Dependency injection using property in C#

In my previous articles, we discussed how we can inject the dependency using constructor and method. This is the final approach we can use to inject the dependency where we will see how we can implement the dependency injection using the property injection. We will be using the same code which we used in our previous discussions.

In property injection, we simply create a property of the type of dependency required by our class. Whenever we need to call a method which needs a dependency to be used, we set the property of the class, to the required concrete implementation of the dependency. In our case, we will create a property named logger which is of type ILogger, in the TestClass. So our code changes to:

public class TestClass  
{  
    public ILogger logger  
    {  
        get;  
        set;  
    }  
  
    public void GetData()  
    {   
      try  
      {  
          logger.SaveException();  
          //Get some data    
      }  
      catch (Exception ex)  
      {  
         logger.SaveException();  
      }  
   }  
}  

Now, when we call the GetData method, we will set the concrete implementation of ILogger i.e. DBLogger or TextLogger to the logger property defined in the class. So the code will look like the following:

TestClass testClass = new TestClass();  
testClass.logger = new DBLogger();  
testClass.GetData();  

That’s it. We are done with the code. This is all we have to do to implement the property injection. Run the code and generate and exception and see the results. 

This is not a much used approach, but it is useful in situations where we need to avoid the use of constructor injection, similar to the method injection. Hope you enjoyed reading these three methods. Happy coding...!!!

Dependency injection using method injection in C#

In my previous article, we discussed how we can inject the dependency using constructor. Continuing on the same lines, we will now discuss how we can implement dependency injection using the method injection. We will be using the same code which we used in our previous discussion.

The disadvantage with the constructor injection is that whenever we create an instance of the class, a new instance of the dependency gets generated and injected. It becomes available for all the method even though it was required for a single method only, as we are passing it through the constructor. So this is just not a good coding practice. So we can avoid this scenario by using the method injection.

In method injection, we change the actual method of the class (which requires dependency), to inject the dependency into it. The method will receive this dependency through parameter. So we add a new parameter to the GetData method. This parameter will be of type ILogger. So the abstraction gets passed to the class through the method itself. So our code changes to:

public class TestClass  
{  
        ILogger logger;  
   
        public void GetData(ILogger iLogger)  
        {  
            logger = iLogger;  
            try  
            {  
                //Get some data    
            }  
            catch (Exception ex)  
            {  
                logger.SaveException();  
            }  
        }  
}  

Now, when we call the GetData method, we will pass the concrete implementation of ILogger i.e. DBLogger or TextLogger to the method as a parameter. So the code will look like the following:

TestClass testClass = new TestClass();  
testClass.GetData(new DBLogger());  

That’s it. We are done with the code. This is all we have to do to implement the method injection. Run the code and generate any exception and see that the DBLogger method get's called.

Dependency injection using constructor in C#

In my previous article we discussed about the concept of dependency injection and inversion of control. Continuing on the same lines, we will now discuss how we can implement the dependency injection using the constructor injection. We will be using the same code which we used in our previous discussion.

As the name suggests itself, in this scenario, we use the constructors of the class, to inject the dependency into it. So we add a new parameterized constructor in the class. This parameter will be of type ILogger. So the abstraction gets passed to the class through the constructor, whenever an instance of the class is created. So our code changes to:

public class TestClass  
{  
    ILogger logger;  
  
    public TestClass(ILogger iLogger)  
    {  
      logger = iLogger;  
    }  
    public void GetData()  
    {  
      try  
      {  
        //Get some data    
      }  
      catch (Exception ex)  
      {  
          logger.SaveException();  
      }  
    }  
}  

Now, when we call the GetData method, we will be creating a new instance of the class and pass the concrete implementation of ILogger i.e. DBLogger or TextLogger to the constructor. So the code will look like the following:

TestClass testClass = new TestClass(new TextLogger());  
testClass.GetData();  

That’s it. We are done with the code. Run the code and generate any exception and see the results. This is all we have to do to implement the constructor injection. In my next article, we will see how we can inject dependency using method injection. Happy coding...!!!

Dependency Injection and Inversion of control using C#

In this article, we will try to understand the concept of dependency injection and inversion control. The basic idea behind dependency injection is that:

1. High-level modules should not depend on low-level modules. Both should depend on abstractions.
2. Abstractions should not depend upon details. Details should depend upon abstractions.

