使用AssociateControlID

Question

调用Web服务时会出现异常，该服务在运行时动态构建HTML元素，并将呈现的元素作为字符串返回。

RenderControl（）方法调用发生以下错误：

System.Web.HttpException：无法找到带有id＆＃39; txtCertificate＆＃39;的控件与Label＆＃39; lblCertificate＆＃39;。

相关联

StringWriter stringWriter = new StringWriter();
HtmlTextWriter writer = new HtmlTextWriter(stringWriter);

// Create System.Web.UI.WebControls.Panel (container)
Panel pnlFRow1 = new Panel();
pnlFRow1.CssClass = "f-row";

// Create System.Web.UI.WebControls.Textbox
TextBox txtCertificate = new TextBox();
txtCertificate.ID = "txtCertificate";
txtCertificate.CssClass = "f-input f-input-full";

// Create System.Web.UI.WebControls.Label
Label lblCertificate = new Label();
lblCertificate.ID = "lblCertificate";
lblCertificate.CssClass = "f-label f-label-full";
lblCertificate.AssociatedControlID = txtCertificate.ID;
lblCertificate.Text = "Certificate:";
Panel pnlCertificate = new Panel();
pnlCertificate.CssClass = "f-label f-label-full";

// Binding child controls to parent controls
pnlFRow1.Controls.Add(lblCertificate);
pnlFRow1.Controls.Add(pnlCertificate);
pnlCertificate.Controls.Add(txtCertificate);

// Render control
pnlContent.RenderControl(writer);

// Return rendered HTML
return writer.InnerWriter.ToString();

我尝试在pnlFRow1.Controls.Add(lblCertificate);行之后放置行pnlCertificate.Controls.Add(txtCertificate);，认为这可能是订单重要的问题，但这会导致同样的错误。

AssociatedControlID属性是必须的，以便Label WebControl呈现为实际的<label>元素，并且必须在输入控件之前显示。