将数据从表复制到组合框

问题描述

我想将一个组合框的数据源设置为表的一列，而此组合框是gridview列之一，我的代码是:

i want to set data source of one combo box to one column of table and this combo box is one of gridview column my code is :

DataTable p = new System.Data.DataTable();
            p = selectcolor();
            (dataGridView1.Columns[4] as DataGridViewComboBoxColumn).DataSource = p;



private DataTable selectcolor()
       {

           DataTable k = new System.Data.DataTable();
           try
           {

               string str = "Data Source=C:\\Documents and Settings\\almas\\Desktop\\BazarKhodro\\khodro.sdf";
               Qconnection.ConnectionString = str;
               Qcommand.Connection = Qconnection;


               string commandText = "select color from foroosh";

               Qcommand.CommandText = commandText;
               Qcommand.CommandType = CommandType.Text;
               SqlCeDataAdapter a = new SqlCeDataAdapter();
               a.SelectCommand = Qcommand;
               a.Fill(k);
               Qconnection.Open();
               Qconnection.Close();
               return k;

           }
           catch (Exception ex)
           {

               throw new Exception(ex.Message);
               return k;
           }
       }

运行后，我看到p的内容，但0出现此错误

对象引用未设置为对象的实例.

请帮助我

after runing i see the content of p but 0ccur this error

Object reference not set to an instance of an object.

pls help me

推荐答案

(dataGridView1.Columns[4] as DataGridViewComboBoxColumn).DataSource

http://msdn.microsoft.com/en-us/library/cscsdfbt％28v = vs.71％29.aspx [ ^ ]

如果这种类型的转换不起作用，它只会返回null，因此您试图在一个null对象上设置.DataSource属性.

我不能说为什么强制转换不起作用，但是在强制转换之前，您需要检查dataGridView1.Columns[4]不为空，并且dataGridView1.Columns[4]是DataGridViewComboBoxColumn类型.

http://msdn.microsoft.com/en-us/library/cscsdfbt%28v=vs.71%29.aspx[^]

If this type of cast doesn''t work, it simply returns null, so you''re trying to set the .DataSource property on an object that is null.

I can''t say why the cast isn''t working but you need to check that dataGridView1.Columns[4] is not null and that dataGridView1.Columns[4] is of type DataGridViewComboBoxColumn before you cast.

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