Cache

Cache.Insert("KeyValue", someValue, null, DateTime.Now.AddMinutes(15), System.Web.Caching.Cache.NoSlidingExpiration);

Display a ToolTip for a DataGrid Cell

private void dataGrid1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
{
try
{
DataGrid.HitTestInfo hti = dataGrid1.HitTest(e.X,e.Y);
if(hti.Type == DataGrid.HitTestType.Cell)
{
toolTip1.SetToolTip(dataGrid1, dataGrid1[hti.Row, hti.Column].ToString());
}
}
catch{}
}

more SQL

// This example needs the
// System.Data.SqlClient library

#region Building the connection string

string Server = "localhost";
string Username = "my_username";
string Password = "my_password";
string Database = "my_database";

string ConnectionString = "Data Source=" + Server + ";";
ConnectionString += "User ID=" + Username + ";";
ConnectionString += "Password=" + Password + ";";
ConnectionString += "Initial Catalog=" + Database;

#endregion


#region Try to establish a connection to the database

SqlConnection SQLConnection = new SqlConnection();

try
{
SQLConnection.ConnectionString = ConnectionString;
SQLConnection.Open();

// You can get the server version
// SQLConnection.ServerVersion
}
catch (Exception Ex)
{
// Try to close the connection
if (SQLConnection != null)
SQLConnection.Dispose();

// Create a (useful) error message
string ErrorMessage = "A error occurred while trying to connect to the server.";
ErrorMessage += Environment.NewLine;
ErrorMessage += Environment.NewLine;
ErrorMessage += Ex.Message;

// Show error message (this = the parent Form object)
MessageBox.Show(this, ErrorMessage, "Connection error", MessageBoxButtons.OK, MessageBoxIcon.Error);

// Stop here
return;
}

#endregion


#region Execute a SQL query

string SQLStatement = "SELECT * FROM ExampleTable";

// Create a SqlDataAdapter to get the results as DataTable
SqlDataAdapter SQLDataAdapter = new SqlDataAdapter(SQLStatement, SQLConnection);

// Create a new DataTable
DataTable dtResult = new DataTable();

// Fill the DataTable with the result of the SQL statement
SQLDataAdapter.Fill(dtResult);

// Loop through all entries
foreach (DataRow drRow in dtResult.Rows)
{
// Show a message box with the content of
// the "Name" column
MessageBox.Show(drRow["Name"].ToString());
}

// We don't need the data adapter any more
SQLDataAdapter.Dispose();

#endregion


#region Close the database link

SQLConnection.Close();
SQLConnection.Dispose();

#endregion

SQLDataReader

public static SqlDataReader Title()
{
SqlConnection connection = ConnectionManager.GetConnection();

var command = new SqlCommand("StoredProcedure", connection);

command.CommandType = CommandType.StoredProcedure;

SqlDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection);

return reader;
}

Linear interpolation, C#

static double interpolate( double x0, double y0, double x1, double y1, double x )
{
return y0*(x - x1)/(x0 - x1) + y1*(x - x0)/(x1 - x0);
}

Country Drop Down List for Web Forms

(please select a country) none Afghanistan Albania Algeria American Samoa Andorra Angola Anguilla Antarctica Antigua and Barbuda Argentina Armenia Aruba Australia Austria Azerbaijan Bahamas Bahrain Bangladesh Barbados Belarus Belgium Belize Benin Bermuda Bhutan Bolivia Bosnia and Herzegowina Botswana Bouvet Island Brazil British Indian Ocean Territory Brunei Darussalam Bulgaria Burkina Faso Burundi Cambodia Cameroon Canada Cape Verde Cayman Islands Central African Republic Chad Chile China Christmas Island Cocos (Keeling) Islands Colombia Comoros Congo Congo, the Democratic Republic of the Cook Islands Costa Rica Cote d'Ivoire Croatia (Hrvatska) Cuba Cyprus Czech Republic Denmark Djibouti Dominica Dominican Republic East Timor Ecuador Egypt El Salvador Equatorial Guinea Eritrea Estonia Ethiopia Falkland Islands (Malvinas) Faroe Islands Fiji Finland France France, Metropolitan French Guiana French Polynesia French Southern Territories Gabon Gambia Georgia Germany Ghana Gibraltar Greece Greenland Grenada Guadeloupe Guam Guatemala Guinea Guinea-Bissau Guyana Haiti Heard and Mc Donald Islands Holy See (Vatican City State) Honduras Hong Kong Hungary Iceland India Indonesia Iran (Islamic Republic of) Iraq Ireland Israel Italy Jamaica Japan Jordan Kazakhstan Kenya Kiribati Korea, Democratic People's Republic of Korea, Republic of Kuwait Kyrgyzstan Lao People's Democratic Republic Latvia Lebanon Lesotho Liberia Libyan Arab Jamahiriya Liechtenstein Lithuania Luxembourg Macau Macedonia, The Former Yugoslav Republic of Madagascar Malawi Malaysia Maldives Mali Malta Marshall Islands Martinique Mauritania Mauritius Mayotte Mexico Micronesia, Federated States of Moldova, Republic of Monaco Mongolia Montserrat Morocco Mozambique Myanmar Namibia Nauru Nepal Netherlands Netherlands Antilles New Caledonia New Zealand Nicaragua Niger Nigeria Niue Norfolk Island Northern Mariana Islands Norway Oman Pakistan Palau Panama Papua New Guinea Paraguay Peru Philippines Pitcairn Poland Portugal Puerto Rico Qatar Reunion Romania Russian Federation Rwanda Saint Kitts and Nevis Saint LUCIA Saint Vincent and the Grenadines Samoa San Marino Sao Tome and Principe Saudi Arabia Senegal Seychelles Sierra Leone Singapore Slovakia (Slovak Republic) Slovenia Solomon Islands Somalia South Africa South Georgia and the South Sandwich Islands Spain Sri Lanka St. Helena St. Pierre and Miquelon Sudan Suriname Svalbard and Jan Mayen Islands Swaziland Sweden Switzerland Syrian Arab Republic Taiwan, Province of China Tajikistan Tanzania, United Republic of Thailand Togo Tokelau Tonga Trinidad and Tobago Tunisia Turkey Turkmenistan Turks and Caicos Islands Tuvalu Uganda Ukraine United Arab Emirates United Kingdom United States United States Minor Outlying Islands Uruguay Uzbekistan Vanuatu Venezuela Viet Nam Virgin Islands (British) Virgin Islands (U.S.) Wallis and Futuna Islands Western Sahara Yemen Yugoslavia Zambia Zimbabwe

