如何在ASP.NET C＃中動態添加文本框並在添加后使用文本框值

Question

我能夠動態添加文本框，而我無法使用動態添加的文本框的值，這是我的代碼

int i = 0;
List<string> controlidlist = new List<string>();
protected override void LoadViewState(object savedState)
{
    base.LoadViewState(savedState);
    controlidlist = (List<string>)ViewState["controlidlist"];
    foreach (string Id in controlidlist)
    {
        i++;
        TextBox tb = new TextBox();
        tb.ID = Id;
        LiteralControl lineBreak = new LiteralControl();
        PlaceHolder1.Controls.Add(tb);
        PlaceHolder1.Controls.Add(lineBreak);
    }
}

在這里執行動態添加文本框

   protected void Button1_Click(object sender, EventArgs e)
{

    i++;
    TextBox tb = new TextBox();
    tb.ID = "textboxes" + i;
    tb.Text = "textbox" + i;

    LiteralControl lineBreak = new LiteralControl("<br>");
    PlaceHolder1.Controls.Add(tb);
    PlaceHolder1.Controls.Add(lineBreak);
    controlidlist.Add(tb.ID);
    ViewState["controlidlist"] = controlidlist;

}

在這里我想嘗試獲取動態添加的文本框值

  protected void datainput_Click(object sender, EventArgs e)
{
    string m = string.Empty;
    for (int f = 0; f < i; f++)
    {
        TextBox t = (TextBox)FindControl("textboxes"+f);
        string k = t.Text;
        m = m +","+k;


        }
    string h = m;
}

得到的錯誤是“ 對象引用未設置為對象的實例 ”。 在字符串k = t.Text處;

Answer 1

將其添加到容器中：

<asp:Panel runat="server" ID="pnlTextboxes"></asp:Panel>

 foreach (string Id in controlidlist)
    {
        i++;
        TextBox tb = new TextBox();
        tb.ID = Id;
        LiteralControl lineBreak = new LiteralControl();
        pnlTextboxes.Controls.Add(tb);
        pnlTextboxes.Controls.Add(lineBreak);
    }

和：

 TextBox t = (TextBox)pnlTextboxes.FindControl("textboxes"+f);

更新：

TextBox t = (TextBox)PlaceHolder1.FindControl("textboxes"+f);