These points here suggest that whenever we have a piece of code, where one class needs to use another class, for some functionality, the main class should not directly refer to the required class. It should always depend on the abstraction rather than its concrete implementation. Let’s see with an example what we mean over here:

public class TestClass  
{  
   ILogger logger;  
   public void GetData()  
   {  
     try  
     {  
        //Get some data    
     }  
     catch (Exception ex)  
     {   
        logger.SaveException();  
     }  
   }  
}  
    
public class Logger    
{    
   public void SaveException()    
   {    
      //Log the exception to textfile  
   }    
} 

Consider the piece of code above. Here, we have a test class, which executes the GetData function. In case any exception occurs, the catch block logs the error in a text file, using the SaveException method in the Logger class. So here we can see that the GetData method is directly dependent on the Logger class to save the exception to text file.

The above implementation seems to be fine until we have a requirement that we would like to save the exception to database, instead of the text file. In such a case, we will add another method and call that method say, SaveExceptionToDatabase. Further, if we need to save the exception in any other form, again we need to change the code in this class and then call that new method. So this will be a problem as we have to change the code whenever there is a new implementation and moreover, we may break the existing GetData method by these changes.

This is where the abstractions are useful. We implement the abstractions using the interfaces and main classes use these abstractions, which is nothing but the concept of Inversion of control, which is used to make a high level module dependent on the abstractions rather then the concrete implementations.

So in order to do this, we will change our code and add an interface named ILogger with a single method named SaveException. We also add two classes named DBLogger and TextLogger. Both these classes will implement the ILogger interface. So the code will change to:

public interface ILogger  
{  
  void SaveException();  
}  
  
public class DBLogger : ILogger  
{  
   public void SaveException()  
   {  
     //Save Exception to database  
   }  
}  
public class TextLogger : ILogger  
{  
   public void SaveException()  
   {  
      //Save Exception to text file  
   }  
}  

Next, we need to change the GetData function to use the dependency through abstraction instead of the concrete implementation. For this, we change the code to remove the Logger class instance and use the ILogger instance. So the code changes to: 

public class TestClass  
{  
  ILogger logger;  
  public void GetData()  
  {  
    try  
    {  
       //Get some data    
    }  
    catch (Exception ex)  
    {   
       logger.SaveException();  
    }  
  }  
}  

Now, the point is, we have changed the main class to use the dependency through interface, but how does the GetData receive the dependency i.e. the concrete implementation for ILogger which could be either DBLogger or TextLogger. This is where we have the concept of dependency injection. We will inject the dependency into the class. For this purpose, we can use the following three techniques.

1. Constructor injectionInject the dependency through the constructor of the class.
2. Method injectionInject the dependency through the method of the class, which requires dependency.
3. Property InjectionInject the dependency through a property in the main class.

We will discuss these techniques in our next articles. For complex scenarios where we may have nested or multiple depdendencies, we have the concept of IoC containers to map the dependencies. Happy coding...!!!

C# 7 Features - out variable initialization

In my previous article, we discussed about the concept of local functions in C# 7.0. In this article, we will see another feature related to the use of out type variables. 

 

Out variables are not new in C# and provide a big advantage of how we can return multiple values from a method. However, in order to pass a out type variable as a method parameter, we have to declare it first and then pass it into the method parameter, with out keyword. Something like the following: 

1. static void Main(string[] args)  
2. {  
3.   
4.             int userId;  
5.             string userName;  
6.             GetDetails(out userId, out userName);  
7.   
8.             Console.ReadKey();  
9. }  
10. public static void GetDetails(out Int32 UserId, out string Username)  
11. {  
12.             UserId = 12;  
13.             Username = "Test User";  
14. }  

However, in C# 7.0, we can declare the variable at the time of passing it as a method parameter, when method is being called. This means the following code will work fine in C# 7.0. 

1. static void Main(string[] args)  
2. {  
3.             GetDetails(out int userId, out string userName);  
4.             Console.ReadKey();  
5. }  

Also, now we can have the out variable being declared as of var type, when passed as method parameter. So following code is valid and works fine in C# 7.0, which did not worked in earlier versions of C#. 

1. static void Main(string[] args)  
2.         {  
3.             GetDetails(out var userId, out var userName);  
4.             Console.ReadKey();  
5.         }  

Hope you enjoyed reading it. Happy coding...!!!

Dynamic methods in C# using CodeDom

In my previous article, we discussed how we can create a dynamic class using CodeDom namespace. Now we will discuss how we can add methods to these classes. For this we will be use the same code as in our previous discussion.

