C# |属性限制
先决条件:c# 中的属性
属性是一种特殊类型的类成员，它提供了一种灵活的机制来读取、写入或计算私有字段的值。属性可以像公共数据成员一样使用，但它们实际上是称为访问器的特殊方法。这使得数据易于访问，并有助于提高方法的灵活性和安全性。信息的封装和隐藏也可以使用属性来实现。它使用预定义的方法，即“获取”和“设置”方法，帮助访问和修改属性。
语法:
<access_modifier> <return_type> <property_name>
{
get { // body }
set { // body }
}
对属性的限制:我们在编写属性时必须遵循一些规则或限制，如下所示:
- 属性不能通过 ref 或 out 参数传递给方法:属性不能通过 out 或 ref 传递，因为属性实际上是方法。在编译时，参考和输出都不被认为是方法签名的一部分。因此，它会给出一个编译时错误。除了从程序中完全删除 ref 或 out 之外，没有解决这个限制的办法。
-
You cannot overload a property: A property cannot be overloaded. It means that one can only put a single get and set accessor and mutator in a class respectively. The program given below shows what happens when we give more than one get accessor in the same class.
```cs // C# program to show what happens when // we try to overload a property using System;
class Myprop {
int _number;
public int Number { get { return this._number; } set { this._number = value; } get {
// Causes a compile time error // which tells get accessor return this._number;
} // has already been called. } }
// Driver Class class GFG {
// Main Method static void Main() { Myprop ex = new Myprop();
// set { } ex.Number = 5; console.WriteLine("If there are only two properties"+ " in class ex we will get the output");
// get { } Console.WriteLine(ex.Number); } } ```
编译时错误:
prog.cs(19，3):错误 CS1007:属性访问器已经定义
但是通过在同一个程序中使用不同类中的属性，可以多次使用 get 和 set。下面给出了一个说明这一点的例子。
```cs // C# program to demonstrate the use // of properties in different classes using System;
class Myprop {
int _number;
public int Number { get { return this._number; } set { this._number = value; } } }
class Myprops {
int _number; public int Number { get { return this._number; } set { this._number = value; } } }
// Driver Class class GFG {
// Main Method static void Main() { Myprop ex = new Myprop(); Myprops exs = new Myprops();
// Calls set mutator from the Myprops class exs.Number = 7;
// Calls set mutator from the Myprop class ex.Number = 5;
// Gets the get accessor form the Myprop class Console.WriteLine("The value set in the class "+ "Myprop is: " + ex.Number);
// Gets the get accessor form the Myprops class Console.WriteLine("The value set in the class"+ " Myprops is: " + exs.Number); } } ```
输出:
```cs The value set in the class Myprop is: 5 The value set in the class Myprops is: 7
```
-
A property should not alter the state of the underlying variable when the get accessor is called: The get accessor of properties is preset to read-only mode while the set command is set to write-only mode. Due to this, if we try to enter values or modify in the scope of the get accessor we’ll get a warning which tells that the code we are trying to access is unreachable. The example given below illustrates that.
```cs // C# program to demonstrate the // above-mentioned restriction using System;
class Myprop {
int _number; public int Number { get { return this._number;
// We get the warning saying that // the code is unreachable. this._number = 5; } set { this._number = value; } } }
// Driver Class class GFG {
static void Main() { Myprop ex = new Myprop();
// set { } ex.Number = 5;
// get { } Console.WriteLine(ex.Number); } } ```
警告:
prog.cs(16，4):警告 CS0162:检测到无法访问的代码
输出:
cs 5从程序的输出可以看出，代码运行成功，但是我们在 get 访问器中添加的值无法使用，因为它不可访问。这就是为什么在调用 get 访问器时没有必要更改基础变量的原因。
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