SUNWEN Tutorial - C# Advanced (6)

Now what I want to talk about is version processing in C#. In fact, this is an issue that must be considered for any software. Every software has more than one version (except for what I wrote), so version processing is very important. Java is very It handles this problem well, and I personally think that C# has learned from JAVA's processing method, so it has done a good job.

In C#, if you use the virtual keyword when declaring a method, then, In a derived class, you can use the override or new keyword to deprecate it or ignore it. If you use the virtual keyword in the parent class, but do not use the override or new keyword in its derived class , and if you directly reference a method with the same name, the compiler will report an error and run it in new mode, which ignores methods in derived classes. The following example can help you understand:

000: // Versioningversioning .cs
001: public class MyBase
002: {
003: public virtual string Meth1()
004: {
005: return "MyBase-Meth1";
006: }
007: public virtual string Meth2()
008 : {
009: return "MyBase-Meth2";
010: }
011: public virtual string Meth3()
012: {
013: return "MyBase-Meth3";
014: }
015: }
016:
017: class MyDerived : MyBase
018: {
019: public override string Meth1()
020: {
021: return "MyDerived-Meth1";
022: }
023: public new string Meth2()
024: {
025: return "MyDerived-Meth2";
026: }
027: public string Meth3() // The system will have a warning here and the method Meth3() will be hidden
028:
029:
030 : {
031: return "MyDerived-Meth3";
032: }
033:
034: public static void Main()
035: {
036: MyDerived mD = new MyDerived();
037: MyBase mB = ( MyBase) mD;
038:
039: System.Console.WriteLine(mB.Meth1());
040: System.Console.WriteLine(mB.Meth2());
041: System.Console.WriteLine(mB. Meth3());
042: }
043: }

Output:

MyDerived-Meth1
MyBase-Meth2
MyBase-Meth3
It can be clearly seen that the output of the last two new keywords is in the parent class The output of the method, so it can be seen that the function of the new keyword is that if there is this method in the previous version, the previous method will be used instead of the content of my current method. The virtual method has the opposite effect. The function is that if there is such a method in the parent class, use the content of the method I wrote now, and let the previous method go away! However, it seems not good to use new here, which is misleading (Oh no, Gai is going to fight again) Me!&*%$#@).

If you remove line 037 and change all mB in 039-041 to mD, the output becomes:

MyDerived-Meth1
MyDerived-Meth2
MyDerived- Meth3

What does this mean? It means that the override and new keywords will only take effect when the object of the derived class is reshaped by the parent class. Haha, this is indeed a bit difficult to understand. You can only do it yourself. Understand the mechanism of this, the so-called "Practice is the only criterion for testing C#", haha!

In C#, you are free to add a method to the derived class, or override the method of the parent class, as shown below , very simple:

class Base {}
class Derived: Base
{
public void F() {}
}
and:

class Base
{
public void F() {}
}
class Derived : Base
{
public void F() {}
}

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