Question

我有一个带有DropDownStyle＆＃34; DropDown＆＃34;的组合框。当我输入文本时，comboBox1.Text不是我在comboBox的文本区域中看到的文本，而且SelectedIndex + SelectedItem与我在特定场景中插入的文本不对应。

似乎selectedItem（+ SelectedIndex）对应于打开下拉列表时的文本，而不是关闭时的文本。

创建一个新表单，在其上放置一个组合框和一个按钮。将事件处理程序添加到comboBox1事件中： - textchanged - 落下 - 下拉关闭并将组合框的以下属性写入输出窗口（或文本框）： - comboBox1.Text - comboBox1.SelectedIndex - comboBox1.SelectedItem - comboBox1.SelectedValue - comboBox1.FormattingEnabled 我为按钮的click事件添加了一个eventhandler，显示了comboBox1.Text。

创建一个非常简单的类（例如TestItems），它有3个属性（代码，描述和DescriptionUppercase）。我通过直接使用TestItems类的实例填充组合框项目并首先将它们添加到List，然后将组合框的DataSource设置为List＆lt;＆gt;来测试它。它的工作方式有点不同，但两者都没有像我期望的那样工作。我会坚持列表。我在列表中填写了100个测试项目（代码=＆＃34; I0＆＃34; ...＆＃34; I99＆＃34;和描述＆＃34;项目1＆＃34; ......项目100＆＃34;）。我将DisplayMember设置为＆＃34;描述＆＃34;和ValueMember到＆＃34; Code＆＃34;。

我插入三次文本＆＃34;项目578＆＃34;使用稍微不同的场景。

场景1：SelectedIndex为-1，SelectedItem为null。 - 只需写下＆＃34;项目578＆＃34;在组合框中（不要打开下拉列表）从输出窗口记录：

TextChanged：ComboBox.Text = [ITEM 0] - ComboBox SelectedIndex = [0] - ComboBox SelectedItem = [I0 + Item 0] - ComboBox SelectedValue = [I0] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [I] - ComboBox SelectedIndex = [ - 1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [It] - ComboBox SelectedIndex = [ - 1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Ite] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 5] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 57] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 578] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True]

场景2：selectedIndex = 0，SelectedItem是＆＃34;项目0＆＃34; - 打开下拉列表（单击组合框右侧的箭头） - 输入＆＃34;项目578＆＃34; - 关闭下拉列表日志记录：

TextChanged：ComboBox.Text = [ITEM 0] - ComboBox SelectedIndex = [0] - ComboBox SelectedItem = [I0 + Item 0] - ComboBox SelectedValue = [I0] - Combobox FormattingEnabled = [True] 下拉列表打开：ComboBox.Text = [ITEM 0] - ComboBox SelectedIndex = [0] - ComboBox SelectedItem = [I0 + Item 0] - ComboBox SelectedValue = [I0] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [I] - ComboBox SelectedIndex = [ - 1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [It] - ComboBox SelectedIndex = [ - 1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Ite] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 5] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 57] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 578] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] DropDownClosed：ComboBox.Text = [Item 578] - ComboBox SelectedIndex = [0] - ComboBox SelectedItem = [I0 + Item 0] - ComboBox SelectedValue = [I0] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 578] - ComboBox SelectedIndex = [0] - ComboBox SelectedItem = [I0 + Item 0] - ComboBox SelectedValue = [I0] - Combobox FormattingEnabled = [True]

场景3：SelectedIndex为57，SelectedItem为＆＃34;项目57＆＃34; - 插入＆＃34;项目57＆＃34; - 打开下拉列表 - 添加＆＃34; 8＆＃34;到最后日志记录：

TextChanged：ComboBox.Text = [ITEM 0] - ComboBox SelectedIndex = [0] - ComboBox SelectedItem = [I0 + Item 0] - ComboBox SelectedValue = [I0] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [I] - ComboBox SelectedIndex = [ - 1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [It] - ComboBox SelectedIndex = [ - 1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Ite] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 5] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [Item 57] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] 下拉列表打开：ComboBox.Text = [Item 57] - ComboBox SelectedIndex = [-1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [ITEM 578] - ComboBox SelectedIndex = [ - 1] - ComboBox SelectedItem = [] - ComboBox SelectedValue = [] - Combobox FormattingEnabled = [True] DropDownClosed：ComboBox.Text = [ITEM 578] - ComboBox SelectedIndex = [57] - ComboBox SelectedItem = [I57 + Item 57] - ComboBox SelectedValue = [I57] - Combobox FormattingEnabled = [True] TextChanged：ComboBox.Text = [ITEM 578] - ComboBox SelectedIndex = [57] - ComboBox SelectedItem = [I57 + Item 57] - ComboBox SelectedValue = [I57] - Combobox FormattingEnabled = [True]