dropdown states

-- Select --
Alabama
Alaska
Arizona
Arkansas
California
Colorado
Connecticut
District of Columbia
Delaware
Florida
Georgia
Hawaii
Idaho
Illinois
Indiana
Iowa
Kansas
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Mississippi
Missouri
Montana
Nebraska
Nevada
New Hampshire
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
Rhode Island
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
Wyoming


public string SelectedValue
{
get
{
return ddlStates.SelectedValue;
}
set
{
ddlStates.SelectedValue = value;
}
}

*

public string id
{
set
{
ddlStates.ID = value;
}
}

public string ValidationEnabled
{
set
{
rfvStates.Enabled = Convert.ToBoolean(value);
}
}

public string ValidationGroup
{
set
{
ddlStates.ValidationGroup = value;
rfvStates.ValidationGroup = value;
}
}

public string ValidationErrorMessage
{
set
{
rfvStates.ErrorMessage = value;
}
}

public string SelectedValue
{
get
{
return ddlStates.SelectedValue;
}
set
{
ddlStates.SelectedValue = value;
}
}

public short TabIndex
{
set
{
ddlStates.TabIndex = value;
}
}

state abbreviations list (Dictionary)

Dictionary stateabbrs = new Dictionary();

stateabbrs.Add("Alabama","AL");
stateabbrs.Add("Alaska","AK");
stateabbrs.Add("Arizona","AZ");
stateabbrs.Add("Arkansas","AR");
stateabbrs.Add("California","CA");
stateabbrs.Add("Colorado","CO");
stateabbrs.Add("Connecticut","CT");
stateabbrs.Add("Delaware","DE");
stateabbrs.Add("Florida","FL");
stateabbrs.Add("Georgia","GA");
stateabbrs.Add("Hawaii","HI");
stateabbrs.Add("Idaho","ID");
stateabbrs.Add("Illinois","IL");
stateabbrs.Add("Indiana","IN");
stateabbrs.Add("Iowa","IA");
stateabbrs.Add("Kansas","KS");
stateabbrs.Add("Kentucky","KY");
stateabbrs.Add("Louisiana","LA");
stateabbrs.Add("Maine","ME");
stateabbrs.Add("Maryland","MD");
stateabbrs.Add("Massachusetts","MA");
stateabbrs.Add("Michigan","MI");
stateabbrs.Add("Minnesota","MN");
stateabbrs.Add("Mississippi","MS");
stateabbrs.Add("Missouri","MO");
stateabbrs.Add("Montana","MT");
stateabbrs.Add("Nebraska","NE");
stateabbrs.Add("Nevada","NV");
stateabbrs.Add("New Hampshire","NH");
stateabbrs.Add("New Jersey","NJ");
stateabbrs.Add("New Mexico","NM");
stateabbrs.Add("New York","NY");
stateabbrs.Add("North Carolina","NC");
stateabbrs.Add("North Dakota","ND");
stateabbrs.Add("Ohio","OH");
stateabbrs.Add("Oklahoma","OK");
stateabbrs.Add("Oregon","OR");
stateabbrs.Add("Pennsylvania","PA");
stateabbrs.Add("Rhode Island","RI");
stateabbrs.Add("South Carolina","SC");
stateabbrs.Add("South Dakota","SD");
stateabbrs.Add("Tennessee","TN");
stateabbrs.Add("Texas","TX");
stateabbrs.Add("Utah","UT");
stateabbrs.Add("Vermont","VT");
stateabbrs.Add("Virginia","VA");
stateabbrs.Add("Washington","WA");
stateabbrs.Add("West Virginia","WV");
stateabbrs.Add("Wisconsin","WI");
stateabbrs.Add("Wyoming","WY");

Unable to add data connection. Key not valid for use in specified state. - MSDN Forums

solution:

1. Open the registry

2. Rename [HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0]

To [HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\8.0back]

3. Restart Visual Studio

Forcing File Downloads

In C# (ASP.NET) it’s just as simple:

private void Page_Load(object sender, System.EventArgs e)
{
// Disable caching this page (C#)
Response.Cache.SetCacheability(HttpCacheability.NoCache);
Response.Buffer = true;
Response.ContentType = "application/binary";
Response.AppendHeader("Content-Disposition: attachment; " +
filename=dlimg.png");
Response.WriteFile(Server.MapPath("images/dlimg.png");
Response.End();
}