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 = 30;
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;
}
}