COM Interop in c# 4.0
// Code simplified for this example
using Microsoft.Office.Interop;
using Microsoft.Office.Interop.Word;
object foo = "MyFile.txt";
object bar = Missing.Value;
object optional = Missing.Value;
Document doc = (Document)Application.GetDocument(ref foo, ref bar, ref optional);
doc.CheckSpelling(ref optional, ref optional, ref optional, ref optional);
There are (at least) three problems with the code above. First, you have to declare all your variables as objects and pass them with the ref keyword. Second, you can't omit parameters and must also pass the Missing.Value even if you are not using the parameter. And third, behind the scenes, you are using huge (in file size) interop assemblies just to make one method call.
C# 4.0 will allow you to write the code above in a much simpler form that ends up looking almost exactly like 'normal' C# code. This is accomplished by using some of the features already discussed; namely dynamic support and optional parameters.
// Again, simplified for example.
using Microsoft.Office.Interop.Word;
var doc = Application.GetDocument("MyFile.txt");
doc.CheckSpelling();
Optional Parameters in C#4.0
Support for optional parameters allows you to give a method parameter a default value so that you do not have to specify it every time you call the method. This comes in handy when you have overloaded methods that are chained together.
The Old Way
public void Process( string data )
{
Process( data, false );
}
public void Process( string data, bool ignoreWS )
{
Process( data, ignoreWS, null );
}
public void Process( string data, bool ignoreWS, ArrayList moreData )
{
// Actual work done here
}
The reason for overloading Process in this way is to avoid always having to include "false, null" in the third method call. Suppose 99% of the time there will not be 'moreData' provided. It seems ridiculous to type and pass null so many times.
// These 3 calls are equivalent
Process( "foo", false, null );
Process( "foo", false );
Process( "foo" );
The New Way
public void Process( string data, bool ignoreWS = false, ArrayList moreData = null )
{
// Actual work done here
}
// Note: data must always be provided because it does not have a default value
Basic interview questions for C# Component Developers
- Explain the differences between public, protected, private and internal.
- What benefit do you get from using a Primary Interop Assembly (PIA)?
- By what mechanism does NUnit know what methods to test?
- What is the difference between typeof(foo) and myFoo.GetType()?
- Explain what’s happening in the first constructor: public class c{ public c(string a) : this() {;}; public c() {;} } How is this construct useful?
- What is this? Can this be used within a static method?
- Explain the importance and use of each component of this string: Foo.Bar, Version=2.0.205.0, Culture=neutral, PublicKeyToken=593777ae2d274679d
- What is the difference between: catch(Exception e){throw e;} and catch(Exception e){throw;}
- Juxtapose the use of override with new. What is shadowing?
- Explain the use of virtual, sealed, override, and abstract.
