ComboBox将不会更新其显示列表，除非您首先更改选择 [英] ComboBox will not update its display list unless you change selections first
问题描述
更新：我检查的答案，我完全测试，它仍然不工作。我更新了下面的代码，所以你应该只能粘贴到一个空的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 in to a empty winforms project and it should compile.
更新：
我发现如果我将ComboBox上的选定项目更改为任何其他项目，它现在的行为正如预期（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.
为什么在组合框中改为不同的项目，
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?
这是一个快速测试用例。
Here is a quick test case of what is happening.
- >
- 在txtBroken中将
test1更改为test1asdf文本 - 将组合框更改为test2
- 将
test 更改为test2asdftext in txtBroken - 提交更改
- 在下拉列表中的第一个项目中立即显示test2asdf仍然显示
test1
- 更改为
test1 - 组合框显示
test1文本框显示test1asdf - 将文本框更新为
test1asd - 组合框会立即显示
test1asd
<
- Change
test1totest1asdftext in txtBroken - click off to commit change
- text in combo box does not update.
- Change combo box to test2
- change
test2totest2asdftext in txtBroken - click off to commit change
- text in combo box immediately shows 'test2asdf' still displays
test1for first item in the drop-down - change to
test1 - combo box displays
test1text box displaystest1asdf - update text box to
test1asd - combo box immediately displays
test1asd
其他比较后面的场景改变选择的项目在加载和更改回来（这看起来像这样的黑客）如何解决这个？
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到 List< Holder> 的 BindingSource c $ c> Holder.Name 作为其显示值。我也有一个绑定到 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。更改所选项目并更改将在文本框中显示更新的文本，但仍会在组合框中显示旧值。如何更新组合框中的项目？
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;
}
}
}
}
我绑定到一个 List< String> ，而不是使用Holder.Name它的工作原理（这只是一个简单的模拟了真正的类不仅仅是一个名称，所以一个列表的字符串将不工作）我认为这是一个线索，什么是错的，但我不知道这是什么意思。使用Observable代替列表没有区别。
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 means. Using a Observable instead of list makes no difference.
推荐答案
使用 BindingList ，而不是 c $ c>。它旨在解决这些问题。 .NET客户团队的成员Dinesh Chandnani在 blog post ：
BindingList< T>是新的通用
IBindingList的实现，
在项目
添加/删除/插入/等时触发ListChanged事件。从
列表。 bindingSource钩在这些
事件上，因此知道这些
变化，并且可以通知控制绑定
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，但是没有很好地重现原始问题，而不稍微调整代码。
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> 我能够在焦点离开文本框时立即得到响应。在添加新的数据绑定时，可以通过使用重载方法来获取即时更新。我还直接设置 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.
您的示例代码：
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);
}
}
注释掉第一个 txt 绑定和取消注释它下面的一个，以查看 DataSourceUpdateMode.OnPropertyChanged 。
Comment out the first txt binding and uncomment the one below it to see the DataSourceUpdateMode.OnPropertyChanged in action.
以下是一些 BindingList 资源：
- BindingSource and BindingList Of T - DataBinding make simple！
- BindingSource - 仔细观察...
- 数据绑定 - 绑定列表，BindingSource和BusinessObjects - 第1部分< a>
- Databinding - BindingList，BindingSource和BusinessObjects：第2部分
- 后台：在.NET Framework 2.0第2部分改进Windows窗体数据绑定
编辑：回答您遇到的问题请更改您的更新代码，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） c> bsBroken = new BindingSource（lstBroken，null）; with：
1) Replace bsBroken = new BindingSource(lstBroken, null); with:
bsBroken = new BindingSource();
bsBroken.DataSource = lstBroken;
或在一行中： bsBroken = new BindingSource（）{DataSource = lstBroken };
Or in one line: bsBroken = new BindingSource() { DataSource = lstBroken };
这产生了一个立即响应变化的预期行为（我在上面也提到过）。请不使用接受 dataMember 的重载，并将其设置为null。
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）完成上述操作后，我发现不需要 txtBroken_TextChanged 事件。注释掉要测试的事件处理程序分配，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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