自定义控件 updatepanel中 Button异步提交成功,但Dropdownlist 的SelectIndexchange 和Textbox 的Textchange 事件都不能异步提交,为什么?

[qingfeng010]

情况是这样:
VS2005 开始一自定义控件,该控件实现 无刷新两级联动.控件中使用了UpdatePanel 技术.
问题是button异步提交成功,(测试成功);使用Dropdownlist中的SelectIndexchange 和TextBox 的TextChange 事件时,变为同步,异步实现不了;

代码:
[ToolboxData(" <{0}:CategoryItemThird runat=\"server\"> </{0}:CategoryItemThird>")]
public class CategoryItemThird :WebControl,INamingContainer(这边是否需要其他接口) {
protected ScriptManagerProxy scriptManagerProxy;
protected UpdatePanel updatePanel;

protected DropDownList dropCategory;
protected Label lblResult;
protected Button btnResult;
protected TextBox txtResult;

protected void txtResult_TextChanged(object sender, EventArgs e)
{
this.lblResult.Text = DateTime.Now+" "+this.txtResult.Text;
}
protected void dropCategory_SelectedIndexChanged(object sender, EventArgs e)
{
lblResult.Text += DateTime.Now;
}
protected void btnResult_Click(object sender, EventArgs e)
{
lblResult.Text += DateTime.Now;
}
protected override void CreateChildControls()
{
Controls.Clear();
scriptManagerProxy = new ScriptManagerProxy();
Controls.Add(scriptManagerProxy);

updatePanel = new UpdatePanel();
updatePanel.UpdateMode = UpdatePanelUpdateMode.Conditional;
updatePanel.ChildrenAsTriggers = true;
updatePanel.RenderMode = UpdatePanelRenderMode.Inline;
updatePanel.EnableViewState = true;
dropCategory = new DropDownList();
dropCategory.SelectedIndexChanged += new EventHandler(dropCategory_SelectedIndexChanged);
dropCategory.AutoPostBack = true;
dropCategory.Items.Add(new ListItem("1", "1"));
dropCategory.Items.Add(new ListItem("2", "2"));
updatePanel.ContentTemplateContainer.Controls.Add(dropCategory);
btnResult = new Button();//此处可实现异步提交
btnResult.Text = "Date";
btnResult.Click +=new EventHandler(btnResult_Click);
updatePanel.ContentTemplateContainer.Controls.Add(btnResult);
txtResult = new TextBox();
txtResult.AutoPostBack = true;
txtResult.TextChanged +=new EventHandler(txtResult_TextChanged);
updatePanel.ContentTemplateContainer.Controls.Add(txtResult);
lblResult = new Label();
updatePanel.ContentTemplateContainer.Controls.Add(lblResult);
Controls.Add(updatePanel);
}
protected override void Render(HtmlTextWriter writer)
{
scriptManagerProxy.RenderControl(writer);
updatePanel.RenderControl(writer);
}

[yangyucau]

这个帮顶，也在学习中。！