Question

我在viewstate上阅读了很多文章，但我无法理解它。

基本上我想要两个带有添加和删除按钮的列表框和一个继续按钮。

当按下Proceed按钮时，隐藏前一个按钮，并为第一个列表框中的每个项目显示一个文本框，其中有2个下拉框用于描述它+第二个列表框中每个项目的文本框（也用于用户添加说明）。

然后我想要一个Finalize Button将所有这些信息保存到数据库中。

到目前为止，我有以下代码：

   <script runat="server">   

    void Page_Load(Object sender, EventArgs e)
    {
        CreateDynamicControls();
        Page.MaintainScrollPositionOnPostBack = true;
        Build2.Visible = false;
        Build3.Visible = false;
        Build4.Visible = false;
        Finish.Visible = false;
    }

    void AddC_Click(Object sender, EventArgs e)
    {
                criteria.Items.Add(addnewc.Text.ToString());
                addnewc.Text = null;
    }

    void RemoveCriterion_Click(Object sender, EventArgs e)
    {
        for (int i = 0; i < criteria.Items.Count; i++)
        {
            if (criteria.Items[i].Selected)
            {
                criteria.Items.Remove(criteria.Items[i]);
                i--;
            }
        }
    }

    void AddAlternative_Click(Object sender, EventArgs e)
    {
                alternatives.Items.Add(addnewa.Text.ToString());
                addnewa.Text = null;
    }

    void RemoveAlternative_Click(Object sender, EventArgs e)
    {
        for (int i = 0; i < alternatives.Items.Count; i++)
        {
            if (alternatives.Items[i].Selected)
            {
                alternatives.Items.Remove(alternatives.Items[i]);
                i--;
            }
        }
    }

    void Continue_Click(Object sender, EventArgs e)
    {
            Build1.Visible = false;
            Build2.Visible = true; 
            Build3.Visible = true;

            CreateDynamicControls();

            Finish.Visible = true;
    }

    void CreateDynamicControls()
    {
        Build2.Controls.Clear();
        Build3.Controls.Clear();

        Build2.Controls.Add(new LiteralControl("<h3>Please define each criterion.</h3><p>By describing it and indicating if it is 1/2 and a/b.</p>"));

        for (int i = 0; i < criteria.Items.Count; i++)
        {
            Build2.Controls.Add(new LiteralControl("<strong>" + criteria.Items[i].Text + "</strong>&nbsp;&nbsp;Description:<br />"));
            TextBox criteriondesc = new TextBox();
            Build2.Controls.Add(criteriondesc);
            criteriondesc.ID = "c" + i.ToString();
            criteriondesc.Rows = 3;
            criteriondesc.Width = 850;
            criteriondesc.TextMode = TextBoxMode.MultiLine;
            Build2.Controls.Add(new LiteralControl("<br />"));

            Build2.Controls.Add(new LiteralControl("Desc1: "));
            DropDownList aim = new DropDownList();
            aim.ID = i.ToString();
            aim.Width = 250;
            aim.Items.Add(new ListItem("1"));
            aim.Items.Add(new ListItem("2"));
            Build2.Controls.Add(aim);

            Build2.Controls.Add(new LiteralControl("&nbsp;&nbsp;&nbsp;&nbsp;Desc2: "));
            DropDownList source = new DropDownList();
            source.ID = i.ToString();
            source.Width = 250;
            source.Items.Add(new ListItem("a"));
            source.Items.Add(new ListItem("b"));
            Build2.Controls.Add(source);

            Build2.Controls.Add(new LiteralControl("<br /><br />"));

        }

        Build3.Controls.Add(new LiteralControl("<h3>Please define each alternative.</h3><p>Please describe each alternaitve in detail.</p>"));

        for (int i = 0; i < alternatives.Items.Count; i++)
        {
            Build3.Controls.Add(new LiteralControl("<strong>" + alternatives.Items[i].Text + "</strong>&nbsp;&nbsp;Description:<br />"));
            TextBox altdesc = new TextBox();
            altdesc.ID = "a" + i.ToString();
            altdesc.Rows = 3;
            altdesc.Width = 850;
            altdesc.TextMode = TextBoxMode.MultiLine;
            Build3.Controls.Add(altdesc);
            Build3.Controls.Add(new LiteralControl("<br />"));
        }