For adding method to the class, we will use CodeMemberMethod class, which provides different properties, to define methods. For our sample we will create a dynamic method which will take two input parameters, calculate their sum and return the sum. Let's with basic method signatures. So our code will look like the following: 

1. CodeTypeReference methodReturnType = new CodeTypeReference(typeof(System.Int32)); 
2. CodeMemberMethod myMethod = new CodeMemberMethod();  
3.   
4.  // Generate Method signatures.  
5.  myMethod.Name = "MySum";  
6.  myMethod.ReturnType = methodReturnType;  
7.  myMethod.Attributes = MemberAttributes.Public;  

We use of the CodeTypeReference class to specify the return type of our method. To add parameters for this method, we will use the CodeParameterDeclarationExpression class. So our code will look like the following: 

1. // Initialize for Method parameters  
2. CodeParameterDeclarationExpression methodPrm1 = new CodeParameterDeclarationExpression(typeof(Int32), "X");  
3. CodeParameterDeclarationExpression methodPrm2 = new CodeParameterDeclarationExpression(typeof(Int32), "Y");  
4. myMethod.Parameters.AddRange(new CodeParameterDeclarationExpression[] { methodPrm1, methodPrm2 });  

Next, to specify the method definition we use the CodeSnippetExpression class. Our method will simply the sum of our input parameters. So we will generate an expression to perform the sum of the numbers and add it to the method. So our code will change to the following: 

1. // Generate method definition  
2. CodeSnippetExpression codeSnippet = new CodeSnippetExpression("return X + Y");  
3.   
4. // Add method definition to method  
5. myMethod.Statements.Add(codeSnippet);  

Finally we add the method to our class definition using following code: 

1. // Add method to the class.  
2. cls.Members.Add(myMethod);  

So our complete code will look like the following: 

1.  CodeNamespace nameSpace = new CodeNamespace("sampleNameSpace");  
2.   
3.  nameSpace.Imports.Add(new CodeNamespaceImport("System"));  
4.  nameSpace.Imports.Add(new CodeNamespaceImport("System.Linq"));  
5.  nameSpace.Imports.Add(new CodeNamespaceImport("System.Text"));  
6.   
7.  CodeTypeDeclaration cls = new CodeTypeDeclaration();  
8.  cls.Name = "SampleClass";  
9.  cls.IsClass = true;  
10.  cls.Attributes = MemberAttributes.Public;  
11.  nameSpace.Types.Add(cls);  
12.   
13.  // Initialize for Method Return type  
14.  CodeTypeReference methodReturnType = new CodeTypeReference(typeof(System.Int32));  
15.  CodeMemberMethod myMethod = new CodeMemberMethod();  
16.   
17.  // Generate Method signatures.  
18.  myMethod.Name = "MySum";  
19.  myMethod.ReturnType = methodReturnType;  
20.  myMethod.Attributes = MemberAttributes.Public | MemberAttributes.Final;  
21.   
22.  // Initialize for Method parameters  
23.  CodeParameterDeclarationExpression methodPrm1 = new CodeParameterDeclarationExpression(typeof(Int32), "X");  
24.  CodeParameterDeclarationExpression methodPrm2 = new CodeParameterDeclarationExpression(typeof(Int32), "Y");  
25.  myMethod.Parameters.AddRange(new CodeParameterDeclarationExpression[] { methodPrm1, methodPrm2 });  
26.   
27.  // Generate method definition  
28.  CodeSnippetExpression codeSnippet = new  CodeSnippetExpression("return X + Y");  
29.   
30. // Add method definition to method  
31.  myMethod.Statements.Add(codeSnippet);  
32.   
33.  // Add method to the class.  
34.  cls.Members.Add(myMethod);  
35.   
36.  CodeCompileUnit compileUnit = new CodeCompileUnit();  
37.  compileUnit.Namespaces.Add(nameSpace);  
38.  CSharpCodeProvider csharpcodeprovider = new CSharpCodeProvider();  
39.   
40.  CSharpCodeProvider provider = new CSharpCodeProvider();  
41.   
42.  using (StreamWriter sw = new StreamWriter(@"C:\TestFile.cs", false))  
43.  {  
44.      IndentedTextWriter tw = new IndentedTextWriter(sw, "    ");  
45.      provider.GenerateCodeFromCompileUnit(compileUnit, tw, new CodeGeneratorOptions());  
46.      tw.Close();  
47.  }  

Run the application and see the code getting generated: 

1. //------------------------------------------------------------------------------  
2. // <auto-generated>  
3. //     This code was generated by a tool.  
4. //     Runtime Version:4.0.30319.42000  
5. //  
6. //     Changes to this file may cause incorrect behavior and will be lost if  
7. //     the code is regenerated.  
8. // </auto-generated>  
9. //------------------------------------------------------------------------------  
10.   
11. namespace sampleNameSpace {  
12.     using System;  
13.     using System.Linq;  
14.     using System.Text;  
15.       
16.       
17.     public class SampleClass {  
18.           
19.         public int MySum(int X, int Y) {  
20.             return X + Y;  
21.         }  
22.     }  
23. }  

So this was about how we can generate the dynamic class and add methods to it. Hope you enjoyed reading it. Happy coding...!!!