FindControl返回空文本框对象/ null

Question

我在页面上有一个html表：

<table id="tblMain" runat="server" style="margin-left: auto; margin-right: auto;">
    <tr>
        <td>
            Safety
        </td>
        <td>
            <asp:TextBox ID="txtSafety" Width="400px" ReadOnly="true" TextMode="MultiLine" runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnSafety" runat="server" Width="150px" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="0" />
        </td>
    </tr>
    <tr>
        <td>
            Environment
        </td>
        <td>
            <asp:TextBox ID="txtEnvironment" Width="400px" ReadOnly="true" TextMode="MultiLine" runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="bntEnvironment" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="1" />
        </td>
    </tr>
    <tr>
        <td>
            Quality
        </td>
        <td>
            <asp:TextBox ID="txtQuality" Width="400px" ReadOnly="true" TextMode="MultiLine" runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnQuality" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="2" />
        </td>
    </tr>
    <tr>
        <td>
            Ferrous System
        </td>
        <td>
            <asp:TextBox ID="txtFerrousSystem" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnFerrousSystem" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="3" />
        </td>
    </tr>
    <tr>
        <td>
            Coke System
        </td>
        <td>
            <asp:TextBox ID="txtCokeSystem" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnCokeSystem" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="4" />
        </td>
    </tr>
    <tr>
        <td>
            Coal Yards
        </td>
        <td>
            <asp:TextBox ID="txtCoalYards" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnCoalYards" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="5" />
        </td>
    </tr>
    <tr>
        <td>
            Screenhouse
        </td>
        <td>
            <asp:TextBox ID="txtScreenhouse" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnScreenhouse" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="6" />
        </td>
    </tr>
    <tr>
        <td>
            Process Plant
        </td>
        <td>
            <asp:TextBox ID="txtProcessPlant" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnProcessPlant" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="7" />
        </td>
    </tr>
    <tr>
        <td>
            New Mill
        </td>
        <td>
            <asp:TextBox ID="txtNewMill" Width="400px" ReadOnly="true" TextMode="MultiLine" runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnNewMill" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="8" />
        </td>
    </tr>
    <tr>
        <td>
            Streamphases
        </td>
        <td>
            <asp:TextBox ID="txtStreamphases" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnStreamphases" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="9" />
        </td>
    </tr>
    <tr>
        <td>
            Furnace Silos Injection
        </td>
        <td>
            <asp:TextBox ID="txtFurnaceSilosInjection" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnFurnaceSilosInjection" Width="150px" runat="server" Text="Edit"
                OnClick="Edit_Text" CommandArgument="10" />
        </td>
    </tr>
    <tr>
        <td>
            CompressedAir
        </td>
        <td>
            <asp:TextBox ID="txtCompressedAir" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnCompressedAir" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="11" />
        </td>
    </tr>
    <tr>
        <td>
            Planned Maintenance
        </td>
        <td>
            <asp:TextBox ID="txtPlannedMaintenance" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnPlannedMaintenance" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="12" />
        </td>
    </tr>
    <tr>
        <td>
            Notifications Raised
        </td>
        <td>
            <asp:TextBox ID="txtNotificationsRaised" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnNotificationsRaised" Width="150px" runat="server" Text="Edit"
                OnClick="Edit_Text" CommandArgument="13" />
        </td>
    </tr>
    <tr>
        <td>
            Manning
        </td>
        <td>
            <asp:TextBox ID="txtManning" Width="400px" ReadOnly="true" TextMode="MultiLine" runat="server"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnManning" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="14" />
        </td>
    </tr>
    <tr>
        <td>
            ShiftHandover
        </td>
        <td>
            <asp:TextBox ID="txtShiftHandover" Width="400px" ReadOnly="true" TextMode="MultiLine"
                runat="server" OnClick="Edit_Text"></asp:TextBox>
        </td>
        <td>
            <asp:Button ID="btnShiftHandover" Width="150px" runat="server" Text="Edit" 
                OnClick="Edit_Text" CommandArgument="15" />
        </td>
    </tr>
</table>

按下按钮时，将调用以下方法：

protected void Edit_Text(object sender, EventArgs e)
{
    Button btn = sender as Button;
    if (btn != null)
    {
        editField = btn.ID.Replace("btn", "");
        btn.Visible = false;
        //Getting and storing rowindex

