ComboBox.SelectedIndexChanged 事件
在 SelectedIndex 属性更改后发生。
**命名空间:**System.Windows.Forms
**程序集:**System.Windows.Forms（在 system.windows.forms.dll 中）
语法
声明
Public Event SelectedIndexChanged As EventHandler
用法
Dim instance As ComboBox
Dim handler As EventHandler
AddHandler instance.SelectedIndexChanged, handler
public event EventHandler SelectedIndexChanged
public:
event EventHandler^ SelectedIndexChanged {
void add (EventHandler^ value);
void remove (EventHandler^ value);
}
/** @event */
public void add_SelectedIndexChanged (EventHandler value)
/** @event */
public void remove_SelectedIndexChanged (EventHandler value)
JScript 支持使用事件，但不支持进行新的声明。
备注
可以为该事件创建事件处理程序，以确定 ComboBox 中选定的索引何时更改。这在需要根据 ComboBox 中的当前选定内容显示其他控件中的信息时非常有用。可以使用该事件的事件处理程序来加载其他控件中的信息。
有关处理事件的更多信息，请参见 使用事件。
示例
下面的代码示例演示如何通过设置 MaxDropDownItems 和 DropDownStyle 属性，以及使用 FindStringExact 方法搜索 ComboBox，从而初始化 ComboBox 控件。它还说明如何处理 SelectedIndexChanged 事件。若要运行该示例，请将下面的代码粘贴到一个包含名为 TextBox1 的 TextBox 的窗体中，并从该窗体的构造函数或 Load 事件中调用 InitializeComboBox 方法。
' Declare comboBox1 as a ComboBox.
Friend WithEvents ComboBox1 As System.Windows.Forms.ComboBox
' This method initializes the combo box, adding a large string
' array but limiting the drop-down size to six rows so the combo box
' doesn't cover other controls when it expands.
Private Sub InitializeComboBox()
Me.ComboBox1 = New System.Windows.Forms.ComboBox
Dim employees() As String = New String() {"Hamilton, David", _
"Hensien, Kari", "Hammond, Maria", "Harris, Keith", _
"Henshaw, Jeff D.", "Hanson, Mark", "Harnpadoungsataya, Sariya", _
"Harrington, Mark", "Harris, Keith", "Hartwig, Doris", _
"Harui, Roger", "Hassall, Mark", "Hasselberg, Jonas", _
"Harnpadoungsataya, Sariya", "Henshaw, Jeff D.", "Henshaw, Jeff D.", _
"Hensien, Kari", "Harris, Keith", "Henshaw, Jeff D.", _
"Hensien, Kari", "Hasselberg, Jonas", "Harrington, Mark", _
"Hedlund, Magnus", "Hay, Jeff", "Heidepriem, Brandon D."}
ComboBox1.Items.AddRange(employees)
Me.ComboBox1.Location = New System.Drawing.Point(136, 32)
Me.ComboBox1.MaxDropDownItems = 5
Me.ComboBox1.DropDownStyle = ComboBoxStyle.DropDown
Me.ComboBox1.Name = "ComboBox1"
Me.ComboBox1.Size = New System.Drawing.Size(136, 81)
Me.ComboBox1.TabIndex = 0
Me.Controls.Add(Me.ComboBox1)
End Sub
...
' This method is called when the user changes his or her selection.
' It searches for all occurrences of the selected employee's
' name in the Items array and adds the employee's name and
' the number of occurrences to TextBox1.Text.
' CAUTION This code exposes a known bug: If the index passed to the
' FindStringExact(searchString, index) method is the last index
' of the array, the code throws an exception.
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
Dim comboBox As comboBox = CType(sender, comboBox)
' Save the selected employee's name, because we will remove
' the employee's name from the list.
Dim selectedEmployee = CType(ComboBox1.SelectedItem, String)
Dim count As Integer = 0
Dim resultIndex As Integer = -1
' Call the FindStringExact method to find the first
' occurrence in the list.
resultIndex = ComboBox1.FindStringExact(ComboBox1.SelectedItem)
' Remove the name as it is found, and increment the found count.
' Then call the FindStringExact method again, passing in the index of the
' current found item so the search starts there instead of
' at the beginning of the list.
While (resultIndex <> -1)
ComboBox1.Items.RemoveAt(resultIndex)
count += 1
resultIndex = ComboBox1.FindStringExact _
(selectedEmployee, resultIndex)
End While
' Update the text in Textbox1.
