1. Code Snippets, Intellisense, Comments, Type Conversion
Additional C# Information
Code Snippets, Intellisense, Comments, Type Conversion
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

2. Topics Regions Using Code Snippets Comments and Intellisense
Data Type Conversion
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

3. Code Outlining
Another feature that aids developers in navigating large code files is code outlining
Regions of code may be designated
Each region may be collapsed into a single line in the code editor
Collapsed regions may be expanded to reveal their detail whenever it is needed
Some regions are “automatically” designated for you including
Method definitions
XML comment blocks
Classes
Namespaces
and more
Odds and Ends
November 16, 2018

4. Code Outlining Region designators Region designators Odds and Ends
November 16, 2018

5. Code Outlining
Clicking on one of the minus signs will collapse the associated region and replace the minus with a plus (for later expansion)
Note that the namespace and class may also be collapsed
Each collapsed region becomes a single line
Odds and Ends
November 16, 2018

6. Designating Other Regions
Developers may use #region and #endregion preprocessor directives to mark beginning and end of a region not already designated by Visual Studio
For example, in a large class, there may be several overloaded constructor methods (the String class has about 8 overloaded constructor methods)
One may use the #region … #endregion directives to designate all of them as one large region
One can then collapse or expand all constructors at once
Odds and Ends
November 16, 2018

7. #region … #endregion The syntax of these preprocessor commands is
#region Title Phrase
. . .
#endregion
The #region and #endregion commands must be paired
Regions may be nested but not overlapping
The Title Phrase will be displayed when the region is collapsed
One is not limited to using regions that correspond to large blocks of code such as methods or classes
One may use these commands anywhere within reason – including turning a logical segment of a method into its own region
One may use the Surrounds With … capability discussed earlier to embed a selected existing segment of code with #region … #endregion
Odds and Ends
November 16, 2018

8. Can be collapsed to this small segment
Example
Three new regions added, each of which has two or three regions already collapsed inside it
Can be collapsed to this small segment
Odds and Ends
November 16, 2018

9. Surround with … and Snippets
Visual Studio tools to help get the construct correct and do it more easily
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

10. Surround With …
If one has existing code and discovers that some of it should be in a loop, an if-else statement, a try block, or some similar construct, VS can help convert to the desired state
Select the code to embed, and right-click on it
From the resulting menu, choose Surround With…
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

11. Surround With …, continued
From the dropdown list, choose the desired structure
Collapsed region
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

12. Code Snippets Using code snippets saves both time and keystrokes
Code snippets are
customizable segments of code
easily inserted when needed
They relieve the programmer from typing the skeleton code in common situations such as for and while loops, try-catch-finally, foreach, class, enum, and so forth
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

13. If you cannot remember …
If the exact format for the construct you need eludes you at the moment you need it, use VS’s Insert Snippet tool
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

14. Snippet A snippet is a tailorable set of code for a common task
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

15. Using Snippets
The names of common code snippets are closely related to the keywords involved
If one types the name of a snippet at the beginning of a line and then presses the tab key twice, the snippet is inserted as shown on the next slide
Names of some snippets
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

16. Using Snippets Continued
If one types a snippet name such as for …
Note: Intellisense helps
… after pressing TAB twice, this code is inserted
The variables are highlighted and selected for easy modification if desired
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

17. Overriding an Inherited Method
To override an inherited method, one may type override and press space key to get a list of all methods one may override from the current base class
These are from System.Object, but the list depends on where the current class is in an inheritance hierarchy
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

18. Email selected snippet
More on Snippets
One may also save a piece of code as a snippet, for later, repeated use
Use the Snippet Manager from the Tools menu
Can also drag/drop code to Toolbox for later use
One may also easily a selected snippet to a colleague or team member
selected snippet
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

19. Similar to Using Snippets …
Intellisense is a great help when typing
If one types the first few characters of a keyword or identifier name, Intellisense shows a list of all such words beginning with those characters and you can select the one you want (highlight it and press TAB)
In VS, Intellisense uses regular expressions to find what you want using a “contains” approach
Typing “mem” gives all choices containing mem such as OutOfMemoryException and MissingMemberException
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

20. Using Pascal Casing with Intellisense
In addition to the “contains” approach Intellisense uses, it also takes advantage of the Pascal Casing C# uses in names
Only type the UPPER CASE characters from the name
To insert the class name OutOfMemoryException in code, one only needs to type OOM and press TAB, for example
Type OOM to get this Intellisense
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

21. Comments in C# Documentation and Intellisense
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

22. Ordinary Comments in C#
Ordinary comments in C# have the same formats as in Java
A single or partial line comment begins with //
A multiline block of comments may consist of
Several lines of single line comments
Comments that begin with /* … and end at some later point with … */
Used for same purposes as in other languages
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

23. Examples: Ordinary Comments in C#
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

24. XML Comments XML comments are used in C# for two primary purposes
Build documentation in a standard way that can be extracted to an XML file that may be formatted into a user’s manual or programmer’s guide, somewhat similar to Javadoc
Generate documentation to be used by Intellisense within any program that uses the class
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

25. XML Comments XML comments have a common format
Begin with three forward slashes: ///
Use specific XML tags such as
<summary></summary>
<param name=“parameter_name"></param>
<returns></returns>
Designate specific items used by Intellisense
VS can auto-generate a skeleton of XML comments for you
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

26. Example
Type /// here
Decisions, Repetition, Code Snippets, Comments, and Intellisense
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27. This skeleton of XML comments is generated instantly
Example, continued
This skeleton of XML comments is generated instantly
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

