/*唯一能画出来的是一个圆，每次图形改变时，有可能需要画矩形，DrawShape必须改变，这样增加了维护成本*还有个不足是，画圆形是，我可以根据圆心和半径画，可能不想这样画，我想根据一段弧来画，那么必须改变*画内部的方法。 */public class ShapeRenderer{private IGraphicsContext _graphicsContext;public void DrawShape(Circle circleShape){_graphicsContext.DrawCircle(circleShape.Position, circleShape.Radius);}}//可以画出多个形状，只需要把形状继承Ishape接口，然后在画的时候中传入绘画时的方法//就可以达到了控制反转的效果了public class ShapeRenderer{private IGraphicsContext graphicsContext;public void DrawShape(IShape shape){shape.Draw(graphicsContext);}}

public class SampleViewModel : INotifyPropertyChanged{/** 最常用的public元素放在最顶端和常用的字段放在最低端* 在此例子中ViewModel不负责计算的过程，而是通过Model来实现的* 属性是View中要使用的* */#region Constructorspublic SampleViewModel(){_model = new SampleModel();}#endregion#region Properties//也是可读写的属性，但是只有ViewModel可以Set//由于ViewModel变化时要通知View所以，会在值改变时//调用PropertyChanged事件public double Result{get { return _result; }private set{if(_result != value){_result = value;if (PropertyChanged != null){PropertyChanged(this, new PropertyChangedEventArgs("Result"));}}}}//可以读写的原因是我们要让用户来写内容，从而使员我们的ViewModel来读取public double Number{get;set;}public ICommand CalculateSquareRootCommand{get{if (_calculateSquareRootCommand == null){_calculateSquareRootCommand = new RelayCommand(param =>this.CalculateSquareRoot());}return _calculateSquareRootCommand;}}#endregion#region Methodsprivate void CalculateSquareRoot(){Result = _model.CalculateSquareRoot(Number);}#endregion#region Fieldspublic event PropertyChangedEventHandler PropertyChanged;private double _result;private RelayCommand _calculateSquareRootCommand;private SampleModel _model;#endregion}