private void InsertRawDataFile(RawDataFile obj)
{
System.Nullable <int> p1 = obj.FileId;
System.Nullable <System.DateTime> p2 = obj.UploadDate;
string p3 = obj.UploaderLogin;
this.RawDataFile_Insert(obj.FileName, obj.FolderName, obj.Contents, ref p1, ref p2, ref p3);
obj.FileId = p1.GetValueOrDefault();
obj.UploadDate = p2.GetValueOrDefault();
obj.UploaderLogin = p3;
}
public static bool IsEmpty(System.Nullable <decimal> value)
{
if (value.HasValue)
{
System.Nullable <decimal> nullable = value;
if (nullable.GetValueOrDefault() == (0M))
{
return(nullable.HasValue);
}
return(false);
}
return(true);
}
public ResumenEmpleados GetResumenEmpleados(String oficio)
{
List <EMP> empleados = this.GetEmpleadosOficio(oficio);
int personas = empleados.Count;
int? maximo = empleados.Max(x => x.SALARIO);
System.Nullable <int> suma = empleados.Sum(z => z.SALARIO);
double? media = empleados.Average(z => z.SALARIO);
ResumenEmpleados resumen = new ResumenEmpleados();
resumen.Personas = personas;
resumen.SumaSalarial = suma.GetValueOrDefault();
resumen.MaximoSalario = maximo.GetValueOrDefault();
resumen.MediaSalarial = media.GetValueOrDefault();
return(resumen);
}
static void Main(string[] args)
{
var numbers = new GenericList <int>();
numbers.Add(10);
//int a = numbers[0];
var dictionary = new GenericDictionary <string, int>();
var num = new Nullable <int>(5);
Console.WriteLine("has Value ? " + num.HasValue);
Console.WriteLine("Value: " + num.GetValueOrDefault());
var num1 = new System.Nullable <int>(5);
Console.WriteLine("has Value ? " + num1.HasValue);
Console.WriteLine("Value: " + num1.GetValueOrDefault());
}
static void Main(string[] args)
{
// 隱式轉換，小的轉大的，可以自動轉換
int i = 10;
long l = i;
C1 c1 = new C2(); // 隱式轉換，向上轉型
// 顯式轉換，大的轉小的，必須強制轉換
double d = 10.05;
int iFormD = (int)d;
Console.WriteLine(iFormD); // 輸出 10，資料會有缺失的風險，以及例外錯誤
C1 c11 = new C1();
try
{
C2 c2 = (C2)c11; // 顯式轉換，向下轉換，執行可能會出現例外錯誤
}
catch (Exception e)
{
Console.WriteLine(e.Message);
// throw e;
}
// 透過 is 判斷型別
Console.WriteLine(c11 is C1); // 輸出 True
Console.WriteLine(c11 is C2); // 輸出 False
// 利用 as，安全的方式進行轉換
C2 c22 = c11 as C2; // 可運行不會出錯，c11在轉換的過程中發現不能轉為 C2 型別，會丟回一個 null 值
Console.WriteLine(c22 == null); // 輸出 True
// int iAS = 5 as int; // as 只能用於參考型別，因為實值型別，不能給予 null 值。
string sFromi = i.ToString(); // ToString() 轉換成字串
int iFromS = Convert.ToInt32("100"); // Convert 轉換型別
//int iFromS2 = Convert.ToInt32("CSharp"); // 錯誤：輸入字串格式不正確。
int iFromS3 = Int32.Parse("101"); // Parse 轉換型別
//int iFromS4 = Int32.Parse("CSharp"); // 錯誤：輸入字串格式不正確。
int iFromS5;
bool succeed = Int32.TryParse("102", out iFromS5); // TryParse 試著去轉換
Console.WriteLine(succeed + " : " + iFromS5); // 輸出 True : 102，轉換成功
bool succeed2 = Int32.TryParse("CSharp", out iFromS5);
Console.WriteLine(succeed2 + " : " + iFromS5); // 輸出 False : 0，轉換失敗，輸出整數的空值 0
// 實作自己的轉換，透過 IConvertible, TypeConverter
int iToBoxing = 100;
object iBoxed = iToBoxing; // boxing 隱式轉換，因為所有的型別都是繼承 System.object，向上轉換
int iUnBoxing = (int)iBoxed; // unBoxing 顯式轉換，由父類別轉為子類別，向下轉型
object nullObject = null;
// int iNull = (int)nullObject; // 錯誤：NullReferenceException。
int?iNullable = null; // 宣告一個可為 null 值的 int
System.Nullable <int> iNullable2 = 100; // 等同於 int?
