Useful piece of code when checking for concurrency in your application.
using System;
using System.Threading;
namespace Utilities
{
public class ConcurrencyCheck : IDisposable
{
private static int _concurrencyCount = 0;
public ConcurrencyCheck()
{
var usage = 0;
if ((usage = Interlocked.Increment(ref _concurrencyCount)) != 1)
{
Console.WriteLine("{0} delegates are running concurrently", usage);
}
}
public void Dispose()
{
Interlocked.Decrement(ref _concurrencyCount);
}
}
}
This simple T4 example shows how to generate a C# enum class from an external resource, in this case a SQL database.
First of all, let’s create our database:
USE [master]
GO
CREATE DATABASE [T4Demo]
GO
USE [T4Demo]
GO
CREATE TABLE [dbo].[AssetClass](
[Id] [int] IDENTITY(1,1) NOT NULL,
[Description] [varchar](50) NOT NULL,
CONSTRAINT [PK_AssetType] PRIMARY KEY CLUSTERED ( [Id] ASC )
)
GO
INSERT [AssetClass] VALUES ('Equity');
INSERT [AssetClass] VALUES ('Fixed Income');
INSERT [AssetClass] VALUES ('Cash');
GO
Next we’ll create a C# console application and add a T4 text template file:
<#@ template debug="false" hostspecific="true" language="C#" #>
<#@ output extension=".cs" #>
<#@ assembly name="System.Data" #>
<#@ import namespace="System.Data.SqlClient" #>
<#@ import namespace="System.Text.RegularExpressions" #>
<#@ import namespace="System.IO" #>
public enum <#= Path.GetFileNameWithoutExtension(Host.TemplateFile) #>
{
<#
if(Validate())
{
BuildEnum();
}
#>
}
<#+
private bool Validate()
{
if(string.IsNullOrEmpty(Server)) { Error("No server was specified"); }
if(string.IsNullOrEmpty(Database)) { Error("No database was specified"); }
if(!IntegratedSecurity)
{
if(string.IsNullOrEmpty(User)) { Error("No user id was specified"); }
if(string.IsNullOrEmpty(Pwd)) { Error("No password was specified"); }
}
if(string.IsNullOrEmpty(Table)) { Error("No table was specified"); }
if(string.IsNullOrEmpty(ValueColumn)) { Error("The value column was specified"); }
if(string.IsNullOrEmpty(TextColumn)) { Error("The text column was specified"); }
return !this.Errors.HasErrors;
}
private void BuildEnum()
{
using (SqlConnection conn = new SqlConnection(BuildConnStr()))
{
SqlCommand cmd = conn.CreateCommand();
cmd.CommandText = string.Format(
"select {0}, {1} from {2}",
ValueColumn,
TextColumn,
Table);
cmd.CommandType = System.Data.CommandType.Text;
conn.Open();
SqlDataReader rdr = cmd.ExecuteReader();
PushIndent("\t");
while (rdr.Read())
{
string enm = string.Format("{0} = {1},",
CreateValidIdentifier(rdr[TextColumn].ToString()),
rdr[ValueColumn].ToString());
WriteLine(enm);
}
WriteLine("Unknown = 0");
PopIndent();
rdr.Close();
conn.Close();
}
}
// Strips spaces and full stops
private string CreateValidIdentifier(string input)
{
string pattern = @"[\.\[\]\s]";
Regex regex = new Regex(pattern, RegexOptions.None);
return regex.Replace(input, "");
}
private string BuildConnStr()
{
SqlConnectionStringBuilder csb = new SqlConnectionStringBuilder();
csb.DataSource = Server;
csb.InitialCatalog = Database;
csb.IntegratedSecurity = IntegratedSecurity;
if(!IntegratedSecurity)
{
csb.UserID = User;
csb.Password = Pwd;
}
return csb.ConnectionString;
}
private string Server = ".";
private string Database = "T4Demo";
private bool IntegratedSecurity = true;
private string User = "";
private string Pwd = "";
private string Table = "dbo.AssetClass";
private string ValueColumn = "Id";
private string TextColumn = "Description";
#>
Now save the file and you'll have your own up-to-date enum class driven from your database:
public enum AssetClass
{
Equity = 1,
FixedIncome = 2,
Cash = 3,
Unknown = 0
}
You can also set up Visual Studio to always regenerate the file on each build if you prefer.
Source code: http://stevenhollidge.com/blog-source-code/T4CodeGenerationEnums.zip
Knockout.js is a rich JavaScript MVVM framework for data binding HTML elements to JavaScript view models, auto UI updates, dependency tracking and templating.
For a Silverlight or WPF developer this is just what we’ve wanted to be able to unit test our presentation layer (the View Model) outside of the UI.
