How can I get the array index of a given object in C# with control arrays?

Question

I am dynamically adding a bunch of controls to a form. Each control calls the same method, and in that method I need to know the array index of the the control that performed the action.

CheckBox[] myCB = new CheckBox[100];
int i;
for (i = 0; i < 100; i++)
{
    myCB[i] = new CheckBox();
    myCB[i].Text = "Clicky!";
    myCB[i].Click += new System.EventHandler(dynamicbutton_Click);
    tableLayoutPanel1.Controls.Add(myCB[i]);
}

private void dynamicbutton_Click(Object sender, System.EventArgs e)
{
    label1.Text = sender.???array index property???.ToString();
}

So if I click myCB[42] label1 will read "42" Of course, if there is an easier way to handle dynamic controls I'd appreciate pointers.

Answer 1

Control's should have a Tag property. Maybe you can attach the index to the Tag. You will incur boxing though...

Answer 2

private void dynamicbutton_Click(Object sender, System.EventArgs e)
{
    label1.Text = Array.IndexOf(myCB, (CheckBox)sender).ToString();
}

Answer 3

One obvious solution would be to set the tag:

CheckBox[] myCB = new CheckBox[100];
for (int i = 0; i < myCB.Length; i++)
{
    myCB[i] = new CheckBox();
    myCB[i].Text = "Clicky!";
    myCB[i].Click += new System.EventHandler(dynamicbutton_Click);
    myCB[i].Tag = i;
    tableLayoutPanel1.Controls.Add(myCB[i]);
}

Then:

private void dynamicbutton_Click(Object sender, System.EventArgs e)
{
    Control control = (Control) sender;
    label1.Text = sender.Tag.ToString();
}

Another alternative is to capture the information in the event handler, most simply using a lambda expression or anonymous method:

CheckBox[] myCB = new CheckBox[100];
for (int i = 0; i < myCB.Length; i++)
{
    int index = i; // This is very important, as otherwise i will
                  // be captured for all of them
    myCB[i] = new CheckBox();
    myCB[i].Text = "Clicky!";
    myCB[i].Click += (s, e) => label1.Text = index.ToString();
    tableLayoutPanel1.Controls.Add(myCB[i]);
}

or for more complicated behaviour:

CheckBox[] myCB = new CheckBox[100];
for (int i = 0; i < myCB.Length; i++)
{
    int index= i; // This is very important, as otherwise i will
                  // be captured for all of them
    myCB[i] = new CheckBox();
    myCB[i].Text = "Clicky!";
    myCB[i].Click += (s, e) => DoSomethingComplicated(index, s, e);
    tableLayoutPanel1.Controls.Add(myCB[i]);
}

(where you declare DoSomethingComplicated appropriately).

Answer 4

int j = i;
myCB[i].Click += delegate(object sender, EventArgs e) {
 // here you can use "j"

};