Question

我的网页上有TextBox和Button。用户在TextBox中输入一个数字，然后点击Button，这会在TextBox中创建（n + 1）Panel个es。

正如您在代码中看到的那样，我已将[{1}}分配给ID个实例，再次尝试使用TextBox访问TextBox个实例时，我保留获得FindControl() 仅最后NullReferenceException（ID：f1），我在这里做错了什么？

最初TextBox不是Button1.Text。

代码

"Find"

页面的ASPX代码

protected void Button1_Click(object sender, EventArgs e)
{
    if (Button1.Text.Equals("Find"))
    {
        for (int i = 0; i < size; i++)
        {
            TextBox tb = (TextBox)Panel1.FindControl("Number" + i);
            n[i] = Convert.ToInt32(tb.Text);
        }
        localhost.Search s = new localhost.Search();
        resultLabel = new Label();
        TextBox tb1 = (TextBox)Panel1.FindControl("f1");
        int fNumber = Convert.ToInt32(tb1.Text);            // tb1 is null
        if (s.LinearSearch(n, fNumber))
            resultLabel.Text = "FOUND!";
        else
            resultLabel.Text = "NOT FOUND!";
        form1.Controls.Add(resultLabel);
    }
    else
    {
        size = Convert.ToInt32(TextBox1.Text);
        n = new int[size];
        TextBox1.Enabled = false;
        boxes = new TextBox[size];
        for (int i = 0; i < size; i++)
        {
            Label l = new Label();
            l.Text = "Number " + (i + 1) + " : ";
            boxes[i] = new TextBox();
            boxes[i].ID = "Number" + i;
            Panel1.Controls.Add(l);
            Panel1.Controls.Add(boxes[i]);
        }
        Label l1 = new Label();
        l1.Text = "Find Number : ";
        Panel1.Controls.Add(l1);
        findBox = new TextBox();
        findBox.ID = "f1";
        Debug.Write("[!D] ID : "+findBox.ID);
        Panel1.Controls.Add(findBox);
        Button1.Text = "Find";
    }
}

Answer 1

尝试在整个页面中搜索ID f1，而不是在面板中搜索。

TextBox tb1 = (TextBox)FindControl("f1");

在文本框中添加ID

<asp:TextBox ID="f1" runat="server"></asp:TextBox>

在你的aspx页面中没有f1 ID，因为在尝试获取元素的Text时你得到了空引用异常。

Answer 2

每当您创建动态控件时，都需要在回发时重新创建它。希望这有帮助

protected void Button1_Click(object sender, EventArgs e)
    {
        CreateControls();
        if (Button1.Text.Equals("Find"))
        {

            for (int i = 0; i < size; i++)
            {
                 TextBox tb = (TextBox)Panel1.FindControl("Number" + i);
                 n[i] = Convert.ToInt32(tb.Text);
            }
           localhost.Search s = new localhost.Search();
           resultLabel = new Label();
           TextBox tb1 = (TextBox)Panel1.FindControl("f1");
           int fNumber = Convert.ToInt32(tb1.Text);            // tb1 is null
         if (s.LinearSearch(n, fNumber))
           resultLabel.Text = "FOUND!";
        else
          resultLabel.Text = "NOT FOUND!";
        form1.Controls.Add(resultLabel);
       }
        else
        {
            Button1.Text = "Find";
        }


    }

    protected void CreateControls()
    {
        var size = Convert.ToInt32(TextBox1.Text);
        var n = new int[size];
            TextBox1.Enabled = false;
            var boxes = new TextBox[size];
            for (int i = 0; i < size; i++)
            {
                Label l = new Label();
                l.Text = "Number " + (i + 1) + " : ";
                boxes[i] = new TextBox();
                boxes[i].ID = "Number" + i;
                Panel1.Controls.Add(l);
                Panel1.Controls.Add(boxes[i]);
            }
            Label l1 = new Label();
            l1.Text = "Find Number : ";
            Panel1.Controls.Add(l1);
            var findBox = new TextBox();
            findBox.ID = "f1";
            Debug.Write("[!D] ID : " + findBox.ID);
            Panel1.Controls.Add(findBox);

        }

C＃ASP.NET FindControl保持返回null

2 个答案: