c# 中的自定义属性
原文:https://www.geeksforgeeks.org/custom-attributes-in-c-sharp/
属性是元数据扩展，在运行时向编译器提供关于程序代码中元素的附加信息。属性用于强加条件或提高一段代码的效率。C# 中存在内置属性，但程序员可以创建自己的属性，这种属性称为自定义属性。要创建自定义属性，我们必须构建从系统派生的类。属性类。
创建自定义属性的步骤
1。使用属性属性:这个标签定义了我们正在构建的属性。它提供诸如属性目标是什么、它是否可以被继承或者这个属性的多个实例是否可以存在等信息。属性属性有三个主要成员，如下所示:
-
属性目标。所有指定属性可以应用于程序的所有部分，而属性。类表示它可以应用于类和属性目标。方法来一个方法。
```cs [AttributeUsageAttribute( AttributeTargets.All )]
```
-
继承成员指示属性是否可以继承。它采用布尔值(真/假)。如果未指定，则默认为真。
```cs [AttributeUsage(AttributeTargets.All, Inherited = false)]
```
-
AllowMultiple 成员告诉我们该属性是否可以存在多个实例。它还需要一个布尔值。默认为假。
```cs [AttributeUsage(AttributeTargets.Method, AllowMultiple = true)]
```
2。定义属性类:它的定义方式与普通类相同，类名通常以“属性”结尾。这个类必须直接或间接继承系统。属性类。
```cs [AttributeUsage(AttributeTargets.All, Inherited = true, AllowMultiple = false)] public class MyAttribute : Attribute { //Class Members }
```
3。定义构造函数和属性:构造函数用于设置属性类的值，非常像典型的类。构造函数重载可用于处理不同的赋值，同时激发属性类对象。
```cs public MyAttribute(dataType value) { this.value = value; }
```
注意:自定义属性也可以为其成员设置 get 和 set 等属性。
```cs public dataType MyProperty { get {return this.value;} set {this.value = newValue;} }
```
示例 1: 下面给出的代码显示了一个名为 MyAttribute 的自定义属性的示例，它有两个私有成员，即名称和操作。“名称”用于定义属性可能应用到的任何程序元素的名称。“动作”描述了元素应该做什么。这里的属性应用于学生类的方法。
```cs // C# program to illustrate the // use of custom attributes using System;
// Creating Custom attribute MyAttribute
[AttributeUsage(AttributeTargets.All)] public class MyAttribute : Attribute {
// Provides name of the member private string name;
// Provides description of the member private string action;
// Constructor public MyAttribute(string name, string action) { this.name = name; this.action = action; }
// property to get name public string Name { get { return name; } }
// property to get description public string Action { get { return action; } } }
class Student {
// Private fields of class Student private int rollNo; private string stuName; private double marks;
// The attribute MyAttribute is applied // to methods of class Student // Providing details of their utility [MyAttribute("Modifier", "Assigns the Student Details")] public void setDetails(int r, string sn, double m) { rollNo = r; stuName = sn; marks = m; }
[MyAttribute("Accessor", "Returns Value of rollNo")] public int getRollNo() { return rollNo; }
[MyAttribute("Accessor", "Returns Value of stuName")] public string getStuName() { return stuName; }
[MyAttribute("Accessor", "Returns Value of marks")] public double getMarks() { return marks; } }
class TestAttributes {
// Main Method static void Main(string[] args) { Student s = new Student(); s.setDetails(1, "Taylor", 92.5);
Console.WriteLine("Student Details"); Console.WriteLine("Roll Number : " + s.getRollNo()); Console.WriteLine("Name : " + s.getStuName()); Console.WriteLine("Marks : " + s.getMarks()); } } ```
Output:
```cs Student Details Roll Number : 1 Name : Taylor Marks : 92.5
```
示例 2: 在本例中，我们可以显示我们创建的自定义属性的内容。这里的 NewAttribute 是一个自定义属性，有两个字段，即标题和描述。图块存储标题，描述存储应用新属性的方法的功能。要将自定义属性应用于程序的任何部分，必须在定义之前调用其构造函数。NewAttribute 还包括一个参数化构造函数和一个显示属性内容的方法。主要是使用类名调用 AttributeDisplay 方法，因为它是一个静态方法，它显示关于应用了该属性的类的方法的信息。
```cs // C# program to display the custom attributes using System; using System.Reflection; using System.Collections.Generic;
// Defining a Custom attribute class class NewAttribute : Attribute {
// Private fields private string title; private string description;
// Parameterised Constructor public NewAttribute(string t, string d) { title = t; description = d; }
// Method to show the Fields // of the NewAttribute // using reflection public static void AttributeDisplay(Type classType) { Console.WriteLine("Methods of class {0}", classType.Name);
// Array to store all methods of a class // to which the attribute may be applied
MethodInfo[] methods = classType.GetMethods();
// for loop to read through all methods
for (int i = 0; i < methods.GetLength(0); i++) {
// Creating object array to receive // method attributes returned // by the GetCustomAttributes method
object[] attributesArray = methods[i].GetCustomAttributes(true);
// foreach loop to read through // all attributes of the method foreach(Attribute item in attributesArray) { if (item is NewAttribute) {
// Display the fields of the NewAttribute NewAttribute attributeObject = (NewAttribute)item; Console.WriteLine("{0} - {1}, {2} ", methods[i].Name, attributeObject.title, attributeObject.description); } } } } }
// Class Employer class Employer {
// Fields of Employer int id; string name;
// Constructor public Employer(int i, string n) { id = i; name = n; }
// Applying the custom attribute // NewAttribute to the getId method [NewAttribute("Accessor", "Gives value of Employer Id")] public int getId() { return id; }
// Applying the custom attribute // NewAttribute to the getName method [NewAttribute("Accessor", "Gives value of Employer Name")] public string getName() { return name; } }
// Class Employee class Employee {
// Fields of Employee int id; string name;
public Employee(int i, string n) { id = i; name = n; }
// Applying the custom // attribute NewAttribute // to the getId method [NewAttribute("Accessor", "Gives value of Employee Id")] public int getId() { return id; }
// Applying the custom attribute // NewAttribute to the getName method [NewAttribute("Accessor", "Gives value of Employee Name")] public string getName() { return name; } }
class Program {
// Main Method static void Main(string[] args) {
// Calling the AttributeDisplay // method using the class name // since it is a static method NewAttribute.AttributeDisplay(typeof(Employer));
Console.WriteLine();
NewAttribute.AttributeDisplay(typeof(Employee)); } } ```
Output:
```cs Methods of class Employer getId - Accessor, Gives value of Employer Id getName - Accessor, Gives value of Employer Name
Methods of class Employee getId - Accessor, Gives value of Employee Id getName - Accessor, Gives value of Employee Name
```
版权属于：月萌API www.moonapi.com，转载请注明出处
