【C#】反射的用法及效率對比
阿新 • • 發佈：2021-02-18
### 反射例項化類
```c#
public class Person
{
public string Name { get; set; }
public Person(string name)
{
this.Name = name;
}
public string Say(string msg)
{
return $"{Name}: {msg}";
}
}
class Program
{
// 測試次數
const int count = 10000000;
static void Main(string[] args)
{
CreateInstance0();
CreateInstance1();
CreateInstance2();
CreateInstance3();
CreateInstance4();
Console.Read();
}
static void CreateInstance0()
{
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
Person person = new Person("張三");
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - new");
}
static void CreateInstance1()
{
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
object person = Activator.CreateInstance(typeof(Person), "張三");
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - Activator.CreateInstance");
}
static void CreateInstance2()
{
Assembly assembly = Assembly.GetExecutingAssembly();
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
Person obj = (Person)assembly.CreateInstance("ConsoleTest.Person", true, BindingFlags.Default, null, new object[] { "張三" }, null, null);
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - Assembly.CreateInstance");
}
static void CreateInstance3()
{
Assembly assembly = Assembly.GetExecutingAssembly();
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
Type type = assembly.GetType("ConsoleTest.Person");
object person = Activator.CreateInstance(type, "張三");
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - Assembly.CreateInstance1");
}
static void CreateInstance4()
{
Assembly assembly = Assembly.GetExecutingAssembly();
Stopwatch watch = new Stopwatch();
watch.Start();
Type type = assembly.GetType("ConsoleTest.Person");
for (var i = 0; i < count; i++)
{
object person = Activator.CreateInstance(type, "張三");
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - Assembly.CreateInstance2");
}
}
```
- 通過反射例項化物件，要比直接 new 要慢 50 倍左右
- `assembly.CreateInstance` 要比 `Activator.CreateInstance` 慢，主要的效能損耗在 `Assembly.GetType`
### 反射呼叫類的方法
```c#
class Program
{
// 測試次數
const int count = 10000000;
static void Main(string[] args)
{
InvokeMethod0();
InvokeMethod1();
InvokeMethod2();
InvokeMethod3();
InvokeMethod4();
Console.Read();
}
static void InvokeMethod0()
{
Person person = new Person("張三");
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
string name = person.Say("Hello World!");
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - 直接呼叫");
}
static void InvokeMethod1()
{
Person person = (Person)Activator.CreateInstance(typeof(Person), "張三");
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
string name = person.Say("Hello World!");
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - 反射快取類呼叫");
}
static void InvokeMethod2()
{
Person person = (Person)Activator.CreateInstance(typeof(Person), "張三");
MethodInfo method = typeof(Person).GetMethod(nameof(Person.Say), new Type[] { typeof(string) });
Func func = (Func)method.CreateDelegate(typeof(Func), person);
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
string result = func("Hello World!");
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - 使用反射創建出來的委託呼叫");
}
static void InvokeMethod3()
{
Person person = (Person)Activator.CreateInstance(typeof(Person), "張三");
MethodInfo method = typeof(Person).GetMethod(nameof(Person.Say), new Type[] { typeof(string) });
object[] parameters = new object[] { "Hello World!" };
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
string name = (string)method.Invoke(person, parameters);
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - 使用反射得到的方法快取呼叫");
}
static void InvokeMethod4()
{
Person person = (Person)Activator.CreateInstance(typeof(Person), "張三");
object[] parameters = new object[] { "Hello World!" };
Stopwatch watch = new Stopwatch();
watch.Start();
for (var i = 0; i < count; i++)
{
string result = (string)(typeof(Person).GetMethod(nameof(Person.Say))?.Invoke(person, parameters));
}
watch.Stop();
Console.WriteLine($"{watch.Elapsed} - 直接使用反射呼叫");
}
}
```
- 反射得到例項後呼叫方法和直接呼叫方法效率一樣
- 快取反射方法呼叫和直接使用反射呼叫都非常耗效率