CODEWITHSUNDEEP
c#listpropertiesreadonly
Brandonm
Brandonm

Reputation: 516

C# Changing the value of an element in a list of type Rectangle

I'm struggling to set the values of an element at a specific index within a list to a new value.

The list is of type object Rectangle and i get the following error when I try change any of the values of the rectangle in the list e.g.

Property or indexer 'System.Drawing.Rectangle.Bottom' cannot be assigned to -- it is read only

I've tried converting the list to an array but i still run into the same issue of the values being read-only.

Basically the app takes in a user defined number of rectangles and draws the rectangles with varying widths and heights but along the same baseline. The code im trying to implement needs to take those rectangles and redraw them vertically from the base upwards, while keeping the same number of rectangles and keeping the same outer shape as the previous rectangles created.

Code:

public void RotateRectangles(List<Rectangle> Rectangles, int startPositionX, int userInput, Graphics DrawingSurface)
    {
        Graphics RectangleGraphics = DrawingSurface;

        try
        {
            // loop in reverse to compare one rectangle to all the other rectangles in the vector

            for (int i = Rectangles.Count - 1; i > -1; --i)
            {
                bool mustChange = true;

                for (int t = Rectangles.Count - 1; t > -1; --t)
                {
                    // only compare if the current position in the vector A if different to the position in vector B.
                    if (i > t)
                    {
                        if (mustChange == true)
                        {
                            // If the top Y coordinate of RECT at Position i in vector A is bigger than Y coordinate
                            // at Position t in vector B

                            if (Rectangles[i].Top >= Rectangles[t].Top)
                            {
                                //adjusting points accordingly
                                Rectangles[i].Left = (Rectangles[t].Left);
                                Rectangles[t].Bottom = (Rectangles[i].Top);
                            }
                            else
                            {
                                // If the Y coordinate is not bigger, then we need to stop checking
                                mustChange = false;
                            }
                        }
                    }
                }
            }

            // loop forward to compare one rectangle to all the other rectangles in the vector
            for (int i = 0; i < Rectangles.Count; ++i)
            {
                bool forwardChange = true;

                for (int t = 0; t < Rectangles.Count; ++t)
                {
                    // If the top Y coordinate of RECT at Position i in vector A is bigger than Y coordinate at Position t
                    // in vector B AND the two rectangales touch

                    if (i < t && Rectangles[i].Top <= Rectangles[t].Bottom)
                    {
                        if (forwardChange == true)
                        {

                            // If the top Y coordinate of RECT at Position i in vector A is bigger than Y coordinate at Position t 

                            // in vector B

                            if (Rectangles[i].Top > Rectangles[t].Top)
                            {
                                //adjusting points accordingly
                                Rectangles[i].Right = (Rectangles[t].Right);
                                Rectangles[t].Bottom = (Rectangles[i].Top);
                            }
                            else
                            {
                                // If the Y coordinate is not bigger, then we need to stop checking
                                forwardChange = false;
                                // Addjust the Y position of each rectangle so it does not overlap with the first drawing

                                for (int z = 0; z < Rectangles.Count; ++z)
                                {
                                    Rectangles[z].Top = (250 - Rectangles[z].Top);
                                    Rectangles[z].Bottom = (250 - Rectangles[z].Bottom);
                                }
                            }
                        }
                    }
                }
            }
            for (int z = 0; z < Rectangles.Count; ++z)
            {

                Rectangle DrawRec = myRectangleClass.MyRectangle(Rectangles[z].Left, Rectangles[z].Top, Rectangles[z].Right, Rectangles[z].Bottom);
                RectangleGraphics.DrawRectangle(Pen, DrawRec);

                ReadWrite.writeOutput(Rectangles[z].Left, Rectangles[z].Top, Rectangles[z].Right, Rectangles[z].Bottom);
            }
        }
        catch (Exception e)
        {
        }
    }

The parts that are giving the errors are:

Rectangles[i].Left = (Rectangles[t].Left);
Rectangles[t].Bottom = (Rectangles[i].Top);

Rectangles[i].Right = (Rectangles[t].Right);
Rectangles[t].Bottom = (Rectangles[i].Top);

Rectangles[z].Top = (250 - Rectangles[z].Top);
Rectangles[z].Bottom = (250 - Rectangles[z].Bottom);

Please can someone help me out or at least direct me in the right direction

Upvotes: 0

Views: 3070

Answers (3)

user287107
user287107

Reputation: 9417

the problem is less the value type of the rectangle, more that the List[] operator returns a new value object. 

List<Rectangle> a; 

a[4].X += 4; // does the same like the following code:

var r = a[4] 
r.X += 4; // will change r, but not a[4]

so you need to store back the rectangle value in the list

Upvotes: 2

Phil
Phil

Reputation: 43021

The properties Right, Left, Top, Bottom are read-only. You can use the methods Offset and Inflate, and the properties Location, Size, Width and Height, to adjust the position and size of the rectangle, or you can replace an existing rectangle with a newly created one.

e.g.

Rectangle ri = Rectangles[i];
Rectangle rt = Rectangles[t];

Rectangle[i] = new Rectangle( rt.Left, ri.Bottom, rt.Height, rt.Width );

Upvotes: 2

YoryeNathan
YoryeNathan

Reputation: 14532

Rectangles[i] = new Rectangle(Rectangles[t].Left, Rectangles[i].Top, Rectangles[i].Width, Rectangles[i].Height);

Assign a new rectangle to the wanted index.

Upvotes: 1

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