.NET运行时编译学习——CodeDomProvider、CodeCompileUnit和CODEDOM（学习资料积累）

This is a bit of a strange article, and may not be that useful, but I think its a very interesting subject, that some will probably not even be aware of. This article will cover some of the less known namespaces within .NET. Such as System.CodeDom and System.CodeDom.Compiler. What I will be demonstrating in this article, is just how neat these namespaces are and what can be done with them. Specifically I will be demonstrating that we are able to build entirely new source code files at runtime using the System.CodeDom namespace and the use the System.CodeDom.Compiler namespace classes to even compile this newly created source code into a runnable application. This will all be created at runtime. My aim for this article is to provide a simple introduction into these 2 namespaces, you will not be an expert at the end of this article, but will have been exposed to enough, to realise what these 2 namespaces allow you to achieve.

Why Would I Want To Create New Source Code And Applications At Runtime

Well the reason that I started looking into this was dynamic code generation for Data Access Layers (DAL) /Business Access Layer (BAL) code based on an initial schema. So thats one possible area where it may be useful to create code at runtime, basically have an application create a bunch of auto generated source code files that can then be used within another project. Thats just where we (at work) found a use for this stuff.

This led me onto investigating the the System.CodeDom.Compiler namespace classes, and as such I thought I would spend a bit of time talking about the possibilities that are available by using these classes.

The rest of this article will be split roughly between a discussion about the System.CodeDom namespace, and the System.CodeDom.Compiler namespace. And finally a short discussion of what the attached demo application will be discussed.

System.CodeDom

The System.CodeDom namespace, contains classes, interface and enmerations that can be used to create source code at runtime. The general idea is that a newly constructed Document Object Model is being created, where methods, constructors using directives, variables are all creatable via using the System.CodeDom namespace. Where CodeDom really comes into its own is that it is lanuage agnostic and simply provides a CodeCompileUnit which can then be used by the System.CodeDom.Compiler namespace which uses this CodeCompileUnit to create the source code in any of the .NET languages

Obviously this only gives you a very small example of what CodeDom is like to work with. I have to say the syntax is very verbose, but the fact that you can create any .NET source from CodeDom, makes it quite appealing. There are also some good wrappers around CodeDom, which shorten the syntax, I have included a list of related articles at the bottom of this article, should you wish to read around this subject a bit more.

System.CodeDom.Compiler

If we want to be able to use the System.CodeDom.Compiler namespace to compile the result of building a CodeDom object, we need to make sure that wherever we built our CodeDom object (using the syntax as shown above) that we return a CodeCompileUnit. It is by using this CodeCompileUnit that we are able to use the System.CodeDom.Compiler namespace, to create the source code in any of the .NET languages.

For example this excerpt of the demo applications code, shows how we built a new source code file using the System.CodeDom and System.CodeDom.Compiler namespaces.

So doing this is enough to create a new source code file, in any of the .NET languages. This is all thanks for the CodeDomProvider class, which is able to create providers for all of the .NET languages. So providing we use the the relevant CodeDomProvider for the CodeCompileUnit that came out of using CodeDom can be generated into a source code any of the .NET languages. Neat Huh.

So what have we got so far, well we create a DOM representing a new class, which eventually gave us a CodeCompileUnit that we then used to create the relevant source code by using the specfic e CodeDomProvider class, for the language we wanted to generate.

So thats cool, we have a source code file. But at the top of this article I also said that I would show you how to compile source code into an Assembly or an Exe. So lets continue to look at that.

And that is enough to get us a EXE created for the source code that we created earlier. Remember this is all being done at runtime, I think thats pretty cool actually. Create a new source code and compile and run it at runtime. That's neat.

The DEMO Application

Anyway, lets just have a quick chat about the demo app. I use the fantastic Fireball code highlighter, available right here at Codeproject. And the basic program that I am trying to create at runtime is as follows

Here is a screen shot of the demo app, just after a generate and compile being performed, where the selected .NET language was Visual Basic

And thats about it. Like I say, you are by no means an expert from reading this, but I hope its given you an idea about what can be done with these 2 very cool namespaces.

Other CodeDom Resources

Generate Code-DOMs directly from C# or VB.NET

If you write applications in .NET that generate .NET language source-code as output, and the output language should be selectable (typically C# or VB.NET), then you will probably end up generating the output from a System.CodeDom graph. Once you have the CodeDOM the actual code generation support in .NET is easy, clean and produces reasonable code. So what's the catch? Well, consider at least the following:

Building CodeDOMs programmatically is a real pain - the .NET API's are convoluted, difficult to understand, error-prone and you often require many lines of code to generate one line of code in the CodeDOM. (Reminds me of the days I used to program in assembler..). For this reason, many people have gone to great pains to abstract the CodeDOM API's into more meaningful, much easier to use, and generally more efficient class libraries. I reference a few of these from CodeProject below:

Refly, makes the CodeDom'er life easier

An Expression Parser for CodeDom

Some of the constructs that you prefer to code yourself just cannot be reproduced in a CodeDOM, and require that you be a lot more creative and defensive in your approach when programmatically building CodeDOMs.

Another approach is to find or build a System.CodeDom.Compiler.ICodeParser implementation for the input.NET language you are generating CodeDOMs from. This allows you to write code in that .NET language, which is then parsed to produce a System.CodeDom.CodeCompileUnit (CodeDOM). Once you have the CodeDOM it is trivial to generate the code (see the CodeGeneration.GenerateCode method below). But again, there is no free-lunch - many ICodeParser implementations exist, but all of them (in my experience) are trivial solutions, mainly geared to generating code for class-interfaces or web-service interfaces.

