Question

I have a program that find coordinates between two point with a predefined interval:

    ArrayList<Point> genPoints(double smallDist, Point a, Point b)
    {
        ArrayList<Point> outputPoints = new ArrayList<Point>();
        double distAB = dist2Points(a, b);

        if (smallDist > distAB)
            return null;

        int numGeneratedPoints = (int)(distAB / smallDist);

        Vector vectorBA = b - a;
        vectorBA.Normalize();
        Point currPoint = a;
        for (int i = 0; i < numGeneratedPoints; i++)
        {
            currPoint = currPoint + vectorBA * smallDist;
            if (dist2Points(currPoint, b) != 0)
                outputPoints.Add(currPoint);
        }

        return outputPoints;
    }

now I called that method using the following code, where I am passing two points P1, P2 and predefined distance.

gp = genPoints(1, p1, p2) 

when I want to show the values, it gives me the following:

4.94974746830583,4.94974746830583
 5.65685424949238,5.65685424949238
 6.36396103067893,6.36396103067893
 7.07106781186548,7.07106781186548
 7.77817459305202,7.77817459305202

---

for (int i = 0; i < gp.Count; i++)
    System.Console.WriteLine(" " + gp[i]);

I don’t know how to access those values individually. I couldn’t even use gp[i].x or gp[i].y. but, somehow I need to access those values separately.

Any help would be greatly appreciated.

Answer 1

The problem is that you’re using a non-generic collection, ArrayList. The indexer is just returning object, so you have to cast:

Point p = (Point) gp[i];
// Now you can use p.x etc

If you’re using .NET 2 or higher, it would be better to use a generic collection such as List<T> – make your method return a List<Point> and you’ll be able to write:

Point p = gp[i];

… no cast is required.

There are a number of benefits to generics – unless you’re forced to use non-generic collections (e.g. you’re writing code for .NET 1.1) you should pretty much avoid them and always use the generic collections.

As an aside, methods conventionally start with a capital letter in .NET – so I would name this method GeneratePoints instead.