YouTipProp Webcontrol Listbox Selectionmode
# ASP.NET WebControl: ListBox SelectionMode Property
The `SelectionMode` property is a key feature of the ASP.NET WebControl `ListBox` class. It determines how users can interact with and select items within the list box control.
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## Definition and Usage
The `SelectionMode` property gets or sets the selection mode of the `ListBox` control. This property allows developers to specify whether a user can select only a single item or multiple items from the list box at one time.
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## Syntax
```xml
```
### Property Values
| Property Value | Description |
| :--- | :--- |
| **`Single`** | **Default.** The user can select only one item at a time from the `ListBox`. |
| **`Multiple`** | The user can select multiple items simultaneously. Users can perform multi-selection by holding down the `Ctrl` or `Shift` keys while clicking. |
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## Code Examples
### Example 1: Basic Declarative Markup
The following example demonstrates how to declare a `ListBox` with `SelectionMode` set to `Multiple` in your `.aspx` page:
```xml
```
### Example 2: Handling Multiple Selections in Code-Behind (C#)
When `SelectionMode` is set to `Multiple`, you need to iterate through the items in the code-behind to determine which options the user selected.
**ASPX Markup:**
```xml
```
**C# Code-Behind (`.aspx.cs`):**
```csharp
protected void btnSubmit_Click(object sender, EventArgs e)
{
string selectedItems = "You selected: ";
bool itemSelected = false;
// Loop through each item in the ListBox
foreach (ListItem item in lbFruits.Items)
{
if (item.Selected)
{
selectedItems += item.Text + ", ";
itemSelected = true;
}
}
if (itemSelected)
{
// Trim the trailing comma and space
lblResult.Text = selectedItems.TrimEnd(',', ' ');
}
else
{
lblResult.Text = "Please select at least one item.";
}
}
```
---
## Key Considerations
1. **Retrieving Selected Values:**
* When `SelectionMode` is set to `Single`, you can easily retrieve the selected item using `ListBox.SelectedValue` or `ListBox.SelectedItem`.
* When `SelectionMode` is set to `Multiple`, `ListBox.SelectedValue` will only return the value of the *first* selected item. To retrieve all selected items, you must iterate through the `ListBox.Items` collection and check the `Selected` property of each `ListItem` (as shown in Example 2).
2. **User Experience (UX):**
* When using `SelectionMode="Multiple"`, it is highly recommended to provide a brief instruction (e.g., *"Hold Ctrl to select multiple items"*) since standard HTML multi-select boxes can sometimes be unintuitive for non-technical users.