ListItems的在回传丢失一个DropDownList属性？ [英] ListItems attributes in a DropDownList are lost on postback?

问题描述

一个同事向我展示了这一点：

A coworker showed me this:

他有一个DropDownList并在网页上的按钮。这里的code背后：

He has a DropDownList and a button on a web page. Here's the code behind:

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            ListItem item = new ListItem("1");
            item.Attributes.Add("title", "A");

            ListItem item2 = new ListItem("2");
            item2.Attributes.Add("title", "B");

            DropDownList1.Items.AddRange(new[] {item, item2});
            string s = DropDownList1.Items[0].Attributes["title"];
        }
    }

    protected void Button1_Click(object sender, EventArgs e)
    {
        DropDownList1.Visible = !DropDownList1.Visible;
    }

在页面加载时，项的工具提示显示，但在第一次回传，属性都将丢失。为什么是这样的情况，以及是否有任何变通办法？

On the page load, the items' tooltips are showing, but on the first postback, the attributes are lost. Why is this the case, and are there any workarounds?

推荐答案

我有同样的问题，并希望贡献<一个href=\"http://blogs.delta-n.nl/dev/Lists/Posts/Post.aspx?List=61dbd0ca-5c9f-4060-9d13-94177fe070a7&ID=85\">this资源在这里笔者创建了一个继承的ListItem消费者坚持属性的ViewState。希望这将节省别人浪费了我，直到我无意中发现它的时候。

I had the same problem and wanted to contribute this resource where the author created an inherited ListItem Consumer to persist attributes to ViewState. Hopefully it will save someone the time I wasted until I stumbled on it.

protected override object SaveViewState()
{
    // create object array for Item count + 1
    object[] allStates = new object[this.Items.Count + 1];

    // the +1 is to hold the base info
    object baseState = base.SaveViewState();
    allStates[0] = baseState;

    Int32 i = 1;
    // now loop through and save each Style attribute for the List
    foreach (ListItem li in this.Items)
    {
        Int32 j = 0;
        string[][] attributes = new string[li.Attributes.Count][];
        foreach (string attribute in li.Attributes.Keys)
        {
            attributes[j++] = new string[] {attribute, li.Attributes[attribute]};
        }
        allStates[i++] = attributes;
    }
    return allStates;
}

protected override void LoadViewState(object savedState)
{
    if (savedState != null)
    {
        object[] myState = (object[])savedState;

        // restore base first
        if (myState[0] != null)
            base.LoadViewState(myState[0]);

        Int32 i = 1;
        foreach (ListItem li in this.Items)
        {
            // loop through and restore each style attribute
            foreach (string[] attribute in (string[][])myState[i++])
            {
                li.Attributes[attribute[0]] = attribute[1];
            }
        }
    }
}

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