在控制生命周期的哪一点Control.Visible停止渲染？

问题描述

我试图写一个简单的工具来三夏显示网页内的单行消息 - 状态更新，错误信息等的信息将来自其他控件的页面上，通过调用夏精的方法。如果控制不具备它得到pre-渲染时间的任何消息，我不希望它在页面上呈现在所有 - 我希望它设置Control.Visible = FALSE。这似乎只对非回发的渲染工作，虽然。这里的code我使用的是：

I am trying to write a simple utility webcontrol to display one-line messages inside a web page - status updates, error messages, etc. The messages will come from other controls on the page, by calling a method on the webcontrol. If the control doesn't have any messages by the time it gets to pre-render, I don't want it to render on the page at all - I want it to set Control.Visible = false. This only seems to work for non-postback rendering though. Here's the code I'm using:

public class MessageList : WebControl
{

#region inner classes

    private struct MessageItem
    {
        string Content, CssClass;

        public MessageItem(string content, string cssClass)
        {
            Content = content;
            CssClass = cssClass;
        }

        public override string ToString()
        { return "<li" + (String.IsNullOrEmpty(CssClass) ? String.Empty : " class='" + CssClass + "'") + ">" + Content + "</li>"; }
    }

    private class MessageQueue : Queue<MessageItem> { }

#endregion

#region fields, constructors, and events

    MessageQueue queue;

    public MessageList() : base(HtmlTextWriterTag.Ul)
    {
        queue = new MessageQueue();
    }

    protected override void OnLoad(EventArgs e)
    {
        this.Controls.Clear();
        base.OnLoad(e);
    }

    protected override void OnPreRender(EventArgs e)
    {
        this.Visible = (queue.Count > 0);

        if (this.Visible)
        {
            while (queue.Count > 0)
            {
                MessageItem message = queue.Dequeue();
                this.Controls.Add(new LiteralControl(message.ToString()));
            }
        }

        base.OnPreRender(e);
    }

#endregion

#region properties and methods

    public void AddMessage(string content, string cssClass)
    { queue.Enqueue(new MessageItem(content, cssClass)); }

    public void AddMessage(string content)
    { AddMessage(content, String.Empty); }

#endregion

}

我试图把里面的CreateChildControls检查过，具有相同的结果。

I tried putting the check inside CreateChildControls too, with the same result.

推荐答案

除了修改为Visible属性，试试这个：

Instead of modifying the 'Visible' property, try this :

    protected override void Render(HtmlTextWriter writer)
    {
        if (queue.Count > 0)
            base.Render(writer);
    }

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