Bridge

一、前言

由于某些类型的固有的实现逻辑，使得它们具有两个变化的维度，乃至多个纬度的变化。桥接模式将抽象部分(业务功能)与实现部分(平台实现)分离，使它们都可以独立地变化，而不引入额外的复杂度。桥接模式类似于策略模式，区别在于策略模式封装一系列算法使得算法可以互相替换。策略模式使抽象部分和实现部分分离，可以独立变化。

二、类图

三、示例

1. 没有使用模式

package bridge

type Image struct {
}

type PCMessageBase struct{
};
func (this *PCMessageBase)PlaySound() {
}
func (this *PCMessageBase)DrawShape() {
}
func (this *PCMessageBase)WriteText() {
}
func (this *PCMessageBase)Connect() {
}

func NewPCMessageLite(pcMessageBase *PCMessageBase) *PCMessageLite {
	return &PCMessageLite {
		PCMessageBase:pcMessageBase,
	}
}
type PCMessageLite struct {
	*PCMessageBase
}
func (this *PCMessageLite)Login(username, password string) {
	this.Connect()
}
func (this *PCMessageLite)SendMessage(message string) {
	this.WriteText()
}
func (this *PCMessageLite)SendPicture(image Image) {
	this.DrawShape()
}

func NewPCMessagePerfect(pcMessageBase *PCMessageBase) *PCMessagePerfect {
	return &PCMessagePerfect {
		PCMessageBase:pcMessageBase,
	}
}
type PCMessagePerfect struct {
	*PCMessageBase
}
func (this *PCMessagePerfect)Login(username, password string) {
	this.PlaySound()
	this.Connect()
}
func (this *PCMessagePerfect)SendMessage(message string) {
	this.PlaySound()
	this.WriteText()
}
func (this *PCMessagePerfect)SendPicture(image Image) {
	this.PlaySound()
	this.DrawShape()
}


type MobileMessageBase struct{
};
func (this *MobileMessageBase)PlaySound() {
}
func (this *MobileMessageBase)DrawShape() {
}
func (this *MobileMessageBase)WriteText() {
}
func (this *MobileMessageBase)Connect() {
}

func NewMobileMessageLite(mobileMessageBase *MobileMessageBase) *MobileMessageLite {
	return &MobileMessageLite {
		MobileMessageBase:mobileMessageBase,
	}
}
type MobileMessageLite struct {
	*MobileMessageBase
}
func (this *MobileMessageLite)Login(username, password string) {
	this.Connect()
}
func (this *MobileMessageLite)SendMessage(message string) {
	this.WriteText()
}
func (this *MobileMessageLite)SendPicture(image Image) {
	this.DrawShape()
}

func NewMobileMessagePerfect(mobileMessageBase *MobileMessageBase) *MobileMessagePerfect {
	return &MobileMessagePerfect {
		MobileMessageBase:mobileMessageBase,
	}
}
type MobileMessagePerfect struct {
	*MobileMessageBase
}
func (this *MobileMessagePerfect)Login(username, password string) {
	this.PlaySound()
	this.Connect()
}
func (this *MobileMessagePerfect)SendMessage(message string) {
	this.PlaySound()
	this.WriteText()
}
func (this *MobileMessagePerfect)SendPicture(image Image) {
	this.PlaySound()
	this.DrawShape()
}

func Process() {
	mb := &MobileMessageBase{}
	mf := NewMobileMessagePerfect(mb)
	mf.Connect()
}

2. 使用模式

package bridge

type Image struct {
}

type Message interface{
	Login(username, password string)
	SendMessage(message string)
	SendPicture(image Image)
}

type MessageImp interface{
	PlaySound()
	DrawShape()
	WriteText()
	Connect()
}

type PCMessageBase struct{
};
func (this *PCMessageBase)PlaySound() {
}
func (this *PCMessageBase)DrawShape() {
}
func (this *PCMessageBase)WriteText() {
}
func (this *PCMessageBase)Connect() {
}

type MobileMessageBase struct{
};
func (this *MobileMessageBase)PlaySound() {
}
func (this *MobileMessageBase)DrawShape() {
}
func (this *MobileMessageBase)WriteText() {
}
func (this *MobileMessageBase)Connect() {
}

func NewMessageLite(messageImp MessageImp) *MessageLite{
	return &MessageLite{
		MessageImp: messageImp,
	}
}
type MessageLite struct {
	MessageImp
}
func (this *MessageLite)Login(username, password string) {
	this.Connect()
}
func (this *MessageLite)SendMessage(message string) {
	this.WriteText()
}
func (this *MessageLite)SendPicture(image Image) {
	this.DrawShape()
}

func NewMessagePerfect(messageImp MessageImp) *MessagePerfect{
	return &MessagePerfect{
		MessageImp: messageImp,
	}
}
type MessagePerfect struct {
	MessageImp
}
func (this *MessagePerfect)Login(username, password string) {
	this.PlaySound()
	this.Connect()
}
func (this *MessagePerfect)SendMessage(message string) {
	this.PlaySound()
	this.WriteText()
}
func (this *MessagePerfect)SendPicture(image Image) {
	this.PlaySound()
	this.DrawShape()
}

func Process() {
	pc := &PCMessageBase{}
	ml := NewMessageLite(pc)
	ml.Login("test", "test")
}

四、总结

• Bridge模式使用对象间的组合关系解耦了抽象和实现之间固有的绑定关系，使得抽象和实现可以沿着各自的维度来变化，所谓抽象和实现沿着各自纬度的变化，即子类化它们。
• Bridge模式的应用一般在两个非常强的变化维度，有时一个 类也有多于两个的变化维度，这时可以使用Bridge的扩展模式。