Back to basics string vs StringBuilder

This is simple stuff but is something I see people easily miss by just not thinking about it.

A string is an immutable object, which means once created it can not be altered. So if you want to do a replace or append some more text to the end a new object will be created.

A StringBuilder however is a buffer of characters that can be altered without the need for a new object to be created.

In the majority of situations a string is a perfectly reasonable choice and creating an extra 1 or 2 objects when you appened a couple of other strings isn’t going to make a significant impact on the performance of your program. But what happens when you are using strings in a loop.

A few weeks ago one of my developers had written some code that went through a loop building up some text. It looked a little like this:

string foo = "";

foreach (string baa in someSortOfList)
{
    foo += " Value for " + baa + " is: ";

    var aValue = from x in anotherList
                 where x.name == baa
                 select x;

    foo += aValue.FirstOrDefault().value;
}

Everything worked apart from the fact it took 30seconds to execute!

He was searching through convinced that the linq expressions in the middle was what was taking the time, and was at the point of deciding it could not go any faster without a new approach.

I pointed out not only had he used strings rather than a StringBuilder, but the loop also created around 10 string objects within it. The loop which repeated a couple thousand times was therefore creating 20000 objects that weren’t needed. After we switched froms strings to a StringBuilders the loop executed in milliseconds.

So remember when your trying to work out why your code may be slow, remember the basic stuff.

.Net Tip: Default Button for Enter Key

I don’t know if I should be happy to now know about this, or just conserned that it’s taken me this long to discover. But one issue that surfaces time and time again when programming in ASP.NET, is that issue that pressing enter/return in a text feild doesn’t always do what you want it to do. 

On a normal website you can have many forms each with their own submit button which becomes the default action when pressing return on one of the forms feilds. However in ASP.NET Web Forms there is only ever one form on a page, but there could be 10 different buttons each needing to be the default action for a particular text box. 

The solution as it turns out is very simple and you have two options both introduced in .NET 2.0 (yes that’s how old it is!) 

1. Default button for the form. If your page has more than one button, but there is only one that you want to fire when you hit enter then in the code behind you can just type… 

Form.DefaultButton = Button1

or it can also be specified in your aspx file 

 
<form runat="server" defaultbutton="Button1">

2. If you need to be more specific a panel can also have a default button… 

Panel1.DefaultButton = Button1

or again is can be specified in your aspx file

<asp:Panel runat="server" DefaultButton="Button1">

Custom Validator Error from Server Side

The built in ASP.NET validators are amazing as we all know. You just drag them on the page, tell them what control to validate, give them a summary control to list the errors and they do it. But what if there’s something you need to add server side? Such as something that needs to check with the database before saving. You already have your validation summary control, so it would be nice to re-user that and have everything automatically looking the same. But it would appear there’s no easy way of doing it built in, so here’s an easy way of doing it… 

Creating a Custom Validation Error

First your going to need a class with some static class’s that you can pass your error message to. Here I have two functions one for simply adding the error to the page and the other for adding the error to the page with a specific validation group. I am using a CustomValidator object to make this all work, another option is to implement IValidator but it’s actually more effort than’s needed. The other section to note is that I’m setting the Error.Text to a non breaking space (this is what would normally go next to the form field you’re validating). This is because if you don’t then it will default to the ErrorMessage which we only want to go into the summary. If you try setting it to a normal space it will still also default to the summary text.

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

/// <summary>
/// Summary description for Validator
/// </summary>
public class ValidationError
{

    public static void Display(string Message)
    {
        Display(Message, "");
    }

  public static void Display(string Message, string ValidationGroup)
    {
  CustomValidator Error = new CustomValidator();
        Error.IsValid = false;
        Error.ErrorMessage = Message;
        Error.ValidationGroup = ValidationGroup;
        Error.Text = "&nbsp;";

  Page currentPage = HttpContext.Current.Handler as Page;
        currentPage.Validators.Add(Error);
    }
}

Now to trigger the error you just need to called the function as below:

ValidationError.Display("Useful error message", "ValidationGroupName");

Creating Events in ASP.NET

Creating your own events on your own controls is something that is essential if you want you web app to work well and also provide you with reusable controls. It’s easy to skip past the problem and find another way to get your code to do what you want it to do and detect the change another way. But you end up with much nicer code if your controls can have proper events for a piece of action, and you web page can have proper event handlers on each. Not only that but the code you need to write in generally a copy and past job and not that hard.

The Code

While it’s not that hard, the amount of code that is needed is quite a lot more than you may expect. Fortunately though it’s code you going to just re-use again and again changing small bits as needed.

    //1 - Event args (use default, but eventually pass in data through here)
    public class SaveCompleteEventArgs : EventArgs
    {
        public SaveCompleteEventArgs(int inDataValue)
        {
            this.DataValue = inDataValue;
        } //end of con

        public readonly int DataValue;
    }



    //2 - define delegate
    public delegate void SaveCompleteEventHandler(object sender, SaveCompleteEventArgs e);

    //3 - define the event itself
    public event SaveCompleteEventHandler SaveComplete;

    //4 - the protected virtual method to notify registered objects of the request
    //	virtual so that it can be overridden.
    protected virtual void OnSaveComplete(SaveCompleteEventArgs e)
    {
        //if the UpdateData event is empty, then a delegate has not been added to it yet.
        if (SaveComplete != null)
        {
            //event exists, call it:
            SaveComplete(this, e);
        } //end of if
    }

    //5 - method that translates the input into the desired event
    public void TriggeringMethod(int strData)
    {

        // get new event args
        //EventArgs e = new EventArgs();
        SaveCompleteEventArgs e = new SaveCompleteEventArgs(strData);

        // call the virtual method
        OnSaveComplete(e);
    }

LINQ to SQL Inserts and Deletes

Inserting and Deleting records in a database using LINQ to SQL is just as easy as selecting information. What’s not so easy is actually finding out how to do it. There are lots of excellent blog posts around such as this one by Scott Guthrie http://weblogs.asp.net/scottgu/archive/2007/07/11/linq-to-sql-part-4-updating-our-database.aspx, however most of them we’re all written for the Beta version of LINQ to SQL which let you do a .Add() or .Remove() on your table, which was  changed on the final release. 

