Order of controls in a form's Control property in C#

Question

I am having a peculiar problem with the order in which FlowLayoutPanels are added in to the form's controls property. This is what I tried,

I added 7 FlowLayoutPanels in to a C# window application from left to right in vertical strips. Then I tagged the flow layouts as 1, 2, 3, ... 7 again from left to right. Now in the load handler of the form, I wrote the following snippet,

    foreach (FlowLayoutPanel aDaysControl in this.Controls)
    {
        MessageBox.Show(aDaysControl.Tag.ToString());
    }

I expected messages to appear in the order of 1, 2, ... 7. But I got it in the reverse order (7, 6, ...1). Could some one help me out with the mistake I did ??

Reason behind preserving the order,

I am trying to make a calendar control with each row representing a day. If a month starts from Wednesday, then I need to add a empty label to the first(Monday) and the second(Tuesday) row. So the order matters a bit

Answer 1

look at the order in which they are added to the form in the yourForm.designer.cs

Answer 2

Is it really a problem?

As long as the UI operates correctly (in terms of tab order, for example), I'd recommend that you don't make any assumptions about the order in which they're enumerated.

EDIT: Thanks for explaining your requirement in more detail. I think I'd still recommend against using the order that they're stored in the Controls collection. It's always best to consider these implementation details to be 'opaque'. You have a tag associated with each control, so you can use this to identify the correct control. In order to speed up the processing, you could build a 7-element array that references the controls by ordinal:

FlowLayoutPanel[] panels = new FlowLayoutPanel[7];

foreach(FlowLayoutPanel panel in this.Controls)
{
    panels[(int)panel.Tag] = panel;
}

// Now, you can reference the panels directly by subscript:

panels[2].BackColor = Color.Aquamarine;

Though I'd put some type-checking in to make this code a bit more robust!

Answer 3

if you look at the code generated by the designer Form1.designer.cs it will look something like this:

        // 
        // Form1
        // 
        this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
        this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
        this.ClientSize = new System.Drawing.Size(658, 160);
        this.Controls.Add(this.flowLayoutPanel7);
        this.Controls.Add(this.flowLayoutPanel6);
        this.Controls.Add(this.flowLayoutPanel5);
        this.Controls.Add(this.flowLayoutPanel4);
        this.Controls.Add(this.flowLayoutPanel3);
        this.Controls.Add(this.flowLayoutPanel2);
        this.Controls.Add(this.flowLayoutPanel1);
        this.Name = "Form1";
        this.Text = "Form1";
        this.ResumeLayout(false);

note how it was built up you added panel 1 first then 2 etc. but as the code runs through it will add 7 first then 6.

this code will be in the InitializeComponent() function generated by the designer.

Why do you need them to run in a certain order?

I wouldn't rely on the designer to keep the order you want.. i would sort the controls my self:

        var flowpanelinOrder = from n in this.Controls.Cast<Control>()
                               where n is FlowLayoutPanel
                               orderby int.Parse(n.Tag.ToString())
                               select n;

        /* non linq
        List<Control> flowpanelinOrder = new List<Control>();
        foreach (Control c in this.Controls)
        {
            if (c is FlowLayoutPanel) flowpanelinOrder.Add(c);                
        }
        flowpanelinOrder.Sort();
         * */

        foreach (FlowLayoutPanel aDaysControl in flowpanelinOrder)
        {
            MessageBox.Show(aDaysControl.Tag.ToString());
        }