Errata

I don't understand this example. It implements a finalizer, but the finalizer calls Dispose(false) which does nothing if the parameter is false. Why implementing a finalizer if it does nothing ? Why implementing a separate Dispose() method with a parameter instead of simply doing its work in Dispose() ? Maybe this example is trying to show a more general pattern, but as it is presented, I fail to see the point. Minor remark: the class is called 'UnmangedWrapper' when I suppose it's meant to be called 'UnmanagedWrapper'

Note from the Author or Editor:
Change the Implementing IDisposable and a finalizer section to:

Implementing IDisposable and a finalizer
Creating your own custom type that implements IDisposable and a finalizer correctly is not a trivial task.
As an example, suppose you have a wrapper class around a file resource and an unmanaged buffer. You implement IDisposable so users of your class can immediately cleanup if they want. You also implement a finalizer in case they forget to call Dispose. Listing 2-84 shows how to do this.
LISTING 2-84 Implementing IDisposable and a finalizer.
using System;
using System.IO;
using System.Runtime.InteropServices;

class UnmanagedWrapper : IDisposable
{
private IntPtr unmanagedBuffer;
public FileStream Stream { get; private set; }

public UnmanagedWrapper()
{
CreateBuffer();
this.Stream = File.Open("temp.dat", FileMode.Create);
}

private void CreateBuffer()
{
byte[] data = new byte[1024];
new Random().NextBytes(data);
unmanagedBuffer = Marshal.AllocHGlobal(data.Length);
Marshal.Copy(data, 0, unmanagedBuffer, data.Length);
}

~UnmanagedWrapper()
{
Dispose(false);
}

public void Close()
{
Dispose();
}

public void Dispose()
{
Dispose(true);
System.GC.SuppressFinalize(this);
}

protected virtual void Dispose(bool disposing)
{
Marshal.FreeHGlobal(unmanagedBuffer);
if (disposing)
{
if (Stream != null)
{
Stream.Close();
}
}
}
}
There are a couple of things to notice about this implementation:
? The finalizer only calls Dispose passing false for disposing.
? The extra dispose method with the Boolean argument does the real work. This method checks if it?s being called in an explicit dispose or if it?s being called from the finalizer:
o If the finalizer called Dispose, you only release the unmanaged buffer. The Stream object also implements a finalizer and the garbage collector will take care of calling the finalizer of the FileStream instance. Because the order in which the garbage collector calls the finalizers is unpredictable you can?t call any methods on the FileStream.
o If Dispose is called explicitly, you also close the underlying FIleStream. It?s important to be defensive in coding this method and always check for any source of possible exceptions It could be that Dispose is called multiple times and that shouldn?t cause any errors.
? The regular Dispose method calls GC.SuppressFinalize(this) to make sure that the object is removed from the finalization list that the garbage collector is keeping track of. The instance has already cleaned up after itself; so it?s not necessary that the garbage collector calls the finalizer.

EXAM TIP
It?s important to know the difference between implementing IDisposable and a finalizer. Both cleanup your object but a finalizer is called by the Garbage Collector while the Dispose method can be called from code.
MORE INFO Implementing IDisposable and a finalizer
For more information on how to implement IDisposable and a finalizer see: http://msdn.microsoft.com/en-us/library/b1yfkh5e.aspx.

"Because the entry method of an application can't be marked as async, the example uses the Wait method in Main. This class uses both the async and await keywords in the DownloadContent method"

I don't find any Wait method in Main, and I don't know which class you are referring to. (The one using the async and await keywords)

Note from the Author or Editor:
Change the first line after Listing 1-18 from:

Because the entry method of an application can't be marked as async, the example uses the Wait method in Main.

to:

Because the entry method of an application can't be marked as async, the example accesses the Result property in the Main method which blocks the code until the async method DownloadContent is finished.

Regarding delegate in the description for a constraint on a class:
"The type argument must be a reference type: for example, a class, interface,
delegate, or array."

Example:
class Class1<T>
where T : Delegate
//Error: Constraint cannot be special class 'System.Delegate'

"C# Language Specification":

primary-constraint:class-typeclassstruct

A class-type constraint must satisfy the following rules:
The type must be a class type.
The type must not be sealed.
The type must not be one of the following types: System.Array, System.Delegate, System.Enum, or System.ValueType.

http://stackoverflow.com/questions/191940/c-sharp-generics-wont-allow-delegate-type-constraints

Note from the Author or Editor:
In Table 2-2 change the description of where T : class to:

The type argument must be a class type that's not sealed and not one of the following types: System.Array, System.Delegate, System.Enum, or System.ValueType.

"The field is a nonstatic instance field."
Is term "instance" correct here? Because the question was not about an instance: "You want to read the value of a private field on a _class_ "?

Note from the Author or Editor:
On page 149, Objective review question 1 change:

You want to read the value of a private field on a class. Which BindingFlags do you need? (Choose all that apply.)

To:

You want to read the value of a private field on a object. Which BindingFlags do you need? (Choose all that apply.)

After generating a file with a certificate:
"You first need to install this certificate on your computer to be able to use it."

It was confusing due to following lines does not tell how to use the file testCert.cerf. Does installation of a certificate somehow relates to this generated file?