Live demo: http://c9.io/stevenh77/knockoutdemo/workspace/demo1.html
In this example we will be:
| Diagram | Steps |
|---|---|
 | 1. Creating a view model in JavaScript called viewModel (see diagram). |
| 2. Three of the properties will be ko.observables which enables data binding: | |
| firstName, familyName and fullNameVisible | |
| 3. firstname and familyName bound to textboxes. | |
| 4. Enforce the update of the viewModel properties after every key press by adding: | |
| valueUpdate: 'afterkeydown' to the data-bind section of the textboxes | |
| 5. Binding the checked property of the checkbox to fullNameVisible along with the label.visible property. | |
| 6. Create a fourth dependentObservable property called fullName, which is dependent on firstName | |
| and familyName and databound to “Hello {fullName}” label. | |
| 7. Bind the changeName function to the Change Name button, which updates firstName and familyName. |
<!DOCTYPE html>
<html>
<head>
<script src="http://cloud.github.com/downloads/SteveSanderson/knockout/knockout-2.0.0rc.debug.js" type="text/javascript"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.js" type="text/javascript"></script>
<script type="text/javascript">
$(function () {
var viewModel = {
firstName: ko.observable("Bob"),
familyName: ko.observable("Smith"),
changeName: function () {
this.firstName("Joe");
this.familyName("Bloggs");
},
fullNameVisible: ko.observable(true),
};
viewModel.fullName = ko.dependentObservable(function() {
return this.firstName() + " " + this.familyName();
}, viewModel);
ko.applyBindings(viewModel);
});
</script>
</head>
<body>
<div>Stockbroker:
<input type="text" data-bind="value: firstName, valueUpdate: 'afterkeydown'" />
<input type="text" data-bind="value: familyName, valueUpdate: 'afterkeydown'" />
<input type="checkbox" data-bind="checked: fullNameVisible" />
<span>Hello </span><span data-bind="text: fullName, visible: fullNameVisible"></span>
<button data-bind="click: changeName">Change name</button>
</div>
</body>
</html>
Here is an example showing lists of data with validating input controls
Live demo: http://c9.io/stevenh77/knockoutdemo/workspace/demo2.html
<!DOCTYPE html>
<html>
<head>
<script src="http://cloud.github.com/downloads/SteveSanderson/knockout/knockout-2.0.0rc.debug.js" type="text/javascript"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.js" type="text/javascript"></script>
<script src="http://ajax.microsoft.com/ajax/jQuery.Validate/1.6/jQuery.Validate.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(function () {
var TradeModel = function(trades) {
var self = this;
self.trades = ko.observableArray(trades);
self.addTrade = function() {
self.trades.push({
ticker: "",
price: ""
});
};
self.removeTrade = function(trade) {
self.trades.remove(trade);
};
self.save = function(form) {
alert("Could now transmit to server: " + ko.utils.stringifyJson(self.trades));
// To actually transmit to server as a regular form post, write this: ko.utils.postJson($("form")[0], self.gifts);
};
};
var viewModel = new TradeModel([
{ ticker: "MSFT", price: "39.95"},
{ ticker: "AAPL", price: "120.00"}
]);
ko.applyBindings(viewModel);
// Activate jQuery Validation
$("form").validate({ submitHandler: viewModel.save });
});
</script>
</head>
<body>
<form action='/someServerSideHandler'>
<p>You have entered <span data-bind='text: trades().length'> </span> trade(s)</p>
<table data-bind='visible: trades().length > 0'>
<thead>
<tr>
<th>Ticker</th>
<th>Price</th>
<th />
</tr>
</thead>
<tbody data-bind='foreach: trades'>
<tr>
<td><input placeholder='Ticker' class='required' data-bind='value: ticker, uniqueName: true' /></td>
<td><input placeholder='Price' class='required number' data-bind='value: price, uniqueName: true' /></td>
<td><a href='#' data-bind='click: $root.removeTrade'>Delete</a></td>
</tr>
</tbody>
</table>
<button data-bind='click: addTrade'>Add Trade</button>
<button data-bind='enable: trades().length > 0' type='submit'>Submit</button>
</form>
</body>
</html>
These bindings come out of the box
| Text and Appearance | visible, text, html, css, style, attr |
| Forms | Click, Event, Submit, Enable, Disable, Value, Checked, Options/Selected options (for dropdown or multi select) |
| Control Flow | if, ifnot, foreach, with |
| Template | Old: Traditional JavaScript template (<script>) New: Inline, template less, comment based syntax |
Sometimes it’s preferred to use custom bindings over the built in bindings as it can keep your code more reusable and succinct.
ko.bindingHandlers.yourBindingName = {
init: function(element, valueAccessor, allBindingsAccessor, viewModel) {
// This will be called when the binding is first applied to an element
// Set up any initial state, event handlers, etc. here
},
update: function(element, valueAccessor, allBindingsAccessor, viewModel) {
// This will be called once when the binding is first applied to an element,
// and again whenever the associated observable changes value.
// Update the DOM element based on the supplied values here.
}
};
Knockout protected observable: Allows you to commit or undo changes to your observable data item, sweet!
You can use the built in Knockout functions to convert to |JavaScript and JSON: ko.ToJS() and ko.ToJSON()
var viewModel = {
firstName : ko.observable("Bert"),
lastName : ko.observable("Smith"),
pets : ko.observableArray(["Cat", "Dog", "Fish"]),
type : "Customer"
};
viewModel.hasALotOfPets = ko.computed(function() {
return this.pets().length > 2
}, viewModel)
var jsonData = ko.toJSON(viewModel);
// Result: jsonData is now a string equal to the following value
// '{"firstName":"Bert","lastName":"Smith","pets":["Cat","Dog","Fish"],"type":"Customer","hasALotOfPets":true}'
var plainJs = ko.toJS(viewModel);
// Result: plainJS is now a plain JavaScript object in which nothing is observable. It's just data.
// The object is equivalent to the following:
// {
// firstName: "Bert",
// lastName: "Smith",
// pets: ["Cat","Dog","Fish"],
// type: "Customer",
// hasALotOfPets: true
// }
$.getJSON("/some/url", function(data) {
// Now use this data to update your view models,
// and Knockout will update your UI automatically
})
var data = /* Your data in JSON format - see below */;
$.post("/some/url", data, function(returnedData) {
// This callback is executed if the post was successful
})
See the knockout documentation for examples on loading and saving JSON data.