Asp.net Validator.RenderControl返回一个空字符串

我已经面临以下问题，并与之斗争了近2天。 我有以下代码

        protected override void Render(HtmlTextWriter writer)
    {
        string controlOutput;
        string validatorOutput;
        string allOutput;
        StringWriter controlStringWriter = new StringWriter();
        HtmlTextWriter controlHtmlWriter = new HtmlTextWriter(controlStringWriter);

        StringWriter validatorsStringWriter = new StringWriter();
        HtmlTextWriter validatorsHtmlWriter = new HtmlTextWriter(validatorsStringWriter);

        base.Render(controlHtmlWriter);
        controlOutput = controlStringWriter.ToString();

        this.renderValidators(validatorsHtmlWriter);
        validatorOutput = validatorsStringWriter.ToString();

        allOutput = String.Format("{0} {1}", controlOutput, validatorOutput);
        writer.Write(allOutput);
    }

renderValidators函数是：

  private void renderValidators(HtmlTextWriter writer)
        {
            foreach (BaseValidator validator in this.ValidatorsCollection)
            {
                validator.RenderControl(writer);
            }
        }

Render函数返回一个空字符串。 集合中验证程序的Visible属性设置为true

我正在OnInit函数中添加验证器。在第一次呈现validator.RenderControl（writer）期间；返回空字符串，回发后开始返回html输入

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也许有人遇到过这样的问题

据我所知，在呈现验证器之前，您需要检查控件是否已添加到页面

        Page page = Page;
        if (page == null || page.Request == null) {
            return false;
        }

一个非常有用的例子可以在