离开组合框（失去焦点）并不会改变SelectedItem。另外一句话：如果你设置＆＃34; FormattingEnabled＆＃34;组合框的属性为false，则combobox1.Text将是selectedItem（displaymember）的文本。因此，在第二个场景中，您将在组合框＆＃34;项目57＆＃34;的textarea中看到，但是当您单击显示combobox.Text的按钮时，它将显示＆＃34;项目0＆＃34;。< / p>

重现此代码的代码：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Diagnostics;

namespace TestCombobox
{
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        this.comboBox1.FormattingEnabled = true;
        comboBox1.DropDownClosed += ComboBox1_DropDownClosed;
        comboBox1.DropDown += ComboBox1_DropDown;
        comboBox1.TextChanged += ComboBox1_TextChanged;
        comboBox1.DisplayMember = "DescriptionUpperCase";
        comboBox1.ValueMember = "Code";
        FillCombo();
    }
    private void ComboBox1_DropDown(object sender, EventArgs e)
    {
        ShowDebugInfoCombobox("Dropdown opened");
    }

    private void ComboBox1_TextChanged(object sender, EventArgs e)
    {
        ShowDebugInfoCombobox("TextChanged");
    }

    private void ShowDebugInfoCombobox(string Info)
    {
        Debug.WriteLine($"{Info}: ComboBox.Text = <{comboBox1.Text}> - ComboBox SelectedIndex = <{comboBox1.SelectedIndex}> - ComboBox SelectedItem = <{comboBox1.SelectedItem}> - ComboBox SelectedValue = <{comboBox1.SelectedValue}>  - Combobox FormattingEnabled = <{comboBox1.FormattingEnabled}>");
    }

    private void ComboBox1_DropDownClosed(object sender, EventArgs e)
    {
        ShowDebugInfoCombobox("DropDownClosed");
    }

    private void FillCombo()
    {
        List<TestItems> aList = new List<TestItems>();
        for (int cnt = 0; cnt < 100; cnt++)
        {
            aList.Add(new TestItems($"I{cnt.ToString()}", $"Item {cnt.ToString()}"));
            //comboBox1.Items.Add(new TestItems($"I{cnt.ToString()}", $"Item {cnt.ToString()}"));
        }
        comboBox1.DataSource = aList;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        MessageBox.Show(this.comboBox1?.SelectedItem?.ToString() + " Text = " + this.comboBox1.Text);

    }
}
public class TestItems
{
    public string Code { get; set; }
    public string Description { get; set; }
    public string DescriptionUpperCase { get { return Description.ToUpper(); }  }

    public TestItems(string code, string description)
    {
        this.Code = code;
        this.Description = description;
    }
    public override string ToString()
    {
        return this.Code + " + " + this.Description;
    }
}

}

对我来说看起来像个错误，不确定你的意见是什么。

亲切的问候，巴特

Answer 1

首先，这是一大堆额外的信息，这就是为什么你还没有得到答案。其次，如果要将文本“输入”到comboBox中，则应使用KeyPress事件并从中获取文本，并通过回车键进行过滤。第三，如果要将所选项目设置为null（如果它不在源数据中），则必须添加条件代码才能执行此操作。这是一个使用通用字符串列表的简单示例：

    List<string> source = new List<string>();

    public Form1()
    {
        InitializeComponent();
        source.Add("Item 1");
        source.Add("Item 2");
        comboBox1.Items.AddRange(source.ToArray());
    }

    // Enter key detection as shown in https://stackoverflow.com/a/1226740/4034168
    private void comboBox1_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (e.KeyChar == 13)
        {
            if (!source.Contains(comboBox1.Text))
            {
                comboBox1.SelectedIndex = -1;
                comboBox1.SelectedItem = null;
            }
        }
    }

此外，如果您想阻止用户输入任何键（但仍然从下拉项中选择），只需使用这样的TextUpdate事件（添加删除KeyPress事件，因为你不需要它）：

    private void comboBox1_TextUpdate(object sender, EventArgs e)
    {
        if (!source.Contains(comboBox1.Text)) comboBox1.SelectedItem = null;
    }

C＃：WinForms：ComboBox：DropDown样式：SelectedItem + SelectedIndex设置不正确：bug？

1 个答案: