访问数据库表记录时发生格式转换错误 [英] Format conversion error while accessing database table record

问题描述

以下代码在尝试检索表的记录时显示错误消息
在组合框中选择的valueMember属性值的基础上.

错误消息是:-输入字符串的格式不正确"

Following code shows error message while attempting to retrieve a table''s records
on the base of selected valueMember property''s value from combobox.

The error message is:- "input string was not in correct format"

comboBox2.DataSource = MainDataSet.Tables["Members"];
comboBox2.DisplayMember = "MemberName";
comboBox2.ValueMember = "MemID";  // int primary key of ''members'' table 

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    DataRow[] bkrow;
    int n=Convert.ToInt32(ComBox1.SelectedValue.ToString());//<--This line shows error
    bkrow = MainDataSet.Tables[0].Select("MemID = ''" + n + "''");   
    string QueryBookName = bkrow[0]["BookName"].ToString();
}

memid是Books表中的int主键.

where memid is int primary key in Books table. How to solve this error?

推荐答案

此错误与数据库无关.此错误来自Convert.ToInt32方法.更好的方法是int.Parse方法.您将需要检查ComBox1.SelectedValue.ToString()是否实际上只是一个包含数字的字符串，或者其中是否包含无效字符.有关有效的输入格式，请参见int.Parse上的MSDN注释:

http://msdn.microsoft.com/en-us/library/b3h1hf19.aspx [ ^ ]

This error is nothing to do with the database. This error is coming from the Convert.ToInt32 method. A better method to use would be int.Parse method. You will need to check whether ComBox1.SelectedValue.ToString() is actually a just a string containing a number or if it has invalid characters in it. See the MSDN coumentation on int.Parse for the valid input formats:

http://msdn.microsoft.com/en-us/library/b3h1hf19.aspx[^]

请像这样将您的代码片段拆开:

Please pull your code fragment apart like this:

comboBox2.DataSource = MainDataSet.Tables["Members"];
comboBox2.DisplayMember = "MemberName";
comboBox2.ValueMember = "MemID";  // int primary key of 'members' table

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    DataRow[] bkrow;
    String selectedValue = ComBox1.SelectedValue.ToString();
    if(!String.IsNullOrEmpty(selectedValue))
    {
        int n=Convert.ToInt32(selectedValue);//<--This line shows error
        bkrow = MainDataSet.Tables[0].Select("MemID = '" + n + "'");
        string QueryBookName = bkrow[0]["BookName"].ToString();
    }
}

现在，在带有if语句的行上放置一个断点，并检查变量slectedValue.该错误很可能是由无法转换为整数的值引起的.

最好的问候，

-MRB

Now place a breakpoint on the line with the if statement and inspect the variable slectedValue. The error is most likely caused by a value which cannot be converted to an integer.

Best regards,

-MRB

将此代码

comboBox2.DataSource = MainDataSet.Tables["Members"];

更改为

comboBox2.DataSource = MainDataSet.Tables["Members"].DefaultView;

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