“每一个模式描述了一个在我们周围不断重复发生的问题, 以及该问题的解决方案的核心。这样,你就能一次又一次 地使用该方案而不必做重复劳动”。
1.2 软件复杂性 1.2.1 复杂性原因 1.2.2 解决方法1) 分而治之 大问题分解成小问题,复杂问题分解为简单问题
2) 抽象 更高层次来讲,人们处理复杂性有一个通用的技术,即抽象。 由于不能掌握全部的复杂对象,我们选择忽视它的非本质细节, 而去处理泛化和理想化了的对象模型。
1.2.3 软件设计的最终目标 1.3 代码区例子:设计一个鼠标事件
1.3.1 分而治之shape1.h
class Point{ public: int x; int y; }; class Line{ public: Point start; Point end; Line(const Point& start, const Point& end){ this->start = start; this->end = end; } }; class Rect{ public: Point leftUp; int width; int height; Rect(const Point& leftUp, int width, int height){ this->leftUp = leftUp; this->width = width; this->height = height; } }; //增加 class Circle{ };
mainform.h
class MainForm : public Form { private: Point p1; Point p2; vector1.3.2 抽象lineVector; vector rectVector; //改变 vector circleVector; public: MainForm(){ //... } protected: virtual void onMouseDown(const MouseEventArgs& e); virtual void onMouseUp(const MouseEventArgs& e); virtual void onPaint(const PaintEventArgs& e); }; void MainForm::onMouseDown(const MouseEventArgs& e){ p1.x = e.X; p1.y = e.Y; //... Form::onMouseDown(e); } void MainForm::onMouseUp(const MouseEventArgs& e){ p2.x = e.X; p2.y = e.Y; if (rdoLine.Checked){ Line line(p1, p2); lineVector.push_back(line); } else if (rdoRect.Checked){ int width = abs(p2.x - p1.x); int height = abs(p2.y - p1.y); Rect rect(p1, width, height); rectVector.push_back(rect); } //改变 else if (...){ //... circleVector.push_back(circle); } //... this->Refresh(); Form::onMouseUp(e); } void MainForm::onPaint(const PaintEventArgs& e){ //针对直线 for (int i = 0; i < lineVector.size(); i++){ e.Graphics.DrawLine(Pens.Red, lineVector[i].start.x, lineVector[i].start.y, lineVector[i].end.x, lineVector[i].end.y); } //针对矩形 for (int i = 0; i < rectVector.size(); i++){ e.Graphics.DrawRectangle(Pens.Red, rectVector[i].leftUp, rectVector[i].width, rectVector[i].height); } //改变 //针对圆形 for (int i = 0; i < circleVector.size(); i++){ e.Graphics.DrawCircle(Pens.Red, circleVector[i]); } //... Form::onPaint(e); }
shape2.h
class Shape{ public: virtual void Draw(const Graphics& g)=0; virtual ~Shape() { } }; class Point{ public: int x; int y; }; class Line: public Shape{ public: Point start; Point end; Line(const Point& start, const Point& end){ this->start = start; this->end = end; } //实现自己的Draw,负责画自己 virtual void Draw(const Graphics& g){ g.DrawLine(Pens.Red, start.x, start.y,end.x, end.y); } }; class Rect: public Shape{ public: Point leftUp; int width; int height; Rect(const Point& leftUp, int width, int height){ this->leftUp = leftUp; this->width = width; this->height = height; } //实现自己的Draw,负责画自己 virtual void Draw(const Graphics& g){ g.DrawRectangle(Pens.Red, leftUp,width,height); } }; //增加 class Circle : public Shape{ public: //实现自己的Draw,负责画自己 virtual void Draw(const Graphics& g){ g.DrawCircle(Pens.Red, ...); } };
mainform2.h
class MainForm : public Form { private: Point p1; Point p2; //针对所有形状 vectorshapeVector; public: MainForm(){ //... } protected: virtual void onMouseDown(const MouseEventArgs& e); virtual void onMouseUp(const MouseEventArgs& e); virtual void onPaint(const PaintEventArgs& e); }; void MainForm::onMouseDown(const MouseEventArgs& e){ p1.x = e.X; p1.y = e.Y; //... Form::onMouseDown(e); } void MainForm::onMouseUp(const MouseEventArgs& e){ p2.x = e.X; p2.y = e.Y; if (rdoLine.Checked){ shapeVector.push_back(new Line(p1,p2)); } else if (rdoRect.Checked){ int width = abs(p2.x - p1.x); int height = abs(p2.y - p1.y); shapeVector.push_back(new Rect(p1, width, height)); } //改变 else if (...){ //... shapeVector.push_back(circle); } //... this->Refresh(); Form::onMouseUp(e); } void MainForm::onPaint(const PaintEventArgs& e){ //针对所有形状 for (int i = 0; i < shapeVector.size(); i++){ shapeVector[i]->Draw(e.Graphics); //多态调用,各负其责 } //... Form::onPaint(e); }
两个设计的区别:
从动态角度来看,当需要增加新的功能(新增画圆功能)。在分而治之的设计模式中,需要更改程序中很多地方,复用性非常差;在抽象的设计模式中,需要改变的地方极少,复用性得到了很高的提升。
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