除非您先更改选择，否则ComboBox不会更新其显示列表 [英] ComboBox will not update its display list unless you change selections first

问题描述

更新：在我完全测试之前，我检查了答案仍然不起作用。我更新了下面的代码，所以你应该能够粘贴到一个空的WinForms项目，它应该编译。

Update: I checked the answer before I fully tested it still does not work. I updated the code below so you should just be able to paste in to a empty WinForms project and it should compile.

更新：
我发现如果我将ComboBox上的所选项目更改为任何其他项目，它现在按预期行为（在我的代码下面我将从test1切换到test2）。因为我还没有收到任何答案，所以我把问题改成了这个。

UPDATE: I have found that if I change the selected item on the ComboBox to any other item, it now behaves as expected (in my code below I would switch from test1 to test2). As I have not received any answers yet, I change the question to this.

为什么我必须改变到组合框中的其他项目才能显示

Why do I have to change to a different item in the combo box before it will show the changes I make to the underlying data-source?

这是一个快速测试案例，发生了什么。

Here is a quick test case of what is happening.

1. 将 test1 更改为 test1asdf txtBroken中的文本


2. 单击关闭以提交更改


3. 组合框中的文本不更新。


4. 将组合框更改为test2


5. 将 test2 更改为 test2asdf txtBroken中的文本


6. 点击关闭提交更改


7. 组合框中的文本立即显示'test2asdf'仍然显示 test1 用于下拉列表中的第一项


8. 更改为 test1


9. 组合框显示 test1 文本框显示 test1asdf


10. 将文本框更新为 test1asd


11. 组合框立即显示 test1asd

1. Change test1 to test1asdf text in txtBroken
2. click off to commit change
3. text in combo box does not update.
4. Change combo box to test2
5. change test2 to test2asdf text in txtBroken
6. click off to commit change
7. text in combo box immediately shows 'test2asdf' still displays test1 for first item in the drop-down
8. change to test1
9. combo box displays test1 text box displays test1asdf
10. update text box to test1asd
11. combo box immediately displays test1asd

除了幕后更改所选项目的加载和改变它（这似乎是一个黑客）我该如何解决这个问题？

Other than behind the scenes changing the selected item on load and changing it back (this seems like such a hack) how can I fix this?

我有一个组合框数据绑定 BindingSource 绑定到列表< Holder> 它具有 Holder.Name 作为其显示值。我还有一个绑定到 Holder.Name 的文本框，但如果我更改文本框中的文本，它不会更改组合框中显示的内容。更改所选项目和更改将显示文本框中更新的文本，但仍将在组合框中显示旧值。如何使组合框中的项目更新？

I have a combo box databound to a BindingSource bound to a List<Holder> it has Holder.Name as its display value. I also have a text box bound to Holder.Name but if I change the text in the text box it will not change what is displayed in the combo box. Changing selected items and changing back will show the updated text in the text box, but will still have the old value displayed in the combo box. How do I make the item in the combo box update?

using System;
using System.ComponentModel;
using System.Windows.Forms;

namespace Sandbox_Form
{
    public class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            lstBroken = new BindingList<Holder>();
            lstBroken.Add(new Holder("test1"));
            lstBroken.Add(new Holder("test2"));
            bsBroken = new BindingSource(lstBroken, null);
            cmbBroken.DataSource = bsBroken;
            cmbBroken.DisplayMember = "Name";
            cmbBroken.SelectedIndex = 0;
            txtBroken.DataBindings.Add("Text", bsBroken, "Name");
            txtBroken.TextChanged += new EventHandler(txtBroken_TextChanged);

        }

        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }

        void txtBroken_TextChanged(object sender, EventArgs e)
        {
            ((Control)sender).FindForm().Validate();
        }
        private BindingSource bsBroken;
        private BindingList<Holder> lstBroken;
        private ComboBox cmbBroken;
        private TextBox txtBroken;
        private Label label1;
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.cmbBroken = new System.Windows.Forms.ComboBox();
            this.txtBroken = new System.Windows.Forms.TextBox();
            this.label1 = new System.Windows.Forms.Label();
            this.SuspendLayout();
            // 
            // cmbBroken
            // 
            this.cmbBroken.DropDownStyle = System.Windows.Forms.ComboBoxStyle.DropDownList;
            this.cmbBroken.FormattingEnabled = true;
            this.cmbBroken.Location = new System.Drawing.Point(12, 32);
            this.cmbBroken.Name = "cmbBroken";
            this.cmbBroken.Size = new System.Drawing.Size(94, 21);
            this.cmbBroken.TabIndex = 0;
            // 
            // txtBroken
            // 
            this.txtBroken.Location = new System.Drawing.Point(13, 60);
            this.txtBroken.Name = "txtBroken";
            this.txtBroken.Size = new System.Drawing.Size(93, 20);
            this.txtBroken.TabIndex = 1;
            // 
            // label1
            // 
            this.label1.AutoSize = true;
            this.label1.Location = new System.Drawing.Point(13, 13);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(41, 13);
            this.label1.TabIndex = 2;
            this.label1.Text = "Broken";
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(284, 262);
            this.Controls.Add(this.label1);
            this.Controls.Add(this.txtBroken);
            this.Controls.Add(this.cmbBroken);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private void cmbWorks_SelectedIndexChanged(object sender, EventArgs e)
        {

