayNumber(int month, int day)

{

// Catch invalid input and return early

if (month < 1 || month > 12 || day < 1 || day > 31) return 0;

if (month == 1 ) return day;

if (month == 2 ) return 31 + day;

if (month == 3 ) return 59 + day;

if (month == 4 ) return 90 + day;

if (month == 5 ) return 120 + day;

if (month == 6 ) return 151 + day;

if (month == 7 ) return 181 + day;

if (month == 8 ) return 212 + day;

if (month == 9 ) return 243 + day;

if (month == 10) return 273 + day;

if (month == 11) return 304 + day;

return 334 + day;

}

int dayNumberToMonth(int dayNumber)

{

// Catch invalid input and return early

if (dayNumber < 1 || dayNumber > 365) return 0;

if (dayNumber <= 31 ) return 1; // Jan

if (dayNumber <= 59 ) return 2; // Feb

if (dayNumber <= 90 ) return 3; // Mar

if (dayNumber <= 120) return 4; // Apr

if (dayNumber <= 151) return 5; // May

if (dayNumber <= 181) return 6; // Jun

if (dayNumber <= 212) return 7; // Jul

if (dayNumber <= 243) return 8; // Aug

if (dayNumber <= 273) return 9; // Sep

if (dayNumber <= 304) return 10; // Oct

if (dayNumber <= 334) return 11; // Nov

return 12; // Dec

}

int dayNumberToDayOfMonth(int dayNumber)

{

// Catch invalid input and return early

if (dayNumber < 1 || dayNumber > 365) return 0;

if (dayNumber <= 31 ) return dayNumber; // Jan

if (dayNumber <= 59 ) return dayNumber - 31; // Feb

if (dayNumber <= 90 ) return dayNumber - 59; // Mar

if (dayNumber <= 120) return dayNumber - 90; // Apr

if (dayNumber <= 151) return dayNumber - 120; // May

if (dayNumber <= 181) return dayNumber - 151; // Jun

if (dayNumber <= 212) return dayNumber - 181; // Jul

if (dayNumber <= 243) return dayNumber - 212; // Aug

if (dayNumber <= 273) return dayNumber - 243; // Sep

if (dayNumber <= 304) return dayNumber - 273; // Oct

if (dayNumber <= 334) return dayNumber - 304; // Nov

return dayNumber - 334; // Dec

}

A touch cheap, but it gets the job done.

Heads up: When I say pointer in this article, I mean a finger or a stylus – anything in contact with the touchscreen.

Multi-touch in Android is a bit of a strange beast, although you could argue that it’s by necessity. With ACTION_DOWN (primary pointer in contact) or ACTION_POINTER_DOWN (non-primary pointer in contact), or even the corresponding ACTION_UP or ACTION_POINTER_UP events it’s fine. But when it comes to ACTION_MOVE events – you can’t just ask which finger moved, all you’re told is that A finger moved, and you have to figure out which one for yourself as far as I can tell.

This is what I’ve come up with to figure out which pointer has actually moved – it falls behind by one ACTION_MOVE event because there doesn’t seem to be a way to ask for the current X location of a pointer by its index location (that is, there’s no getX(pointerIndex), only a getHistoricalX(pointerIndex, historyPosition)) – so this code misses the very first move event when a pointer moves – BUT – moving your finger generates a large number of move events, so I’m thinking this might not be that much of an issue.

Update: I’d forgotten you can getX(pointerIndex) and as well as getHistoricalX(pointerIndex, historyLocation) – so I’ve modified the code below to do that, which means I don’t think we miss any move events anymore because we’re now comparing current location to historical(0) rather than historical(0) to historical(1).

Anyway, here’s my code which addresses this finicky problem:

@Override
public boolean onTouchEvent(MotionEvent event)
{
    // Get pointer index from the event object...
    int pointerIndex = event.getActionIndex();

    // ...which we can use to find the pointer ID!
    int pointerId = event.getPointerId(pointerIndex);

    // Get masked action (i.e. action which is not specific to a pointer)
    int maskedAction = event.getActionMasked();

    // Depending on what the action was, act appropriately...
    switch (maskedAction)
    {
        case MotionEvent.ACTION_DOWN:
            System.out.println("Pointer with Id: " + pointerId + " at index " + pointerIndex + " down i.e. Primary pointer down!");
            break;

        case MotionEvent.ACTION_POINTER_DOWN:
            System.out.println("Pointer with Id: " + pointerId + " at index " + pointerIndex + " down i.e. NON-Primary pointer down!");
            break;

