TypeScript 模板方法模式讲解和代码示例
模版方法是一种行为设计模式， 它在基类中定义了一个算法的框架， 允许子类在不修改结构的情况下重写算法的特定步骤。
复杂度：
流行度：
使用示例： 模版方法模式在 TypeScript 框架中很常见。 开发者通常使用它来向框架用户提供通过继承实现的、 对标准功能进行扩展的简单方式。
识别方法： 模版方法可以通过行为方法来识别， 该方法已有一个在基类中定义的 “默认” 行为。
概念示例
本例说明了模版方法设计模式的结构并重点回答了下面的问题：
- 它由哪些类组成？
- 这些类扮演了哪些角色？
- 模式中的各个元素会以何种方式相互关联？
index.ts: 概念示例
/**
* The Abstract Class defines a template method that contains a skeleton of some
* algorithm, composed of calls to (usually) abstract primitive operations.
*
* Concrete subclasses should implement these operations, but leave the template
* method itself intact.
*/
abstract class AbstractClass {
/**
* The template method defines the skeleton of an algorithm.
*/
public templateMethod(): void {
this.baseOperation1();
this.requiredOperations1();
this.baseOperation2();
this.hook1();
this.requiredOperation2();
this.baseOperation3();
this.hook2();
}
/**
* These operations already have implementations.
*/
protected baseOperation1(): void {
console.log('AbstractClass says: I am doing the bulk of the work');
}
protected baseOperation2(): void {
console.log('AbstractClass says: But I let subclasses override some operations');
}
protected baseOperation3(): void {
console.log('AbstractClass says: But I am doing the bulk of the work anyway');
}
/**
* These operations have to be implemented in subclasses.
*/
protected abstract requiredOperations1(): void;
protected abstract requiredOperation2(): void;
/**
* These are "hooks." Subclasses may override them, but it's not mandatory
* since the hooks already have default (but empty) implementation. Hooks
* provide additional extension points in some crucial places of the
* algorithm.
*/
protected hook1(): void { }
protected hook2(): void { }
}
/**
* Concrete classes have to implement all abstract operations of the base class.
* They can also override some operations with a default implementation.
*/
class ConcreteClass1 extends AbstractClass {
protected requiredOperations1(): void {
console.log('ConcreteClass1 says: Implemented Operation1');
}
protected requiredOperation2(): void {
console.log('ConcreteClass1 says: Implemented Operation2');
}
}
/**
* Usually, concrete classes override only a fraction of base class' operations.
*/
class ConcreteClass2 extends AbstractClass {
protected requiredOperations1(): void {
console.log('ConcreteClass2 says: Implemented Operation1');
}
protected requiredOperation2(): void {
console.log('ConcreteClass2 says: Implemented Operation2');
}
protected hook1(): void {
console.log('ConcreteClass2 says: Overridden Hook1');
}
}
/**
* The client code calls the template method to execute the algorithm. Client
* code does not have to know the concrete class of an object it works with, as
* long as it works with objects through the interface of their base class.
*/
function clientCode(abstractClass: AbstractClass) {
// ...
abstractClass.templateMethod();
// ...
}
console.log('Same client code can work with different subclasses:');
clientCode(new ConcreteClass1());
console.log('');
console.log('Same client code can work with different subclasses:');
clientCode(new ConcreteClass2());
Output.txt: 执行结果
Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass1 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass1 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway
Same client code can work with different subclasses:
AbstractClass says: I am doing the bulk of the work
ConcreteClass2 says: Implemented Operation1
AbstractClass says: But I let subclasses override some operations
ConcreteClass2 says: Overridden Hook1
ConcreteClass2 says: Implemented Operation2
AbstractClass says: But I am doing the bulk of the work anyway
