Reflection is a mechanism for dynamically checking and operating types and their members at runtime. Its core uses include: 1. Obtain type information and create instances dynamically; 2. Dynamically call methods and access attributes, including private members; 3. Check the types in the assembly, suitable for plug-in systems, serialization libraries and other scenarios. Common usage methods include loading DLL to create objects, traversing attributes for unified processing, calling private methods, etc. However, the reflection performance is low, and the main problems include slow first calls, slower frequent calls, and inability to optimize inline. Therefore, it is recommended to cache the reflection results, use delegate calls or alternatives to improve efficiency. The rational use of reflection can balance flexibility and performance.

In C#, reflection is a powerful mechanism that allows us to dynamically check, load, and operate types and their members at runtime. Although reflection is very flexible, its use requires a trade-off between performance and functionality.

Basic uses of reflection: dynamic viewing and operation types

The core function of reflection is to enable you to "see" the object structure and perform corresponding operations when the program is running. For example, you can:

• Get information about attributes, methods, fields, etc. of a type
• Dynamically create object instances
• Call methods or access properties even if they are private
• Check all types in the assembly

For example, if you have a class name represented by a string, you can get its type information through Type.GetType() or call .GetType() from a known object, and then create an instance and call a method through reflection.

 Type type = typeof(string); // Or Type.GetType("System.String")
object obj = Activator.CreateInstance(type);

This method is very suitable for scenarios such as plug-in systems, serialization libraries, or dependency injection containers.

Common application scenarios and usage methods

1. Dynamically load the type and create an instance

Suitable for plug-in architectures or modular systems, you can load DLLs and call functions without modifying the main program.

 Assembly assembly = Assembly.LoadFile("MyPlugin.dll");
Type pluginType = assembly.GetType("MyNamespace.MyPlugin");
object pluginInstance = Activator.CreateInstance(pluginType);

2. Get and set property values

Used for data binding, ORM mapping, configuration reading and other scenarios. For example, you can traverse all the properties of the object and do unified processing.

 PropertyInfo prop = obj.GetType().GetProperty("Name");
prop.SetValue(obj, "New Value");

3. Calling methods (including private methods)

This is useful in unit testing, especially when testing private logic. It can also be used to implement a common method caller.

 MethodInfo method = obj.GetType().GetMethod("MyMethod", BindingFlags.NonPublic | BindingFlags.Instance);
method.Invoke(obj, null);

These are just some common uses of reflection, and practical applications are much more than these.

Performance issues: Reflection is not fast

Despite its powerful reflection, it also has a significant performance cost:

• The first call is slow : The reflection operation requires parsing metadata, which is much slower than calling IL instructions directly.
• Frequent calls are slower : if you use reflection in loops or high-frequency functions, the performance degradation will be very noticeable.
• Unable to inline optimization : The JIT compiler cannot do many optimizations for reflected calls, such as method inline.

For example: calling a normal method may only take a few nanoseconds, while calling the same method through reflection may take hundreds of nanoseconds or even more.

To alleviate performance problems, consider the following practices:

• Try to cache reflected results (such as MethodInfo , PropertyInfo , etc.) to avoid repeated queries
• Convert reflection to delegate calls using Delegate.CreateDelegate or Expression Trees
• For scenarios with extreme performance requirements, you can consider using IL Emit or third-party libraries such as FastMember

summary

Reflection is a very practical tool in C#, especially suitable for scenarios where high flexibility is required. However, when using it, you should pay attention to performance impact, especially on high-frequency paths. Only by using reasonably, caching properly, and replacing it with a faster method if necessary, can the reflection be both easy to use and efficient.

Basically that's it.

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