What's the Constructor Execution Order in C# Inheritance?

Detailed explanation of C# constructor execution order

When defining a constructor in C#, a key question is: Is the constructor of the current class executed before or after calling the base class constructor?

Execution order

The execution sequence follows the following steps:

1. Member variables of all classes in the inheritance hierarchy are initialized to default values.
2. Start with the most derived class:
   • Execute a variable initializer for the most derived type.
   • The constructor chain determines the base class constructor to be called.
   • Initialize the base class (apply these steps recursively).
   • Constructor bodies in this class's inheritance chain are executed sequentially.
3. Please note that unlike Java, the base class is initialized after the variable initializer is executed.

Example

Consider the following class hierarchy:

<code class="language-csharp">class Base
{
    public Base(int param1)
    {
        // 构造函数主体
    }
}

class Derived : Base
{
    public Derived(int param1, int param2) : base(param1)
    {
        // 构造函数主体
    }
}</code>

When creating a Derived instance, the execution sequence is as follows:

1. Assign default values ​​to the member variables of Base and Derived.
2. Execute Derived’s variable initializer and set its own member variables.
3. Call the base class constructor (Base(int param1)) with the specified parameters.
4. Execute the constructor body of Derived.

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