Question

I have chess table and my elements are now moving according to rules .But when I drag out of rules my button is disappearing…How I can solve it ???
(red buttons are showing where can I go my elements)
for example knight is moving as rules now (if I don’t pass over the red buttons there is no problem)but when I pass over the red places and if I drop there the knight disappears and red places turns back to their original color ( no more red places which indicates where my knight can go ). i tried to make debug but since i am new in c# and debugging i haven’t solved the problem. i will be happy if u enlighten my way. how can i solve it? thanks

        void btn_DragEnter(object sender, DragEventArgs e)
        {
        Button button = (Button)sender;
        e.Effect = DragDropEffects.Move;
        for (int x = 0; x <= 7; x++)
        {
        for (int y = 0; y <= 7; y++)
        {
        btn[x, y].Image = null;
        if ((x + y) % 2 == 0)
        btn[x, y].BackColor = Color.Black;
        else
        btn[x, y].BackColor = Color.White;
        }
        }
        }

        void btn_DragDrop(object sender, DragEventArgs e)
        {
        Button button = (Button)sender;
        button.Image = (Bitmap)e.Data.GetData(DataFormats.Bitmap);

        int[] dizi = (int[])button.Tag;
        int x = dizi[0];
        int y = dizi[1];

        for (int a = 0; a <= 7; a++)
        {
        for (int b = 0; b <= 7; b++)
        {
        btn[a, b].AllowDrop = false;
        }
        }

        if ((x + 1 >= 0 && y + 2 <= 7) && (y + 2 >= 0 && x + 1 <= 7))
        {
        btn[x + 1, y + 2].BackColor = Color.Red;
        btn[x + 1, y + 2].AllowDrop = true;
        }
        if ((x + 1 >= 0 && y - 2 <= 7) && (y - 2 >= 0 && x + 1 <= 7))
        {
        btn[x + 1, y - 2].BackColor = Color.Red;
        btn[x + 1, y - 2].AllowDrop = true;
        }
        if ((x - 1 >= 0 && y + 2 <= 7) && (y + 2 >= 0 && x - 1 <= 7))
        {
        btn[x - 1, y + 2].BackColor = Color.Red;
        btn[x - 1, y + 2].AllowDrop = true;
        }
        if ((x - 1 >= 0 && y - 2 <= 7) && (y - 2 >= 0 && x - 1 <= 7))
        {
        btn[x - 1, y - 2].BackColor = Color.Red;
        btn[x - 1, y - 2].AllowDrop = true;
        }
        if ((x + 2 >= 0 && y + 1 <= 7) && (y + 1 >= 0 && x + 2 <= 7))
        {
        btn[x + 2, y + 1].BackColor = Color.Red;
        btn[x + 2, y + 1].AllowDrop = true;
        }
        if ((x + 2 >= 0 && y - 1 <= 7) && (y - 1 >= 0 && x + 2 <= 7))
        {
        btn[x + 2, y - 1].BackColor = Color.Red;
        btn[x + 2, y - 1].AllowDrop = true;
        }
        if ((x - 2 >= 0 && y + 1 <= 7) && (y + 1 >= 0 && x - 2 <= 7))
        {
        btn[x - 2, y + 1].BackColor = Color.Red;
        btn[x - 2, y + 1].AllowDrop = true;
        }
        if ((x - 2 >= 0 && y - 1 <= 7) && (y - 1 >= 0 && x - 2 <= 7))
        {
        btn[x - 2, y - 1].BackColor = Color.Red;
        btn[x - 2, y - 1].AllowDrop = true;
        }
        }

Answer 1

DoDragDrop is called only when actually dropping the piece. Your logic for determining where the piece can be dropped should be run when starting the drag, in MouseDown or MouseMove, before the call to DoDragDrop. It also seems you are clearing the red buttons in the DragEnter function. That also should be done in the MouseDown/MouseMove function, after the call to DoDragDrop.