C#

treeView2.Nodes.Clear();
foreach(TreeNode node in treeView1.Nodes){
    treeView2.Nodes.Add(node);
}

AngryC wrote:

You must first remove it from its current location or clone it.

foreach (TreeNode tn in treeView1.Nodes) {
    treeView2.Nodes.Add(tn.Clone() as TreeNode);
}

Color c = Color.FromArgb(r, g, b);

BoneSoft wrote:

Color is a struct and therefore mutable,

BoneSoft wrote:

And my understanding was that all structs are immutable, trying to change them just creates and swaps a new one behind the scenes, like strings or any other stacked value

Point pt = new Point(1,1);
pt.X = 2;

private void checkBox_CheckedChanged(object sender, EventArgs e) {
    if(sender is CheckBox){
        if(((CheckBox)sender).Checked){
            foreach(CheckBox ck in list){
                if(ck != sender){ //Object comparison
                    ck.Checked = false;
                }
            }
        }
    }
}