当您的一个或多个字段包含NULL（DBNull.Value）时，您将无法对其使用GetString。 您需要使用IsDBNull方法检查它们是否为空，然后选择要在文本框中输入的值。通常是一个空字符串
private void combo@R_768_2419@1_SelectedIndexChanged(object sender, EventArgs e)
{
string constring = "datasource=localhost;port=3306;username=root;password=root";
string Query = "SELECT * from database.check WHERE patientname IS NOT NULL";
using(MysqLConnection conDataBase = new MysqLConnection(constring))
using(MysqLCommand cmdDataBase = new MysqLCommand(Query, conDataBase))
{
try
{
conDataBase.open();
using(MysqLDataReader myReader = cmdDataBase.ExecuteReader())
{
int namePos = myReader.GetOrdinal("namethestore");
int checkerPos = myReader.GetOrdinal("checkername");
while (myReader.Read())
{
string namethestore = myReader.IsDBNull(namePos)
? string.Empty
: myReader.GetString("namethestore");
string checkername = myReader.IsDBNull(checkerPos)
? string.Empty
: myReader.GetString("checkername");
this.text@R_768_2419@65.Text = namethestore;
this.text@R_768_2419@66.Text = checkername;
}
}
}
}
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