C＃呼叫

Question

public static class RectangleExtension 
{ 
    public static Rectangle Offseted(this Rectangle rect, int x, int y) 
    { 
     rect.X += x; 
     rect.Y += y; 
     return rect; 
    } 
} 


.... 

public void foo() 
{ 
    Rectangle rect; 

    rect = new Rectangle(0, 0, 20, 20); 
    Console.WriteLine("1: " + rect.X + "; " + rect.Y); 

    rect.Offseted(50, 50); 
    Console.WriteLine("2: " + rect.X + "; " + rect.Y); 

    rect = rect.Offseted(50, 50); 
    Console.WriteLine("3: " + rect.X + "; " + rect.Y); 
} 

输出：

1：0; 0

2：0; 0

3：50; 50

我的预期：

1：0; 0

2：50; 50

为什么rect.Offseted（50,50）不能修改步骤2中矩形的x和y？

我需要用我的RectangleExtension方法来获得预期的结果？

Answer 1

答案是：structs总是按C＃中的值传递，而您的情况中的Rectangle是struct而不是class。

尝试这种情况：

public class A { 
    public int x; 
} 
public struct B { 
    public int x; 
} 
public static class Extension { 
    public static A Add(this A value) { 
     value.x += 1; 
     return value; 
    } 
    public static B Add(this B value) { 
     value.x += 1; 
     return value; 
    } 
} 
class Program { 
    static void Main(string[] args) { 
     A a = new A(); 
     B b = new B(); 
     Console.WriteLine("a=" + a.x); 
     Console.WriteLine("b=" + b.x); 
     a.Add(); 
     b.Add(); 
     Console.WriteLine("a=" + a.x); //a=1 
     Console.WriteLine("b=" + b.x); //b=0 
     Console.ReadLine(); 
    } 
}