将值添加到for循环内的PointF数组时，出现“预期为常数”错误

Question

im a newbie in C# programming. I having difficulties with my project. Here is the thing. - I have a list of MCvBox2dD name lstRectangles - I want to get the center of each box and place it all on PointF array named center.

here is my code:

        List<MCvBox2D> lstRectangles; // stores data of detected boxes
        ...

        int size = lstRectangles.Count(); //total boxes detected
        PointF[] center = null; //array of PointF where I want to transfer the center of each detected boxes

        for (int j = 0; j < lstRectangles.Count(); j++) 
        {
            center = new PointF[j] // here is the error, "A constant value is expected"
            {
                new PointF(lstRectangles[j].center.X , lstRectangles[j].center.Y)
            };

        }

Answer 1

In this case you've both specified an exact size of the array and the set of elements that make up the array. C# has to pick one of these values to use as the size of the array. In this case j is not a constant hence it can't validate that these two numbers match up and it's issuing an error.

To fix this just remove the size argument and let C# infer the size based on the number of elements you use

center = new PointF[]
{
  new PointF(lstRectangles[j].center.X , lstRectangles[j].center.Y)
};

Based on the context though it looks like what you're really trying to do is assign a new PointF into the array at j . If so then do the following

center[j] = new PointF(lstRectangles[j].center.X , lstRectangles[j].center.Y);

Answer 2

First you need to declare the size for your array of PointF (equals to the lstRectangle elements)
Then the correct syntax to add a new PointF to the array is the following

    int size = lstRectangles.Count(); 
    PointF[] center = new PointF[size];
    for (int j = 0; j < lstRectangles.Count(); j++) 
    {
        center[j] = new PointF(lstRectangles[j].center.X , lstRectangles[j].center.Y)
    }

However, instead of using an array, I suggest to use a List<PointF>

    List<PointF> center = new List<PointF>();
    foreach(MCvBox2D box in lstRectangles) 
    {
        center.Add(new PointF(box.center.X , box.center.Y));

    }