文本框自動完成與MySQL作爲數據庫

我將嘗試使用下面的代碼做文本框自動完成，但它給該線路上的錯誤文本框自動完成與MySQL作爲數據庫

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

：

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

誰能請幫我？

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; 
}

來源

2011-06-14 user682417

你確定'dt.Rows'不是NULL？ – jao 2011-06-14 10:13:07

'dt'可能爲空，這就是爲什麼錯誤 – V4Vendetta 2011-06-14 10:14:54

dt爲空，prolly（除非u有一個紀錄烏爾表具有以下名稱「tbMemberName.Text 「）......我想是這樣的 - tbMemberName是一個TextBox，所以如果你想它的值傳遞給SQL字符串，而不是

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

u必須寫

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

我剛剛誤用了引號。

來源

2011-06-14 10:46:50

數據沒有加載到名稱集合在此statementnamecollection.Add（dt.Rows [0] [「member_Firstname」]。ToString（））;你會幫我 – user682417 2011-06-14 11:42:26

所以最後你在'for'循環中。如果你仍然在使用'SELECT DISTINCT（member_Firstname +''+ member_Lastname）AS Name'語句'dt.Rows [0] [「member_Firstname」]'將失敗。因爲沒有「member_Firstname」列。列你想要解決的是「名稱」（別名你給），所以改爲使用'dt.Rows [0] [「名稱」]'。如果在新的'select'語句後仍然有問題 – 2011-06-14 12:11:28

我覺得DT必須是null，且其實際上面的行for循環從而未能

來源

2011-06-14 10:13:34 cusimar9

我用這個代碼基於msdn microsoft和先生P.K.的代碼。我想你應該考慮這個

首先，我在Form_Load插入這些代碼
例如：

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

要訪問我的例子中框TextChanged屬性我用組合框代替文本框（我插入他們的外部形式並用它作爲通用變種由combobox1_textchange以後可以訪問）

AutoCompleteStringCollection collection = new AutoCompleteStringCollection();

如果你正在使用MySQL我用這個（也插入的Form_Load）將數據保存在收集

 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();

那麼最後一步是我在cmbSchool_TextChanged

插入這段代碼

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

附：這是我第一次對我的解釋和錯誤的編碼後抱歉，但希望它有幫助

來源

2017-05-31 06:01:11

文本框自動完成與MySQL作爲數據庫

回答

相關問題