Thursday, June 01, 2006

Simple Control.Invoke

Just read a great post by John Wood on dotnetjunkies.com called "SafeInvoke: Making GUI Thread Programming Easier in C#". It takes a lot of the drudgery out of the way by avoiding the direct typing of delegates. The code is here, and I include it here in case the link disappears.

using System;
using System.Collections;
using System.Reflection;
using System.Reflection.Emit;
...

public class SafeInvokeHelper
{
static readonly ModuleBuilder builder;
static readonly AssemblyBuilder myAsmBuilder;
static readonly Hashtable methodLookup;

static SafeInvokeHelper()
{
AssemblyName name = new AssemblyName();
name.Name = "temp";
myAsmBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(name, AssemblyBuilderAccess.Run);
builder = myAsmBuilder.DefineDynamicModule("TempModule");
methodLookup = new Hashtable();
}

public static object Invoke(System.Windows.Forms.Control obj, string methodName, params object[] paramValues)
{
Delegate del = null;
string key = obj.GetType().Name + "." + methodName;
Type tp;

if (methodLookup.Contains(key))
tp = (Type)methodLookup[key];
else
{
Type[] paramList = new Type[obj.GetType().GetMethod(methodName).GetParameters().Length];
int n = 0;
foreach (ParameterInfo pi in obj.GetType().GetMethod(methodName).GetParameters()) paramList[n++] = pi.ParameterType;
TypeBuilder typeB = builder.DefineType("Del_" + obj.GetType().Name + "_" + methodName, TypeAttributes.Class | TypeAttributes.AutoLayout | TypeAttributes.Public | TypeAttributes.Sealed, typeof(MulticastDelegate), PackingSize.Unspecified);
ConstructorBuilder conB = typeB.DefineConstructor(MethodAttributes.HideBySig | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName, CallingConventions.Standard, new Type[] { typeof(object), typeof(IntPtr) });
conB.SetImplementationFlags(MethodImplAttributes.Runtime);
MethodBuilder mb = typeB.DefineMethod( "Invoke", MethodAttributes.Public | MethodAttributes.Virtual | MethodAttributes.HideBySig, obj.GetType().GetMethod(methodName).ReturnType, paramList );
mb.SetImplementationFlags( MethodImplAttributes.Runtime );
tp = typeB.CreateType();
methodLookup.Add(key, tp);
}

del = MulticastDelegate.CreateDelegate(tp, obj, methodName);
return obj.Invoke(del, paramValues);
}
}