Enter IC#Code and their #Develop (SharpDevelop) product.

As part of this product, they ship an assembly - ICSharpCode.NRefactory.dll (and you can build the source code) which provides a fairly comprehensive ICodeParser implementation. Using the CodeDOMVisitor 'visitor' object, it is easy to generate source-code from a CodeDOM created by parsing source-code, as demonstrated in the code below. Note, though, that as before your input source-code will have to be very standard (no funny stuff), and there are some quirks with the CodeDOMVisitor object (which includes some issues with class constructor generation, and some of the looping constructs). In general the results are pleasing, and I look forward to future updates to this assembly. Interestingly, they also provide other 'visit-ations', including a working C#-to-VB.NET converter.

The code below was written for VS2005/.NET 2.0 and uses the #Develop 2.0.0.1462RC2 version source-code and DLL's. You will need to add a reference in your project to the ICSharpCode.NRefactory.dll assembly to get your project to build.

CodeGenerator Classes for .NET 2.0

using System;

using System.CodeDom;

using System.CodeDom.Compiler;

using System.Collections.Generic;

using System.Text;

using System.IO;

using ICSharpCode.NRefactory.Parser;

namespace CodeGeneration

{

  public class CodeGenerator

  {

    private ICodeParser parser;

    public ICodeParser Parser

    {

      get { return parser; }

      set { parser = value; }

    }

    private CodeDomProvider provider;

    public CodeDomProvider Provider

    {

      get { return provider; }

      set { provider = value; }

    }

    private CodeGeneratorOptions options;

    public CodeGeneratorOptions Options

    {

      get { return options; }

      set { options = value; }

    }

    protected virtual CodeGeneratorOptions 

      GetDefaultOptions()

    {

      CodeGeneratorOptions options = 

        new CodeGeneratorOptions();

      options.BracingStyle = "C";

      options.BlankLinesBetweenMembers = false;

      options.IndentString = "\t";

      return options;

    }

    public virtual void GenerateCode(TextReader reader, 

      TextWriter writer)

    {

      CodeCompileUnit codeCompileUnit = Parser.Parse(reader);

      Provider.GenerateCodeFromCompileUnit(codeCompileUnit, writer, Options);

      reader.Close();

      // Important to flush the output stream.

      writer.Flush();

      writer.Close();

    }

    public CodeGenerator(ICodeParser parser, 

      CodeDomProvider provider)

    {

      Options = GetDefaultOptions();

      Parser = parser;

      Provider = provider;

    }

    public CodeGenerator(ICodeParser parser, 

      CodeDomProvider provider,

      CodeGeneratorOptions options)

    {

      Options = options;

      Parser = parser;

      Provider = provider;

    }

  }

  public class Parser : ICodeParser

  {

    #region ICodeParser Members

    public CodeCompileUnit Parse(TextReader codeStream)

    {

      // Set the parser for the correct language.

      IParser parser = ParserFactory.CreateParser(Language,

        codeStream);

      parser.Parse();

      // Use a CodeDom visitor to gen. a CodeCompileUnit.

      CodeDOMVisitor visit = new CodeDOMVisitor();

      CodeNamespace globalNamespace =  (CodeNamespace)

        visit.Visit(parser.CompilationUnit, null);

      // Mostly, you need to remove the "Global"

      // code namespace from the compile unit.

      visit.codeCompileUnit.Namespaces.Remove(globalNamespace);

      return visit.codeCompileUnit;

    }

    #endregion

    private SupportedLanguage language = SupportedLanguage.CSharp;

    public SupportedLanguage Language

    {

      get { return language; }

      set { language = value; }

    }

    public Parser(SupportedLanguage language)

    {

      Language = language;

    }

  }

}

posted on Monday, July 24, 2006 8:55 AM

C# 3.0 and CodeDOM

The CodeDOM is a very handy .NET API which allows you to programatically compile code using the .NET compilers and programatically construct code without just pasting together strings.

With the new version of the language, we've heard a numer of questions about how to use the CodeDOM with the new compiler.

Example of programatically compiling C#3.0 source code:

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.CSharp;
using System.CodeDom.Compiler;
class Program
{
    static void Main(string[] args)
    {
        var csc = new CSharpCodeProvider(new Dictionary<string, string>() { { "CompilerVersion", "v3.5" } });
        var parameters = new CompilerParameters(new[] { "mscorlib.dll", "System.Core.dll" }, "foo.exe", true);
        parameters.GenerateExecutable = true;
        CompilerResults results = csc.CompileAssemblyFromSource(parameters,
        @"using System.Linq;
            class Program {
              public static void Main(string[] args) {
                var q = from i in Enumerable.Rnge(1,100)
                          where i % 2 == 0
                          select i;
              }
            }");
        results.Errors.Cast<CompilerError>().ToList().ForEach(error => Console.WriteLine(error.ErrorText));
    }
}

.NET运行时编译学习——CodeDomProvider、CodeCompileUnit和CODEDOM（学习资料积累）

Introduction

Why Would I Want To Create New Source Code And Applications At Runtime

System.CodeDom

Creating Namespaces

Creating A Class

Creating A Main Method

System.CodeDom.Compiler

The DEMO Application

Other CodeDom Resources

Future Work

History

License

About the Author

Describes a collection of WebReference objects.

Describes a collection of WebReference objects.

C# 3.0 and CodeDOM

Example of programatically compiling C#3.0 source code:

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