Nov 2005 MSc Slide 1 - Another Example of a Structural Pattern Alternative way of adding Functionality to an existing class (alternative to a derived class) Favors Composition over Inheritance Often referred to as a Wrapper Advantage: No need for several levels of Inheritence (reduces Complexity) Decorator Pattern

Nov 2005 MSc Slide 2 Instead of: Decorator Pattern X Y Z Z p = new Z(); X YZ Z p=new Z(new Y(new X())); Can add functionality by adding more Objects

Nov 2005 MSc Slide 3 Typically used to change appearance of a Visual Component One big advantage is that you can dynamically change appearance/functionality of a component Decorator Pattern

Nov 2005 MSc Slide 4 Decorator Pattern Want to decorate a Button

Nov 2005 MSc Slide 5 using System; using System.Windows.Forms; using System.Drawing; abstract class Decorator : Panel { protected Control ctrl; public Decorator(Control c) { this.Size=c.Size; ctrl=c; Controls.Add(c); c.Paint += new PaintEventHandler( paint); } virtual public void paint(object sender, PaintEventArgs pe){} }

Nov 2005 MSc Slide 6 class SlashDecorator : Decorator { public SlashDecorator(Control c):base(c) {} override public void paint(object sender, PaintEventArgs pe){ Pen aPen = new Pen(Color.Black, 1); Graphics g = pe.Graphics; int x2 = this.Size.Width; int y2 = this.Size.Height; g.DrawLine(aPen,0,0,x2,y2); }

Nov 2005 MSc Slide 7 class GFrame:Form { private Button cbutton=new Button(); private Button dbutton=new Button(); private SlashDecorator d; public GFrame():base(){ cbutton.Text="cbutton"; dbutton.Text="dbutton"; d=new SlashDecorator(dbutton); cbutton.SetBounds(10,10,cbutton.Size.Width, cbutton.Size.Height); d.SetBounds(100,10,d.Size.Width,d.Size.Height); Controls.Add(cbutton); Controls.Add(d); }}

Nov 2005 MSc Slide 8 public class Test92{ public static void Main(string[] args){ Application.Run(new GFrame()); }

Nov 2005 MSc Slide 9 Example 2: This time we have a Decorated Label

Nov 2005 MSc Slide 10 using System; using System.Windows.Forms; using System.Drawing; abstract class Decorator : Panel { protected Control ctrl; public Decorator(Control c) { this.Size=c.Size; ctrl=c; Controls.Add(c); c.Paint += new PaintEventHandler( paint); } virtual public void paint(object sender, PaintEventArgs pe){} } As before

Nov 2005 MSc Slide 11 class CoolDecorator : Decorator { public CoolDecorator(Control c):base(c) { } override public void paint(object sender, PaintEventArgs pe){ Pen aPen = new Pen(Color.Red, 2); Graphics g = pe.Graphics; int x2 = this.Size.Width; int y2 = this.Size.Height; g.DrawRectangle(aPen,0,0,x2,y2); } Draw a Rectangle

Nov 2005 MSc Slide 12 class GFrame:Form { private Label l=new Label(); private CoolDecorator c; public GFrame():base(){ l.Text="MyLabel"; c=new CoolDecorator(l); c.SetBounds(10,10,c.Size.Width, c.Size.Height-5); Controls.Add(c); }

Nov 2005 MSc Slide 13 public class Test92{ public static void Main(string[] args){ Application.Run(new GFrame()); }

Nov 2005 MSc Slide 14 Now to add Dynamic Behaviour, change Colour to Blue

Nov 2005 MSc Slide 15 class CoolDecorator : Decorator { bool mouse_over=false; public CoolDecorator(Control c):base(c) { EventHandler evh = new EventHandler(mouseEnter); ctrl.MouseEnter+= evh; ctrl.MouseLeave += new EventHandler(mouseLeave); } public void mouseEnter(object sender, EventArgs e){ mouse_over = true; ctrl.Refresh (); } public void mouseLeave(object sender, EventArgs e){ mouse_over = false; this.Refresh (); }

Nov 2005 MSc Slide 16 override public void paint(object sender, PaintEventArgs pe){ Pen aPen = new Pen(Color.Red, 2); Pen bPen = new Pen(Color.Blue, 2); Graphics g = pe.Graphics; int x2 = this.Size.Width; int y2 = this.Size.Height; g.DrawRectangle(aPen,0,0,x2,y2); if (mouse_over == true){ g.DrawRectangle(bPen,0,0,x2,y2);} } }

Nov 2005 MSc Slide 17 UML Class Diagram Control CoolDecorator SlashDecorator GFrame DecoratorControl Panel

Nov 2005 MSc Slide 18 Big Advantage of Decorator(Wrapper) is that you can add functionality by adding Objects Label lab=new Label(); lab.Text="Example"; SlashDecorator c=new SlashDecorator(lab); Controls.Add(c);

Nov 2005 MSc Slide 19 Combining Decorators c=new CoolDecorator(b); Normally: Want: c=new SlashDecorator(new CoolDecorator(b));

Nov 2005 MSc Slide 20 Combining Decorators c=new CoolDecorator(null, b); Normal Wrapper: Embedded Wrapper: sd=new SlashDecorator(new CoolDecorator(null,b),b); In practice new a ref to parent and underlying control:

Nov 2005 MSc Slide 21 abstract class Decorator : Panel { protected Control ctrl; public Decorator(Control c) { this.Size=c.Size; ctrl=c; Controls.Add(c); c.Paint += new PaintEventHandler( paint); } virtual public void paint(object sender, PaintEventArgs pe){} } As before

Nov 2005 MSc Slide 22 class CoolDecorator : Decorator { bool mouse_over=false; SlashDecorator sdec; public CoolDecorator(SlashDecorator sdec,Control c) :base(c) { this.sdec = sdec; if (sdec !=null) c.Paint += new PaintEventHandler( sdec.paint); EventHandler evh = new EventHandler(mouseEnter); ctrl.MouseEnter+= evh; MouseEventHandler(mouseMove); ctrl.MouseLeave += new EventHandler(mouseLeave); } override public void paint(object sender, … As before

Nov 2005 MSc Slide 23 class SlashDecorator : Decorator { private CoolDecorator cd=null; public SlashDecorator(CoolDecorator cd,Control c) :base(c) { this.cd=cd; if (cd !=null) c.Paint += new PaintEventHandler( cd.paint); } override public void paint(object sender, … As before

Nov 2005 MSc Slide 24 class GFrame:Form { private Label l=new Label(); private SlashDecorator sd; public GFrame():base(){ l.Text="MyLabel"; sd=new SlashDecorator(new CoolDecorator(null,l),l); sd.SetBounds(100,10,sd.Size.Width,sd.Size.Height); Controls.Add(sd); this.Refresh();}

Nov 2005 MSc Slide 25 Exercise 0: Modify the first Decorator (test0.java) so its in the following format

Nov 2005 MSc Slide 26 Exercise 1: Modify Exercise 0 to include some dynamic Behaviour Red X