TextBox1.Text = TextBox1.Text & Microsoft.VisualBasic.vbCrLf _
& selectedEmployee & ": " & count
End Sub
// Declare comboBox1 as a ComboBox.
internal System.Windows.Forms.ComboBox ComboBox1;
// This method initializes the combo box, adding a large string array
// but limiting the drop-down size to six rows so the combo box doesn't
// cover other controls when it expands.
private void InitializeComboBox()
{
this.ComboBox1 = new System.Windows.Forms.ComboBox();
string[] employees = new string[]{"Hamilton, David", "Hensien, Kari",
"Hammond, Maria", "Harris, Keith", "Henshaw, Jeff D.",
"Hanson, Mark", "Harnpadoungsataya, Sariya",
"Harrington, Mark", "Harris, Keith", "Hartwig, Doris",
"Harui, Roger", "Hassall, Mark", "Hasselberg, Jonas",
"Harnpadoungsataya, Sariya", "Henshaw, Jeff D.",
"Henshaw, Jeff D.", "Hensien, Kari", "Harris, Keith",
"Henshaw, Jeff D.", "Hensien, Kari", "Hasselberg, Jonas",
"Harrington, Mark", "Hedlund, Magnus", "Hay, Jeff",
"Heidepriem, Brandon D."};
ComboBox1.Items.AddRange(employees);
this.ComboBox1.Location = new System.Drawing.Point(136, 32);
this.ComboBox1.MaxDropDownItems = 5;
this.ComboBox1.DropDownStyle = ComboBoxStyle.DropDownList;
this.ComboBox1.Name = "ComboBox1";
this.ComboBox1.Size = new System.Drawing.Size(136, 81);
this.ComboBox1.TabIndex = 0;
this.Controls.Add(this.ComboBox1);
// Associate the event-handling method with the
// SelectedIndexChanged event.
this.ComboBox1.SelectedIndexChanged +=
new System.EventHandler(ComboBox1_SelectedIndexChanged);
}
...
// This method is called when the user changes his or her selection.
// It searches for all occurrences of the selected employee's
// name in the Items array and adds the employee's name and
// the number of occurrences to TextBox1.Text.
// CAUTION This code exposes a known bug: If the index passed to the
// FindStringExact(searchString, index) method is the last index
// of the array, the code throws an exception.
private void ComboBox1_SelectedIndexChanged(object sender,
System.EventArgs e)
{
ComboBox comboBox = (ComboBox) sender;
// Save the selected employee's name, because we will remove
// the employee's name from the list.
string selectedEmployee = (string) ComboBox1.SelectedItem;
int count = 0;
int resultIndex = -1;
// Call the FindStringExact method to find the first
// occurrence in the list.
resultIndex = ComboBox1.FindStringExact(selectedEmployee);
// Remove the name as it is found, and increment the found count.
// Then call the FindStringExact method again, passing in the
// index of the current found item so the search starts there
// instead of at the beginning of the list.
while (resultIndex!=-1)
{
ComboBox1.Items.RemoveAt(resultIndex);
count += 1;
resultIndex = ComboBox1.FindStringExact(selectedEmployee,
resultIndex);
}
// Update the text in Textbox1.
TextBox1.Text = TextBox1.Text+ "\r\n" + selectedEmployee + ": "
+ count;
}
// Declare comboBox1 as a ComboBox.
internal:
System::Windows::Forms::ComboBox^ ComboBox1;
private:
// This method initializes the combo box, adding a large string array
// but limiting the drop-down size to six rows so the combo box doesn't
// cover other controls when it expands.
void InitializeComboBox()
{
this->ComboBox1 = gcnew System::Windows::Forms::ComboBox;
array<String^>^ employees = {"Hamilton, David","Hensien, Kari",
"Hammond, Maria","Harris, Keith","Henshaw, Jeff D.",
"Hanson, Mark","Harnpadoungsataya, Sariya",
"Harrington, Mark","Harris, Keith","Hartwig, Doris",
"Harui, Roger","Hassall, Mark","Hasselberg, Jonas",
"Harnpadoungsataya, Sariya","Henshaw, Jeff D.",
"Henshaw, Jeff D.","Hensien, Kari","Harris, Keith",
"Henshaw, Jeff D.","Hensien, Kari","Hasselberg, Jonas",
"Harrington, Mark","Hedlund, Magnus","Hay, Jeff",
"Heidepriem, Brandon D."};
ComboBox1->Items->AddRange( employees );
this->ComboBox1->Location = System::Drawing::Point( 136, 32 );
this->ComboBox1->MaxDropDownItems = 5;
this->ComboBox1->DropDownStyle = ComboBoxStyle::DropDownList;
this->ComboBox1->Name = "ComboBox1";
this->ComboBox1->Size = System::Drawing::Size( 136, 81 );
this->ComboBox1->TabIndex = 0;
this->Controls->Add( this->ComboBox1 );
// Associate the event-handling method with the
// SelectedIndexChanged event.
this->ComboBox1->SelectedIndexChanged +=
gcnew System::EventHandler( this, &Form1::ComboBox1_SelectedIndexChanged );
}
...
private:
// This method is called when the user changes his or her selection.
