英文:
Error pulling data into ComboBox2: According to the index selected in ComboBox1
问题
我尝试从数据库中根据在ComboBox1中选择的索引提取数据到ComboBox2，但出现错误，原因是什么？
错误CS1503：2个参数：无法将“string”转换为“NpgsqlTypes.NpgsqlDbType”
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
string selectedValue = (string)comboBox1.SelectedValue;
using (var connection = new NpgsqlConnection(""))
{
connection.Open();
var command = new NpgsqlCommand("SELECT brand_name FROM brand WHERE material_type = @Value", connection);
command.Parameters.AddWithValue("Value", selectedValue);
command.ExecuteNonQuery();
var reader = command.ExecuteReader();
while (reader.Read())
{
comboBox3.Items.Add(reader["brand_name"]);
}
connection.Close();
}
}
英文:
I am trying to pull data from the database into ComboBox2 according to the index selected in ComboBox1, but I get an error, what is the reason?
Error CS1503 2 argument: Cannot convert from 'string' to 'NpgsqlTypes.NpgsqlDbType'
private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
string selectedValue = (string)comboBox1.SelectedValue;
using (var connection = new NpgsqlConnection(""))
{
connection.Open();
var command = new NpgsqlCommand("SELECT brand_name FROM brand WHERE material_type = Value", connection);
command.Parameters.AddWithValue("Value", selectedValue , NpgsqlDbType.Char);
command.ExecuteNonQuery();
var reader = command.ExecuteReader();
while (reader.Read())
{
comboBox3.Items.Add(reader["brand_name"]);
}
connection.Close();
}
}
答案1
得分: 0
你在AddWithValue()中传递参数的顺序错误。
你的调用应该看起来像这样：
command.Parameters.AddWithValue("Value", NpgsqlDbType.Char, selectedValue);
英文:
You passed the parameters of AddWithValue() in the wrong order.
public NpgsqlParameter AddWithValue(
string parameterName,
NpgsqlDbType parameterType,
object value)
Your call should look something like this:
command.Parameters.AddWithValue("Value", NpgsqlDbType.Char, selectedValue);
答案2
得分: -1
我使用这个更改修复了错误。
comboBox1.SelectedValueChanged += new EventHandler(comboBox1_SelectedIndexChanged);
我忘记在我的form_load中添加这个代码块。
英文:
I fix the error with this change.
comboBox1.SelectedValueChanged += new EventHandler(comboBox1_SelectedIndexChanged);
I forgot to add this code block to my form_load.
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