c# - How to get the index of an element within a range in ArrayList

Get the index of an element within a range of elements in an ArrayList
The ArrayList class implements the IList interface using an array whose size is dynamically increased as required. It is designed to hold heterogeneous collections of objects. ArrayList is not guaranteed to be sorted. The ArrayList capacity is the number of elements it can hold. Its capacity is automatically increased while adding elements. ArrayList elements can be accessed by index and it is zero-based. The ArrayList accepts null as a valid value and also allows duplicate elements.

The following .net c# tutorial code demonstrates how we can get the index of an element within a range of elements in an ArrayList. That means we will find the specified element within a range of elements in an ArrayList. Here we will use the ArrayList class IndexOf() method to get the index of an element within a range in an ArrayList object. We only take the index of the element’s first occurrence within a range of elements in an ArrayList.

The ArrayList IndexOf() method returns the zero-based index of the first occurrence of a value in the ArrayList or in a portion of it. The ArrayList IndexOf(Object, Int32, Int32) method overload searches for the specified Object and returns the zero-based index of the first occurrence within the range of elements in the ArrayList that starts at the specified index and contains the specified number of elements.

The ArrayList IndexOf(object? value, int startIndex, int count) method overload has three parameters. The value parameter is the Object to locate in the ArrayList. The value can be null. The startIndex parameter is the zero-based starting index of the search. 0 (zero) is valid in an empty list. And the count parameter is the number of elements in the section to search.

The ArrayList IndexOf(object? value, int startIndex, int count) method returns the zero-based index of the first occurrence of value within the range of elements in the ArrayList that starts at startIndex and contains the count number of elements if found otherwise it returns -1.

The ArrayList IndexOf(object? value, int startIndex, int count) method throws ArgumentOutOfRangeException If the startIndex is outside the range of valid indexes for the ArrayList or the count is less than zero or the startIndex and count do not specify a valid section in the ArrayList. The ArrayList is searched forward starting at startIndex and ending at startIndex plus count minus 1 if the count is greater than 0.
ArrayListIndexOfMethodWithStartIndexAndCount.aspx

<%@ Page Language="C#" AutoEventWireup="true" %>

<!DOCTYPE html>

<script runat="server">
    protected void Button1_Click(object sender, System.EventArgs e)
    {
        ArrayList colors = new ArrayList() { "ForestGreen", "Orange", "SkyBlue", "Navy", "Orange", "Olive" };

        Label1.Text = "ArrayList Elements....";
        Label1.Text += "<font color=SkyBlue>";
        foreach (string color in colors)
        {
            Label1.Text += "<br />" + color;
        }
        Label1.Text += "</font>";

        Label1.Text += "<br /><br />IndexOf(object Orange, startIndex 2, count 4)";
        Label1.Text += "<font color=Crimson>";
        Label1.Text += "<br />Index of 'Orange': " + colors.IndexOf("Orange", 2, 4);
        Label1.Text += "</font>";
    }
</script>

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<head id="Head1" runat="server">
    <title>How to use System.Collections.ArrayList IndexOf(Object, Int32, Int32) Method</title>
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<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:MidnightBlue; font-style:italic;">
            System.Collections.ArrayList IndexOf(Object, Int32, Int32) Method
            <br /> How to search specified Object and get zero-based index of first
            <br /> occurrence within the range of elements in ArrayList that starts
            <br /> at specified index and contains specified number of elements
        </h2>
        <hr width="575" align="left" color="Navy" />
        <br />
        <asp:Label
             ID="Label1"
             runat="server"
             ForeColor="DarkOrchid"
             Font-Size="Large"
             Font-Names="Courier New"
             Font-Italic="true"
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             >
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        <br /><br />
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            ID="Button1"
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            OnClick="Button1_Click"
            Text="Test ArrayList IndexOf(Object, Int32, Int32) Method"
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            Font-Bold="true"
            ForeColor="DodgerBlue"
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    </div>
    </form>
</body>
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