        Build3.Controls.Add(new LiteralControl("<br /><h3>Review dates.</h3><p>Please select a date for a meeting.</p>"));
        OboutInc.Calendar2.Calendar selectdates = new OboutInc.Calendar2.Calendar();
        Build3.Controls.Add(selectdates);
    }

    void Finish_Click(Object sender, EventArgs e)
    {

            Build4.Visible = true;

            foreach (var control in Build2.Controls)
            {
                if (control.GetType() == typeof(TextBox))
                {
                    Build4.Controls.Add(new LiteralControl(((TextBox)control).Text + "<br>"));
                }
            }

            foreach (var control in Build3.Controls)
            {
                if (control.GetType() == typeof(TextBox))
                {
                    Build4.Controls.Add(new LiteralControl(((TextBox)control).Text + "<br>"));
                }
            }

    }
</script>

<asp:Content runat="server" ID="MainContent" ContentPlaceHolderID="MainContent">
    <asp:Panel ID="Build1" runat="server">
    <h3>What is your aim?</h3>
    <p>
        <asp:TextBox ID="goal" runat="server" Width="850px"></asp:TextBox>
    </p>

        <h3>What are the criteria of your decision?</h3>
    <p>
        <asp:ListBox ID="criteria" runat="server" Rows="8" Width="850px"></asp:ListBox><br />
        <asp:Button ID="RemoveCriterion" runat="server" Text="Remove" OnClick="RemoveCriterion_Click" />&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:TextBox ID="addnewc" runat="server" Width="650px"></asp:TextBox>
        <asp:Button ID="AddC" runat="server" Text="Add" OnClick="AddC_Click" />
    </p>

        </p>
        <h3>What are the alternatives of your decision?</h3>

    <p>
        <asp:ListBox ID="alternatives" runat="server" Rows="8" Width="850px"></asp:ListBox><br />
        <asp:Button ID="RemoveAlternative" runat="server" Text="Remove" OnClick="RemoveAlternative_Click" />&nbsp;&nbsp;&nbsp;&nbsp;
        <asp:TextBox ID="addnewa" runat="server" Width="650px"></asp:TextBox>
        <asp:Button ID="AddAlternative" runat="server" Text="Add" OnClick="AddAlternative_Click" />
    </p>
    <p align="right"><asp:Button ID="continue" runat="server" Text="Continue" OnClick="Continue_Click" /></p>


    </asp:Panel>

        <asp:Panel ID="Build2" runat="server">
        </asp:Panel>
            <asp:Panel ID="Build3" runat="server">
        </asp:Panel>
                <asp:Panel ID="Build4" runat="server">
        </asp:Panel>

    <p align="right"><asp:Button ID="Finish" runat="server" Text="Finish" OnClick="Finish_Click" /></p>


</asp:Content>

如您所见，我刚刚尝试从动态创建的文本框字段输出用户的文本。

但是，我收到了错误

无法加载视图状态。 viewstate所在的控制树正在加载必须与用于保存的控制树匹配在上一个请求期间查看状态。例如，添加时动态控制，回发期间添加的控件必须匹配初始期间添加的控件的类型和位置请求。

at：第169行：Build3.Controls.Add（altdesc）;

有谁知道如何使用viewstate修复此问题？

我是ASP.NET新手，我的背景主要是WinForms。

感谢您的帮助和建议！

Answer 1

您创建控件的时间太晚了。您应该在页面的Init事件期间创建它们，而不是Page Load。我建议你阅读关于page life cycle

的abit

Answer 2

我认为最好的办法是：

protected void Page_Load(Object sender, EventArgs e)
{
    if(!IsPostBack)
    {
        CreateDynamicControls();
    }
}
protected override void LoadViewState(object savedState)
{
    base.LoadViewState(savedState);
    CreateDynamicControls();<br/>
}

小样本：

http://class10e.com/Microsoft/which-method-should-you-add-to-the-web-page http://msdn.microsoft.com/en-us/library/ms178472(v=vs.100).aspx

无法加载viewstate - ASP.NET中的动态控件

2 个答案: