ComboBox 数据源动态变化

Question

首先：我有 List 填充了 Customer

的对象类型

List<Customer> Customers = new List<Customer>();

第二：我有 2 个 ComboBox，一个用于 Customer Name，另一个用于 Customer Phone。并将 DataSource 设置为 Customers 列表。

CustomersPhone_ComBx.DataSource = Customers.Select(Customer => Customer.Phone).ToList();
CustomersName_ComBx.DataSource = Customers.Select(Customer => Customer.Name).ToList();

第三：当用户更改 Phone ComboBox 中的选定项目时，我想过滤 Name ComboBox 中的名称，该名称与选择的电话号码相同。 （因为可能是注册了多个名字的电话号码）。我有这个代码

private void CustomersPhone_ComBx_Leave(object sender, EventArgs e)
{
    if (CustomersPhone_ComBx.Text != "")
         CustomersName_ComBx.DataSource = Customers.Where(Customer => Customer.Phone == CustomersPhone_ComBx.Text).Select(Customer => Customer.Name).ToList();
    else
         CustomersName_ComBx.DataSource = Customers.Select(Customer => Customer.Name).ToList();
}

但是当我测试它并更改 Phone ComboBox 中的选定项目时，Name ComboBox 中没有任何变化。

---

更新 1

第四：如果我使用foreach，它可以像下面的代码一样正常工作，但不适用于DataSource

private void CustomersPhone_ComBx_SelectedIndexChanged(object sender, EventArgs e)
{
    List<Customer> FilteredCustomers = Customers
                       .Where(Customer => Customer.Phone == CustomersPhone_ComBx.Text).ToList();

    foreach (Customer C in FilteredCustomers)
        CustomersName_ComBx.Items.Add(C.Name);
}

---

更新 2

2个ComboBox的这些属性，它们是一样的。

        // CustomersName_ComBx
        // 
        this.CustomersName_ComBx.AutoCompleteMode = System.Windows.Forms.AutoCompleteMode.SuggestAppend;
        this.CustomersName_ComBx.AutoCompleteSource = System.Windows.Forms.AutoCompleteSource.ListItems;
        this.CustomersName_ComBx.Dock = System.Windows.Forms.DockStyle.Fill;
        this.CustomersName_ComBx.Font = new System.Drawing.Font("Janna LT", 12F, System.Drawing.FontStyle.Bold);
        this.CustomersName_ComBx.FormattingEnabled = true;
        this.CustomersName_ComBx.Location = new System.Drawing.Point(0, 65);
        this.CustomersName_ComBx.Margin = new System.Windows.Forms.Padding(0, 7, 0, 0);
        this.CustomersName_ComBx.Name = "CustomersName_ComBx";
        this.CustomersName_ComBx.Size = new System.Drawing.Size(583, 46);
        this.CustomersName_ComBx.Sorted = true;
        this.CustomersName_ComBx.TabIndex = 52;
        // 
        // CustomersPhone_ComBx
        // 
        this.CustomersPhone_ComBx.AutoCompleteMode = System.Windows.Forms.AutoCompleteMode.SuggestAppend;
        this.CustomersPhone_ComBx.AutoCompleteSource = System.Windows.Forms.AutoCompleteSource.ListItems;
        this.CustomersPhone_ComBx.Dock = System.Windows.Forms.DockStyle.Fill;
        this.CustomersPhone_ComBx.Font = new System.Drawing.Font("Janna LT", 12F, System.Drawing.FontStyle.Bold);
        this.CustomersPhone_ComBx.FormattingEnabled = true;
        this.CustomersPhone_ComBx.Location = new System.Drawing.Point(0, 7);
        this.CustomersPhone_ComBx.Margin = new System.Windows.Forms.Padding(0, 7, 0, 0);
        this.CustomersPhone_ComBx.Name = "CustomersPhone_ComBx";
        this.CustomersPhone_ComBx.Size = new System.Drawing.Size(583, 46);
        this.CustomersPhone_ComBx.Sorted = true;
        this.CustomersPhone_ComBx.TabIndex = 51;
        this.CustomersPhone_ComBx.SelectedIndexChanged += new System.EventHandler(this.CustomersPhone_ComBx_SelectedIndexChanged);

还有名为 NewReceipt_Delivery_Form 的表单以及我如何显示它。

NewReceipt_Delivery_Form NewReceipt_Delivery_Form = new NewReceipt_Delivery_Form();
NewReceipt_Delivery_Form.ChangeUI();
NewReceipt_Delivery_Form.ShowDialog();

