Enterprise Library深入解析与灵活应用(3)：倘若将Unity、PIAB、Exception Handling引入MVP模式.. .. ..

最近在做一个Smart Client Software Factory的项目。熟悉SCSF或者CAB的都应该很清楚MVP这种设计模式。MVP是MVC的一种变体，View和Mode分别关注于UI的呈现和业务模型，View和Mode完全分离，View通过Presenter实现对业务模型的访问，Presenter“间接”地调用View实现对UI的操作。对于MVP中的异常处理，我们是直接通过Enterprise Library的Exception Handling Application Block来实现的。具体的做法是：在View中的每个控件的事件中添加try/catch block， 并在catch中通过ExceptionPolicy实现对异常的处理。这样导致的问题是，相同的代码重复散布于整个应用的各个角落，所以我又这样的想法：通过Policy Injection以AOP的方式实现对异常的处理，当有了这个想法后，我又多想了一步，何不再将Unity也一并整合进来。(Source Code 下载)

1、ICalculator：Calculator的接口，定义了一个用于进行除法运算的操作

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

2、Calculator：实现了ICalculator接口

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

3、CalculatePresenter：被View调用进行数学运算，并将运算结果显示到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 ：定义了一个用于显示运算结果的操作，该操作被CalculatePresenter调用

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

5、CalculateView：在本例中是一个Form，并实现了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);
        }
    }
}

• 为了让Policy Injection能够起作用，我让其继承，并且以Custom Attribute的形式应用了ExceptionCallHandler，并制定exception handling policy（在真正的项目开发中，我推荐通过configuration的方式应用Policy injection）。
• 通过实现了基于Unity的Property dependency.

然后我们接着对View进行改造，由于我们在CalculatePresenter使用了和我们需要通过Unity Container的方式来创建CalculatePresenter对象，为此我定义了View的基类：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>
这就使所有的实现。如何运算出现异常，比如将第二个操作数设为零，我们定义的MessageBoxHandler就会被执行，并通过MessageBox将Message显示出来，就像这样：

 

P.S.　虽然讲Policy Injection应用到Presenter可以通过ＡＯＰ的方式来进行异常的处理，但是这要求View上的所有具有潜在异常抛出的逻辑都需要通过Presenter来实现，因为ExceptionHandler是应用到Presenter上面的。

作者：蒋金楠
微信公众账号：大内老A
微博：www.weibo.com/artech
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