c＃中，部分方法为什么不能有返回值呢？
本帖最后由 AceHung 于 2011-01-05 13:22:37 编辑 正在看《c＃入门经典》，在第十章提到部分方法不能有返回值，不是很明白，特此请教，谢谢！
ps :本人没任何编程基础，刚开始自学，如果问的问题有什么不妥之处，请不要见怪，谢谢！
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呵呵，我跟楼主一样都在自学，也看过C#入门经典，但是很多都看不明白，现在我在看C#图解教程和C#与.NET3.5高级程序设计，感觉非常不错，通俗易懂，我这里有电子版的，如果有需要就站内联系我，我发给你。感觉C#入门经典并不适合0基础的初学者。
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你说的是void ？
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举个例子，方法1：bool 我叫xxx去吃饭（饭的坐标）｛｝
执行结果，xxx去吃了，吃完返回true，由于种种原因没吃，那返回false。
如果我根本不关心他吃饭成功了没有，那就有了方法2：void 我叫xxx去吃饭（饭的坐标）｛｝
结果：吃完没吃完我不知道，但是确实叫他去吃了。
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楼上的解释很形象。
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如果你另外一个方法需要一个值！！比如说一个方法传进去2个参数 1 和 2,你这个方法是要把他们相加..而另外一个方法需要这个相加的值！你就需要返回一个Int
如果你的方法只是执行一下不需要值！比如说你这个方法需要显示一句话，你大可以Console.writeline("");不需要给他返回值！
不知道我有没有说明白！反正这个返不返回值 是你决定的 你想让他返回他就返回 不想让他返回就不返回
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lz说的是Partial Method吧
Partial Method要求必须是Private的，不能有返回值，参数不能是out的。不能用virtual , abstract , override , new , sealed , or extern修饰
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贴下原文:
Partial classes may also define partial methods. Partial methods are defined in one partial class
definition without a method body, and implemented in another partial class definition. In both places,
the partial keyword is used:
public partial class MyClass
{
partial void MyPartialMethod();
}
public partial class MyClass
{
partial void MyPartialMethod()
{
// Method implementation
}
}
Partial methods can also be static, but they are always private and can ’ t have a return value. Any
parameters they use can ’ t be out parameters, although they can be ref parameters. They also can ’ t use
the virtual , abstract , override , new , sealed , or extern modifier.
Given these limitations, it is not immediately obvious what purpose partial methods fulfill. In fact, they
are important when it comes to code compilation, rather than usage. Consider the following code:
public partial class MyClass
{
partial void DoSomethingElse();
public void DoSomething()
{
Console.WriteLine(“DoSomething() execution started.”);
DoSomethingElse();
Console.WriteLine(“DoSomething() execution finished.”);
}
}
public partial class MyClass
{
partial void DoSomethingElse()
{
Console.WriteLine(“DoSomethingElse() called.”);
}
}
Here, the partial method DoSomethingElse is defined and called in the first partial class definition,
and implemented in the second. The output, when DoSomething is called from a console application, is
what you might expect:
DoSomething() execution started.
DoSomethingElse() called.
DoSomething() execution finished.
If you were to remove the second partial class definition or partial method implementation entirely (or
comment out the code), the output would be as follows:
DoSomething() execution started.
DoSomething() execution finished.
You might assume that what is happening here is that when the call to DoSomethingElse is made, the
runtime discovers that the method has no implementation and therefore continues executing the next
line of code. What actually happens is a little subtler. When you compile code that contains a partial
method definition without an implementation, the compiler actually removes the method entirely. It also
removes any calls to the method. When you execute the code, no check is made for an implementation
because there is no call to check. This results in a slight — but nevertheless significant — improvement in
performance.
As with partial classes, partial methods are useful when it comes to customizing autogenerated or
designer - created code. The designer may declare partial methods that you can choose to implement or
not depending on the situation. If you don ’ t implement them, you incur no performance hit because
effectively the method does not exist in the compiled code.
Consider at this point why partial methods can ’ t have a return type. If you can answer that to your own
satisfaction, you can be sure that you fully understand this topic — so that is left as an exercise for you.
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方法可以向调用方返回值。如果返回类型（方法名称前列出的类型）不是 void，则方法可以使用 return 关键字来返回值。如果语句中 return 关键字的后面是与返回类型匹配的值，则该语句将该值返回给方法调用方。return 关键字还会停止方法的执行。如果返回类型为 void，则可使用没有值的 return 语句来停止方法的执行。如果没有 return 关键字，方法执行到代码块末尾时即会停止。具有非 void 返回类型的方法才能使用 return 关键字返回值。例如，下面的两个方法使用 return 关键字来返回整数：
可以查询msdn
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Partial Method 必须经 Partial Class 才能使用
在类中只能是 private ，类外部是无法对 Partial Method 进行访问的
编译器设计者不知道如何处理特别的情况
语法规定分部方法声明必须返回void
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不能有返回值是因为Partial method可能不被实现。
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