C# App: "Foreach" doesn't seem to loop through all controls on form

[AHayes]

_Background
I'm attempting to build a C# Windows application for work where I need to dynamically create and remove menu items (buttons). I've figured out how to dynamically create and (I think) remove these items, but I noticed that not all of my buttons are getting removed from the screen.

_The Code
This is a sample of how I'm CREATING the buttons:

for (int i = 0; i < arrButtonData.GetLength(0); i++)
{
        //Make new button               
            Button btn_DynModify = new Button();
 
            //Initialize data.
            btn_DynModify.Location = pntCurrentLoc;
            btn_DynModify.Name = "btn_Modify_" + arrButtonData[i, 1];
            btn_DynModify.BackColor = System.Drawing.Color.FromArgb(231, 241, 255);
            btn_DynModify.Cursor = Cursors.Hand;
            btn_DynModify.Width = 90;
            btn_DynModify.Height = 90;
            btn_DynModify.FlatStyle = FlatStyle.Flat;
            btn_DynModify.FlatAppearance.BorderSize = 0;
            btn_DynModify.Click += new System.EventHandler(btn_DynModify_Click);
            btn_DynModify.Text = arrButtonData[i, 0];
            btn_DynModify.TextAlign = ContentAlignment.BottomCenter;
 
            //Update location                
            if (intCounter % intMaxCol == 0)
            {
                pntCurrentLoc.X -= (btn_DynModify.Width + intOffsetX) * (intMaxCol - 1);
                        pntCurrentLoc.Y += btn_DynModify.Height + intOffsetY;
            }
            else
            {
                        pntCurrentLoc.X += btn_DynModify.Width + intOffsetX;
            }
 
 
            //Add button to form and bring it to the front of the z-order stack.
            Controls.Add(btn_DynModify);
            btn_DynModify.BringToFront();
}
 

And this is how I'm attempting to remove the buttons:

//Clear pre-existing menu items.
foreach (Control ctl in Controls)
{
    if (ctl.Name.StartsWith("btn_Modify_"))
    {
        Controls.Remove(ctl);
    }
}
 

_What SEEMS to Be the Problem
I stepped through my code, specifically keeping an eye on the "foreach" loop each time. My assumption on what's going on is that it's not looping through ALL controls on the page, only some of them (seems to be only half of the buttons I want "removed" on screen are actually being removed when I call the "foreach" loop.


Anybody know why this might be happening?

[r035198x]

_Background
I'm attempting to build a C# Windows application for work where I need to dynamically create and remove menu items (buttons). I've figured out how to dynamically create and (I think) remove these items, but I noticed that not all of my buttons are getting removed from the screen.

_The Code
This is a sample of how I'm CREATING the buttons:

for (int i = 0; i < arrButtonData.GetLength(0); i++)
{
        //Make new button               
            Button btn_DynModify = new Button();
 
            //Initialize data.
            btn_DynModify.Location = pntCurrentLoc;
            btn_DynModify.Name = "btn_Modify_" + arrButtonData[i, 1];
            btn_DynModify.BackColor = System.Drawing.Color.FromArgb(231, 241, 255);
            btn_DynModify.Cursor = Cursors.Hand;
            btn_DynModify.Width = 90;
            btn_DynModify.Height = 90;
            btn_DynModify.FlatStyle = FlatStyle.Flat;
            btn_DynModify.FlatAppearance.BorderSize = 0;
            btn_DynModify.Click += new System.EventHandler(btn_DynModify_Click);
            btn_DynModify.Text = arrButtonData[i, 0];
            btn_DynModify.TextAlign = ContentAlignment.BottomCenter;
 
            //Update location                
            if (intCounter % intMaxCol == 0)
            {
                pntCurrentLoc.X -= (btn_DynModify.Width + intOffsetX) * (intMaxCol - 1);
                        pntCurrentLoc.Y += btn_DynModify.Height + intOffsetY;
            }
            else
            {
                        pntCurrentLoc.X += btn_DynModify.Width + intOffsetX;
            }
 
 
            //Add button to form and bring it to the front of the z-order stack.
            Controls.Add(btn_DynModify);
            btn_DynModify.BringToFront();
}
 

And this is how I'm attempting to remove the buttons:

//Clear pre-existing menu items.
foreach (Control ctl in Controls)
{
    if (ctl.Name.StartsWith("btn_Modify_"))
    {
        Controls.Remove(ctl);
    }
}
 

_What SEEMS to Be the Problem
I stepped through my code, specifically keeping an eye on the "foreach" loop each time. My assumption on what's going on is that it's not looping through ALL controls on the page, only some of them (seems to be only half of the buttons I want "removed" on screen are actually being removed when I call the "foreach" loop.


Anybody know why this might be happening?

The foreach loop works by iterating over a collection. You cannot modify a collection while you are iterating over it at the same time. You should convert Controls ToArray and then modify that array.

[AHayes]

The foreach loop works by iterating over a collection. You cannot modify a collection while you are iterating over it at the same time. You should convert Controls ToArray and then modify that array.

So, if I understand you correctly, the problem is occurring because I'm removing parts of the collection while trying to read it...which is causing it to "skip" over some of them.


That makes sense. Thanks.

[Plater]

There is also a situation (at least in windows applications) where you would need to look at CHILD controls of the controls in Page.Controls.
like if you put a textbox in a groupbox and then put the groupbox on the page, you would only get the groupbox in the iteration, you would need to iterate through child controls of the groupbox to find the textbox.