Note from the Author or Editor:
Change the last paragraph on page 202 from:

This command generates a file called testCert.cer that you can use as a certificate. You first need to install this certificate on your computer to be able to use it. After installation, it?s stored in a certificate store. The following line creates a certificate and installs it in a custom certificate store named testCertStore:

to:

This command generates a file called testCert.cer that you can use as a certificate.
You can install this certificate by using CertMgr. However, it's easier to create and install the certificate in one go. The following line creates a certificate and installs it in a custom certificate store named testCertStore:

operator
byte[] signature = Sign(textToSign, ?cn=WouterDeKort?);
method
static byte[] Sign(string text, string certSubject)

The parameter certSubject is not used. It can be found following way:

var certCollection = x509Store.Certificates
.Find(X509FindType.FindBySubjectName, subjectName, false)
.Find(X509FindType.FindByTimeValid, DateTime.Now, false);
return certCollection.Count > 0? certCollection[0]: null;

Where subjectName is case insensitive, should not contain "cn=".
E.g. if subjectName="testcert" it finds:
"CN=TestCert"
"CN=TestCert123"
"CN=MyTestCert"

Note from the Author or Editor:
Change the line:
byte[] signature = Sign(textToSign, "cn=WouterDeKort");

to

byte[] signature = Sign(textToSign);

And
private static byte[] Sign(string text, string certSubject)
to
private static byte[] Sign(string text)

The answer to question 3 of the Objective 3.1 Review is missing. Page 247 ends with the answer to question 2, and page 248 begins with the Objective 3.2 Thought experiment.

Note from the Author or Editor:
The answer for Objective 3.1, question 1 is missing. The answer should be:

1. Correct answer: B
A. Incorrect: The regular Parse method will throw an exception if the value the user entered is not a DateTime. This is something you need to expect when you parse user input. Using TryParse avoids the exception.
B. Correct: TryParse should be used when working with user input.
C. Incorrect: Convert.ToDateTime calls Parse internally. This will throw an exception when the user input is not in the correct format.
D. Incorrect: RegEx.Match will search the input string for the first match to the specified regular expression. It won't convert the input string to a DateTime.

In the errata the "Note from the Author or Editor" to the error report submited by Daniel D Aug 12 2013 is not correct. Daniels comment about the answers to question 3 is still valid. There is no answer to the question about validating an xml file.which is question 3.

Note from the Author or Editor:
The answer to question 3 in objective 3.1 is missing. Add the following answer on page 247

3 Correct answer: D
A. Incorrect: The JavaScript serializer is used to serialize and deserialize objects from and to JSON. It's used in AJAX applications.
B. Incorrect: Although RegEx is suited for validating strings, validating a complete XML document with a RegEx is undoable.
C. Incorrect: StringBuilder is used to construct a string at runtime without constructing a new string in memory each time you make change.
D. Correct: An XSD is used to validate the schema of an XML file.

The original question includes the directive to "Choose all that apply". Deploying to the GAC requires the assembly to have a strong name. As such, it seems to me the correct answer to this question should include "D. Strongly name the assembly" in addition to "B. Deploy the assembly to the GAC".

Note from the Author or Editor:
Mark answer D for question 2 of objective 3.3 on page 249 as correct. Change the answer to:

Correct. Strongly naming an assembly is required to deploy an assembly to the GAC where it can be shared by all applications.

You have a list of dates. You want to filter the dates to the current year and then select the highest date. Which query do you use?
A.
DateTime result = dates.Where(d => d == DateTime.Now).OrderBy(d => d).First();
B.
DateTime result = dates.Where(d => d.Year == DateTime.Now.Year).OrderByDescending(d => d).FirstOrDefault();
C.
DateTime result = dates.Where(d => d.Year == DateTime.Now.Year).OrderByDescending(d => d).First();
D.
DateTime result = dates.Where(d => d.Year == DateTime.Now.Year).OrderByDescending(d => d).Single();

-----------------------------------------------------------------------------------

By Book: B,D

A. Incorrect: Comparing DateTime.Now to the dates will give you only the dates for
today, not for the whole year. Also, using OrderBy instead of OrderByDescending
will give you the lowest date, not the highest.
B. Correct: This will return the highest date for the current year. If your filter can?t
find a value for the current year, it will return ?1-1-0001 00:00:00? (DateTime.Min-
Value).
C. Incorrect: If your filter doesn?t return a value, you will get an error. You should use
FirstOrDefault instead.
D. Correct: Using Single will throw an exception if there are multiple dates for the
current year.

-----------------------------------------------------------------------------------

I guess, that right answer is only C. (B and D are incorrect)

C is correct because:
It returns only item with current year, but it don't return default value, which it haven't been required

B is incorrect becase:
It returns default value if don't exist any result.
(But in question don't want default value, they want only current year)


And answer D is incorrect too, becase:
If expression method Where returns more results, so Single expression throw error, so we don't get any result.

Note from the Author or Editor:
On page 331, question 1 only has one good answer: B

Change option D to start with Incorrect

Objective 4.5: Objective Review Nr 2, point B states that B is correct. I don't understand why this is correct, because a Queue does not have an Add method.

Note from the Author or Editor:
On page 333 question 2 for Objective 4.5, the answer B should be removed both from the first line and the Correct should be changed to incorrect. Only answer D is correct.

I guess that this is a follow up comment to the confirmed errata reported by Rudi Janse van Rensburg Aug 28, 2013
Objective 4.5: objective review No 1 states that D is correct but I don't understand why this is correct, how can a user easily select an order by its order number in a queue?

Note from the Author or Editor:
On page 333 Objective 4.5 Objective review, the first answer should only have B marked as correct. D should be incorrect.