Monday, December 26, 2011

What is the use of AsyncCallback in Client server programs and GUI improvements? why should we use it?

When the asyn method finishes processing, the AsyncCallback method is automatically called, where post processing stmts can be executed. With this technique there is no need to poll or wait for the asyn thread to complete.

This is some explanation on Aynsc Call back usage:

Callback Model: The callback model requires that we specify a method to callback on and include any state that we need in the callback method to complete the call. The callback model can be seen in the following example:

static byte[] buffer = new byte[100];

static void TestCallbackAPM()
string filename = System.IO.Path.Combine (System.Environment.CurrentDirectory, "mfc71.pdb");

FileStream strm = new FileStream(filename,
FileMode.Open, FileAccess.Read, FileShare.Read, 1024,

// Make the asynchronous call
IAsyncResult result = strm.BeginRead(buffer, 0, buffer.Length,
new AsyncCallback(CompleteRead), strm);

In this model, we are creating a new AsyncCallback delegate, specifying a method to call (on another thread) when the operation is complete. In addition, we are specifying some object that we might need as the state of the call. For this example, we are sending the stream object in because we will need to call EndRead and close the stream.

The method that we create to be called at the end of the call would look somewhat like this:

static void CompleteRead(IAsyncResult result)
Console.WriteLine("Read Completed");

FileStream strm = (FileStream) result.AsyncState;

// Finished, so we can call EndRead and it will return without blocking
int numBytes = strm.EndRead(result);

// Don't forget to close the stream

Console.WriteLine("Read {0} Bytes", numBytes);

Other techniques are wait-until-done and pollback

Wait-Until-Done Model The wait-until-done model allows you to start the asynchronous call and perform other work. Once the other work is done, you can attempt to end the call and it will block until the asynchronous call is complete.

// Make the asynchronous call
strm.Read(buffer, 0, buffer.Length);
IAsyncResult result = strm.BeginRead(buffer, 0, buffer.Length, null, null);

// Do some work here while you wait

// Calling EndRead will block until the Async work is complete
int numBytes = strm.EndRead(result);

Or you can use wait handles.


Polling Model The polling method is similar, with the exception that the code will poll the IAsyncResult to see whether it has completed.

// Make the asynchronous call
IAsyncResult result = strm.BeginRead(buffer, 0, buffer.Length, null, null);

// Poll testing to see if complete
while (!result.IsCompleted)
// Do more work here if the call isn't complete

Thursday, December 22, 2011

How to open DateTime picker C# control programmatically on Button Click

You have to use interop to to send request to windows that show DataTimePicker 
on click of the button

//include namespace section 
using System.Runtime.InteropServices;

private static extern bool PostMessageForCalender(
IntPtr hWnd, // handle to destination window
Int32 msg, // message
Int32 wParam, // first message parameter
Int32 lParam // second message parameter

const Int32 WM_LBUTTONDOWN = 0x0201;

//method to call calender dropdown
private void button1_Click(object sender, EventArgs e)
Int32 x = dateTimePicker1.Width - 10;
Int32 y = dateTimePicker1.Height / 2;
Int32 lParam = x + y * 0x00010000;

PostMessageForCalender(dateTimePicker1.Handle, WM_LBUTTONDOWN, 1,lParam);


Monday, December 12, 2011

Most Useful free .Net Libraries

  • Math.NET Numerics - special functions, linear algebra, probability models, random numbers, interpolation, integral transforms and more
Package managers for external libraries
  • NuGet (formerly known as NuPack) - Microsoft (developer-focused package management system for the .NET platform intent on simplifying the process of incorporating third party libraries into a .NET application during development)
  • OpenWrap - Sebastien Lambla - Open Source Dependency Manager for .net applications
Build Tools
  • Prebuild - Generate project files for all VS version, including major IDE's and tools like SharpDevelop, MonoDevelop, NAnt and Autotools
Dependency Injection/Inversion of Control
Design by Contract
Data Mapper
PDF Creators/Generators
Unit Testing/Mocking
Automated Web Testing
Misc Testing/Quality Support/Behavior Driven Development (BDD)
URL Rewriting
Web Debugging
  • Glimpse - Firebug for your webserver
MS Word/Excel Documents Manipulation
  • DocX to create, read, manipulate formatted word documents. Easy syntax, working nicely, actively developed. No Microsoft Office necessary.
  • Excel XML Writer allows creation of .XLS (Excel) files. No Microsoft Office necessary. Been a while since it has been updated. It also provides code generator to create code from already created XLS file (saved as xml). Haven't tested this but looks very promising. Too bad author is long time gone.
  • Excel Reader allows creation/reading of .XLS (Excel) files. No Microsoft Office necessary. Been a while since it has been updated.
  • Excel Package allows creation/reading of .XLSX (Excel 2007) files. No Microsoft Office necessary. Author is gone so it's out of date.
  • EPPlus is based on Excel Package and allows creation/reading of .XLSX (Excel 2007). It is actually the most advanced even comparing to NPOI.
  • NPOI is the .NET version of POI Java project at POI is an open source project which can help you read/write xls, doc, ppt files.
Social Media
  • LinqToTwitter - Linq-based wrapper for all Twitter API functionality in C#
  • Facebook C# SDK - A toolkit for creating facebook applications / integrating websites with Facebook using the new Graph API or the old rest API.
  • sharpserializer - xml/binary serializer for wpf, and silverlight
  • protobuf-net - .NET implementation of google's cross-platform binary serializer (for all .NET platforms)
Machine learning
  • Encog C# - Neural networks
  • - AI, computer vision, genetic algorithms, machine learning
Paid Libraries:

Check more at stackoverflow