In this example I’m going to show the basic way on how to bind a different collections to a DropDownList control.
Note that you can also apply the code mentioned in this example to a ListBox, RadioButtonList and CheckBoxList. I just used DropDownList for this demo because I think it is the most commonly used in the page.
To get started, let’s go ahead and grab a DropDownList control from the Visual Studio toolbox and place it in the WebForm. The ASPX mark up should look something like below:
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<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Bind Collections Demo</title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList ID="DropDownList1" runat="server">
</asp:DropDownList>
</div>
</form>
</body>
</html>
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Now let’s switch to Code-Behind part of the page. The first step to do is add the following namespaces below so that we can use the Collections object provided by .NET:
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using System.Collections.Generic;
using System.Collections.Specialized;
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After that, we can start creating a simple method that returns a data from a collection and bind it to the DropDownList control. Here are the code blocks below:
* Using a List
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private List<ListItem> GetDataFromList()
{
List<ListItem> myList = new List<ListItem>();
myList.Add(new ListItem("Item 1", "Item 1 Value"));
myList.Add(new ListItem("Item 2", "Item 2 Value"));
myList.Add(new ListItem("Item 3", "Item 3 Value"));
return myList;
}
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Binding the DropDownList with data from the List object.
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protected void Page_Load(object sender, EventArgs e)
{
//Manually adding the items to the DDL
if (!Page.IsPostBack)
{
foreach (ListItem item in GetDataFromList())
{
DropDownList1.Items.Add(item);
}
}
}
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* Using a Dictionary
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private Dictionary<string,string> GetDataFromDictionary()
{
Dictionary<string, string> myDictionary = new Dictionary<string, string>();
myDictionary.Add("Item 1 Value", "Item 1");
myDictionary.Add("Item 2 Value", "Item 2");
myDictionary.Add("Item 3 Value", "Item 3");
return myDictionary;
}
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You can populate the DropDownList with the data from the Dictionary by (a) manually adding the items to it or (b) using the Dictionary directly as the DataSource and set the DataTextField and DataValueField to it. Check the following code blocks below:
(a)
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protected void Page_Load(object sender, EventArgs e)
{
// Manually adding the items to the DDL
if (!Page.IsPostBack)
{
foreach (KeyValuePair<string, string> kValuePair in GetDataFromDictionary())
{
ListItem item = new ListItem(kValuePair.Value, kValuePair.Key);
DropDownList1.Items.Add(item);
}
}
}
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(b)
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protected void Page_Load(object sender, EventArgs e)
{
//Using Dictionary as the DataSource of the DDL
if (!Page.IsPostBack)
{
DropDownList1.DataSource = GetDataFromDictionary();
DropDownList1.DataTextField = "Value";
DropDownList1.DataValueField = "Key";
DropDownList1.DataBind();
}
}
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* Using a HashTable
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private Hashtable GetDataFromHash()
{
Hashtable myHash = new Hashtable();
myHash.Add("Item 1 Value", "Item 1");
myHash.Add("Item 2 Value", "Item 2");
myHash.Add("Item 3 Value", "Item 3");
return myHash;
}
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You can also populate the DropDownList in two ways just like what we did above using the Dictionary. Here are the code blocks below:
(a)
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protected void Page_Load(object sender, EventArgs e)
{
// Manually adding the items to the DDL
if (!Page.IsPostBack)
{
foreach (DictionaryEntry entry in GetDataFromHash())
{
ListItem item = new ListItem(entry.Value.ToString(), entry.Key.ToString());
DropDownList1.Items.Add(item);
}
}
}
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(b)
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protected void Page_Load(object sender, EventArgs e)
{
//Using the HashTable as the DataSource of the DDL
if (!Page.IsPostBack)
{
DropDownList1.DataSource = GetDataFromHash();
DropDownList1.DataTextField = "Value";
DropDownList1.DataValueField = "Key";
DropDownList1.DataBind();
}
}
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* Using a SortedList
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private SortedList GetDataFromSortedList()
{
SortedList mySortedList = new SortedList();
mySortedList.Add("Item 1 Value", "Item 1");
mySortedList.Add("Item 2 Value", "Item 2");
mySortedList.Add("Item 3 Value", "Item 3");
return mySortedList;
}
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You can also populate the DropDownList in two ways just like what we did above. Here are the code blocks below:
(a)
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protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
foreach (DictionaryEntry entry in GetDataFromSortedList())
{
ListItem item = new ListItem(entry.Value.ToString(), entry.Key.ToString());
DropDownList1.Items.Add(item);
}
}
}
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(b)
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protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
DropDownList1.DataSource = GetDataFromSortedList();
DropDownList1.DataTextField = "Value";
DropDownList1.DataValueField = "Key";
DropDownList1.DataBind();
}
}
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* Using an ArrayList
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private ArrayList GetDataFromArrayList()
{
ArrayList myArray = new ArrayList();
myArray.Add(new ListItem("Item 1", "Item 1 Value"));
myArray.Add(new ListItem("Item 2", "Item 2 Value"));
myArray.Add(new ListItem("Item 3", "Item 3 Value"));
return myArray;
}
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And here’s the code block for populating the DropDownList with data from ArrayList.
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protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
foreach (ListItem item in GetDataFromArrayList())
{
DropDownList1.Items.Add(item);
}
}
}
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* Using a StringCollection
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private StringCollection GetDataFromStrCollection()
{
StringCollection myStrCol = new StringCollection();
myStrCol.Add("Item1,Item 1 Value");
myStrCol.Add("Item2,Item 2 Value");
myStrCol.Add("Item3,Item 3 Value");
return myStrCol;
}
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And here’s the code block for populating the DropDownList with data from StringCollection.
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protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
string[] splitItem = null;
foreach (String item in GetDataFromStrCollection())
{
if (item.Contains(","))
{
splitItem = item.Split(",".ToCharArray());
ListItem newItem = new ListItem(splitItem[0].ToString(), splitItem[1].ToString());
DropDownList1.Items.Add(newItem);
}
}
}
}
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Running the code above will give this page output below:
That’s it! Hope you will find this example useful!