C# Property ExamplesMake properties with the get and set keywords. Understand that properties are used for data access.
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Property. Consider the physical computer you are using. It has many properties—a size, a weight, a date it was built. Properties describe this computer.
Property use. In C#, we use properties on a class (like a Computer class) to describe the class. They can be set and read from like other fields, and special code can be run.
First example. We introduce an Example class. One field, an integer, is present. It is used as a backing store for the Number property.
Number This is an int property. Number provides get { } and set { } implementations.
Get The get { } implementation must include a return statement. It can access any member on the class.
Set The set { } implementation receives the implicit argument "value." This is the value to which the property is assigned.
C# program that uses public int property
using System; class Example { int _number; public int Number { get { return this._number; } set { this._number = value; } } } class Program { static void Main() { Example example = new Example(); example.Number = 5; // set { } Console.WriteLine(example.Number); // get { } } }
Enum. This example shows the DayOfWeek enum type in a property. We also insert code in the getter (or setter) that checks the backing store or the parameter value.
Types Like a method, a property can act on any type, even enum types like DayOfWeek. Many properties will use string or int.
C# program that uses enum property
using System; class Example { DayOfWeek _day; public DayOfWeek Day { get { // We don't allow this to be used on Friday. if (this._day == DayOfWeek.Friday) { throw new Exception("Invalid access"); } return this._day; } set { this._day = value; } } } class Program { static void Main() { Example example = new Example(); example.Day = DayOfWeek.Monday; Console.WriteLine(example.Day == DayOfWeek.Monday); } }
Private. We make a private property. Here the IsFound property can only be set in the Example class. We set it in the Example constructor.
Then We can only get the property in the Program.Main method by using an Example instance.
C# program that uses private setter in property
using System; class Example { public Example() { // Set the private property. this.IsFound = true; } bool _found; public bool IsFound { get { return this._found; } private set { // Can only be called in this class. this._found = value; } } } class Program { static void Main() { Example example = new Example(); Console.WriteLine(example.IsFound); } }
Entire property. We can also make an entire property private. If we do this, we can only use the property in the same enclosing class.
Private The Display method in the example shows how to use the private property.
Note This syntax is less useful in most programs. But it exists, and may be helpful in a complex class.
C# program that uses private property
using System; class Example { int _id; private int Id { get { return this._id; } set { this._id = value; } } public void Display() { // Access the private property in this method. this.Id = 7; Console.WriteLine(this.Id); } } class Program { static void Main() { Example example = new Example(); example.Display(); } }
Static. Properties can also be static. This means they are associated with the type and not an instance. Static classes can only have static properties.
Count This property has a side effect. It causes the field to be incremented upon each access.
Caution Side effects are not usually a good design feature in programs. They can make the logic hard to follow.
Setter This is omitted. This makes sense for a property that computes a value entirely in memory, or based on other fields or properties.
C# program that uses static property
using System; class Example { static int _count; public static int Count { get { // Side effect of this property. _count++; return _count; } } } class Program { static void Main() { Console.WriteLine(Example.Count); Console.WriteLine(Example.Count); Console.WriteLine(Example.Count); } }
1 2 3
Automatic. Next, we see automatically implemented property syntax. A hidden field is generated. Then, the get and set statements are expanded to use that hidden field.
Expression The *= operator is used to multiply the property by itself. Because properties are meant to look like fields, this is allowed.
C# program that uses automatically implemented property
using System; class Example { public int Number { get; set; } } class Program { static void Main() { Example example = new Example(); example.Number = 8; example.Number *= 4; Console.WriteLine(example.Number); } }
Automatic, private. Let us consider how to make getters or setters on an automatic property. We cannot omit either the getter or setter in this kind of property.
Note The error reported by the C# compiler reads: "Automatically implemented properties must define both get and set accessors."
C# program that uses private setter, auto property
using System; class Example { public Example() { // Use private setter in the constructor. this.Id = new Random().Next(); } public int Id { get; private set; } } class Program { static void Main() { Example example = new Example(); Console.WriteLine(example.Id); } }
Automatic, default values. Automatic properties have support for default values much like fields. Here we assign the Quantity property of Medication to 30 by default.
C# program that uses default value
using System; class Medication { public int Quantity { get; set; } = 30; // Has default value. } class Program { static void Main() { Medication med = new Medication(); // The quantity is by default 30. Console.WriteLine(med.Quantity); // We can change the quantity. med.Quantity *= 2; Console.WriteLine(med.Quantity); } }
30 60
Expression-bodied properties. We can use lambda-style syntax to specify properties. These are expression-bodied properties—we use "get" and "set" and then the result on the right side.
C# program that uses expression-bodied properties
class Program { private static int test; public static int Test { get => test; set => test = value; } static void Main() { // Use the property. Program.Test = 200; System.Console.WriteLine(Program.Test); } }
Benchmark, properties. Compiler optimizations ensure that properties are efficient. These same optimizations are used on methods, which share the underlying implementation with properties.
Version 1 This code uses a property. It sets a property, and then gets the value of the property.
Version 2 This version of the code uses a field directly. It performs the same logical steps that version 1 does.
Result There was no difference in performance with the property and the field. It is apparent the property access is inlined.
Tip The JIT compiler can inline properties that don't have logic inside of them. So they are as efficient as fields.
C# program that benchmarks properties
using System; using System.Diagnostics; class Program { static string _backing; // Backing store for property. static string Property // Getter and setter. { get { return _backing; } set { _backing = value; } } static string Field; // Static field. static void Main() { const int m = 100000000; for (int x = 0; x < 10; x++) // Ten tests. { Stopwatch s1 = new Stopwatch(); s1.Start(); // Version 1: test property. for (int i = 0; i < m; i++) { Property = "string"; if (Property == "cat") { } } s1.Stop(); Stopwatch s2 = new Stopwatch(); s2.Start(); // Version 2: test field. for (int i = 0; i < m; i++) { Field = "string"; if (Field == "cat") { } } s2.Stop(); Console.WriteLine("{0},{1}", s1.ElapsedMilliseconds, s2.ElapsedMilliseconds); } } }
Property get/set: 604.6 ms Field read/assign: 603.6 ms
Indexers. These are properties. They allow element access (like an array). They use the token "this" for their name, and square brackets with an argument.
Interface. A property can be part of an interface. There is a special syntax for this. On types that implement the interface, we must provide implementations for the property.
Prop. I like the prop snippet. It is one of my favorites. In Visual Studio, try typing prop and pressing tab twice where you want to put a property.
Then Change the fields as needed. We get an automatically implemented property.
A review. Properties are used throughout programs. They are a powerful way to replace methods. They present a more intuitive way to use objects.
On a conceptual level, properties combine fields and methods. But in terms of implementation, properties are just methods. They are optimized, in the JIT compiler, just like methods.
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