Question

我在动态生成的用户控件中保留其选定值时遇到了一些困难。我创建了一个包含多个表单字段的usercontrol。在主页面上，我有一个按钮，可以将我的usercontrol放在占位符中。用户可以根据需要创建尽可能多的这些内容。我在控件本身也有一个按钮，允许用户删除任何给定的控件。这个功能似乎工作正常。

但是，在以下情况中出现了奇怪的现象：

单击按钮在页面上创建用户控件。填写表格领域。
再次单击按钮以创建第二个UC并填写表单领域。一切都很顺利。 UC＃1中的值保留了它值。
点击按钮创建第三个UC，所有选定的值都是从UC＃1和＃2中消失。
如果我重新填写所有UC的字段，然后单击按钮创建第4个UC，然后UC＃1和UC＃3保留其值，但UC＃2会丢失它的值。

任何帮助都会受到大力赞赏。我正试图弄清楚这一点。这是我第一次涉足动态用户控制，到目前为止，它正在踢我的屁股。而且我仍然需要弄清楚如何使用db中的值来填充这些UC，以便用户可以返回并编辑表单，但一次只能做一件事。

ASPX：

    <asp:PlaceHolder ID="placeholderOffenseCodes"  runat="server">  </asp:PlaceHolder>
    <asp:Button ID="btnAddOffense" runat="server" Text="Add an Offense" CausesValidation="false" OnClick="btnAddOffense_Click" />
<!--The text value determines how many items are initially displayed on the page-->
    <asp:Literal ID="ltlCount" runat="server" Text="0" Visible="false" />
    <asp:Literal ID="ltlRemoved" runat="server" Visible="false" />

aspx.cs：

protected void Page_Load(object sender, EventArgs e)
{
    AddAndRemoveDynamicOffenseControls();
}

private void AddAndRemoveDynamicOffenseControls()
{
    //Determine which control fired the postback event. 
    Control c = GetPostBackOffenseControl(Page);

    if ((c != null))
    {
        //If the add button was clicked, increase 
        //the count to let the page know we want
        //to display an additional user control
        if (c.ID.ToString() == "btnAddOffense")
        {
            ltlCount.Text = Convert.ToString(Convert.ToInt16(ltlCount.Text) + 1);
        }
    }

    //Be sure everything in the placeholder control is cleared out
    placeholderOffenseCodes.Controls.Clear();

    int ControlID = 0;

    //Re-add controls every time the page loads.
    for (int i = 0; i <= (Convert.ToInt16(ltlCount.Text) - 1); i++)
    {
        IncidentGroupA_Offenses uc = (IncidentGroupA_Offenses)LoadControl("IncidentGroupA_Offenses.ascx");

        //If this particular control id has been deleted 
        //from the page, DO NOT use it again. If we do, it will
        //pick up the viewstate data from the old item that 
        //had this control id, instead of generating
        //a completely new control. Instead, increment 
        //the control ID so we're guaranteed to get a "new"
        //control that doesn't have any lingering information in the viewstate.
        while (InDeletedOffenseList("offense" + ControlID) == true)
        {
            ControlID += 1;
        }

        //Note that if the item has not been deleted from the page, 
        //we DO want it to use the same control id
        //as it used before, so it will automatically maintain 
        //the viewstate information of the user control
        //for us.
        uc.ID = "offense" + ControlID;

        //Add an event handler to this control to raise 
        //an event when the delete button is clicked
        //on the user control
        uc.RemoveOffenseUC += this.HandleRemoveOffenseUserControl;

        //Add the user control to the panel
        placeholderOffenseCodes.Controls.Add(uc);

        //Add Offense number to label on usercontrol
        int OffenseNum = i + 1;
        uc.OffenseNumber = "Offense " + OffenseNum;

        //Increment the control id for the next round through the loop
        ControlID += 1;
    }
}

protected void btnAddOffense_Click(object sender, EventArgs e)
{
    //handled in page_load
}

private bool InDeletedOffenseList(string ControlID)
{
    //Determine if the passed in user control ID 
    //has been stored in the list of controls that
    //were previously deleted off the page
    string listvalues = ltlRemoved.Text;
    string[] stringSeparators = new string[] { "|" };
    string[] DeletedList = listvalues.Split(stringSeparators, StringSplitOptions.RemoveEmptyEntries);
    for (int i = 0; i <= DeletedList.GetLength(0) - 1; i++)
    {
        if (ControlID == DeletedList[i])
        {
            return true;
        }
    }
    return false;
}

public void HandleRemoveOffenseUserControl(object sender, EventArgs e)
{
    //This handles delete event fired from the user control

    //Get the user control that fired this event, and remove it
    LinkButton linkBtn = sender as LinkButton;
    IncidentGroupA_Offenses uc = (IncidentGroupA_Offenses)linkBtn.Parent;

    if (uc != null)
    {
        placeholderOffenseCodes.Controls.Remove(uc);
    }

    //Keep a pipe delimited list of which user controls were removed.  This will increase the 
    //viewstate size if the user keeps removing dynamic controls, but under normal use
    //this is such a small increase in size that it shouldn't be an issue.
    ltlRemoved.Text += uc.ID.ToString() + "|";

    //Also, now that we've removed a user control decrement the count of total user controls on the page
    ltlCount.Text = Convert.ToString(Convert.ToInt16(ltlCount.Text) - 1);
}

public Control GetPostBackOffenseControl(Page page)
{
    Control control = null;

    string ctrlname = page.Request.Params.Get("__EVENTTARGET");
    if ((ctrlname != null) & ctrlname != string.Empty)
    {
        control = page.FindControl(ctrlname);
    }
    else
    {
        foreach (string ctl in page.Request.Form)
        {
            Control c = page.FindControl(ctl);
            if (c is System.Web.UI.WebControls.Button)
            {
                control = c;
                break; 
            }
        }
    }
    return control;
}

.ascx.cs：

public event EventHandler RemoveOffenseUC;

protected void btnRemoveOffense_Click(object sender, EventArgs e)
{
    //Raise this event so the parent page can handle it
    if (RemoveOffenseUC != null)
    {
        RemoveOffenseUC(sender, e);
    }
}

public string OffenseNumber
{
    get { return lblOffenseNumber.Text; }
    set { lblOffenseNumber.Text = value; }
}

Answer 1

我一直认为你必须在Page_Init中添加动态控件以确保正确加载ViewState。也许这个简单的改变会解决你的问题吗？

否则，我过去很幸运，完全避免使用转发器进行动态控制。而不是添加动态控件，哪些webforms绝对不擅长，将数据添加到数据结构（如List或ADO DataTable），然后将其绑定到具有所需控件的asp：Repeater。没有乱七八糟的动态控制。

祝你好运！

在回发时动态创建用户控件的奇怪行为

1 个答案: