替换项目DataGridViewComboBoxCell c＃

Question

我想创建DataGridView中每行的两列之间的依赖关系。 我添加了两列（品牌，型号）运行时（从数据库中选择数据）。我的目标是在品牌单元格更改时在模型单元格中加载新项目。 填充数据：

private void autoOptionsForm_Load(object sender, EventArgs e) 
{ 
    Connection.ds.Tables.Clear(); 
    Connection.adap = new SqlDataAdapter("SELECT * FROM autoOptions", Connection.conn); 
    Connection.adap.Fill(Connection.ds, "autoOptions"); 
    aoGV.DataSource = Connection.ds.Tables[0];   
    // Additing ComboBox column 
    DataGridViewComboBoxColumn carCB = new DataGridViewComboBoxColumn(); 
    carCB.Name = "Model"; 
    aoGV.Columns.Add(carCB); 

    DataGridViewComboBoxColumn brandCB = new DataGridViewComboBoxColumn(); 
    brandCB.Name = "Brand"; 
    aoGV.Columns.Add(brandCB); 
    foreach (DataGridViewRow row in aoGV.Rows) { 
     if (row.Index == aoGV.Rows.Count - 1) continue; 
     //Additing CB for Models 
    SqlCommand cmd = new SqlCommand(@"SELECT Model FROM Cars WHERE 
         Brand_ID = (SELECT Brand_ID FROM Cars WHERE id='" + row.Cells["Car_ID"].Value + "')", Connection.conn); 
    SqlDataReader sqlReader = cmd.ExecuteReader(); 
    while (sqlReader.Read()) ((DataGridViewComboBoxCell)row.Cells["Model"]).Items.Add(sqlReader["Model"].ToString()); 

     //Current Model ComboBox 
    cmd = new SqlCommand(@"SELECT Model FROM Cars WHERE id = "+ row.Cells["Car_ID"].Value, Connection.conn); 
    sqlReader = cmd.ExecuteReader(); 
    sqlReader.Read(); 
    int iId = ((DataGridViewComboBoxCell)row.Cells["Model"]).Items.IndexOf(sqlReader["Model"].ToString()); 

    ((DataGridViewComboBoxCell)row.Cells["Model"]).Value = ((DataGridViewComboBoxCell)row.Cells["Model"]).Items[iId]; 

     //Additing CB for Brands 
    cmd = new SqlCommand(@"SELECT Brand_name FROM Brands", Connection.conn); 
     sqlReader = cmd.ExecuteReader(); 
     while (sqlReader.Read()) ((DataGridViewComboBoxCell)row.Cells["Brand"]).Items.Add(sqlReader["Brand_name"].ToString()); 

     cmd = new SqlCommand(@"SELECT Brand_name FROM Brands WHERE id = 
          (SELECT Brand_ID FROM Cars WHERE id = " + row.Cells["Car_ID"].Value + ")", Connection.conn); 
     sqlReader = cmd.ExecuteReader(); 
     sqlReader.Read(); 
     iId = ((DataGridViewComboBoxCell)row.Cells["Brand"]).Items.IndexOf(sqlReader["Brand_name"].ToString()); 
     ((DataGridViewComboBoxCell)row.Cells["Brand"]).Value = ((DataGridViewComboBoxCell)row.Cells["Brand"]).Items[iId]; 
    } 
} 

我的方式来解决代码：

private void aoGV_CellEndEdit(object sender, DataGridViewCellEventArgs e) 
{ 
    if (aoGV.Columns[aoGV.SelectedCells[0].ColumnIndex].Name != "Brand") return; 
    DataGridViewRow row = aoGV.Rows[aoGV.SelectedCells[0].RowIndex]; 
    SqlCommand cmd = new SqlCommand(@"SELECT Model FROM Cars WHERE 
         Brand_ID = (SELECT id FROM Brands WHERE Brand_name = '"+row.Cells["Brand"].Value.ToString()+"')", Connection.conn); 
    SqlDataReader sqlReader = cmd.ExecuteReader(); 
    ((DataGridViewComboBoxCell)row.Cells["Model"]).Items.Clear(); 
    while (sqlReader.Read()) ((DataGridViewComboBoxCell)row.Cells["Model"]).Items.Add(sqlReader["Model"].ToString()); 
} 

，并试图清除细胞的物品时，我有一个错误。为什么会出现此错误？（添加列在运行时手动执行）。是否有其他解决方案来解决问题？

Answer 1

我知道这是一个老问题，但仍然是一个答案可能有助于下一个。

我只是有同样的问题，一点点的调试表明，问题是对象的值变量。 值变量保存组合框当前选定的值，但是当您清除项目时，此值变为无效并导致错误。 在清除之前将value变量设置为null删除错误。