// It searches for all occurrences of the selected employee's
// name in the Items array and adds the employee's name and
// the number of occurrences to TextBox1.Text.
// CAUTION This code exposes a known bug: If the index passed to the
// FindStringExact(searchString, index) method is the last index
// of the array, the code throws an exception.
void ComboBox1_SelectedIndexChanged( Object^ sender,
System::EventArgs^ e )
{
ComboBox^ comboBox = (ComboBox^)(sender);
// Save the selected employee's name, because we will remove
// the employee's name from the list.
String^ selectedEmployee = (String^)(ComboBox1->SelectedItem);
int count = 0;
int resultIndex = -1;
// Call the FindStringExact method to find the first
// occurrence in the list.
resultIndex = ComboBox1->FindStringExact( selectedEmployee );
// Remove the name as it is found, and increment the found count.
// Then call the FindStringExact method again, passing in the
// index of the current found item so the search starts there
// instead of at the beginning of the list.
while ( resultIndex != -1 )
{
ComboBox1->Items->RemoveAt( resultIndex );
count += 1;
resultIndex = ComboBox1->FindStringExact( selectedEmployee,
resultIndex );
}
TextBox1->Text = TextBox1->Text + "\r\n" + selectedEmployee + ": " +
count;
}
// Declare comboBox1 as a ComboBox.
System.Windows.Forms.ComboBox comboBox1;
// This method initializes the combo box, adding a large string array
// but limiting the drop-down size to six rows so the combo box doesn't
// cover other controls when it expands.
private void InitializeComboBox()
{
this.comboBox1 = new System.Windows.Forms.ComboBox();
String employees[] = new String[] { "Hamilton, David", "Hensien, Kari",
"Hammond, Maria", "Harris, Keith", "Henshaw, Jeff D.",
"Hanson, Mark", "Harnpadoungsataya, Sariya", "Harrington, Mark",
"Harris, Keith", "Hartwig, Doris", "Harui, Roger", "Hassall, Mark",
"Hasselberg, Jonas", "Harnpadoungsataya, Sariya",
"Henshaw, Jeff D.","Henshaw, Jeff D.", "Hensien, Kari",
"Harris, Keith", "Henshaw, Jeff D.", "Hensien, Kari",
"Hasselberg, Jonas", "Harrington, Mark", "Hedlund, Magnus",
"Hay, Jeff", "Heidepriem, Brandon D." };
comboBox1.get_Items().AddRange(employees);
this.comboBox1.set_Location(new System.Drawing.Point(136, 32));
this.comboBox1.set_MaxDropDownItems(5);
this.comboBox1.set_DropDownStyle(ComboBoxStyle.DropDownList);
this.comboBox1.set_Name("comboBox1");
this.comboBox1.set_Size(new System.Drawing.Size(136, 81));
this.comboBox1.set_TabIndex(0);
this.get_Controls().Add(this.comboBox1);
// Associate the event-handling method with the
// SelectedIndexChanged event.
this.comboBox1.add_SelectedIndexChanged(new System.EventHandler(
comboBox1_SelectedIndexChanged));
} //InitializeComboBox
...
// This method is called when the user changes his or her selection.
// It searches for all occurrences of the selected employee's
// name in the Items array and adds the employee's name and
// the number of occurrences to textBox1.Text.
// CAUTION This code exposes a known bug: If the index passed to the
// FindStringExact(searchString, index) method is the last index
// of the array, the code throws an exception.
private void comboBox1_SelectedIndexChanged(Object sender,
System.EventArgs e)
{
ComboBox comboBox = (ComboBox)sender;
// Save the selected employee's name, because we will remove
// the employee's name from the list.
String selectedEmployee = (String)(comboBox1.get_SelectedItem());
int count = 0;
int resultIndex = -1;
// Call the FindStringExact method to find the first
// occurrence in the list.
resultIndex = comboBox1.FindStringExact(selectedEmployee);
// Remove the name as it is found, and increment the found count.
// Then call the FindStringExact method again, passing in the
// index of the current found item so the search starts there
// instead of at the beginning of the list.
while (resultIndex != -1) {
comboBox1.get_Items().RemoveAt(resultIndex);
count += 1;
resultIndex = comboBox1.FindStringExact(selectedEmployee,
resultIndex);
}
// Update the text in textBox1.
textBox1.set_Text(textBox1.get_Text() + "\r\n" + selectedEmployee
+ ": " + count);
} //comboBox1_SelectedIndexChanged
平台
Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0
.NET Compact Framework
受以下版本支持：2.0、1.0