C# 将函数（带参数）作为参数传递？
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Passing a Function (with parameters) as a parameter?
提问by klkitchens
I want to create a generic to which I can pass a function as a parameter, however this function may include parameters itself so...
我想创建一个泛型，我可以将一个函数作为参数传递给它，但是这个函数可能包含参数本身，所以......
int foo = GetCachedValue("LastFoo", methodToGetFoo)
Such that:
这样：
protected int methodToGetFoo(DateTime today)
{ return 2; // example only }
Essentially I want to have a method that will check the cache for a value, otherwise will generate the value based on the passed in method.
本质上，我想要一个方法来检查缓存中的值，否则将根据传入的方法生成值。
Thoughts?
想法？
采纳答案by Marc Gravell
It sounds like you want a Func<T>:
听起来你想要一个Func<T>：
T GetCachedValue<T>(string key, Func<T> method) {
T value;
if(!cache.TryGetValue(key, out value)) {
value = method();
cache[key] = value;
}
return value;
}
The caller can then wrap this in many ways; for simple functions:
然后调用者可以通过多种方式包装它；对于简单的功能：
int i = GetCachedValue("Foo", GetNextValue);
...
int GetNextValue() {...}
or where arguments are involved, a closure:
或者在涉及参数的地方，一个闭包：
var bar = ...
int i = GetCachedValue("Foo", () => GetNextValue(bar));
回答by mqp
You can create your own delegate, but in C# 3.0 you may find it more convenient to use the built-in Func<T>delegate family to solve this problem. Example:
您可以创建自己的委托，但在 C# 3.0 中，您可能会发现使用内置Func<T>委托系列来解决这个问题更方便。例子：
public int GetCachedValue(string p1, int p2,
Func<DateTime, int> getCachedValue)
{
// do some stuff in here
// you can call getCachedValue like any normal function from within here
}
This method will take three arguments: a string, an int, and a function that takes a DateTime and returns an int. For example:
此方法将采用三个参数：一个字符串、一个 int 和一个接受 DateTime 并返回一个 int 的函数。例如：
int foo = GetCachedValue("blah", 5, methodToGetFoo); // using your method
int bar = GetCachedValue("fuzz", 1, d => d.TotalDays); // using a lambda
Different Func<T, U, V...>etc. types exist in the framework to accommodate methods with different amounts of arguments.
Func<T, U, V...>框架中存在不同的类型以适应具有不同数量参数的方法。
回答by Dead account
Create a delegate for the method methodToGetFoo
为方法创建委托 methodToGetFoo
public delegate object GenerateValue(params p);
public event GenerateValue OnGenerateValue;
Define GetCachedValue to use the delegate
定义 GetCachedValue 以使用委托
int GetCachedValue(string key, GenerateValue functionToCall);
Then in the implementation of OnGenerateValue you can check the param's.
然后在 OnGenerateValue 的实现中，您可以检查参数。
回答by leppie
Hereis something simple I started that can be taken a bit further (as I did for a commercial project).
这是我开始的一些简单的事情，可以更进一步（就像我为商业项目所做的那样）。
In my case this was to cache web service calls, and was used something like:
在我的情况下，这是缓存 Web 服务调用，并且使用了以下内容：
WebService ws = new WebService();
var result = ws.Call( x => x.Foo("bar", 1)); // x is the ws instance
回答by empirico gutierrez
Use System.Actionand a lambda expression (anonymous method). For example:
使用System.Action和 lambda 表达式（匿名方法）。例如：
public void myMethod(int integer) {
// Do something
}
public void passFunction(System.Action methodWithParameters) {
// Invoke
methodWithParameters();
}
// ...
// Pass anonymous method using lambda expression
passFunction(() => myMethod(1234));
