ASP.NET 在页面上放置动态控件会导致事件反向混乱
当我将文本框反向放置在页面上时，我遇到了这个奇怪的问题。整个事件系统都乱了。更改一个文本框会在所有文本框上触发 TextChange。我可以通过首先将控件放入列表中，然后在反向迭代列表时调用 add 来解决此问题。但我只是想知道为什么会失败。这是一些代码（.net 2.0）
public partial class _Default : Page
{
protected void Page_Load(object sender, EventArgs e)
{
InitFields();
}
private void InitFields()
{
int nrFields;
//We have a static textbox called nrElements, this determines the number
//of fields to initialize
if (int.TryParse(nrElements.Text, out nrFields))
{
//Put all the dynamic fields on the screen in reverse order
foreach(Control t in GetDynamicFields(nrFields))
{
//Calling Controls.Add works fine
//Calling Controls.AddAt messes up the events
//Try changing different textboxes
plhFields.Controls.AddAt(0, t);
}
}
}
private IEnumerable<Control> GetDynamicFields(int nrFields)
{
for (int i = 0; i < nrFields; i++)
{
TextBox txtBox = new TextBox();
txtBox.ID = string.Format("dynTextBox{0}", i.ToString());
txtBox.AutoPostBack = true;
txtBox.TextChanged += t_TextChanged;
yield return txtBox;
}
}
private void t_TextChanged(object sender, EventArgs e)
{
TextBox txtBox = sender as TextBox;
if (txtBox != null)
txtBox.Text = txtBox.Text + "Changed ";
}
}
I have this weird problem when putting textboxes on the page in reverse. The whole event system is messed up. Changing one textbox fires TextChange on all textboxes. I can fix this by putting the controls in a list first and then call add while iterating trough the list in reverse. But i just want to know why this fails. Heres some code (.net 2.0)
public partial class _Default : Page
{
protected void Page_Load(object sender, EventArgs e)
{
InitFields();
}
private void InitFields()
{
int nrFields;
//We have a static textbox called nrElements, this determines the number
//of fields to initialize
if (int.TryParse(nrElements.Text, out nrFields))
{
//Put all the dynamic fields on the screen in reverse order
foreach(Control t in GetDynamicFields(nrFields))
{
//Calling Controls.Add works fine
//Calling Controls.AddAt messes up the events
//Try changing different textboxes
plhFields.Controls.AddAt(0, t);
}
}
}
private IEnumerable<Control> GetDynamicFields(int nrFields)
{
for (int i = 0; i < nrFields; i++)
{
TextBox txtBox = new TextBox();
txtBox.ID = string.Format("dynTextBox{0}", i.ToString());
txtBox.AutoPostBack = true;
txtBox.TextChanged += t_TextChanged;
yield return txtBox;
}
}
private void t_TextChanged(object sender, EventArgs e)
{
TextBox txtBox = sender as TextBox;
if (txtBox != null)
txtBox.Text = txtBox.Text + "Changed ";
}
}
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评论（2）
尝试在 Page_PreInit 事件而不是 Page_Load 上调用 InitFields()。
或者另一种方法是重写 CreateChildControls() 方法 (MSDN 文章），如果您使用 CreateChildControls()，则需要在 Page_Load 方法上调用 EnsureChildControls()，以确保在尝试访问具有以下功能的任何控件之前已调用 CreateChildControls() 方法：是在该方法中创建的。
Try calling InitFields() on the Page_PreInit event rather than Page_Load.
Or an alternative would be to override the CreateChildControls() method (MSDN Article), if you use CreateChildControls() you'll need to call EnsureChildControls() on the Page_Load method to make sure the CreateChildControls() method has been called before you try to access any controls which have been created within that method.
始终将动态控件放在 OnInit 事件中。然后视图状态序列化器/反序列化器将起作用。而且您必须为每个请求添加控件，而不仅仅是在 !IsPostBack 中。
Always put dynamic controls in OnInit event. Then viewstate serializer/deserializer will work. And you have to add controls on every request, not just in !IsPostBack.