TypeScript 外观模式讲解和代码示例
外观是一种结构型设计模式， 能为复杂系统、 程序库或框架提供一个简单 （但有限） 的接口。
尽管外观模式降低了程序的整体复杂度， 但它同时也有助于将不需要的依赖移动到同一个位置。
复杂度：
流行度：
使用示例： 使用 TypeScript 开发的程序中会经常使用外观模式。 它在与复杂程序库和 API 协作时特别有用。
识别方法： 外观可以通过使用简单接口， 但将绝大部分工作委派给其他类的类来识别。 通常情况下， 外观管理其所使用的对象的完整生命周期。
概念示例
本例说明了外观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 Facade class provides a simple interface to the complex logic of one or
* several subsystems. The Facade delegates the client requests to the
* appropriate objects within the subsystem. The Facade is also responsible for
* managing their lifecycle. All of this shields the client from the undesired
* complexity of the subsystem.
*/
class Facade {
protected subsystem1: Subsystem1;
protected subsystem2: Subsystem2;
/**
* Depending on your application's needs, you can provide the Facade with
* existing subsystem objects or force the Facade to create them on its own.
*/
constructor(subsystem1?: Subsystem1, subsystem2?: Subsystem2) {
this.subsystem1 = subsystem1 || new Subsystem1();
this.subsystem2 = subsystem2 || new Subsystem2();
}
/**
* The Facade's methods are convenient shortcuts to the sophisticated
* functionality of the subsystems. However, clients get only to a fraction
* of a subsystem's capabilities.
*/
public operation(): string {
let result = 'Facade initializes subsystems:\n';
result += this.subsystem1.operation1();
result += this.subsystem2.operation1();
result += 'Facade orders subsystems to perform the action:\n';
result += this.subsystem1.operationN();
result += this.subsystem2.operationZ();
return result;
}
}
/**
* The Subsystem can accept requests either from the facade or client directly.
* In any case, to the Subsystem, the Facade is yet another client, and it's not
* a part of the Subsystem.
*/
class Subsystem1 {
public operation1(): string {
return 'Subsystem1: Ready!\n';
}
// ...
public operationN(): string {
return 'Subsystem1: Go!\n';
}
}
/**
* Some facades can work with multiple subsystems at the same time.
*/
class Subsystem2 {
public operation1(): string {
return 'Subsystem2: Get ready!\n';
}
// ...
public operationZ(): string {
return 'Subsystem2: Fire!';
}
}
/**
* The client code works with complex subsystems through a simple interface
* provided by the Facade. When a facade manages the lifecycle of the subsystem,
* the client might not even know about the existence of the subsystem. This
* approach lets you keep the complexity under control.
*/
function clientCode(facade: Facade) {
// ...
console.log(facade.operation());
// ...
}
/**
* The client code may have some of the subsystem's objects already created. In
* this case, it might be worthwhile to initialize the Facade with these objects
* instead of letting the Facade create new instances.
*/
const subsystem1 = new Subsystem1();
const subsystem2 = new Subsystem2();
const facade = new Facade(subsystem1, subsystem2);
clientCode(facade);
Output.txt: 执行结果
Facade initializes subsystems:
Subsystem1: Ready!
Subsystem2: Get ready!
Facade orders subsystems to perform the action:
Subsystem1: Go!
Subsystem2: Fire!
