Table of contents
Signatures of standard query operators
Query Expressions and Standard Query Operators
takes the delegate as a parameter
LINQ predefined delegate types
Example using delegate parameters
Example using Lambda expression parameters
1. Create, save, load and display XML documents
XComment XDeclaration XProcessingInstruction
LINQ Queries using LINQ to XML
standard query operators
Standard query operators consist of a series of API methods
Sequence refers to the class that implements the Ienumerable<> interface, including List<>, Dictionary<>, Stack<>, Array, etc.
Signatures of standard query operators
An extension method is a public static method. Although it is defined in a class, its purpose is to add functionality to another class (the first parameter), which must be preceded by the keyword this
Query Expressions and Standard Query Operators
Each query expression can also be written using method syntax with standard query operators. The compiler translates each query expression into the form of the standard query operators
takes the delegate as a parameter
Many operators accept generic delegates as parameters.
Generic delegates are used to provide user-defined code to operators
LINQ predefined delegate types
The return type parameter has an out keyword, which means that it can be covariant, that is, it can accept the declared type or a type derived from this type. The input parameter has a keyword in, which means that it can be inverted, that is, it can accept the declared type or the type derived from this class
Looking at the statement of Count, the second parameter must be a delegate object, which accepts a single parameter of type T as a method parameter and returns a value of type bool. This form of delegation is called a predicate
Example using delegate parameters
Output: 4
Example using Lambda expression parameters
If the function used to initialize the delegate does not need to be called elsewhere, or the code statement in the function body is equal to a
Then using lambda expression is a good choice
Anonymous method:
LINQ to XML
Extensible Markup Language (XML) is an important method of storing and exchanging data
markup language
A markup language is a set of tags in a document that provide information about the document and organize its content. That is, markup tags are not data about the document -- they contain data about the data. Data about data is called metadata
XML basics
The data in an XML document consists of an XML tree, which mainly consists of nested elements
Elements are the basic elements of an XML tree. Each element has a name and contains data, and some elements can contain other nested elements. Elements are delimited by opening and closing tags. Any element containing data is between the opening and closing tags
XML class
I haven't touched this part, so I can only take screenshots of it all.
1. Create, save, load and display XML documents
Create an XML tree
Use the value of the XML tree
Add nodes and manipulate XML
Using XML features
Other types of nodes
XComment XDeclaration XProcessingInstruction
LINQ Queries using LINQ to XML
