Enterprise Library深入解析與靈活應用(3)：倘若將Unity、PIAB、Exception Handling引入MVP模式.. .. ..

最近在做一個Smart Client Software Factory的項目。熟悉SCSF或者CAB的都應該很清楚MVP這種設計模式。MVP是MVC的一種變體，View和Mode分別關注於UI的呈現和業務模型，View和Mode完全分離，View通過Presenter實現對業務模型的訪問，Presenter“間接”地調用View實現對UI的操作。對於MVP中的異常處理，我們是直接通過Enterprise Library的Exception Handling Application Block來實現的。具體的做法是：在View中的每個控件的事件中添加try/catch block， 並在catch中通過ExceptionPolicy實現對異常的處理。這樣導致的問題是，相同的代碼重複散布於整個應用的各個角落，所以我又這樣的想法：通過Policy Injection以AOP的方式實現對異常的處理，當有了這個想法後，我又多想了一步，何不再將Unity也一並整合進來。(Source Code 下載)

1、ICalculator：Calculator的接口，定義了一個用於進行除法運算的操作

namespace Artech.UnityInMVP
{
    public interface ICalculator
    {
        int Divide(int op1, int op2);
    }
}

2、Calculator：實現了ICalculator接口

namespace Artech.UnityInMVP
{
    public class Calculator:ICalculator
    {
        public  int Divide(int op1, int op2)
        {
            return op1 / op2;
        }
    }
}

3、CalculatePresenter：被View調用進行數學運算，並將運算結果顯示到View中

namespace Artech.UnityInMVP
{
     public class CalculatePresenter
    {
        public CalculatePresenter()
        {
           this.Calculator = new Calculator();
        }

        public ICalculateView View
        { get; set; }

        public ICalculator Calculator
        { get; set; }

        public void Calculate(int op1, int op2)
        {
            int result = this.Calculator.Divide(op1, op2);
            this.View.DisplayResult(result);
        }
    }
}

4、ICalculateView ：定義了一個用於顯示運算結果的操作，該操作被CalculatePresenter調用

namespace Artech.UnityInMVP
{
   public interface ICalculateView
    {
        void DisplayResult(int result);
    }
}

5、CalculateView：在本例中是一個Form，並實現了ICalculateView

namespace Artech.UnityInMVP
{
    public partial class CalculateView : ICalculateView
    {      

        public CalculatePresenter Presenter
        { get; set; }

        public void DisplayResult(int result)
        {
            this.textBoxResult.Text = result.ToString();
        }

        private void buttonCalculate_Click(object sender, EventArgs e)
        {
            int op1;
            int op2;
            if(!int.TryParse(this.textBoxOp1.Text.Trim(), out op1))
            {
                return;
            }

             if(!int.TryParse(this.textBoxOp2.Text.Trim(), out op2))
            {
                return;
            }

try
             {
                 this.Presenter.Calculate(op1, op2);
             }
             catch (Exception ex)
             {
                 if (ExceptionPolicy.HandleException(ex, "UI Exception Policy"))
                 {
                     throw;
                 }
             }
        }

        private void CalculateView_Load(object sender, EventArgs e)
        {
            this.Presenter = new CalculatePresenter ();
            this.Presenter.View = this;
        }
    }
}

namespace Artech.UnityInMVP
{
   
    public class CalculatePresenter:
    {
        public CalculatePresenter()
        {
            this.Calculator = new Calculator();
        }

        public ICalculateView View
        { get; set; }

[Dependency]
        public ICalculator Calculator
        { get; set; }

        public void Calculate(int op1, int op2)
        {
            int result = this.Calculator.Divide(op1, op2);
            this.View.DisplayResult(result);
        }
    }
}

• 為了讓Policy Injection能夠起作用，我讓其繼承，並且以Custom Attribute的形式應用了ExceptionCallHandler，並製定exception handling policy（在真正的項目開發中，我推薦通過configuration的方式應用Policy injection）。
• 通過實現了基於Unity的Property dependency.

