[Ironruby-core] WPF databinding with ruby objects. Workaround :)

Robert Brotherus robert.brotherus at napa.fi
Fri Dec 12 07:32:55 EST 2008


Great work Joshua!
 
IronRuby-objects don't work in many parts of dotnet-framework because
they are instances of Ruby-classes that are not dotnet-classes. Another
example that has causes headache to me is XAML where names of
user-defined classes can be used as elements but they must be
user-defined dotnet-classes (not Ruby).
 
I suppose and hope that with the support for dynamic languages
increasing in dotnet 4 / C# 4, there will be more built-in support for
this (it would be really nice to use dynamic types as XAML-elements...)
Robert Brotherus
Software architect
Napa Ltd
Tammasaarenkatu 3, Helsinki FI-00180
P.O.Box 470, Helsinki FI-00181

Tel. +358 9 22 813 1 
Direct. +358 9 22 813 611 
GSM +358 45 11 456 02 
Fax. +358 9 22 813 800 

Email: Robert.Brotherus at napa.fi <mailto:Robert.Brotherus at napa.fi>  
www.napa.fi <http://www.napa.fi/>  



  _____  

From: ironruby-core-bounces at rubyforge.org
[mailto:ironruby-core-bounces at rubyforge.org] On Behalf Of Joshua
Nussbaum
Sent: Friday, December 12, 2008 8:56 AM
To: ironruby-core at rubyforge.org
Subject: [Ironruby-core] WPF databinding with ruby objects. Workaround
:)


Hey yall

Seems IronRuby objects do not yet work with WPF databinding. One
approach to a workaround is to emit a wrapper type that defines CLR
properties. When WPF calls the getter/setter the call is forwarded ot
the contained contained ruby object. This will allow defining business
objects in ruby and databing them to the UI. 

This might be useful to thers, so here is my approach. The first part is
C# code that defines a type given a list of property names. The second
part is ruby code that creates a wrapper instance for a given ruby
object and caches the type so that you dont generate a type for each
element in an array..

The C# code to generate a type:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using System.Reflection.Emit;

namespace GenerateType
{

    public class TypeGenerator
    {
        public delegate object GetPropertyDelegate(string propertyName);
        public delegate object SetPropertyDelegate(string propertyName,
object value);

        public static Type Generate(string className, List<string>
properties)
        {
            AssemblyName asmName = new AssemblyName("BindingTypes");
            AssemblyBuilder asmBuilder = AppDomain.CurrentDomain. 
DefineDynamicAssembly(asmName, AssemblyBuilderAccess.Run);
            ModuleBuilder modBuilder =
asmBuilder.DefineDynamicModule("Types");
            TypeBuilder typeBuilder = modBuilder.DefineType(className,
                        TypeAttributes.Public |
                        TypeAttributes.Class |
                        TypeAttributes.AutoClass |
                        TypeAttributes.AnsiClass |
                        TypeAttributes.BeforeFieldInit |
                        TypeAttributes.AutoLayout);


            FieldBuilder getFieldBuilder =
typeBuilder.DefineField("OnGet", typeof(GetPropertyDelegate),
FieldAttributes.Public);
            FieldBuilder setFieldBuilder =
typeBuilder.DefineField("OnSet", typeof(SetPropertyDelegate),
FieldAttributes.Public);

            MethodAttributes getSetAttr =
                        MethodAttributes.Public |
MethodAttributes.SpecialName |
                            MethodAttributes.HideBySig;
            

            foreach (string propertyName in properties)
            {
                PropertyBuilder propBuilder =
typeBuilder.DefineProperty(propertyName, PropertyAttributes.None,
typeof(object), new Type[] {});

                MethodBuilder getter =
                                   typeBuilder.DefineMethod("get_" +
propertyName,
                                   getSetAttr,
                                   typeof(string),
                                   Type.EmptyTypes);

                ILGenerator ilGen = getter.GetILGenerator();
                
                ilGen.Emit(OpCodes.Ldarg_0);
                ilGen.Emit(OpCodes.Ldfld, getFieldBuilder);
                ilGen.Emit(OpCodes.Ldstr, propertyName);
                ilGen.Emit(OpCodes.Callvirt,
typeof(GetPropertyDelegate).GetMethod("Invoke"));
                ilGen.Emit(OpCodes.Ret);

