docs/csharp/programming-guide/classes-and-structs/snippets/object-collection-initializers/BasicObjectInitializers.cs - main - aprogrammer/dotnet-docs

docs/csharp/programming-guide/classes-and-structs/snippets/object-collection-initializers/BasicObjectInitializers.cs
396 строк11 KB
Bill Wagner
Replace "auto implemented" with "automatically" (#43211)
26 окт 2024, 00:50
26 окт 2024, 00:50ed97bb1

namespace object_collection_initializers;

public class BasicObjectInitializers
{
    // <SnippetCatDeclaration>
    public class Cat
    {
        // Automatically implemented properties.
        public int Age { get; set; }
        public string? Name { get; set; }

        public Cat()
        {
        }

        public Cat(string name)
        {
            this.Name = name;
        }
    }
    // </SnippetCatDeclaration>

    // <SnippetCatOwnerDeclaration>
    public class CatOwner
    {
        public IList<Cat> Cats { get; } = new List<Cat>();
    }
    // </SnippetCatOwnerDeclaration>

    // <SnippetMatrixDeclaration>
    public class Matrix
    {
        private double[,] storage = new double[3, 3];

        public double this[int row, int column]
        {
            // The embedded array will throw out of range exceptions as appropriate.
            get { return storage[row, column]; }
            set { storage[row, column] = value; }
        }
    }
    // </SnippetMatrixDeclaration>

    public class Product
    {
        public string? ProductName { get; set; }
        public decimal UnitPrice { get; set; }
    }

    public static void ObjectInitializerExamples()
    {
        // <SnippetObjectPropertyInitialization>
        Cat cat = new Cat { Age = 10, Name = "Fluffy" };
        Cat sameCat = new Cat("Fluffy"){ Age = 10 };
        // </SnippetObjectPropertyInitialization>

        // <SnippetMatrixInitialization>
        var identity = new Matrix
        {
            [0, 0] = 1.0,
            [0, 1] = 0.0,
            [0, 2] = 0.0,

            [1, 0] = 0.0,
            [1, 1] = 1.0,
            [1, 2] = 0.0,

            [2, 0] = 0.0,
            [2, 1] = 0.0,
            [2, 2] = 1.0,
        };
        // </SnippetMatrixInitialization>

        var products = new List<Product>();

        // <SnippetAnonymousUse>
        var productInfos =
            from p in products
            select new { p.ProductName, p.UnitPrice };
        // </SnippetAnonymousUse>

        // <SnippetListInitializer>
        List<Cat> cats = new List<Cat>
        {
            new Cat{ Name = "Sylvester", Age=8 },
            new Cat{ Name = "Whiskers", Age=2 },
            new Cat{ Name = "Sasha", Age=14 }
        };
        // </SnippetListInitializer>

        // <SnippetListInitializerWithNull>
        List<Cat?> moreCats = new List<Cat?>
        {
            new Cat{ Name = "Furrytail", Age=5 },
            new Cat{ Name = "Peaches", Age=4 },
            null
        };
        // </SnippetListInitializerWithNull>

        // <SnippetDictionaryIndexerInitializer>
        var numbers = new Dictionary<int, string>
        {
            [7] = "seven",
            [9] = "nine",
            [13] = "thirteen"
        };
        // </SnippetDictionaryIndexerInitializer>

        // <SnippetDictionaryAddInitializer>
        var moreNumbers = new Dictionary<int, string>
        {
            {19, "nineteen" },
            {23, "twenty-three" },
            {42, "forty-two" }
        };
        // </SnippetDictionaryAddInitializer>

        {
            // <SnippetReadOnlyPropertyCollectionInitializer>
            CatOwner owner = new CatOwner
            {
                Cats =
                {
                    new Cat{ Name = "Sylvester", Age=8 },
                    new Cat{ Name = "Whiskers", Age=2 },
                    new Cat{ Name = "Sasha", Age=14 }
                }
            };
            // </SnippetReadOnlyPropertyCollectionInitializer>
        }

        {
            // <SnippetReadOnlyPropertyCollectionInitializerTranslation>
            CatOwner owner = new ();
            owner.Cats.Add(new Cat{ Name = "Sylvester", Age=8 });
            owner.Cats.Add(new Cat{ Name = "Whiskers", Age=2 });
            owner.Cats.Add(new Cat{ Name = "Sasha", Age=14 });
            // </SnippetReadOnlyPropertyCollectionInitializerTranslation>
        }

        InitializationSample.Main();
        FullExample.Main();
        DictionaryExample.Main();
    }
}

// The following code consolidates examples from the topic.
// <SnippetFullExample>
public class InitializationSample
{
    public class Cat
    {
        // Automatically implemented properties.
        public int Age { get; set; }
        public string? Name { get; set; }

        public Cat() { }

        public Cat(string name)
        {
            Name = name;
        }
    }

    public static void Main()
    {
        Cat cat = new Cat { Age = 10, Name = "Fluffy" };
        Cat sameCat = new Cat("Fluffy"){ Age = 10 };

        List<Cat> cats = new List<Cat>
        {
            new Cat { Name = "Sylvester", Age = 8 },
            new Cat { Name = "Whiskers", Age = 2 },
            new Cat { Name = "Sasha", Age = 14 }
        };

        List<Cat?> moreCats = new List<Cat?>
        {
            new Cat { Name = "Furrytail", Age = 5 },
            new Cat { Name = "Peaches", Age = 4 },
            null
        };

