Question

我正在尝试使用下面的代码执行文本框自动完成，但它会给出错误

ERROR :"Object reference not set to an instance of an object"

在这一行：

for (int count = 0; count < dt.Rows.Count; count++)

任何人都可以帮助我吗？

private void tbMemberName_TextChanged_1(object sender, EventArgs e)
{
    tbMemberName.AutoCompleteMode = AutoCompleteMode.Suggest;
    tbMemberName.AutoCompleteSource = AutoCompleteSource.CustomSource;
    AutoCompleteStringCollection namec = new AutoCompleteStringCollection();

    //string search ="%"+ tbMemberName.Text +"%";
    //string @Name = tbMemberName.Text; 
    String sql =
        @"SELECT DISTINCT(member_Firstname +''+ member_Lastname) AS Name FROM members WHERE Name  Like '%'+tbMemberName.Text+'%'";
    DataTable dt = MemberFormHelper.GetData(sql, mf);
    if (dt.Rows.Count >= 0)
    {
        for (int count = 0; count < dt.Rows.Count; count++)
        {
            namec.Add(dt.Rows[count][Name].ToString());
        }
    }
    tbMemberName.AutoCompleteCustomSource = namec;
}

Answer 1

dt为null，为多数（除非你在ur表中有一个记录，其名称为'tbMemberName.Text'）...我想是的 - tbMemberName是TextBox ，所以如果你试图将其值传递给sql字符串而不是

@"SELECT DISTINCT(member_Firstname +''+ member_Lastname) AS Name FROM members WHERE Name Like '%'+tbMemberName.Text+'%'";

你必须写

@"SELECT DISTINCT(member_Firstname +''+ member_Lastname) AS Name FROM members WHERE Name Like '%"+tbMemberName.Text+"%'";

你刚刚误用了引号。

Answer 2

我根据msdn microsoft和先生P.K.的代码使用了这段代码。我认为你应该考虑这个

首先，我将这些代码插入form_load
中例如：

this.cmbSchool.AutoCompleteMode = AutoCompleteMode.SuggestAppend;
this.cmbSchool.AutoCompleteSource = AutoCompleteSource.CustomSource;

要访问我的示例中的textchanged属性，我使用了comboBox而不是Textbox（我将它们插入到表单之外，并将其用作通用var，以后可以通过combobox1_textchange访问）

AutoCompleteStringCollection collection = new AutoCompleteStringCollection();

如果您使用的是Mysql，我使用它（也插入form_load）将数据保存在集合中

        string querySelect = "SELECT * FROM tblschools";
        MySqlCommand commandSelect = new MySqlCommand(querySelect, connectionMain);
        MySqlDataReader reader = commandSelect.ExecuteReader();
        while (reader.Read())
        {
            string type = reader[1].ToString();
            cmbSchool.Items.Add(type); //data inserted in combobox list (dropdownstyle in c# dropdown) so that I can still type
            collection.Add(type); //data inserted in collection so that it will be autocomplete when you type keywords
        }
        reader.Close();

然后最后一步是在cmbSchool_TextChanged

中插入此代码

this.cmbSchool.AutoCompleteCustomSource = collection; //everytime you type it will initiate and gather data from the collection

P.S。这是我第一次发布抱歉我的解释和错误的编码，但希望它有所帮助

Answer 3

我认为DT必须为null，并且它实际上是for循环上面的行

使用mysql作为数据库的文本框自动完成

3 个答案: