Introduction
Sometimes, we need to carry out several computations / algorithms depending on certain conditions. We go ahead in implementing those generally by applying either switch
or ternary operator or if else
. Though initially somehow we manage to write those programs, but if the program demands are too complex then it is difficult to frame such as well as to maintain.
Moreover, writing all the logic in a single place is not at all advisable as it yields to tight coupling.
Background
In many situations, we come across the need to write computational logic/algorithms which we generally accomplish by using if else
/ switch
or ternary operator. It becomes difficult at times to write such a program and later on adds a lot of cost during maintenance.
Rescuer
Strategy design pattern. It comes under the category of Behavioral Patterns.
How
- Decouples the client and the algorithm/ computation logic in separate classes
- Helps to switch algorithms at any time
- Easily allows to plug in a new algorithm
Pattern Components
The strategy pattern comprises the following components:
- Strategy Interface - Interface common to all concrete strategies
- Concrete Strategies / Different algorithm classes - Various concrete classes that implement the strategy interface for the sake of algorithm implementation specific to itself
- Context Class - Delegates requests to the indicated Concrete Strategies received from the client. It does so as it keeps reference of the concrete strategies.
- Client - In this case, the Windows form
Case Study
Let us take the example of MSWord application. The various Font Styles (e.g. Bold, Italic, etc.) can be implemented by using this design pattern. Let us see the same as under.
Implementation of Strategy Interface
The IFontStyle
interface looks as below:
public interface IFontStyle
{
public Font GetNewFontStyle(Control c);
}
Implementation of Concrete Strategies
There are four concrete strategy classes, viz Bold.cs, Italic.cs, Underline.cs and StrikeThru.cs.
Since all follows the same pattern in this example, so for the sake of simplicity I am describing only for the Bold
concrete class.
It goes as below:
public class Bold : IFontStyle
{
#region IFontStyle Members
public Font GetNewFontStyle(System.Windows.Forms.Control c)
{
return new Font(c.Font, FontStyle.Bold);
}
#endregion
}
The code is self explanatory. The Bold
class implemented the strategy interface IFontStyle
where it is returning the font style as bold
.
Implementation of Context
The FontStyleContext
class is as under:
public class FontStyleContext
{
IFontStyle _IFontStyle;
public FontStyleContext(IFontStyle IFontStyle)
{
this._IFontStyle = IFontStyle;
}
public Font GetFontStyle(Control c)
{
return _IFontStyle.GetNewFontStyle(c);
}
}
Implementation of Client
The client design is as under:
And the code behind for the Bold
Button click is as under:
private void btnBold_Click(object sender, EventArgs e)
{
objFontStyleContext = new FontStyleContext(new Bold());
richTextArea.Font = objFontStyleContext.GetFontStyle(richTextArea);
}
First, we have created an instance of the FontStyleContext
class and then instantiated the same with the appropriate StrategyConcrete
class. Next by calling the GetFontStyle
method, we were able to set the appropriate Font
style for the richtextbox
.
The other buttons will have the same implementation with only call to appropriate concrete classes.
Output
Resource
Conclusion
Strategy pattern is of great importance while implementing program logic that will be invoked depending on conditions. This is just a simple example to demonstrate the pattern idea. In real time, we will be adorned with more complex situations but the underlying concept will be the same.
Comments are highly appreciated for the improvement of the topic.
Thanks for reading the article.
History
- 26th October, 2010: Initial post