How i write MessageBox using dnlib

Question

When i write code to show messagebox in Entry point it will not run but if i replace the messagebox to file write it will run without problem. And if i make compile in dnspy and save the assembly again it will run!. Code ** i used dnlib ** :

 private void MakeMessageBoxMethod(ModuleDefMD module)
        {
            var newtype = new TypeDefUser("MBNS", "MB", module.CorLibTypes.Object.TypeDefOrRef);
            newtype.Attributes = dnlib.DotNet.TypeAttributes.NotPublic | dnlib.DotNet.TypeAttributes.AutoLayout | dnlib.DotNet.TypeAttributes.Class | dnlib.DotNet.TypeAttributes.AnsiClass;
            module.Types.Add(newtype);
          
            // Method that will call the messagebox
            var MsgBoxMethod = new MethodDefUser("sh",
               MethodSig.CreateStatic(module.CorLibTypes.Void, module.CorLibTypes.String));
            MsgBoxMethod.Attributes = dnlib.DotNet.MethodAttributes.Public | dnlib.DotNet.MethodAttributes.Static;
            MsgBoxMethod.ImplAttributes = dnlib.DotNet.MethodImplAttributes.IL | dnlib.DotNet.MethodImplAttributes.Managed;
            MsgBoxMethod.ParamDefs.Add(new ParamDefUser("_", 1));
            newtype.Methods.Add(MsgBoxMethod);        
            var MessageBoxRef = new TypeRefUser(module, "System.Windows.Forms", "MessageBox", module.CorLibTypes.AssemblyRef);
            var ShowRef = new MemberRefUser(module, "Show",
                        MethodSig.CreateStatic(module.CorLibTypes.Void, module.CorLibTypes.String,module.CorLibTypes.String),
                        MessageBoxRef);
            var epBody = new CilBody();
            MsgBoxMethod.Body = epBody;
            MsgBoxMethod.Body.Instructions.Add(OpCodes.Ldarg_0.ToInstruction());
            MsgBoxMethod.Body.Instructions.Add(OpCodes.Ldstr.ToInstruction("MessageBox Title"));
            MsgBoxMethod.Body.Instructions.Add(OpCodes.Call.ToInstruction(ShowRef));
            MsgBoxMethod.Body.Instructions.Add(OpCodes.Ret.ToInstruction());
            MsgBoxMethod.Body.Instructions.OptimizeBranches();
            // Entry point
            var MainMethod = module.GetTypes().First(t => t.Name == "Program").Methods.First(m => m.Name == "Main");
            MainMethod.Body.Instructions.Insert(1, OpCodes.Ldstr.ToInstruction("The message"));
            MainMethod.Body.Instructions.Insert(2, OpCodes.Call.ToInstruction(MsgBoxMethod));
        }

The Entrypoint Method | The Method i added it

If i decompile the program and compile it again it will run without any problem. I used dnspy ^

How i write MessageBox using dnlib

0 Answers0