        }
    }
    public class Holder
    {
        public Holder(string name)
        {
            Name = name;
        }
        private string _Name;
        public string Name
        {
            get { return _Name; }
            set
            {
                _Name = value;
            }
        }
    }
}

如果我使用 Holder.Name 绑定到列表< String> ，它的工作原理（这只是一个简单的模拟-up，真正的类不仅仅是一个名字，所以字符串列表将不起作用）。我认为这是一个错误的线索，但我不知道是什么。使用一个可观察而不是列表没有任何区别。

If I bind to a List<String> instead using Holder.Name it works as expected (this is just a simple mock-up, the real class has more than just a name so a list of strings will not work). I think this is a clue to what is wrong but I don't know what it is. Using an Observable instead of a list makes no difference.

推荐答案

使用 BindingList 而不是列表。它旨在解决这些问题。 .NET客户端团队成员Dinesh Chandnani在一个博客：

Use a BindingList instead of a List. It was designed to address such issues. Dinesh Chandnani, a member of the .NET Client Team, states the following in a blog post:

BindingList< T> 是新的通用
实现的IBindingList，
在项目
添加/删除/插入/ etc时触发ListChanged事件。从
列表。 bindingSource挂钩到这些
事件，因此知道这些
更改，并可以通知控件绑定
这个BindingSource。

BindingList<T> is the new generic implementation of IBindingList which fires ListChanged event when items are added/removed/inserted/etc. from the list. bindingSource hooks on to these events and is thus "aware" of these changes and can notify controls bound thos this BindingSource.

我能够重现您在更新的条目中描述的问题，但是并不能很好地重现原始问题，而不会稍微调整代码。

I was able to reproduce the issue you described in your updated entry, but didn't quite reproduce the original issue without tweaking the code slightly.

通过使用 BindingList< Holder> 当焦点离开文本框时，我能够立即得到响应。当添加新的数据绑定时，可以使用重载方法获取即时更新。我还直接使用 BindingSource 的 DataSource ，因为使用 null dataMember 在重载的构造函数中没有产生预期的行为。

By using a BindingList<Holder> I was able to get an immediate response when focus left the textbox. It's possible to get instant updates by using an overloaded method when adding a new data binding. I also set the BindingSource's DataSource directly since using a null dataMember in the overloaded constructor was not yielding the expected behavior.

这里是我最终基于关闭您的示例代码：

Here's the code I ended up with based off your sample code:

public partial class Form1 : Form
{
    private BindingSource bs;
    private BindingList<Holder> bList;

    public Form1()
    {
        InitializeComponent();

        bList = new BindingList<Holder>();
        bList.Add(new Holder("test1"));
        bList.Add(new Holder("test2"));

        bs = new BindingSource();
        bs.DataSource = bList;

        cmb.DataSource = bs;
        cmb.DisplayMember = "Name";
        cmb.ValueMember = "Name";

        // updates when focus leaves the textbox
        txt.DataBindings.Add("Text", bs, "Name");

        // updates when the property changes
        //txt.DataBindings.Add("Text", bs, "Name", false, DataSourceUpdateMode.OnPropertyChanged);
    }
}

注释第一个 txt 绑定和取消注释下面的一个，以查看 DataSourceUpdateMode.OnPropertyChanged 在行动。

Comment out the first txt binding and uncomment the one below it to see the DataSourceUpdateMode.OnPropertyChanged in action.

这里有一些 BindingList 资源：

• BindingSource和BindingList T - DataBinding简单！


• BindingSource - 一个更仔细的看...


• 数据绑定 - 绑定列表，BindingSource和BusinessObjects - 第1部分


• 数据绑定ing - BindingList，BindingSource和BusinessObjects：第2部分


• 背后的场景：.NET Framework 2.0第2部分中Windows窗体数据绑定的改进
  

  ---

  
  编辑：在回覆您所更新代码所面临的问题时，请进行以下更改：

• BindingSource and BindingList Of T - DataBinding made simple!
• BindingSource - A Closer Look...
• Databinding - Bindinglist, BindingSource and BusinessObjects - Part 1
• Databinding - BindingList, BindingSource, and BusinessObjects: Part 2
• Behind the Scenes: Improvements to Windows Forms Data Binding in the .NET Framework 2.0, Part 2

  ---

  in reply to the issues you're facing with your updated code, please make these changes:

1）替换 bsBroken = new BindingSource（lstBroken，null）; 与：

bsBroken = new BindingSource();
bsBroken.DataSource = lstBroken;

或在一行中： bsBroken = new BindingSource（）{DataSource = lstBroken };

这将产生预期的行为，立即响应更改（我也在上面提到过）。 不使用接受 dataMember 的重载，并将其设置为null。执行此操作可以提供您遇到的错误行为。

This yields the expected behavior with an immediate response to changes (I also mentioned this before above). Do not use the overload that accepts a dataMember and set it to null. Doing so gives the buggy behavior you're experiencing.

2）执行上述操作后，我看不到 txtBroken_TextChanged 事件。评论事件处理程序分配测试，但您应该能够完全删除它。

2) After doing the above, I see no need for the txtBroken_TextChanged event. Comment out the event handler assignment to test, but you should be able to remove it completely.

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