当没有数据是present无效尝试读取 | 当没有数据是present无效尝试读取

本文介绍了当没有数据是present无效尝试读取的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

    private void button1_Click(object sender, EventArgs e)
    {
        string name;
        name = textBox5.Text;
        SqlConnection con10 = new SqlConnection("con strn");
        SqlCommand cmd10 = new SqlCommand("select * from sumant where username=@name");
        cmd10.Parameters.AddWithValue("@name",name);
        cmd10.Connection = con10;
        cmd10.Connection.Open();//line 7
        SqlDataReader dr = cmd10.ExecuteReader();
    }

    if ( textBox2.Text == dr[2].ToString())
    {
        //do something;
    }

当我调试，直到第7行，这是确定的，但医生后抛出一个异常：无效尝试当没有数据是present阅读。那是不可能的，因为我有在表的用户名= sumant数据。请告诉我是否'如果'语句的正确与否.........

When I debug until line 7, it is ok but after that dr throws an exception:Invalid attempt to read when no data is present.That is not possible as I do have data in table with username=sumant.Please tell me whether the 'if' statement is correct or not.........

和我怎么删除错误??

And how do I remove the error??

推荐答案

您必须调用<$c$c>DataReader.Read获取结果：

You have to call DataReader.Read to fetch the result:

SqlDataReader dr = cmd10.ExecuteReader();
if (dr.Read()) {
  // read data for first record here
}

DataReader.Read返回一个布尔值，表示如果有数据读取更多的块，所以如果你有超过1的结果，你可以这样做：

DataReader.Read returns a boolean indicating if there are more blocks of data to read, so if you have more than 1 result, you can do:

while (dr.Read()) {
  // read data for each record here
}

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