        // The MOVE event must be done separately. This is because the ACTION_MOVE event always gets
        // zero as the pointerId for some strange reason. As such, you always have to loop over the
        // pointer indexes and compare positions to the pointer's previous (i.e. historical) position.
        case MotionEvent.ACTION_MOVE:
            int pointerCount = event.getPointerCount();
            for(int i = 0; i < pointerCount; ++i)
            {
                // To find out WHICH pointer moved we must compare pointer historical locations
                if (event.getHistorySize() > 0)
                {
                    // X or Y location for that pointer index moved?
                    // Corner-case: Pointer index changed (pointer up or down promoted or demoted pointer index while moving?) 
                    // Fix: Track by pointer Id via sparse array as outlined in second potential solution below.
                    if ( (int)event.getX(i) != (int)event.getHistoricalX(i,0) || (int)event.getY(i) != (int)event.getHistoricalY(i, 0) )
                    {
                        pointerId = event.getPointerId(i);
                        System.out.println("Pointer with Id: " + pointerId + " at index " + i + " moved!");
                    }
                }
            }
            break;

        case MotionEvent.ACTION_UP:
            System.out.println("Pointer with Id: " + pointerId + " at index " + pointerIndex + " up i.e. Primary pointer up!");
            break;

        case MotionEvent.ACTION_POINTER_UP:
            System.out.println("Pointer with Id: " + pointerId + " at index " + pointerIndex + " up i.e. NON-Primary pointer up!");
            break;
    }

    // Consume the event so that it is not processed any further
    return true;

} // End of onTouchEvent method

@Override

public boolean onTouchEvent(MotionEvent event)

{

// Get pointer index from the event object...

int pointerIndex = event.getActionIndex();

// ...which we can use to find the pointer ID!

int pointerId = event.getPointerId(pointerIndex);

// Get masked action (i.e. action which is not specific to a pointer)

int maskedAction = event.getActionMasked();

// Depending on what the action was, act appropriately...

switch (maskedAction)

{

case MotionEvent.ACTION_DOWN:

System.out.println("Pointer with Id: " + pointerId + " at index " + pointerIndex + " down i.e. Primary pointer down!");

break;

case MotionEvent.ACTION_POINTER_DOWN:

System.out.println("Pointer with Id: " + pointerId + " at index " + pointerIndex + " down i.e. NON-Primary pointer down!");

break;

// The MOVE event must be done separately. This is because the ACTION_MOVE event always gets

// zero as the pointerId for some strange reason. As such, you always have to loop over the

// pointer indexes and compare positions to the pointer's previous (i.e. historical) position.

case MotionEvent.ACTION_MOVE:

int pointerCount = event.getPointerCount();

for(int i = 0; i < pointerCount; ++i)

{

// To find out WHICH pointer moved we must compare pointer historical locations

if (event.getHistorySize() > 0)

{

// X or Y location for that pointer index moved?

// Corner-case: Pointer index changed (pointer up or down promoted or demoted pointer index while moving?)

// Fix: Track by pointer Id via sparse array as outlined in second potential solution below.

if ( (int)event.getX(i) != (int)event.getHistoricalX(i,0) || (int)event.getY(i) != (int)event.getHistoricalY(i, 0) )

{

pointerId = event.getPointerId(i);

System.out.println("Pointer with Id: " + pointerId + " at index " + i + " moved!");

}

break;

case MotionEvent.ACTION_UP:

System.out.println("Pointer with Id: " + pointerId + " at index " + pointerIndex + " up i.e. Primary pointer up!");

break;

case MotionEvent.ACTION_POINTER_UP:

System.out.println("Pointer with Id: " + pointerId + " at index " + pointerIndex + " up i.e. NON-Primary pointer up!");

break;

}

// Consume the event so that it is not processed any further

return true;

} // End of onTouchEvent method

As I’ve been playing around with this it seems to match up with what I’m doing very well without issue, for example:

Pointer with Id: 0 at index 0 down i.e. Primary pointer down!      <--- 1st finger down
Pointer with Id: 0 at index 0 moved!                               <--- 1st finger moved
Pointer with Id: 0 at index 0 moved!
...
Pointer with Id: 1 at index 1 down i.e. NON-Primary pointer down!  <--- 2nd finger down
Pointer with Id: 1 at index 1 moved!                               <--- 2nd finger moved
Pointer with Id: 1 at index 1 moved!
...
Pointer with Id: 0 at index 0 up i.e. NON-Primary pointer up!      <--- 1st finger up, promoting 2nd finger to primary!
Pointer with Id: 1 at index 0 moved!                               <--- 2nd finger (now primary) moved
Pointer with Id: 1 at index 0 moved!
...
Pointer with Id: 0 at index 0 down i.e. NON-Primary pointer down!  <--- 1st finger back down, DEMOTING 2nd finger from primary!
Pointer with Id: 0 at index 0 moved!                               <--- 1st finger moved
...
Pointer with Id: 1 at index 1 up i.e. NON-Primary pointer up!      <--- 2nd finger up
Pointer with Id: 0 at index 0 up i.e. Primary pointer up!          <--- 1st finger up

Pointer with Id: 0 at index 0 down i.e. Primary pointer down! <--- 1st finger down

Pointer with Id: 0 at index 0 moved! <--- 1st finger moved

Pointer with Id: 0 at index 0 moved!