然後我們接著對View進行改造，由於我們在CalculatePresenter使用了和我們需要通過Unity Container的方式來創建CalculatePresenter對象，為此我定義了View的基類：ViewBase.

namespace Artech.UnityInMVP
{
    public partial class ViewBase : Form
    {     

        protected IUnityContainer UnityContainer
        {
            get
            {
                if (this._unityContainer == null)
                {
                    this._unityContainer = new UnityContainer();
                    UnityConfigurationSection unityConfigSection = ConfigurationManager.GetSection("unity") as UnityConfigurationSection;
                    unityConfigSection.Containers.Default.Configure(this._unityContainer);
                }
                return this._unityContainer;
            }
        }
    }
}

namespace Artech.UnityInMVP
{
    public partial class CalculateView : ViewBase, ICalculateView
    {
        public CalculateView()
        {
            InitializeComponent();                   
        }

        public CalculatePresenter Presenter
        { get; set; }

        public void DisplayResult(int result)
        {
            this.textBoxResult.Text = result.ToString();
        }

        private void buttonCalculate_Click(object sender, EventArgs e)
        {
            int op1;
            int op2;
            if(!int.TryParse(this.textBoxOp1.Text.Trim(), out op1))
            {
                return;
            }

             if(!int.TryParse(this.textBoxOp2.Text.Trim(), out op2))
            {
                return;
            }

this.Presenter.Calculate(op1, op2);
        }

        private void CalculateView_Load(object sender, EventArgs e)
        {
            this.Presenter =
            this.Presenter.View = this;
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <section name="exceptionHandling" type="Microsoft.Practices.EnterpriseLibrary.ExceptionHandling.Configuration.ExceptionHandlingSettings, Microsoft.Practices.EnterpriseLibrary.ExceptionHandling, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
    <section name="unity" type="Microsoft.Practices.Unity.Configuration.UnityConfigurationSection,Microsoft.Practices.Unity.Configuration, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
  </configSections>
  <exceptionHandling>
    <exceptionPolicies>
      <add name="UI Exception Policy">
        <exceptionTypes>
          <add type="System.Exception, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
            postHandlingAction="None" name="Exception">
            <exceptionHandlers>
              <add type="Artech.UnityInMVP.ExceptionHandlers.MessageBoxHandler,Artech.UnityInMVP"
                name="Custom Handler" />
            </exceptionHandlers>
          </add>
        </exceptionTypes>
      </add>
    </exceptionPolicies>
  </exceptionHandling>
  <unity>
    <containers>
      <container>
        <types>
            <type type=" Artech.UnityInMVP.ICalculator,Artech.UnityInMVP" mapTo="Artech.UnityInMVP.Calculator,Artech.UnityInMVP"/>
        </types>
        <extensions>
          <add type="Artech.UnityInMVP.UnityExtensions.PolicyInjectionExtension,Artech.UnityInMVP" />
        </extensions>
      </container>
    </containers>
  </unity>
</configuration>

<exceptionHandling>
    <exceptionPolicies>
      <add name="UI Exception Policy">
        <exceptionTypes>
          <add type="System.Exception, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
            postHandlingAction="None" name="Exception">
            <exceptionHandlers>
              <add type="Artech.UnityInMVP.ExceptionHandlers.MessageBoxHandler,Artech.UnityInMVP"
                name="Custom Handler" />
            </exceptionHandlers>
          </add>
        </exceptionTypes>
      </add>
    </exceptionPolicies>
  </exceptionHandling>

 

。
<unity>
    <containers>
      <container>
        <types>
            <type type=" Artech.UnityInMVP.ICalculator,Artech.UnityInMVP" mapTo="Artech.UnityInMVP.Calculator,Artech.UnityInMVP"/>
        </types>
        <extensions>
          <add type="Artech.UnityInMVP.UnityExtensions.PolicyInjectionExtension,Artech.UnityInMVP" />
        </extensions>
      </container>
    </containers>
  </unity>
這就使所有的實現。如何運算出現異常，比如將第二個操作數設為零，我們定義的MessageBoxHandler就會被執行，並通過MessageBox將Message顯示出來，就像這樣：

 

P.S.　雖然講Policy Injection應用到Presenter可以通過ＡＯＰ的方式來進行異常的處理，但是這要求View上的所有具有潛在異常拋出的邏輯都需要通過Presenter來實現，因為ExceptionHandler是應用到Presenter上麵的。

作者：蔣金楠
微信公眾賬號：大內老A
微博：www.weibo.com/artech
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原文鏈接