Save a copy of a object before being dispose

David Smith

1. How to save a copy of object before being dispose. Basically if a user is creating a multiple Color objects. I want to save a copy of previous Car object if that makes sense. This way I can maintain all data if user decides to go crazy on creating multiple objects.

2. How to determine in software when a object is being dispose.

3 Replies

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Vulpes13y ago
Accepted answer
Sure, this program illustrates all 3 approaches:

using System;
using System.IO;
using System.Xml.Serialization;

public class A
{
public int I {get; set;}
public double D {get; set;}

public A()
{
}

public A(int i, double d)
{
I = i;
D = d;
}

public A Clone()
{
return (A)MemberwiseClone();
}
}

public class B
{
public A A {get; set;}

public long L {get; set;}

public B()
{
}

public B(A a, long l)
{
A = a;
L = l;
}
}

public class C
{
public A A {get; set;}
public B B {get; set;}

public C()
{
// need a parameterless constructor for XML serialization
}

public C(A a, B b)
{
A = a;
B = b;
}
}

class Test
{
static void Main()
{
// using MemberwiseClone
A a = new A(5, 10.0);
Console.WriteLine("a.I = {0}, a.D = {1}", a.I, a.D);
A aa = a.Clone();
Console.WriteLine("aa.I = {0}, aa.D = {1}", aa.I, aa.D);
Console.WriteLine();

// by hand
B b = new B(a, 20);
Console.WriteLine("b.A.I = {0}, b.L = {1}", b.A.I, b.L);
B bb = new B(b.A.Clone(), b.L);
Console.WriteLine("bb.A.I = {0}, bb.L = {1}", bb.A.I, bb.L);
Console.WriteLine();

// using XML serialization
C c = new C(a, b);
Console.WriteLine("c.A.I = {0}, c.B.A.D = {1}", c.A.I, c.B.A.D);
XmlSerializer xs = new XmlSerializer(typeof(C));
MemoryStream ms = new MemoryStream();
xs.Serialize(ms, c);
ms.Position = 0;
C cc = (C)xs.Deserialize(ms);
Console.WriteLine("cc.A.I = {0}, cc.B.A.D = {1}", cc.A.I, cc.B.A.D);

Console.ReadKey();
}
}

The output should be:

a.I = 5, a.D = 10
aa.I = 5, aa.D = 10

b.A.I = 5, b.L = 20
bb.A.I = 5, bb.L = 20

c.A.I = 5, c.B.A.D = 10
cc.A.I = 5, cc.B.A.D = 10
David Smith13y ago
Yea that's a little to complicated. I rewrote the application. so I wont have to clone. Can you send me examples of cloning
Vulpes13y ago
1. Basically, you need to write a Clone method to produce an object whose field values are the same as the one to be disposed of and call it before you call Dispose().

Unfortunately, writing Clone methods is not always straightforward. In some simple cases (all fields are value types) you can just call the protected MemberwiseClone method which all classes inherit from System.Object.

In other cases, you could serialize the object to a memory stream and then deserialize it back to a new object.

However, in complex cases, you might have to resort to cloning each field 'by hand'.

2. There's no built in way to detect this. However, you could define a custom event in the disposable class to which outside methods could subscribe and provide their own handlers. When Dispose is called it could then notify all subscribers that the object is being disposed of.

However, the trouble with this approach is that it may then be too late to clone the object which could be left in an unstable state after Dispose has been called.