datasource报错object reference not set to an instance of an object for combo box
private void Form_Load(object sender, EventArgs e)
{
string[] installs = new string[] { "Dailymovement", "FDPS" };
comboBox2.Items.AddRange(installs);
comboBox2.SelectedIndex = 0;
}
private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
{
int s = 0;
foreach (Control c in this.Controls)
{
if (c is ListBox)
{
s++;
}
}
for (int ss=1;ss<=s;ss++)
{
ListBox tb = this.Controls["listBox" + ss] as ListBox;
if (comboBox2.SelectedItem.ToString() == "Dailymovement")
{
MySqlCommand cmd1 = new MySqlCommand("select field_name from Dailymovement_name ", con);
MySqlDataAdapter adp1 = new MySqlDataAdapter();
adp1.SelectCommand = cmd1;
DataSet ds1 = new DataSet();
adp1.Fill(ds1, "field");
tb.DataSource = ds1.Tables["field"];
tb.DisplayMember = "field_name";
tb.ValueMember = "field_name";
}
}
}
form load时comboBox2_SelectedIndexChanged事件里 tb.DataSource = ds1.Tables["field"];这句报错,object reference not set to an instance of an object for combo box.为什么有这个错,怎么改