Question

我动态创建我需要的控件这是代码

public void cmdButton1_OnClick(object sender, EventArgs e)
{

        Label myLabel = new Label();
        myLabel.ID = "lblNameL" + i.ToString();
        myLabel.Text = "Трите имена на латиница ";
        TextBox myTextBox1 = new TextBox();
        myTextBox1.ID = "txtNameL" + i.ToString();
        Page.FindControl("form1").Controls.Add(myLabel);
        Page.FindControl("form1").Controls.Add(myTextBox1);

        Label mylabel2 = new Label();
        mylabel2.ID = "lblNameK" + i.ToString();
        mylabel2.Text = "Трите имена на кирилица";
        TextBox myTextBox2 = new TextBox();
        myTextBox2.ID = "txtNameK" + i.ToString();
        Page.FindControl("form1").Controls.Add(mylabel2);
        Page.FindControl("form1").Controls.Add(myTextBox2);
}

在这里，我尝试执行sql查询，以便我可以将文本框txbNameK的内容插入到表Tourist中，异常位于行cmd.Parameters.add

public void cmdInsert_OnClick(object sender, EventArgs e)
{

        TextBox tx888 = (TextBox)FindControl("txtNameK" + i.ToString());
        TextBox tx99 = (TextBox)FindControl("txtNameL" + i.ToString());

        string insertSQL = "INSERT INTO Tourist ( Name_kir, Name_lat) VALUES (@Name_kir, @Name_lat, )";

        string connectionString = "Data Source = localhost\\SQLExpress;Initial Catalog=Pubs;Integrated Security=SSPI";
        SqlConnection con = new SqlConnection(connectionString);
        SqlCommand cmd = new SqlCommand(insertSQL, con);
        cmd.Parameters.AddWithValue("@Name_kir",tx888);
        cmd.Parameters.AddWithValue("@Name_lat", tx99);

        int added = 0;
        try
        {
            con.Open();
            added = cmd.ExecuteNonQuery();
            lblResult.Text = added.ToString() + "records added";

        }
        catch (Exception ex)
        {
            lblResult.Text = ex.Message;
        }
        finally
        {
            con.Close();

        }
    }
}

Answer 1

两件事：

TextBox tx888 = (TextBox)FindControl("txtNameK" + i.ToString());
TextBox tx99 = (TextBox)FindControl("txtNameL" + i.ToString());
if(tx888 == null)
    return;
if(tx99 == null)
    return;

上面将检查您的文本框是否为空另一件事是：

cmd.Parameters.AddWithValue("@Name_kir",tx888.Text);
cmd.Parameters.AddWithValue("@Name_lat", tx99.Text);

Answer 2

只要null对象尝试访问任何值，就会发生对象引用异常。例如..

以下代码可以正常使用。

Exception ex = new Exception()
Textbox1.Text = ex.Message;

以下代码将引发异常

Exception ex= null;    //one and the same thing

Textbox1.Text = ex.Message;     //Object reference not set....exception will be raised since ex is null

这是您的代码中发生的事情。尝试放置断点并进行调试。对于最佳实践，请始终按照Prashant的建议检查对象是否为空。

当我尝试执行此sql查询时，此代码给出了一个异常“对象引用未设置为对象的实例”

2 个答案: