WeakReference 弱引用

弱引用是使用WeakReference类创建的.因为对象可能在任意时刻被回收,所以在引用该对象前必须确认它存在.

 class MainEntryPoint
 {
 static void Main()
 {
 // Instantiate a weak reference to MathTest object
 WeakReference mathReference = new WeakReference(new MathTest());
 MathTest math;
 if(mathReference.IsAlive)
 {
 math = mathReference.Target as MathTest;
 math.Value = ;
 Console.WriteLine(
 "Value field of math variable contains " + math.Value);
 Console.WriteLine("Square of 30 is " + math.GetSquare());

 }
 else
 {
 Console.WriteLine("Reference is not available.");
 }

 GC.Collect();

 if(mathReference.IsAlive)
 {
 math = mathReference.Target as MathTest;
 }
 else
 {
 Console.WriteLine("Reference is not available.");
 }
 }
 }

 // Define a class named MathTest on which we will call a method
 class MathTest
 {
 public int Value;

 public int GetSquare()
 {
 return Value*Value;
 }

 public static int GetSquareOf(int x)
 {
 return x*x;
 }

 public static double GetPi()
 {
 return 3.14159;
 }
 }