        TextBox txt = this.FindControl("txt" + editField) as TextBox;
        txt.ReadOnly = false;
        txt.BackColor = System.Drawing.ColorTranslator.FromHtml("#FFFFB2");
        txt.Focus();
        comment = txt.Text;
        //Further methods unnecessary for this question
    }
}

正如您所看到的，前缀从控件中被剥离，然后在必要时添加以在该点找到正确的控件，因此FindControl方法的字符串是正确的并且应该返回一个TextBox。

然而，通过单步执行，我可以看到它传递的是一个空的TextBox实例，而不是预期的结果或null。

我已经在桌子上尝试了findcontrol功能，我用过这个＆＃39;这个＆＃39;作为第二次检查，但两者产生了相同的结果。

我怀疑html表是一个问题，因为我在html表中手动找到按钮时遇到问题：

Button editbtn = tblMain.Rows[GetRowIndex(hdnRowIndex.Value)].Cells[2].Controls[0] as Button;

尽管每个行的单元格中都有一个单元格按钮

，但是返回null

编辑 - 这是执行的绑定

private void bindData(DataTable dt)
{
    if (dt.Rows.Count > 0)
    {
        foreach (DataColumn col in dt.Columns)
        {
            TextBox txt = tblMain.FindControl("txt" + col.ColumnName) as TextBox;
            if (txt != null)
            {
                txt.Text = dt.Rows[0][col].ToString();
            }
        }
    }
}

Answer 1

你的问题在这里：

this.FindControl("txt" + editField) as TextBox;

FindControl不是递归的，只能找到它被调用的控件的直接子节点。在这里你称之为页面实例，因此它只搜索控制树中页面的直接子节点（可能这只是一个表单元素）。

您需要做的是在文本框/按钮上方选择一个服务器端控件并运行它的FindControl。例如，假设它是你的表，它被声明为：

<table>
<%--...all the content from the post goes here...--%>
</table>

将此表设为服务器端：

<table id="TheTable" runat="server">

然后在此表上调用FindControl：

TextBox txt = TheTable.FindControl("txt" + editField) as TextBox;

您当然可以将表保留在客户端，并使用一些包装此表的控件。只需确保在您的控件和相关文本框之间没有其他服务器端控件。

Answer 2

 <table style="width:100%; margin-left:auto; margin-right:auto;" id="tblTst" runat="server">
        <tr>
            <td>
                <h2>
                    Vehicle Information
                    <asp:Label ID="lblTest" Text="THis is a Test" ForeColor="Salmon" runat="server" />
                    <asp:Button ID="btnTest" CommandArgument="0" OnClick="btnTest_click" runat="server" Text="Test" />
                </h2>
            </td>
        </tr>
        <tr>
            <td>
                    <asp:Label ID="lblTst2" Text="This is also a Test" ForeColor="Salmon" runat="server" />
                    <asp:Button ID="btnTest2" CommandArgument="1" OnClick="btnTest_click" runat="server" Text="Test" />

            </td>
        </tr>
        <tr>
            <td>
                <asp:Label ID="lblMsg" runat="server" />
            </td>
        </tr>
    </table>


    protected void btnTest_click(object sender, EventArgs e)
{
    Button btn = sender as Button;
    string comment = "";
    string editField = "";
    if (btn != null)
    {
        editField = btn.ID.Replace("btn", "");
        btn.Visible = false;
        //Getting and storing rowindex
        foreach(HtmlTableCell cl in tblTst.Rows[Convert.ToInt32(btn.CommandArgument)].Cells)
        {
            foreach (Control ctrl in cl.Controls)
            {
                if(ctrl is Label)
                {
                    Label txt = new Label();
                    txt = ctrl as Label;
                    txt.BackColor = System.Drawing.ColorTranslator.FromHtml("#FFFFB2");
                    txt.Focus();
                    comment = txt.Text;
                    lblMsg.Text = comment;
                    return;
                }
            }
        }
        //Further methods unnecessary for this question
    }
}

}

这就是我提出的，这确实有效;然而，这是一种相当肮脏的方式，我确定你可以清理它很多。这只是一个起点。最大的不同之处在于，您需要在单元格中查找不在表格或页面中的控件，单元格也是一个htmltable单元格而不仅仅是表格单元格。