问题描述
委托中的 Invoke 和 DynamicInvoke 有什么区别?请给我一些代码示例来解释这两种方法之间的区别.
What is the difference between Invoke and DynamicInvoke in delegates? Please give me some code example which explain difference between that two methods.
推荐答案
当你有一个委托实例时，你可能知道确切的类型，或者你可能只知道它是一个 Delegate.如果您知道确切的类型，则可以使用 Invoke，它非常快 - 一切都已预先验证.例如:
When you have a delegate instance, you might know the exact type, or you might just know that it is a Delegate. If you know the exact type, you can use Invoke, which is very fast - everything is already pre-validated. For example:
Func<int,int> twice = x => x * 2;
int i = 3;
int j = twice.Invoke(i);
// or just:
int j = twice(i);
但是！如果你只知道它是 Delegate，它必须手动解析参数等 - 这可能涉及拆箱等 - 很多反思正在进行.例如:
However! If you just know that it is Delegate, it has to resolve the parameters etc manually - this might involve unboxing, etc - a lot of reflection is going on. For example:
Delegate slowTwice = twice; // this is still the same delegate instance
object[] args = { i };
object result = slowTwice.DynamicInvoke(args);
请注意，我写了 args 长手，以明确涉及到 object[].这里有很多额外的费用:
Note I've written the args long hand to make it clear that an object[] is involved. There are lots of extra costs here:
- 数组
- 验证传递的参数是否适合实际的
MethodInfo - 根据需要拆箱等
- 反射调用
- 那么调用者需要做一些事情来处理返回值
基本上，尽可能避免 DynamicInvoke.Invoke 总是更可取的，除非你只有一个 Delegate 和一个 object[].
Basically, avoid DynamicInvoke when-ever you can. Invoke is always preferable, unless all you have is a Delegate and an object[].
为了进行性能比较，在调试器(控制台 exe)之外的发布模式下打印以下内容:
For a performance comparison, the following in release mode outside of the debugger (a console exe) prints:
Invoke: 19ms
DynamicInvoke: 3813ms
代码:
Func<int,int> twice = x => x * 2;
const int LOOP = 5000000; // 5M
var watch = Stopwatch.StartNew();
for (int i = 0; i < LOOP; i++)
{
twice.Invoke(3);
}
watch.Stop();
Console.WriteLine("Invoke: {0}ms", watch.ElapsedMilliseconds);
watch = Stopwatch.StartNew();
for (int i = 0; i < LOOP; i++)
{
twice.DynamicInvoke(3);
}
watch.Stop();
Console.WriteLine("DynamicInvoke: {0}ms", watch.ElapsedMilliseconds);
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