C# Advanced

##Reflection use case: factory pattern

Use for some common classes have the same pattern, to do operate for each class.

The code (shape factory) doesn’t require a change even if we add new classes (Triangle, Trapezoidal) that derive shape.

public interface Shape {     void Draw(); } public class Square : Shape {     public void Draw()     {         Console.WriteLine(" _ \n|_|");     } } public class Circle : Shape {     public void Draw()     {         Console.WriteLine("O");     } } public static class ShapeFactory {     public static Shape GetShape(string shapeName)     {         Assembly currentAssembly = Assembly.GetExecutingAssembly();         var currentType = currentAssembly.GetTypes().SingleOrDefault(t => t.Name == shapeName);         return (Shape)Activator.CreateInstance(currentType);     } }

Use for the properties in a class. The code doesn’t require a change even if we add new properties in the class.

public class Person     {         private int age = -1;         private string name = String.Empty;         public void Load()         {             if (File.Exists("settings.dat"))             {                 Type type = this.GetType();                 string propertyName, value;                 string[] temp;                 char[] splitChars = new char[] { '|' };                 PropertyInfo propertyInfo;                 string[] settings = File.ReadAllLines("settings.dat");                 foreach (string s in settings)                 {                     temp = s.Split(splitChars);                     if (temp.Length == 2)                     {                         propertyName = temp[0];                         value = temp[1];                         propertyInfo = type.GetProperty(propertyName);                         if (propertyInfo != null)                             this.SetProperty(propertyInfo, value);                     }                 }             }         }         public void Save()         {             Type type = this.GetType();             PropertyInfo[] properties = type.GetProperties();             TextWriter tw = new StreamWriter("settings.dat");             foreach (PropertyInfo propertyInfo in properties)             {                 tw.WriteLine(propertyInfo.Name + "|" + propertyInfo.GetValue(this, null));             }             tw.Close();         }         public void SetProperty(PropertyInfo propertyInfo, object value)         {             switch (propertyInfo.PropertyType.Name)             {                 case "Int32":                     propertyInfo.SetValue(this, Convert.ToInt32(value), null);                     break;                 case "String":                     propertyInfo.SetValue(this, value.ToString(), null);                     break;             }         }         public int Age         {             get { return age; }             set { age = value; }         }         public string Name         {             get { return name; }             set { name = value; }         }     }

##Safely Cast by Using as and is Operators

Simple cast may cause InvalidCastException. That is why C# provides the is and as operators. You can use these operators to test whether a cast will succeed without causing an exception to be thrown.

void UseIsOperator(Animal a)     {         if (a is Mammal)         {             Mammal m = (Mammal)a;             m.Eat();         }     }     void UseAsOperator(object o)     {         Mammal m = o as Mammal;    // if cast not failed, return null pointer         if (m != null)         {             Console.WriteLine(m.ToString());         }         else         {             Console.WriteLine("{0} is not a Mammal", o.GetType().Name);         }     }     void UseAsWithNullable(System.ValueType val)     {         int? j = val as int?;  //int? is shorthand for Nullable<int>.         if (j != null)         {             Console.WriteLine(j);         }         else         {             Console.WriteLine("Could not convert " + val.ToString());         }     }

##Params

C#	Java
public static int add (params int[] array) {        int sum = 0;        foreach (int i in array)            sum += i;        return sum;     }	public void aMethod(String... args) {     for(String s : args) {         System.out.println(s);     } }

##Delegate

A delegate acts like a pointer to a function.

// declare the DelegateCalculation delegate class public delegate double DelegateCalculation( double acceleration, double time ); public class MotionCalculations { // FinalSpeed() calculates the final speed public static double FinalSpeed(double acceleration, double time) { double finalSpeed = acceleration * time; return finalSpeed; } // Distance() calculates the distance traveled public static double Distance(double acceleration, double time) { double distance = acceleration * Math.Pow(time, 2) / 2; return distance; } }

DelegateCalculation myDelegateCalculation = new DelegateCalculation(MotionCalculations.FinalSpeed); // You can then call the FinalSpeed() method through myDelegateCalculation. For example: double acceleration = 10; // meters per second per second double time = 5; // seconds double finalSpeed = myDelegateCalculation(acceleration, time); myDelegateCalculation = new DelegateCalculation(MotionCalculations.Distance); // You can then call the Distance() method using myDelegateCalculation. For example: double distance = myDelegateCalculation(acceleration, time);