Center multiple rows of controls in a FlowLayoutPanel

Question

I'm trying to make a panel that would host dynamically added controls. There are two caveats:

• There are going to be a lot of controls, so the panel should wrap the elements into new rows as it reaches its width limits and scroll vertically.
• Controls can change in size, which would change the number of elements
  that can fit into a single row.

I've seen a couple proposed solutions to center dynamic controls in a Form and rejected those for following reasons:

• TableLayoutPanel - main issue I have with using this are the events when elements grown and have to shift from 3-2 grid to 2-4, as TableLayoutPanel does not seem to deal well with those.
• AutoSize FlowLayoutPanel that can grow and shrink inside of TableLayoutControl - my main problem with this solution is that it only centers one row inside the Form, once it wraps to a new row, the elements start to align to the right side. I suppose I can dynamically add new FlowLayoutPanels to new rows of a TableLayoutControl, but then I have a similar issue as the first scenario where I need to manually redistribute elements between rows if they grow/shrink in size.

I was wondering if I'm missing some functionality that can help me handle grows/shrink event without creating my own variation of TableLayoutPanel?

Edit:
Below is a draft of functionality:

• A - Two elements centered in panel
• B - Third element added, all three are centered
• C - Forth element added, wrapped to a new row and centered
• D - Elements enlarged, now wraps on the second element, centered

Answer 1

Here's an example that reproduces the behaviour you described.
It makes use of a TableLayoutPanel which hosts multiple FlowLayoutPanels.

One important detail is the anchoring of the child FlowLayoutPanels: they need to be anchored to Top-Bottom: this causes the panel to be positioned in the center of a TableLayoutPanel Row.

Note that, in the Form constructor, one of the RowStyles is removed. This is also very important: the TLP (which is quite the eccentric guy), even if you have just one Row (or one Column, same thing), will keep 2 RowStyles. The second style will be applied to the first Row you add; just to the first one, not the others: this can screw up the layout.

Another anomaly, it doesn't provide a method to remove a Row, so I've made one. It's functional but bare-bones and needs to be extended, including further validations.

See the graphic sample about the current functionality. If you need help in implementing something else, leave a comment.

---

To build this add the following controls to a Form (here, called FLPTest1):

1. Add one Panel, set Dock.Bottom. Right click and SendToBack(),
2. Add a TableLayoutPanel (here, called tlp1), set:
   • AutoScroll = true, AutoSize = true,
   • AutoSizeMode = GrowAndShrink, Dock.Fill
   • Keep 1 Column, set to AutoSize and one Row, set to AutoSize
3. Add a FlowLayoutPanel (here, called flp1), positioned inside the TableLayoutPanel. It's not actually necessary, just for this sample code
   • Set its Anchor to Top, Bottom <= this is !important, the layout won't work correctly without it: it allows to center the FLP inside the TLP Row,
   • AutoSize = true, AutoSizeMode = GrowAndShrink
4. Add a Button (called btnAddControl)
5. Add a second Button (called btnRemoveControl)
6. Add a CheckBox (called chkRandom)
7. Paste the code here inside a Form's code file

---

using System.Drawing;
using System.Linq;
using System.Windows.Forms;


public partial class TLPTest1 : Form
{
    public TLPTest1()
    {
        InitializeComponent();
        tlp1.RowStyles.RemoveAt(1);
    }

    private void TLPTest1_Load(object sender, EventArgs e)
    {
        PictureBox pBox = new PictureBox() {
            Anchor = AnchorStyles.None,
            BackColor = Color.Orange,
            MinimumSize = new Size(125, 125),
            Size = new Size(125, 125),
        };
        flp1.Controls.Add(pBox);
        tlp1.Controls.Add(flp1);
    }

    Random rnd = new Random();
    Size[] sizes = new Size[] { new Size(75, 75), new Size(100, 100), new Size(125, 125)};
    Color[] colors = new Color[] { Color.Red, Color.LightGreen, Color.YellowGreen, Color.SteelBlue };
    Control selectedObject = null;

    private void btnAddControl_Click(object sender, EventArgs e)
    {
        Size size = new Size(125, 125);
        if (chkRandom.Checked) size = sizes[rnd.Next(sizes.Length)];
        
        var pBox = new PictureBox() {
            Anchor = AnchorStyles.None,
            BackColor = colors[rnd.Next(colors.Length)],
            MinimumSize = size,
            Size = size
        };

        bool drawborder = false;
        // Just for testing - use standard delegates instead of Lambdas in real code
        pBox.MouseEnter += (s, evt) => { drawborder = true;  pBox.Invalidate(); };
        pBox.MouseLeave += (s, evt) => { drawborder = false; pBox.Invalidate(); };
        pBox.MouseDown += (s, evt) => { selectedObject = pBox;  pBox.Invalidate(); };
        pBox.Paint += (s, evt) => { if (drawborder) {
            ControlPaint.DrawBorder(evt.Graphics, pBox.ClientRectangle, 
                                    Color.White, ButtonBorderStyle.Solid);
            }
        };

        var ctl = tlp1.GetControlFromPosition(0, tlp1.RowCount - 1);
        int overallWith = ctl.Controls.OfType<Control>().Sum(c => c.Width + c.Margin.Left + c.Margin.Right);
        overallWith += (ctl.Margin.Right + ctl.Margin.Left);

        if ((overallWith + pBox.Size.Width + pBox.Margin.Left + pBox.Margin.Right) >= tlp1.Width) {
            var flp = new FlowLayoutPanel() {
                Anchor = AnchorStyles.Top | AnchorStyles.Bottom,
                AutoSize = true,
                AutoSizeMode = AutoSizeMode.GrowAndShrink,
            };

            flp.Controls.Add(pBox);

            tlp1.SuspendLayout();
            tlp1.RowCount += 1;
            tlp1.Controls.Add(flp, 0, tlp1.RowCount - 1);
            tlp1.ResumeLayout(true);
        }
        else {
            ctl.Controls.Add(pBox);
        }
    }

    private void btnRemoveControl_Click(object sender, EventArgs e)
    {
        if (selectedObject is null) return;
        Control parent = selectedObject.Parent;
        selectedObject.Dispose();

        if (parent?.Controls.Count == 0) {
            TLPRemoveRow(tlp1, parent);
            parent.Dispose();
        }
    }

    private void TLPRemoveRow(TableLayoutPanel tlp, Control control)
    {
        int ctlPosition = tlp.GetRow(control);
        if (ctlPosition < tlp.RowCount - 1) {
            for (int i = ctlPosition; i < tlp.RowCount - 1; i++) {
                tlp.SetRow(tlp.GetControlFromPosition(0, i + 1), i);
            }
        }
        tlp.RowCount -= 1;
    }
}