How to implement DataGridView Add and remove changes?

1. Create a WinForm form application

2. Drag into the DataGridView control on the interface

3, add the appropriate columns

4, start writing the following code:

Private DataTable Countrydt = new DataTable ();
Private DataTable Citydt = new DataTable ();

Public Main ()
{
InitializeComponent ();

Initcountrydt ();
Initcitydt ();
Initgrid ();
}

private void Initcitydt ()
{
String[] Citys = {"cn|1| Beijing", "cn|2| Tianjin", "cn|3| Shanxi", "Jp|4| Osaka", "jp|5| Yokohama", "Jp|6| Nagoya", "jp|7| Kobe", "us|8| New York
, "us|9| Los Angeles", "us|10| Chicago", "us|11| Houston", "us|12| Philadelphia", "us|13| San Francisco"};
CITYDT.COLUMNS.ADD ("Citycode");
CITYDT.COLUMNS.ADD ("CityName");
CITYDT.COLUMNS.ADD ("Pid");
for (int i = 0; i < Citys. Length; i++)
{
var newRow = Citydt.newrow ();
newrow["Citycode"] = Citys[i]. Split (' | ') [1];
newrow["CityName"] = Citys[i]. Split (' | ') [2];
newrow["Pid"] = Citys[i]. Split (' | ') [0];
CITYDT.ROWS.ADD (NewRow);
}
}
private void Initcountrydt ()
{
String[] Countrys = {"cn| China", "jp| Japan", "us| USA"};
COUNTRYDT.COLUMNS.ADD ("CountryCode");
COUNTRYDT.COLUMNS.ADD ("CountryName");
for (int i = 0; i < Countrys. Length; i++)
{
var newRow = Countrydt.newrow ();
newrow["CountryCode"] = Countrys[i]. Split (' | ') [0];
newrow["countryname"] = Countrys[i]. Split (' | ') [1];
COUNTRYDT.ROWS.ADD (NewRow);
}

}
private void Initgrid ()
{
var dt = new DataTable ();
Dt. Columns.Add ("Id");
Dt. Columns.Add ("CountryCode");
Dt. Columns.Add ("Citycode");
for (int i = ten; i <; i++)
{
var newRow = dt. NewRow ();
newrow["Id"] = i.ToString ();
Dt. Rows.Add (NewRow);
}
Datagridview1.datasource = DT;
}

private void btnAdd_Click (object sender, EventArgs e)
{
var dt = Datagridview1.datasource as DataTable;

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);
}
}
}