Console.WriteLine(iNullable2.Value); // 輸出 100
// Console.WriteLine(iNullable.Value); // 錯誤：可為 Null 的物件必須具有值
Console.WriteLine(iNullable.HasValue); // 輸出：false，可以預先判斷
Console.WriteLine(iNullable.GetValueOrDefault()); // 輸出：0，若為空值，給予預設的 null 值
Console.WriteLine(iNullable2.GetValueOrDefault()); // 輸出：100
int i2 = iNullable ?? 500; // 若 ?? 前的變數值為 null，那就給予 ?? 後面的值
Console.WriteLine(i2); // 輸出：500
int i3 = iNullable2 ?? 500; // 若 ?? 前的變數值為 null，那就給予 ?? 後面的值
Console.WriteLine(i3); // 輸出 100
}
static void Main(string[] args)
{
//隐式转换
int i = 10;
long l = i;
C1 c1 = new C2();
//显示转换
double d = 10.05;
int iFromD = (int)d;
Console.WriteLine(iFromD);
C1 c11 = new C1();
//C2 c2 = (C2)c11;
try
{
C2 c2 = (C2)c11;
}
catch (Exception e)
{
Console.WriteLine(e.Message);
}
Console.WriteLine(c11 is C1); //true
Console.WriteLine(c11 is C2); //false
C2 c22 = c11 as C2; //编译成功,运行成功,无法转换时,返回null.
Console.WriteLine(c22 == null); //true,降低消耗,只能用于非null类型或引用类型,比如值类型,就不是非null类型
//int iAs = "s" as int;
//错误 1 as 运算符必须用于引用类型或可以为 null 的类型(“int”是不可以为 null 值的类型) E:\极客学院2\ASP.NET工程师\1.初级ASP.NET工程师\2.C#语言基础\4.C#的类型转换\Lession5TypeConvertion\Lession5TypeConvertion\Program.cs 38 23 Lession5TypeConvertion
Console.WriteLine("------------------------");
string sFrom1 = i.ToString();
int iFroms = Convert.ToInt32("10");
//int iFroms2 = Convert.ToInt32("zilong");//System.FormatException
int iFrom3 = Int32.Parse("101");
//int iFrom4 = Int32.Parse("zilong");//System.FormatException
int iFrom5;
bool succeed = Int32.TryParse("zilong", out iFrom5);
Console.WriteLine(iFrom5);//0
//IConvertible,TypeConverter
Console.WriteLine("------------------------");
int iToBoxing = 100;
object iBoxed = iToBoxing;
int iUnBoxing = (int)iBoxed;
object nullOjbect = iFrom5;
int iNUll = (int)nullOjbect;
int?iNUllable = null; // = null;
System.Nullable <int> iNUllable2 = 100; //和上一句等价
//Console.WriteLine(iNUllable.Value);
Console.WriteLine(iNUllable.HasValue);
Console.WriteLine(iNUllable.GetValueOrDefault());
Console.WriteLine(iNUllable2.GetValueOrDefault());
int iii = iNUllable ?? 999;
int iiii = iNUllable2 ?? 999;
Console.WriteLine(iii);
Console.WriteLine(iiii);
Console.ReadLine();
}