28. Fill in details as shown
Example, cont.
Fill in details as shown
Decisions, Repetition, Code Snippets, Comments, and Intellisense
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29. Example, cont.
Hover the cursor over the name of the constructor when it is used in code to see Intellisense
Note the second line is exactly the <summary> provided in the XML comment
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

30. From the XML <param> comment we wrote
Example, cont.
When writing code that uses this constructor, Intellisense updates as we type to show what is next, using the XML comments we wrote
Where we are in typing
From the XML <param> comment we wrote
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

31. Can Generate User’s Manual
CodeRush
Documentor Plugin
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

32. Two places after the decimal in this output
Another Example
Another tag
Two places after the decimal in this output
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

33. XML Documentation Tags
See Visual Studio “Help” for information on each tag
Decisions, Repetition, Code Snippets, Comments, and Intellisense
November 16, 2018

34. Type conversion Casting and conversion methods Odds and Ends
November 16, 2018

35. Data Types and Conversions
Two items may be of compatible or incompatible types
An integer is compatible with a double because both are numeric and an integer can be converted into a double without loss of data
“Matt” is a string that cannot be converted into a double in any intuitive way; the two types are not compatible
Odds and Ends
November 16, 2018

36. Implicit/Explicit Conversions
For compatible types, there may or may not be implicit conversions from one type to another
Depends on whether the compiler knows how to make the conversion
Depends on whether there is a potential for loss of data
Example, the following produces an implicit conversion from the integer on the right-hand-side to the double on the left. No data loss is possible
If there is a possibility of data loss, an explicit operation is required: the programmer must ask for a conversion
Odds and Ends
November 16, 2018

37. Explicit Conversions
One way to request a conversion is to cast between compatible types
A cast operation may be an acknowledgement of possible data loss and “it is OK with me”
May be a statement that “I know the object is really of this other type and it is OK to treat it that way”
Casting as string means we can use string methods and string properties
Odds and Ends
November 16, 2018

38. Casting The syntax for requesting a cast is (new type) item
Item must be of a type compatible with the requested type so that a conversion is possible
If, at run time, it is determined that one cannot make the requested conversion, an exception is thrown
For example, an array of Object may contain any types of items such as strings, doubles, PigLatin objects, Employee objects, etc. If we try to cast and use one of the items as a string, that will work only if that particular item is a string rather than one of the other types of items; it will fail for a double or an Employee object.
Odds and Ends
November 16, 2018

39. Casting Casting is a “temporary” operation
It does not permanently change the type of data being cast
Internally, C# makes a temporary variable of the converted type and converts the item being cast into the temporary variable
The value in the temporary is used for the rest of the operation – at which time it ceases to exist
Odds and Ends
November 16, 2018

40. Casting
An object of a derived class isa object of its base class (an Employee isa Person), but the reverse is not true (some Persons are not Employees)
Casting is required when an object is defined to be of a base type, but it actually refers to a derived type of object
To use the methods and properties of the derived type, one must first cast the object to that type
The casting is OK because the object really is of the derived type
See the Object array example several slides back
Odds and Ends
November 16, 2018

41. Using “as” to Cast to a Different Type
Exception-free “Casting” approach

42. Check to see if the as cast was successful
The as Keyword
The as operator provides a type of casting operation
Ordinary cast operations throw an exception if the cast is not valid
If the conversion is not possible, as returns null instead of raising an exception
Use of the as keyword
Check to see if the as cast was successful

43. Was the as cast successful?
Another as Example
Trying to cast as a string. It works on those items that are strings, but returns null otherwise
Was the as cast successful?
Results

44. Other Explicit Conversions
Casting can only be used in cases in which the types are compatible and the compiler knows how to do the conversion
There are cases in which a conversion is needed but a cast cannot be done. Example:
To input a salary from the keyboard, one may use Console.ReadLine ( );
This inputs a string, hopefully the string representation of a number such as “ ”
We cannot cast this string as a Decimal or a Double however since they are incompatible types
Odds and Ends
November 16, 2018

45. Explicit Conversions
Explicit Conversions that cannot be done by casting require the programmer to invoke a method to do the conversion
Example 1:
char [ ] cArray = strVowels.ToCharArray ( );
is used to convert a string into an array of characters
Example 2:
string strLine = MyTrip.ToString ( );
may convert a decimal MilesPerGallon object to a string
Any class may have methods that convert objects of some other type to its type or vice versa
Odds and Ends
November 16, 2018

46. String to Numeric Conversions
The standard .NET numeric data types such as Int32, Double, Decimal, and so forth have static methods named Parse
Each takes a string argument – the string representation of a number of that type
Method converts the value argument to the appropriate numeric type
Example:
Throws exception if the string cannot be parsed as the specified type
Odds and Ends
November 16, 2018

47. String Conversions
To avoid exceptions in cases where the Parse argument is invalid, use TryParse
public static bool TryParse ( string s, out double result )
Works similar to Parse, but returns true or false to indicate whether it was successful
If it was successful, the second argument has the result in it
out specifies that the argument need not have a value going in because the method will assign one to be returned
Odds and Ends
November 16, 2018

48. Example: String Conversions
Odds and Ends
November 16, 2018

49. Conversion between numeric types
Conversion from one numeric type to another is typically done implicitly (if appropriate) or by casting (if needed)
However, .NET numeric structs have conversion methods
Example: Decimal has the following methods
Odds and Ends
November 16, 2018