Tutorial by Examples

The Skip method returns a collection excluding a number of items from the beginning of the source collection. The number of items excluded is the number given as an argument. If there are less items in the collection than specified in the argument then an empty collection is returned. The Take meth...

All six methods return a single value of the sequence type, and can be called with or without a predicate. Depending on the number of elements that match the predicate or, if no predicate is supplied, the number of elements in the source sequence, they behave as follows: First() Returns the fir...

To create an empty IEnumerable of int: IEnumerable<int> emptyList = Enumerable.Empty<int>(); This empty IEnumerable is cached for each Type T, so that: Enumerable.Empty<decimal>() == Enumerable.Empty<decimal>(); // This is True Enumerable.Empty<int>() == Enumerab...

The Except method returns the set of items which are contained in the first collection but are not contained in the second. The default IEqualityComparer is used to compare the items within the two sets. There is an overload which accepts an IEqualityComparer as an argument. Example: int[] first =...

var color = "Black"; var age = 4; var query = "Select * from Cats where Color = :Color and Age > :Age"; var dynamicParameters = new DynamicParameters(); dynamicParameters.Add("Color", color); dynamicParameters.Add("Age", age); using (var connectio...

Event declaration: public event EventHandler<EventArgsT> EventName; Event handler declaration: public void HandlerName(object sender, EventArgsT args) { /* Handler logic */ } Subscribing to the event: Dynamically: EventName += HandlerName; Through the Designer: Click the Events...

Event declaration: public event EventHandler<EventArgsType> EventName; Event handler declaration using lambda operator => and subscribing to the event: EventName += (obj, eventArgs) => { /* Handler logic */ }; Event handler declaration using delegate anonymous method syntax: Eve...

Events can be of any delegate type, not just EventHandler and EventHandler<T>. For example: //Declaring an event public event Action<Param1Type, Param2Type, ...> EventName; This is used similarly to standard EventHandler events: //Adding a named event handler public void HandlerNa...

Given an async method like this: Task<string> GetNameAsync(CancellationToken cancellationToken) Wrap it as an IObservable<string> like this: Observable.FromAsync(cancellationToken => GetNameAsync(cancellationToken))

Given an IObservable<Offer> of offers from merchants to buy or sell some type of item at a fixed price, we can match pairs of buyers and sellers as follows: var sellers = offers.Where(offer => offer.IsSell).Select(offer => offer.Merchant); var buyers = offers.Where(offer => offer.Is...

using System; using System.Reflection; using System.Reflection.Emit; class DemoAssemblyBuilder { public static void Main() { // An assembly consists of one or more modules, each of which // contains zero or more types. This code creates a single-module // a...

using System.Linq.Expressions; // Manually build the expression tree for // the lambda expression num => num < 5. ParameterExpression numParam = Expression.Parameter(typeof(int), "num"); ConstantExpression five = Expression.Constant(5, typeof(int)); BinaryExpression numLessTh...

// Define an expression tree, taking an integer, returning a bool. Expression<Func<int, bool>> expr = num => num < 5; // Call the Compile method on the expression tree to return a delegate that can be called. Func<int, bool> result = expr.Compile(); // Invoke the dele...

using System.Linq.Expressions; // Create an expression tree. Expression<Func<int, bool>> exprTree = num => num < 5; // Decompose the expression tree. ParameterExpression param = (ParameterExpression)exprTree.Parameters[0]; BinaryExpression operation = (BinaryExpression)exp...

Set function inserts a cache entry into the cache by using a CacheItem instance to supply the key and value for the cache entry. This function Overrides ObjectCache.Set(CacheItem, CacheItemPolicy) private static bool SetToCache() { string key = "Cache_Key"; string value = &quo...

var sequenceOfSequences = new [] { new [] { 1, 2, 3 }, new [] { 4, 5 }, new [] { 6 } }; var sequence = sequenceOfSequences.SelectMany(x => x); // returns { 1, 2, 3, 4, 5, 6 } Use SelectMany() if you have, or you are creating a sequence of sequences, but you want the result as one long sequen...

The SelectMany linq method 'flattens' an IEnumerable<IEnumerable<T>> into an IEnumerable<T>. All of the T elements within the IEnumerable instances contained in the source IEnumerable will be combined into a single IEnumerable. var words = new [] { "a,b,c", "d,e&quo...

This code will subscribe to the emails observable twice: emails.Where(email => email.From == "John").Subscribe(email => Console.WriteLine("A")); emails.Where(email => email.From == "Mary").Subscribe(email => Console.WriteLine("B")); To share a...

This code contains an overloaded method named Hello: class Example { public static void Hello(int arg) { Console.WriteLine("int"); } public static void Hello(double arg) { Console.WriteLine("double"); } public static vo...

The following program: class Program { static void Method(params Object[] objects) { System.Console.WriteLine(objects.Length); } static void Method(Object a, Object b) { System.Console.WriteLine("two"); } static void Main(string[] a...