通过

ComboBox.SelectedIndexChanged 事件

  • 参考

定义

命名空间:
System.Windows.Forms
程序集:
System.Windows.Forms.dll

在 SelectedIndex 属性更改后发生。

public:
 event EventHandler ^ SelectedIndexChanged;
public event EventHandler SelectedIndexChanged;
public event EventHandler? SelectedIndexChanged;
member this.SelectedIndexChanged : EventHandler 
Public Custom Event SelectedIndexChanged As EventHandler

事件类型

EventHandler

示例

下面的代码示例演示如何通过设置 和 属性并使用 FindStringExact 方法来搜索 ComboBox来初始化ComboBox控件。MaxDropDownItemsDropDownStyle 它还演示如何处理 SelectedIndexChanged 事件。

#using <System.Drawing.dll>
#using <System.dll>
#using <System.Windows.Forms.dll>

using namespace System::Windows::Forms;
using namespace System;

public ref class Form1: public System::Windows::Forms::Form
{
public:
   Form1() : Form()
   {
      InitializeComboBox();
      InitializeTextBox();
      this->Label1 = gcnew System::Windows::Forms::Label;
      this->SuspendLayout();
      this->Label1->Location = System::Drawing::Point( 8, 24 );
      this->Label1->Name = "Label1";
      this->Label1->Size = System::Drawing::Size( 120, 32 );
      this->Label1->TabIndex = 1;
      this->Label1->Text = "Use drop-down to choose a name:";
      this->Label1->TextAlign = System::Drawing::ContentAlignment::MiddleRight;
      this->ClientSize = System::Drawing::Size( 292, 266 );
      this->Controls->Add( this->Label1 );
      this->Name = "Form1";
      this->Text = "Form1";
      this->ResumeLayout( false );
   }

internal:
   System::Windows::Forms::Label ^ Label1;

   // Declare and initialize the text box.
internal:
   // This text box text will be update programmatically. The user is not 
   // allowed to update it, so the ReadOnly property is set to true.
   System::Windows::Forms::TextBox^ TextBox1;

private:
   void InitializeTextBox()
   {
      this->TextBox1 = gcnew System::Windows::Forms::TextBox;
      this->TextBox1->ScrollBars = ScrollBars::Vertical;
      this->TextBox1->Location = System::Drawing::Point( 64, 128 );
      this->TextBox1->Multiline = true;
      this->TextBox1->Name = "TextBox1";
      this->TextBox1->ReadOnly = true;
      this->TextBox1->Size = System::Drawing::Size( 184, 120 );
      this->TextBox1->TabIndex = 4;
      this->TextBox1->Text = "Employee and Number of Awards:";
      this->Controls->Add( this->TextBox1 );
   }

   // 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->IntegralHeight = false;
      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;
   }
};

int main()
{
   Application::Run( gcnew Form1 );
}

using System.Windows.Forms;

public class Form1:
    System.Windows.Forms.Form

{
    public Form1() : base()
    {        
        InitializeComboBox();
        InitializeTextBox();
        this.Label1 = new System.Windows.Forms.Label();
        this.SuspendLayout();
        this.Label1.Location = new System.Drawing.Point(8, 24);
        this.Label1.Name = "Label1";
        this.Label1.Size = new System.Drawing.Size(120, 32);
        this.Label1.TabIndex = 1;
        this.Label1.Text = "Use drop-down to choose a name:";
        this.Label1.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
        this.ClientSize = new System.Drawing.Size(292, 266);
        this.Controls.Add(this.Label1);
        this.Name = "Form1";
        this.Text = "Form1";
        this.ResumeLayout(false);
    }

    public static void Main()
    {
        Application.Run(new Form1());
    }

    internal System.Windows.Forms.Label Label1;


    // Declare and initialize the text box.
    // This text box text will be update programmatically. The user is not 
    // allowed to update it, so the ReadOnly property is set to true.
    internal System.Windows.Forms.TextBox TextBox1;

    private void InitializeTextBox()
    {
        this.TextBox1 = new System.Windows.Forms.TextBox();
        this.TextBox1.ScrollBars = ScrollBars.Vertical;
        this.TextBox1.Location = new System.Drawing.Point(64, 128);
        this.TextBox1.Multiline = true;
        this.TextBox1.Name = "TextBox1";
        this.TextBox1.ReadOnly = true;
        this.TextBox1.Size = new System.Drawing.Size(184, 120);
        this.TextBox1.TabIndex = 4;
        this.TextBox1.Text = "Employee and Number of Awards:";
        this.Controls.Add(this.TextBox1);
    }

    // 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.IntegralHeight = false;
        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;
    }
}

Imports System.Windows.Forms

Public Class Form1
    Inherits System.Windows.Forms.Form

    Public Sub New()
        MyBase.New()
        InitializeComboBox()
        InitializeTextBox()
        Me.Label1 = New System.Windows.Forms.Label
        Me.SuspendLayout()
        Me.Label1.Location = New System.Drawing.Point(8, 24)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(120, 32)
        Me.Label1.TabIndex = 1
        Me.Label1.Text = "Use drop-down to choose a name:"
        Me.Label1.TextAlign = System.Drawing.ContentAlignment.MiddleRight
        Me.ClientSize = New System.Drawing.Size(292, 266)
        Me.Controls.Add(Me.Label1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)
    End Sub

    Shared Sub Main()
        Application.Run(New Form1)
    End Sub

   
    Friend WithEvents Label1 As System.Windows.Forms.Label
    
    
    

    ' Declare and initialize the text box.
    ' This text box text will be update programmatically. The user is not 
    ' allowed to update it, so the ReadOnly property is set to true.
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox

    Private Sub InitializeTextBox()
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.TextBox1.ScrollBars = ScrollBars.Vertical
        Me.TextBox1.Location = New System.Drawing.Point(64, 128)
        Me.TextBox1.Multiline = True
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.ReadOnly = True
        Me.TextBox1.Size = New System.Drawing.Size(184, 120)
        Me.TextBox1.TabIndex = 4
        Me.TextBox1.Text = "Employee and Number of Awards:"
        Me.Controls.Add(Me.TextBox1)
    End Sub


    ' 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.IntegralHeight = False
        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

End Class

注解

可以为此事件创建事件处理程序，以确定 中所选索引 ComboBox 已更改的时间。 当需要根据 中的当前选择在其他控件中显示信息时， ComboBox这非常有用。 可以使用此事件的事件处理程序在其他控件中加载信息。

有关处理事件的详细信息，请参阅 处理和引发事件。

适用于