R – WinForm designer and right snapline for controls in container when resizing it

I KNEW there had to be a way to do this (and I found a way to do this cleanly). Sheng's solution is exactly what I came up with as a temporary workaround but after a friend pointed out that the Form class eventually inherited from an abstract class, we SHOULD be able to get this done. If they can do it, we can do it.

We went from this code to the problem

Form1 : Form

Problem

public class Form1 : BaseForm
...
public abstract class BaseForm : Form

This is where the initial question came into play. As said before, a friend pointed out that System.Windows.Forms.Form implements a base class that is abstract. We were able to find...

Proof of a better solution

• Inheritance Hierarchy:

  • System.Object
    • System.MarshalByRefObject (public **abstract** class MarshalByRefObject)
      • System.ComponentModel.Component
        • System.Windows.Forms.Control
          • System.Windows.Forms.ScrollableControl
            • System.Windows.Forms.ContainerControl
              • System.Windows.Forms.Form

From this, we knew that it was possible for the designer to show a class that implemented a base abstract class, it just couldn't show a designer class that immediately implemented a base abstract class. There had to be at max 5 inbetween, but we tested 1 layer of abstraction and initially came up with this solution.

Initial Solution

public class Form1 : MiddleClass
...
public class MiddleClass : BaseForm
... 
public abstract class BaseForm : Form
... 

This actually works and the designer renders it fine, problem solved.... except you have an extra level of inheritance in your production application that was only necessary because of an inadequacy in the winforms designer!

This isn't a 100% surefire solution but its pretty good. Basically you use #if DEBUG to come up with the refined solution.

Refined Solution

Form1.cs

public class Form1
#if DEBUG
    : MiddleClass
#else 
    : BaseForm
#endif
...

MiddleClass.cs

public class MiddleClass : BaseForm
... 

BaseForm.cs

public abstract class BaseForm : Form
... 

What this does is only use the solution outlined in "initial solution", if it is in debug mode. The idea is that you will never release production mode via a debug build and that you will always design in debug mode.

The designer will always run against the code built in the current mode, so you cannot use the designer in release mode. However, as long as you design in debug mode and release the code built in release mode, you are good to go.

The only surefire solution would be if you can test for design mode via a preprocessor directive.

Based on your comments and what I think you are trying to accomplish, I think you need to replace the FlowLayoutPanel with a TableLayoutPanel because it sounds like you are just stacking one TextBox below another.

Create a TableLayoutPanel with 1 column and 1 row.

Here is a working example:

tableLayoutPanel1.AutoScroll = true;
tableLayoutPanel1.GrowStyle = TableLayoutPanelGrowStyle.AddRows;
tableLayoutPanel1.RowStyles.Clear();
tableLayoutPanel1.RowStyles.Add(new RowStyle(SizeType.Absolute, 150));
for (int i = 0; i < 4; i++) {
  AddTextBox("TextBox #" + i.ToString());
}

private void AddTextBox(string info) {
  TextBox tx = new TextBox();
  tx.Multiline = true;
  tx.Text = info;
  tx.ScrollBars = ScrollBars.Vertical;
  tx.WordWrap = true;
  tx.Height = 150;
  tx.Anchor  = AnchorStyles.Left | AnchorStyles.Top | AnchorStyles.Right;
  tableLayoutPanel1.Controls.Add(tx);
}

Instead of docking, I set the height of the TextBox and then I set the Anchors so that when the SplitPanel resizes, the TextBoxes resize appropriately.