C# 你如何声明一个 Predicate Delegate 内联？
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How do you declare a Predicate Delegate inline?
提问by Curtis
I'm using C#.
我正在使用 C#。
So I have an object which has some fields, doesn't really matter what. I have a generic list of these objects.
所以我有一个包含一些字段的对象，这并不重要。我有这些对象的通用列表。
List<MyObject> myObjects = new List<MyObject>();
myObjects.Add(myObject1);
myObjects.Add(myObject2);
myObjects.Add(myObject3);
So I want to remove objects from my list based on some criteria.
For instance, myObject.X >= 10.I would like to use the RemoveAll(Predicate<T> match)method for to do this.
所以我想根据一些标准从我的列表中删除对象。例如，myObject.X >= 10.我想使用RemoveAll(Predicate<T> match)方法来做到这一点。
I know I can define a delegate which can be passed into RemoveAll, but I would like to know how to define this inline with an anonymous delegate, instead of creating a bunch of delegate functions which are only used in once place.
我知道我可以定义一个可以传递给 RemoveAll 的委托，但我想知道如何使用匿名委托来定义这个内联，而不是创建一堆只在一次使用的委托函数。
采纳答案by Erik van Brakel
There's two options, an explicit delegate or a delegate disguised as a lamba construct:
有两个选项，一个显式委托或一个伪装成 Lamba 结构的委托：
explicit delegate
显式委托
myObjects.RemoveAll(delegate (MyObject m) { return m.X >= 10; });
lambda
拉姆达
myObjects.RemoveAll(m => m.X >= 10);
Addition:
添加：
Performance wise both are equal. As a matter of fact, both language constructs generate the same IL when compiled. This is because C# 3.0 is basically an extension on C# 2.0, so it compiles to C# 2.0 constructs :)
性能方面两者是平等的。事实上，两种语言结构在编译时都会生成相同的 IL。这是因为 C# 3.0 基本上是 C# 2.0 的扩展，所以它编译为 C# 2.0 构造:)
回答by Mark Brackett
The lambda C# 3.0 way:
lambda C# 3.0 方式：
myObjects.RemoveAll(m => m.x >= 10);
The anonymous delegate C# 2.0 way:
匿名委托 C# 2.0 方式：
myObjects.RemoveAll(delegate (MyObject m) {
return m.x >= 10;
});
And, for the VB guys, the VB 9.0 lambda way:
而且，对于 VB 人员，VB 9.0 lambda 方式：
myObjects.RemoveAll(Function(m) m.x >= 10)
Unfortunately, VB doesn't support an anonymous delegate.
不幸的是，VB 不支持匿名委托。
回答by Mark Cidade
//C# 2.0
RemoveAll(delegate(Foo o){ return o.X >= 10; });
or
或者
//C# 3.0
RemoveAll(o => o.X >= 10);
or
或者
Predicate<Foo> matches = delegate(Foo o){ return o.X >= 10; });
//or Predicate<Foo> matches = o => o.X >= 10;
RemoveAll(matches);
回答by Nayas Subramanian
Predicate is a delegate which takes an param and returns a boolean.
Predicate 是一个委托，它接受一个参数并返回一个布尔值。
We can do the same in following ways
我们可以通过以下方式做同样的事情
1) Using inline Lambda expression
1)使用内联 Lambda 表达式
RemoveAll(p=> p.x > 2);
2) Using anonymous function
2)使用匿名函数
RemoveAll(delegate(myObject obj){
return obj.x >=10;
})
3) Using Predicate delegate
3)使用谓词委托
Predicate<myObject> matches = new Predicate<myObject>(IsEmployeeIsValid);
RemoveAll(matches);
Predicate<Foo> matches = delegate(Foo o){ return o.X >= 20; });
RemoveAll(matches);
3) Declaring a delegate explicitily and pointing to a function
3)显式声明委托并指向函数
public delegate bool IsInValidEmployee (Employee emp);
IsInValidEmployee invalidEmployeeDelegate = new IsInValidEmployee(IsEmployeeInValid);
myObjects.RemoveAll(myObject=>invalidEmployeeDelegate(myObject);
// Actual function
// 实际功能
public static bool IsEmployeeInValid(Employee emp)
{
if (emp.Id > 0 )
return true;
else
return false;
}