和ChangeUI方法

private List<Customer> Customers = new List<Customer>();
public void ChangeUI()
{
    OleDbCommand SelectCustomersCMD = new OleDbCommand("SELECT * FROM Customers ORDER BY [ID] ASC", Program.GeneralConnection);
    OleDbDataReader SelectCustomersREAD = SelectCustomersCMD.ExecuteReader();
    while (SelectCustomersREAD.Read())
    {
        Customer Customer = new Customer();
        Customer.ID = Convert.ToInt32(SelectCustomersREAD[0].ToString());
        /* And so on. */
        Customers.Add(Customer);
    }
    SelectCustomersREAD.Close();
    CustomersPhone_ComBx.DataSource = Customers.Select(Customer => Customer.Phone).ToList();
    CustomersName_ComBx.DataSource = Customers.Select(Customer => Customer.Name).ToList();
    CustomersPhone_ComBx.SelectedIndex = -1;
    CustomersName_ComBx.SelectedIndex = -1;
}

SelectedIndexChanged 事件为Aleksandar's answer

private void CustomersPhone_ComBx_SelectedIndexChanged(object sender, EventArgs e)
{
    string selectedPhone = (string)CustomersPhone_ComBx.SelectedItem;
    if (!String.IsNullOrEmpty(selectedPhone))
        CustomersName_ComBx.DataSource = Customers.Where(Customer => Customer.Phone == selectedPhone).Select(Customer => Customer.Name).ToList();
    else
        CustomersName_ComBx.DataSource = Customers.Select(Customer => Customer.Name).ToList();
}

Answer 1

有了关于组合框属性的新信息，我终于可以重现您的问题了。似乎是 Sorted 属性导致了这个问题：

this.CustomersName_ComBx.Sorted = true;

解决办法是设置为false

this.CustomersName_ComBx.Sorted = false;

要让显示仍然有序，只需在初始化DataSource 时使用OrderBy：

CustomersPhone_ComBx.DataSource = Customers.Select(Customer => Customer.Phone)
                                           .OrderBy(x=>x).Distinct().ToList();
CustomersName_ComBx.DataSource  = Customers.Select(Customer => Customer.Name)
                                           .OrderBy(x => x).ToList();

A（某种解释）可以在属性 Sorted 的文档中找到

在备注部分它说：

此属性指定 ComboBox 是否对现有条目进行排序并添加新条目到列表中的适当的排序位置。您可以使用此属性自动对 ComboBox 中的项目进行排序。当项目添加到排序的 ComboBox 时，项目将移动到排序列表中的适当位置。

我猜当你更改 DataSource 时，新元素只是简单地放在旧元素的位置。但是实际的DataSource 现在元素更少了。您可以在调试器中检查它。分配过滤后的集合后，DataSource 的计数将减少！

我的第二个猜测是，如果您设置Sorted = true，它实际上会在初始初始化后忽略DataSource 集合，并且从此刻开始它只显示Items 集合中的内容。调试器显示Items.Count 在分配过滤后的DataSource 后保持不变，但DataSource.Count 已更改。这似乎是一种模棱两可的状态。 您无法修改Items 集合，因为ComboBox 是数据绑定的，但您无法显示DataSource，因为Sorted 设置为true。其实言论是这样说的：

尝试在数据绑定控件上设置 Sorted 属性会引发 ArgumentException。您必须使用底层数据模型对数据进行排序。

但它并没有说明当您设置它在绑定之前会发生什么！

Answer 2

这是对我有用的解决方案，唯一的区别是我使用了 CustomersPhone_ComBx.SelectedItem 而不是它的文本属性。

 public partial class Form1 : Form
 {
    public List<Customer> Customers { get; set; } = new List<Customer>
    {
        new Customer
        {
            Name = "John",
            Phone = "123"
        },
        new Customer
        {
            Name = "Mary",
            Phone = "123"
        },
        new Customer
        {
            Name = "Peter",
            Phone = "555"
        },
        new Customer
        {
            Name = "George",
            Phone = "222"
        },
        new Customer
        {
            Name = "Christine",
            Phone = "555"
        }
    };

    public Form1()
    {
        InitializeComponent();
        CustomersPhone_ComBx.DataSource = Customers.Select(Customer => Customer.Phone).ToList();
        CustomersName_ComBx.DataSource = Customers.Select(Customer => Customer.Name).ToList();
    }

    private void CustomersPhone_ComBx_SelectedIndexChanged(object sender, EventArgs e)
    {
        string selectedPhone = (string) CustomersPhone_ComBx.SelectedItem;
        if (!String.IsNullOrEmpty(selectedPhone))
            CustomersName_ComBx.DataSource = Customers.Where(Customer => Customer.Phone == selectedPhone).Select(Customer => Customer.Name).ToList();
        else
            CustomersName_ComBx.DataSource = Customers.Select(Customer => Customer.Name).ToList();
    }
}

public class Customer
{
    public string Name { get; set; }
    public string Phone { get; set; }
}