我有一个数据集，它存储在XML文件中。当应用程序启动并且XML文件尚不存在时，我想在我的数据集中添加一些行并将其保存为XML。我使用以下代码来执行此操作：
partiesDb = new Parties();
//...
DataTable partyDsTable = partiesDb.Tables["party"]; //partiesDb is DataSet object
for (int i = 0; i < size; i++)
{
DataRow row = partyDsTable.NewRow(); // HERE THE CODE STOPS
row["sth"] = sth;
row["sth"] = "0";
row["id"] = "1";
if (!partyDsTable.Rows.Contains(row))
{
partyDsTable.Rows.Add(row);
}
}
System.Windows.Forms.MessageBox.Show(partyDsTable.Rows[0]["sth"].ToString());
partiesDb.WriteXml(path);
没有任何反应。甚至消息框也没有显示。该功能在创建新行时停止，我不知道为什么。你能救我吗？
[编辑]： 这段代码工作正常：
partiesDb = new Parties();
DataTable dsTable = partiesDb.Tables["party"];
DataRow dsRow = dsTable.NewRow();
dsRow["name"] = "";
dsRow["id"] = "";
dsRow["votes"] = "";
dsTable.Rows.Add(dsRow);
partiesDb.WriteXml(partiesDbPath);
我不知道为什么会这样，但是当我添加循环时它不会......
答案 0 :(得分：1)
您无法向null变量添加内容。因此，如果它为空，则需要实例化partyDsTable。
DataTable partyDsTable = partiesDb.Tables["party"]; //partiesDb is DataSet object
if(partyDsTable == null) // instantiate it
partyDsTable = new DataTable();
for (int i = 0; i < size; i++)
{
....
答案 1 :(得分：0)
DataTable partyDsTable = partiesDb.Tables["party"]; //partiesDb is DataSet object
for (int i = 0; i < size; i++)// "size" does not look like it's set to anything. If "size" is 0, then the loop will not loop.
{
partyDsTable.Rows.Add(new object[] {sth,"0","1"});//you should probably make the columns into the correct type if you are using integers.
}
System.Windows.Forms.MessageBox.Show(partyDsTable.Rows[0]["sth"].ToString());
partiesDb.WriteXml(path);
答案 2 :(得分：0)
此外，如果您创建的字段与数据库表中的项目匹配，您可以使用反射执行各种操作，以使您的数据始终良好：
public static DataTable create_DataTable_From_Generic_Class(Type t)
{
DataTable d = new DataTable();
FieldInfo[] fI = t.GetFields();
for(int i = 0; i < fI.Length; i++)
{
DataColumn dC = new DataColumn(fI[i].Name, fI[i].FieldType);
d.Columns.Add(dC);
}
return d;
}
public static object[] Create_Datatable_Row_From_Generic_Class(Type t, object instance,DataTable dt)
{
FieldInfo[] f = t.GetFields();
object[] ret = new object[f.Length];
for (int i = 0; i < dt.Columns.Count; i++)
{
ret[i] = t.GetField(dt.Columns[i].ColumnName).GetValue(instance);
}
return ret;
}
public static List<string[]> getParams(Type type, bool convertToSQL)
{
List<string[]> ret = new List<string[]>();
Dictionary<string, object> properties = new Dictionary<string, object>();
foreach (FieldInfo prop in type.GetFields())
properties.Add(prop.Name, prop.FieldType);
foreach (string key in properties.Keys)
{
string[] r = { key, properties[key].ToString().Replace("System.", "") };
ret.Add(r);
}
if (convertToSQL)
{
return convertFromNetToSQLDataTypes(ret);
}
else
{
return ret;
}
}
private static List<string[]> convertFromNetToSQLDataTypes(List<string[]> list)
{
foreach (string[] data in list)
{
data[1] = data[1].Replace("Int16", "tinyint");
data[1] = data[1].Replace("Int32", "int");
data[1] = data[1].Replace("Int64", "bigint");
data[1] = data[1].Replace("Double", "float");
data[1] = data[1].Replace("Boolean", "tinyint");
data[1] = data[1].Replace("Double", "float");
data[1] = data[1].Replace("Long", "bigint");
data[1] = data[1].Replace("String", "varchar(100)");
}
return list;
}
public static object[] sql_Reader_To_Type(Type t, SqlDataReader r)
{
List<object> ret = new List<object>();
while (r.Read())
{
FieldInfo[] f = t.GetFields();
object o = Activator.CreateInstance(t);
for (int i = 0; i < f.Length; i++)
{
string thisType = f[i].FieldType.ToString();
switch (thisType)
{
case "System.String":
f[i].SetValue(o, Convert.ToString(r[f[i].Name]));
break;
case "System.Int16":
f[i].SetValue(o, Convert.ToInt16(r[f[i].Name]));
break;
case "System.Int32":
f[i].SetValue(o, Convert.ToInt32(r[f[i].Name]));
break;
case "System.Int64":
f[i].SetValue(o, Convert.ToInt64(r[f[i].Name]));
break;
case "System.Double":
// Console.WriteLine("converting " + f[i].Name + " to double");
double th;
if (r[f[i].Name] == null)
{
th = 0;
}
else
{
if (r[f[i].Name].GetType() == typeof(DBNull))
{
th = 0;
}
else
{
th = Convert.ToDouble(r[f[i].Name]);
}
}
try { f[i].SetValue(o, th); }
catch (Exception e1)
{
throw new Exception("can't convert " + f[i].Name + " to doube - value =" + th);
}
break;
case "System.Boolean":
f[i].SetValue(o, Convert.ToInt32(r[f[i].Name]) == 1 ? true : false);
break;
case "System.DateTime":
f[i].SetValue(o, Convert.ToDateTime(r[f[i].Name]));
break;
default:
throw new Exception("Missed data type in sql select in getClassMembers class line 73");
}
}
ret.Add(o);
}
return ret.ToArray();
}
不断。您可以使用这样的反射来创建与您的类匹配的表，自动创建插入或过程调用，从不使用不正确的数据类型或再次使字段无序。