        // Display results.
        System.Console.WriteLine(cat.Name);

        foreach (Cat c in cats)
        {
            System.Console.WriteLine(c.Name);
        }

        foreach (Cat? c in moreCats)
        {
            if (c != null)
            {
                System.Console.WriteLine(c.Name);
            }
            else
            {
                System.Console.WriteLine("List element has null value.");
            }
        }
    }
    // Output:
    //Fluffy
    //Sylvester
    //Whiskers
    //Sasha
    //Furrytail
    //Peaches
    //List element has null value.
}
// </SnippetFullExample>

// <SnippetFullListExample>
public class FullExample
{
    class FormattedAddresses : IEnumerable<string>
    {
        private List<string> internalList = new List<string>();
        public IEnumerator<string> GetEnumerator() => internalList.GetEnumerator();

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => internalList.GetEnumerator();

        public void Add(string firstname, string lastname,
            string street, string city,
            string state, string zipcode) => internalList.Add($"""
            {firstname} {lastname}
            {street}
            {city}, {state} {zipcode}
            """
            );
    }

    public static void Main()
    {
        FormattedAddresses addresses = new FormattedAddresses()
        {
            {"John", "Doe", "123 Street", "Topeka", "KS", "00000" },
            {"Jane", "Smith", "456 Street", "Topeka", "KS", "00000" }
        };

        Console.WriteLine("Address Entries:");

        foreach (string addressEntry in addresses)
        {
            Console.WriteLine("\r\n" + addressEntry);
        }
    }

    /*
        * Prints:

        Address Entries:

        John Doe
        123 Street
        Topeka, KS 00000

        Jane Smith
        456 Street
        Topeka, KS 00000
        */
}
// </SnippetFullListExample>

// <SnippetFullDictionaryInitializer>
public class DictionaryExample
{
    class RudimentaryMultiValuedDictionary<TKey, TValue> : IEnumerable<KeyValuePair<TKey, List<TValue>>> where TKey : notnull
    {
        private Dictionary<TKey, List<TValue>> internalDictionary = new Dictionary<TKey, List<TValue>>();

        public IEnumerator<KeyValuePair<TKey, List<TValue>>> GetEnumerator() => internalDictionary.GetEnumerator();

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => internalDictionary.GetEnumerator();

        public List<TValue> this[TKey key]
        {
            get => internalDictionary[key];
            set => Add(key, value);
        }

        public void Add(TKey key, params TValue[] values) => Add(key, (IEnumerable<TValue>)values);

        public void Add(TKey key, IEnumerable<TValue> values)
        {
            if (!internalDictionary.TryGetValue(key, out List<TValue>? storedValues))
            {
                internalDictionary.Add(key, storedValues = new List<TValue>());
            }
            storedValues.AddRange(values);
        }
    }

    public static void Main()
    {
        RudimentaryMultiValuedDictionary<string, string> rudimentaryMultiValuedDictionary1
            = new RudimentaryMultiValuedDictionary<string, string>()
            {
                {"Group1", "Bob", "John", "Mary" },
                {"Group2", "Eric", "Emily", "Debbie", "Jesse" }
            };
        RudimentaryMultiValuedDictionary<string, string> rudimentaryMultiValuedDictionary2
            = new RudimentaryMultiValuedDictionary<string, string>()
            {
                ["Group1"] = new List<string>() { "Bob", "John", "Mary" },
                ["Group2"] = new List<string>() { "Eric", "Emily", "Debbie", "Jesse" }
            };
        RudimentaryMultiValuedDictionary<string, string> rudimentaryMultiValuedDictionary3
            = new RudimentaryMultiValuedDictionary<string, string>()
            {
                {"Group1", new string []{ "Bob", "John", "Mary" } },
                { "Group2", new string[]{ "Eric", "Emily", "Debbie", "Jesse" } }
            };

        Console.WriteLine("Using first multi-valued dictionary created with a collection initializer:");

        foreach (KeyValuePair<string, List<string>> group in rudimentaryMultiValuedDictionary1)
        {
            Console.WriteLine($"\r\nMembers of group {group.Key}: ");

            foreach (string member in group.Value)
            {
                Console.WriteLine(member);
            }
        }

        Console.WriteLine("\r\nUsing second multi-valued dictionary created with a collection initializer using indexing:");

        foreach (KeyValuePair<string, List<string>> group in rudimentaryMultiValuedDictionary2)
        {
            Console.WriteLine($"\r\nMembers of group {group.Key}: ");

            foreach (string member in group.Value)
            {
                Console.WriteLine(member);
            }
        }
        Console.WriteLine("\r\nUsing third multi-valued dictionary created with a collection initializer using indexing:");

        foreach (KeyValuePair<string, List<string>> group in rudimentaryMultiValuedDictionary3)
        {
            Console.WriteLine($"\r\nMembers of group {group.Key}: ");

            foreach (string member in group.Value)
            {
                Console.WriteLine(member);
            }
        }
    }

    /*
        * Prints:

        Using first multi-valued dictionary created with a collection initializer:

        Members of group Group1:
        Bob
        John
        Mary

        Members of group Group2:
        Eric
        Emily
        Debbie
        Jesse

        Using second multi-valued dictionary created with a collection initializer using indexing:

        Members of group Group1:
        Bob
        John
        Mary

        Members of group Group2:
        Eric
        Emily
        Debbie
        Jesse

        Using third multi-valued dictionary created with a collection initializer using indexing:

        Members of group Group1:
        Bob
        John
        Mary

        Members of group Group2:
        Eric
        Emily
        Debbie
        Jesse
        */
}
// </SnippetFullDictionaryInitializer>