...

Pointer with Id: 1 at index 1 down i.e. NON-Primary pointer down! <--- 2nd finger down

Pointer with Id: 1 at index 1 moved! <--- 2nd finger moved

Pointer with Id: 1 at index 1 moved!

...

Pointer with Id: 0 at index 0 up i.e. NON-Primary pointer up! <--- 1st finger up, promoting 2nd finger to primary!

Pointer with Id: 1 at index 0 moved! <--- 2nd finger (now primary) moved

Pointer with Id: 1 at index 0 moved!

...

Pointer with Id: 0 at index 0 down i.e. NON-Primary pointer down! <--- 1st finger back down, DEMOTING 2nd finger from primary!

Pointer with Id: 0 at index 0 moved! <--- 1st finger moved

...

Pointer with Id: 1 at index 1 up i.e. NON-Primary pointer up! <--- 2nd finger up

Pointer with Id: 0 at index 0 up i.e. Primary pointer up! <--- 1st finger up

Alternative Solution

Keep a sparse array of whatever you’re keeping track of – for example, let’s say we’ve got the world’s simplest Circle class:

public class Circle
{
	public float x;
	public float y;
}

public class Circle

{

public float x;

public float y;

}

Then in your class handling the onTouchEvent() method you could have something like this (in this particular example we have a view which responds to multi-touch events):

// imports here...

public class MultiTouchCircleView extends View
{
    private static final int SIZE = 150;

    // Note: A SparseArray is kind-of like a hash-map, it maps an
    // integer to an object in a key/value manner.
    private SparseArray<Circle> circleArray;

    private Paint paint;

    // Array of 10 colours
    private int[] colours = {Color.BLUE, Color.GREEN, Color.RED,
            Color.YELLOW, Color.CYAN, Color.GRAY, Color.MAGENTA, Color.DKGRAY,
            Color.LTGRAY, Color.YELLOW};

    private Paint textPaint;

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

    private void initView()
    {
        circleArray = new SparseArray<Circle>();
        paint = new Paint(Paint.ANTI_ALIAS_FLAG);

        // set painter color to a color you like
        paint.setColor(Color.BLUE);
        paint.setStyle(Paint.Style.FILL_AND_STROKE);
        textPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        textPaint.setTextSize(50);
        textPaint.setColor(Color.BLUE);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // Get pointer index from the event object
        int pointerIndex = event.getActionIndex();

        // Get pointer ID
        int pointerId = event.getPointerId(pointerIndex);

        // Get masked (not specific to a pointer) action
        int maskedAction = event.getActionMasked();

        switch (maskedAction) {

            case MotionEvent.ACTION_DOWN:
            case MotionEvent.ACTION_POINTER_DOWN: {
                // A finger has touched the screen - so let's create a new
                // Circle at the touch location and add it to the list!
                Circle circle = new Circle();
                circle.x = event.getX(pointerIndex);
                circle.y = event.getY(pointerIndex);
                circleArray.put(pointerId, circle);
                break;
            }

            case MotionEvent.ACTION_MOVE: {
                // How many pointers are in contact with the screen?
                int pointerCount = event.getPointerCount();

                // Loop over them all...
                for (int i = 0; i < pointerCount; ++i) {
                    // i is the pointer index but we'll update our pointerIndex variable for clarity
                    pointerIndex = i;

                    // Get the pointerId at that pointerIndex (pointerId never changes while pointer is in contact)
                    pointerId = event.getPointerId(pointerIndex);

                    // Get access to the circle with that pointer id...
                    Circle circle = circleArray.get(pointerId);

                    // ...and update the circle's location.
                    circle.x = event.getX(pointerIndex);
                    circle.y = event.getY(pointerIndex);
                }
                break;
            }

            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_POINTER_UP: {
                // Finger has left contact - remove the circle from the array
                circleArray.remove(pointerId);
                break;
            }

        } // End of switch block

        // Trigger redraw to display any changes
        invalidate();

