Advanced NET Programming I 6 th Lecture http

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Advanced. NET Programming I 6 th Lecture http: //d 3 s. mff. cuni. cz/~jezek

Advanced. NET Programming I 6 th Lecture http: //d 3 s. mff. cuni. cz/~jezek Pavel Ježek pavel. [email protected] 3 s. mff. cuni. cz CHARLES UNIVERSITY IN PRAGUE faculty of mathematics and physics Some of the slides are based on University of Linz. NET presentations. © University of Linz, Institute for System Software, 2004 published under the Microsoft Curriculum License (http: //www. msdnaa. net/curriculum/license_curriculum. aspx)

Anonymous Types Following expression: new { p 1 = e 1 , p 2

Anonymous Types Following expression: new { p 1 = e 1 , p 2 = e 2 , … pn = en } Can be used to define an anonymous type : class __Anonymous 1 { private T 1 f 1 ; private T 2 f 2 ; … private Tn fn ; public T 1 p 1 { get { return f 1 ; } set { f 1 = value ; } } public T 2 p 2 { get { return f 2 ; } set { f 2 = value ; } } … public T 1 p 1 { get { return f 1 ; } set { f 1 = value ; } } } And create its instance using object initializer Different anonymous object initilizers that define properties with same names in the same order generate the same anonymous type: var p 1 = new { Name = "Lawnmower", Price = 495. 00 }; var p 2 = new { Name = "Shovel", Price = 26. 95 }; p 1 = p 2;

Query Expressions – Examples Query expression: from c in customers where c. City ==

Query Expressions – Examples Query expression: from c in customers where c. City == "London“ select c Gets translated to: customers. Where(c => c. City == "London")

Query Expressions – Examples Query expression: from c in customers where c. City ==

Query Expressions – Examples Query expression: from c in customers where c. City == "London" select c. Name Gets translated to: customers. Where(c => c. City == "London"). Select(c => c. Name)

Query Expressions – Examples Query expression: from c in customers orderby c. Name select

Query Expressions – Examples Query expression: from c in customers orderby c. Name select new { c. Name, c. City } Gets translated to: customers. Order. By(c => c. Name). Select(c => new { Name = c. Name, City = c. City })

Query Expressions – Examples Query expression: from c in customers where c. City ==

Query Expressions – Examples Query expression: from c in customers where c. City == "London" orderby c. Name select new { c. City, c. Name } Gets translated to: customers. Where(c => c. City == "London"). Order. By(c => c. Name). Select(c => new { c. City, c. Name }) NOTE – is equivalent to (i. e. “c” variables in lambdas are not related to each other): customers. Where(c 1 => c 1. City == "London"). Order. By(c 2 => c 2. Name). Select(c 3 => new { c 3. City, c 3. Name })

Query Expressions Query expressions or LINQ (Language INtergrated Queries) are the key feature of.

Query Expressions Query expressions or LINQ (Language INtergrated Queries) are the key feature of. NET 3. 5 Query expressions are translated to method calls – works on classes like: delegate R Func<A, R>(A arg); class C<T> { public public … } C<T> Where(Func<T, bool> predicate); C<S> Select<S>(Func<T, S> selector); C<S> Select. Many<S>(Func<T, C<S>> selector); O<T> Order. By<K>(Func<T, K> key. Expr); O<T> Order. By. Descending<K>(Func<T, K> key. Expr); C<G<K, T>> Group. By<K>(Func<T, K> key. Expr); C<G<K, E>> Group. By<K, E>(Func<T, K> key. Expr, Func<T, E> elem. Expr);

LINQ to Objects Set of generic extension methods (Select, Where, Order. By, etc. )

LINQ to Objects Set of generic extension methods (Select, Where, Order. By, etc. ) implemented for IEnumerable<T> interface (provided by static class Enumerable), example: int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; var number. Groups = from n in numbers group n by n % 5 into g select new { Remainder = g. Key, Numbers = g }; foreach (var g in number. Groups) { Console. Write. Line( "Numbers with a remainder of {0} when divided by 5: ", g. Remainder ); Numbers with a remainder of 0 when divided by 5: foreach (int n in g. Numbers) { 5 Console. Write. Line(n); 0 Numbers with a remainder of 4 when divided by 5: } 4 9 } LINQ to * - Classes for * data access using query expressions NOTE: For any LINQ implementation it is commonly expected (but not enforced [see Linq. To. Nothing example]), that the “resulting” type of any query implements at least the IEnumerable interface. Numbers with a remainder of 1 when divided by 5: 1 6 Numbers with a remainder of 3 when divided by 5: 3 8 Numbers with a remainder of 2 when divided by 5: 7 2

Partial Methods Can appear only in partial classes or structs, and must be void,

Partial Methods Can appear only in partial classes or structs, and must be void, private and without parameters: partial class A { string _name; partial void On. Name. Changed(); public string Name { set { _name = value; On. Name. Changed(); } } } partial class A { partial void On. Name. Changed() { // Do something } }