How to implement addition, deletion and modification of DataGridView?

1, create a winform form application

2, drag the DataGridView control into the interface

3, add the corresponding columns as shown:

4, start writing the following code:

private DataTable CountryDt = new DataTable();
private DataTable CityDt = new DataTable();

public Main( )
{
InitializeComponent ();

InitCitydt ();
Initgrid ();

PriveCitydt ( ; |Yokohama", "JP|6|Nagoya", "JP|7|Kobe", "US|8|New York"

CityDt.Columns.Add("cityCode");
CityDt.Columns.Add("cityName");
Citydt.columns.add ("PID");
For (int i = 0; I & LT; Citys.length; I ++)
{## var newRow = CityDt.newrow ();
newRow["cityCode"] = cities[i].Split('|')[1];
newRow["cityName"] = cities[i].Split('|')[2];
newRow["Pid"] = cities[i].Split('|')[0];
CityDt.Rows.Add(newRow);
}
}
private void InitCountryDt ()
                                                                                                                          # CountryDt.Columns.Add("countryName");
newRow["countryCode"] = countries[i].Split('|')[0];
            newRow["countryName"] = countries[i].Split('|')[1];
CountryDt.Rows.Add(newRow);
}

}
          private void InitGrid()
          var dt = new DataTable(); Add ("Id");
i++)
                                                                                                                                                                         ;
      }
DataGridView1.datasource = DT;
}

PRIVATE VOID BTNADD_CLICK (Object SENDER, EVENTARGS E)

var newRow = dt.NewRow();
newRow["Id"] = dt.Rows.Count + 1;
dt.Rows.Add(newRow);

for (int i = 0; i < dt.Rows.Count; i++)
           {
               var countryCell = new DataGridViewComboBoxCell();
               countryCell.DataSource = CountryDt;
               countryCell.ValueMember = "countryCode";
               countryCell.DisplayMember = "countryName";
               dataGridView1.Rows[i].Cells["countryCode"] = countryCell;
           }
       }

private void dataGridView1_CellValueChanged(object sender, DataGridViewCellEventArgs e)
       {
           var dt = this.dataGridView1.DataSource as DataTable;
           if (dataGridView1.Columns[e.ColumnIndex].Name == nameof(CountryCode))
           {
               var countryCode = dataGridView1.Rows[e.RowIndex].Cells[e.ColumnIndex].Value;
               var drs = CityDt.Select("Pid='" + countryCode + "'");
               var newCityDt = new DataTable();
               newCityDt.Columns.Add("cityCode");
               newCityDt.Columns.Add("cityName");
               newCityDt.Columns.Add("Pid");
               foreach (DataRow row in drs)
               {
                   var newRow = newCityDt.NewRow();
                   newRow["cityCode"] = row["cityCode"];
                   newRow["cityName"] = row["cityName"];
                   newRow["Pid"] = row["Pid"];
                   newCityDt.Rows.Add(newRow);
               }
               var cityCell = new DataGridViewComboBoxCell();

cityCell.DataSource = newCityDt;
               cityCell.DisplayMember = "cityName";
               cityCell.ValueMember = "cityCode";
               dataGridView1.Rows[e.RowIndex].Cells["CityCode"] = cityCell;
           }
       }

private void Main_Load(object sender, EventArgs e)
       {
           var vdt = dataGridView1.DataSource as DataTable;
           for (int i = 0; i < vdt.Rows.Count; i++)
           {
               var cell = new DataGridViewComboBoxCell()
               {
                   DisplayMember = "countryName",
                   ValueMember = "countryCode",
                   DataSource = CountryDt
               };

dataGridView1.Rows[i].Cells["CountryCode"] = cell;
               if (i % 2 == 0)
               {
                   dataGridView1.Rows[i].Cells["CountryCode"].Value = "JP";
                   dataGridView1.Rows[i].Cells["CityCode"].Value = new Random().Next(4, 7);
               }
               //else {
               //    dataGridView1.Rows[i].Cells["CountryCode"].Value = "CN";
               //}
               if (i % 5 == 0)
               {
                   dataGridView1.Rows[i].Cells["CountryCode"].Value = "CN";
                   dataGridView1.Rows[i].Cells["CityCode"].Value = new Random().Next(1, 3);
               }
               if (i % 9 == 0)
               {
                   dataGridView1.Rows[i].Cells["CountryCode"].Value = "US";
                   dataGridView1.Rows[i].Cells["CityCode"].Value = new Random().Next(8, 13);
               }
           }
       }

private void btnRemove_Click(object sender, EventArgs e)
       {

var selected = dataGridView1.SelectedRows;
           var dt = dataGridView1.DataSource as DataTable;
           if (selected.Count > 0)
           {
               for (var i = 0; i < selected.Count; i++)
               {
                   var row = selected[i];
                   dt.Rows.RemoveAt(row.Index);
               }
           }
       } 

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