        // Return true to consume the MotionEvent
        return true;
    }

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

        // Draw circles for each pointer in contact with the screen
        int numCircles = circleArray.size();
        for (int i = 0; i < numCircles; ++i)
        {
            // Get the circle at index location i
            Circle circle = circleArray.valueAt(i);

            // ...to choose a colour between 0 and 9.
            if (circle != null)
            {
                int colourNum = i % 9;
                paint.setColor(colours[colourNum]);
                paint.setColor(colours[i]);
            }

            // Draw a circle in our chosen colour
            canvas.drawCircle(circle.x, circle.y, SIZE, paint);
        }
        canvas.drawText("Total pointers: " + numCircles, 10, 100, textPaint);

    } // End of onDraw method

} // End of MultiTouchCircleView class

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// imports here...

public class MultiTouchCircleView extends View

{

private static final int SIZE = 150;

// Note: A SparseArray is kind-of like a hash-map, it maps an

// integer to an object in a key/value manner.

private SparseArray<Circle> circleArray;

private Paint paint;

// Array of 10 colours

private int[] colours = {Color.BLUE, Color.GREEN, Color.RED,

Color.YELLOW, Color.CYAN, Color.GRAY, Color.MAGENTA, Color.DKGRAY,

Color.LTGRAY, Color.YELLOW};

private Paint textPaint;

public MultiTouchCircleView(Context context, AttributeSet attrs)

{

super(context, attrs);

initView();

}

private void initView()

{

circleArray = new SparseArray<Circle>();

paint = new Paint(Paint.ANTI_ALIAS_FLAG);

// set painter color to a color you like

paint.setColor(Color.BLUE);

paint.setStyle(Paint.Style.FILL_AND_STROKE);

textPaint = new Paint(Paint.ANTI_ALIAS_FLAG);

textPaint.setTextSize(50);

textPaint.setColor(Color.BLUE);

}

@Override

public boolean onTouchEvent(MotionEvent event) {

// Get pointer index from the event object

int pointerIndex = event.getActionIndex();

// Get pointer ID

int pointerId = event.getPointerId(pointerIndex);

// Get masked (not specific to a pointer) action

int maskedAction = event.getActionMasked();

switch (maskedAction) {

case MotionEvent.ACTION_DOWN:

case MotionEvent.ACTION_POINTER_DOWN: {

// A finger has touched the screen - so let's create a new

// Circle at the touch location and add it to the list!

Circle circle = new Circle();

circle.x = event.getX(pointerIndex);

circle.y = event.getY(pointerIndex);

circleArray.put(pointerId, circle);

break;

}

case MotionEvent.ACTION_MOVE: {

// How many pointers are in contact with the screen?

int pointerCount = event.getPointerCount();

// Loop over them all...

for (int i = 0; i < pointerCount; ++i) {

// i is the pointer index but we'll update our pointerIndex variable for clarity

pointerIndex = i;

// Get the pointerId at that pointerIndex (pointerId never changes while pointer is in contact)

pointerId = event.getPointerId(pointerIndex);

// Get access to the circle with that pointer id...

Circle circle = circleArray.get(pointerId);

// ...and update the circle's location.

circle.x = event.getX(pointerIndex);

circle.y = event.getY(pointerIndex);

}

break;

}

case MotionEvent.ACTION_UP:

case MotionEvent.ACTION_POINTER_UP: {

// Finger has left contact - remove the circle from the array

circleArray.remove(pointerId);

break;

}

} // End of switch block

// Trigger redraw to display any changes

invalidate();

// Return true to consume the MotionEvent

return true;

}

@Override

protected void onDraw(Canvas canvas)

{

super.onDraw(canvas);

// Draw circles for each pointer in contact with the screen

int numCircles = circleArray.size();

for (int i = 0; i < numCircles; ++i)

{

// Get the circle at index location i

Circle circle = circleArray.valueAt(i);

// ...to choose a colour between 0 and 9.

if (circle != null)

{

int colourNum = i % 9;

paint.setColor(colours[colourNum]);

paint.setColor(colours[i]);

}

// Draw a circle in our chosen colour

canvas.drawCircle(circle.x, circle.y, SIZE, paint);

}

canvas.drawText("Total pointers: " + numCircles, 10, 100, textPaint);

} // End of onDraw method

} // End of MultiTouchCircleView class

This technique doesn’t miss any ACTION_MOVE events because it looks them up by pointerId in the SparseArray – which is potentially a nicer solution. Go with whatever works for you.

Category: Coding

How To: Convert Day Number to Month and Day

The robots are coming…

How To: Learn any new programming concept

How To: Identify which pointer moved in Android

Alternative Solution

How-To: Fix IntelliJ / Android Studio screen display corruption

1 – Find your user folder

2 – Add this switch

Wrap up and secondary workaround