                // Define the "set" accessor method for CustomerName.
                MethodBuilder setter =
                    typeBuilder.DefineMethod("set_" + propertyName,
                                               getSetAttr,
                                               null,
                                               new Type[] {
typeof(string) });

                ilGen = setter.GetILGenerator();

                ilGen.Emit(OpCodes.Ldarg_0);
                ilGen.Emit(OpCodes.Ldfld, setFieldBuilder);
                ilGen.Emit(OpCodes.Ldstr, propertyName);
                ilGen.Emit(OpCodes.Ldarg_1);
                ilGen.Emit(OpCodes.Callvirt,
typeof(SetPropertyDelegate).GetMethod("Invoke"));
                ilGen.Emit(OpCodes.Pop);
                ilGen.Emit(OpCodes.Ret);

                // Last, we must map the two methods created above to
our PropertyBuilder to 
                // their corresponding behaviors, "get" and "set"
respectively. 
                propBuilder.SetGetMethod(getter);
                propBuilder.SetSetMethod(setter);

            }

            return typeBuilder.CreateType();            
        }
    }
}


And here is the ruby code to generate the wrapper type

require 'mscorlib'
require 'C:\Documents and Settings\Josh\My Documents\Visual Studio
2008\Projects\GenerateType\GenerateType\bin\Release\GenerateType.dll'
require 'PresentationFramework, Version=3.0.0.0 <http://3.0.0.0/>
,Culture=neutral, PublicKeyToken=31bf3856ad364e35'
require 'PresentationCore, Version=3.0.0.0 <http://3.0.0.0/> ,
Culture=neutral, PublicKeyToken=31bf3856ad364e35'
require 'WindowsBase, Version=3.0.0.0 <http://3.0.0.0/> ,
Culture=neutral, PublicKeyToken=31bf3856ad364e35'

include System
include System::Collections::Generic
include GenerateType
include System::Collections::ObjectModel
include System::Windows
include System::Windows::Controls
include System::Windows::Data
include System::Windows::Input

class WrapperGenerator
  def initialize
    @wrapper_cache = {}
  end

  def wrap(ruby_object)
    if ruby_object.is_a? Array
      ruby_object.map {|o| wrap(o) }
    else
      cache(ruby_object) unless cached(ruby_object)
      wrapper_class = cached(ruby_object)
      wrapper_class.new(ruby_object)
    end
  end

  def invalidate
    @wrapper_cache.clear
  end
private
  def cached(object)
    @wrapper_cache[object.class.name <http://object.class.name/> ]
  end
  
  def cache(object)
    @wrapper_cache[object.class.name <http://object.class.name/> ] =
generate_wrapper(object)
  end

  def generate_wrapper(object)
    wrapper_name = "#{object.class.name <http://object.class.name/>
}Wrapper"
    properties = List.of(System::String).new

    (object.methods - Object.instance_methods).each {|m| properties.add
m.to_s}

    wrapper_base_type = TypeGenerator.generate("#{wrapper_name}Base",
properties)
    base_instance = Activator.create_instance wrapper_base_type

    eval <<EOS
      class #{wrapper_name} < base_instance.class
        def initialize(original)
          self.on_get = lambda do |prop|
            original.send prop
          end

          self.on_set = lambda do |prop, val|
            original.send "\#{prop}=", val
          end
        end
      end
      return #{wrapper_name} # return the class
EOS
    
  end
end

class Person 
  attr_accessor :first_name, :last_name

  def initialize(first_name, last_name)
    @first_name, @last_name = first_name, last_name
  end

  def full_name
    "#{last_name}, #{first_name}"
  end
end


# A sample UI

people = []

10.times { |n| people << Person.new("John #{n}", "Smith") }

wrapper = WrapperGenerator.new

w = Window.new
combo = ComboBox.new
combo.items_source = wrapper.wrap(people) # wrap people objects
combo.display_member_path = "full_name"
combo.margin = 20
w.content = combo

Application.new.run w
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