Tag: C#

Quy luật của dãy số Fibonacci: số tiếp theo bằng tổng của 2 số trước, 2 số đầu tiên của dãy số là 0, 1. Ví dụ: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, …

Sử dụng yield trong C# để trả về dãy số Fibonacci

static void Main()
{
 foreach(var value in Fibonacci())
 {
 Console.Write(value + " ");
 if(value > 1000) 
 {
 break;
 }
 }
}

static IEnumerable<int>  Fibonacci()
{
 int current = 0;
 int next = 1;
 while(true)
 {
 yield return current;
 int oldCurrent = current;
 current = next;
 next = next + oldCurrent;
 } 
}

Kết quả:

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 1597

This article will help you to learn how we can convert an image into a base64 string and base64 string back to image.

public string ImageToBase64(Image image, System.Drawing.Imaging.ImageFormat format)
{
  using (MemoryStream ms = new MemoryStream())
  {
    // Convert Image to byte[]
    image.Save(ms, format);
    byte[] imageBytes = ms.ToArray();

    // Convert byte[] to Base64 String
    string base64String = Convert.ToBase64String(imageBytes);
    return base64String;
  }
}

public Image Base64ToImage(string base64String)
{
  // Convert Base64 String to byte[]
  byte[] imageBytes = Convert.FromBase64String(base64String);
  MemoryStream ms = new MemoryStream(imageBytes, 0, imageBytes.Length);

  // Convert byte[] to Image
  ms.Write(imageBytes, 0, imageBytes.Length);
  Image image = Image.FromStream(ms, true);
  return image;
}

How to create own dynamic type or dynamic object in C#
How to create own dynamic type or dynamic object in C#

using System.Reflection;
using System.Reflection.Emit;
public static class MyTypeBuilder
{

public static System.Collections.IList CreateInstanceIList(Type _type)
{
Type customList = typeof(List<>).MakeGenericType(_type);
var result = (System.Collections.IList)Activator.CreateInstance(customList);
return result;
}
public static Type CompileResultType(Dictionary listOfFields)
{
TypeBuilder tb = GetTypeBuilder();
foreach (var field in listOfFields)
CreateProperty(tb, field.Key, field.Value);

Type objectType = tb.CreateType();

return objectType;
}

private static TypeBuilder GetTypeBuilder()
{
var typeSignature = “MyDynamicType_” + DateTime.Now.ToString(“yyyyMMddHHmmss”);
var an = new AssemblyName(typeSignature);
AssemblyBuilder assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(an, AssemblyBuilderAccess.Run);
ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule(“MainModule”);
TypeBuilder tb = moduleBuilder.DefineType(typeSignature,
TypeAttributes.Public |
TypeAttributes.Class |
TypeAttributes.AutoClass |
TypeAttributes.AnsiClass |
TypeAttributes.BeforeFieldInit |
TypeAttributes.AutoLayout,
null);
return tb;
}

private static void CreateProperty(TypeBuilder tb, string propertyName, Type propertyType)
{
FieldBuilder fieldBuilder = tb.DefineField(“_” + propertyName, propertyType, FieldAttributes.Private);

PropertyBuilder propertyBuilder = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);
MethodBuilder getPropMthdBldr = tb.DefineMethod(“get_” + propertyName, MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, propertyType, Type.EmptyTypes);
ILGenerator getIl = getPropMthdBldr.GetILGenerator();

getIl.Emit(OpCodes.Ldarg_0);
getIl.Emit(OpCodes.Ldfld, fieldBuilder);
getIl.Emit(OpCodes.Ret);

MethodBuilder setPropMthdBldr =
tb.DefineMethod(“set_” + propertyName,
MethodAttributes.Public |
MethodAttributes.SpecialName |
MethodAttributes.HideBySig,
null, new[] { propertyType });

ILGenerator setIl = setPropMthdBldr.GetILGenerator();
Label modifyProperty = setIl.DefineLabel();
Label exitSet = setIl.DefineLabel();

setIl.MarkLabel(modifyProperty);
setIl.Emit(OpCodes.Ldarg_0);
setIl.Emit(OpCodes.Ldarg_1);
setIl.Emit(OpCodes.Stfld, fieldBuilder);

setIl.Emit(OpCodes.Nop);
setIl.MarkLabel(exitSet);
setIl.Emit(OpCodes.Ret);

propertyBuilder.SetGetMethod(getPropMthdBldr);
propertyBuilder.SetSetMethod(setPropMthdBldr);
}
}
How to use

public JsonResult DynamicObject()
{

Dictionary listOfFields = new Dictionary();

listOfFields.Add(“Name”, typeof(string));
listOfFields.Add(“Age”, typeof(int));
var myType = MyTypeBuilder.CompileResultType(listOfFields);
var myObject = Activator.CreateInstance(myType);

myType.GetProperty(“Name”).SetValue(myObject, “Tuan”, null);
myType.GetProperty(“Age”).SetValue(myObject, 20, null);

object name = myType.GetProperty(“Name”).GetValue(myObject);

return Json(name.ToString(), JsonRequestBehavior.AllowGet);
// return Json(myObject, JsonRequestBehavior.AllowGet);
}
Mapping data to List

public JsonResult DynamicObject2()
{
Dictionary listOfFields = new Dictionary();
listOfFields.Add(“Name”, typeof(string));
listOfFields.Add(“Age”, typeof(int));

var myType = MyTypeBuilder.CompileResultType(listOfFields);
var list = MyTypeBuilder.CreateInstanceIList(myType);
var listString = listOfFields.Select(x => x.Key).ToArray();

Type t = typeof(YourObject); // your class define
PropertyInfo[] props = t.GetProperties().Where(x => listString.Contains(x.Name)).ToArray();

var data = ListYourObjects(); // your list data

// mapping only you need
foreach (var item in data)
{
var myObject = Activator.CreateInstance(myType);
foreach (var prop in props)
{
object name = t.GetProperty(prop.Name).GetValue(item);
myType.GetProperty(prop.Name).SetValue(myObject, name, null);

}
list.Add(myObject);
}

return Json(list, JsonRequestBehavior.AllowGet);
}