So to insert do something like this: 

DataClassesDataContext dataContext = new DataClassesDataContext(); 

//Create my new Movie record
Movie movie = new Movie();
movie.Name = "Tim's movie"; 

//Insert the movie into the data context
dataContext.Movies.InsertOnSubmit(movie); 

//Submit the change to the database
dataContext.SubmitChanges();

And to delete do something like this:

DataClassesDataContext dataContext = new DataClassesDataContext();

var movies = from m in dataContext.Movies
                  where m.Name == "Tim's movie"
                  select m;

dataContext.Movies.DeleteAllOnSubmit(movies);

dataContext.SubmitChanges();

LINQ to SQL Connection Strings

LINQ to SQL is great but like all great things at some point it does something that you don’t expect and gives you a headache. An example of this happened to me this week with the differences between how connection strings are handeled when you LINQ to SQL model is in a class library rather than a Website or Web Application.

What makes this issue particulalry annoying is that it only appears when you try and change the database server that your code is looking at which could end up being when it’s going live or moving to a staging server.

So we all know about connection strings, their quite simple and you just store them in your web.config file, which is how LINQ to SQL works when your using them in a Website. But as soon as you move them to a class library things change. First your connection string name is no longer that simple name you gave it e.g. ConnectionString, now it is prefixed with the namespace which is annoying but not the end of the world. Second discovery though is no matter what you do, it just doesn’t seem to pick up the connection string from the web.config file. Reason being your origional connection string has now compiled itself in the class library’s dll and that is what it is using.

The Solution

Depending when you discovered this the solution is not to bad as you either have a lot of code to change or only a small amount. You can always pass a connection string to the constructor when you are createing an instance of the data context e.g.

DataClasses1DataContext da = new DataClasses1DataContext(connectionstring);

You can also set the connection string on your LINQ to SQL model to be blank, this will remove the default contructor and force you to pass a connection string. This way you web application has the choice of what connection string to use and you can keep re-using your class library in different projects.

.NET Charts (Pleasing clients by giving them a graph to look at)

Irruspective of if your working on some kind of company extranet or the admin side of a public facing site, one thing that will make you’re clients go ooooooo and love your work is the inclusion of a funky looking chart. It may not serve any amazing purpose, but as there looking through all the boring text area’s and buttons that actually make up the functinality of the site, the inclusion of nice looking chart is going to make them go “oooo that’s nice” and like you even more. For those of us working in .NET, thank’s to an update from Microsoft at the end of 2008 it’s also something that’ve very quick an easy to do. Better yet the update was free so the only cost is the time you take to impletement it. 

First off if you want to use the chart’s and you haven’t downloaded them then that’s what you need to do. The chart’s shipped after .NET 3.5 so there a seperate install, .NET 4 however has them included by default. 

Using the Chart Control

Like I said adding a chart to a page is a quick and easy thing to do. Once you have the Visual Studio add on installed you can also drag and drop everything into place. However im going to go into a bit more detail. 

To start your going to need a data source. In this example im using a SQL Data Source object for ease of use, in a production environment I heavely recomend against using them as there going to make your code a completly unmanagable mess, instead I would use something like a Entity Data Source. My chart is going to be showing a graph of mobile phone handset popularity so my SQL is simply just returning a table of phone names and how many people use them. 

Code so far: 

<asp:SqlDataSource ID=”ChartDB” runat=”server” ConnectionString=”<%$ ConnectionStrings:ConnectionString %> SelectCommand=”SELECT [Name], [People] FROM [PhonePopularity]”>
</asp:SqlDataSource> 
 

Next we need to add a chart, the easiest way to do this is to just drag a chart object onto the page from the toolbox, however if you do want to type it yourself it’s not particularly complex. 

First you will need to register the assembly on the page.. 

 <%@ Register assembly=”System.Web.DataVisualization, Version=3.5.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35″ namespace=”System.Web.UI.DataVisualization.Charting” tagprefix=”asp” %> 

And then add the chart like so…

<asp:Chart ID=”Chart1″ runat=”server” DataSourceID=”ChartDB” Height=”400px” Width=”400px”>
 </asp:Chart>

Now we’re ready to start customizing what type of chart we’re going to have and what data it should show from our data source.

To actually show a chart there’s two bits of information you have to describe, area’s and series’. The first area’s is used to define an area for a chart to appear, one interesting thing about the chart control is you arn’t limited to just one area. In fact in this example I’m going to have to chart’s one showing a pie chart of phone popularity that will quickly show what kind of share each phone has, and then a second bar chart making it more clear the actual numbers people have of each phone. Area’s also let you set properties on what the chart is actually going to look like as well. In this instance I’m going to set for both charts to be 3D.

The second bit of information is the Series. This is where you’re actually specifying what data is going to be shown in which area and what kind of chart it is (e.g. Pie, Column, Donut etc). My completed code then looks like this…

<asp:Chart ID=”Chart1″ runat=”server” DataSourceID=”ChartDB” Height=”400px” Width=”400px”>

<series>

<asp:Series ChartArea=”ChartArea1″ ChartType=”Pie” Name=”Series1″ XValueMember=”Name” YValueMembers=”People”>
</asp:Series>
<asp:Series ChartArea=”ChartArea2″ Name=”Series2″ XValueMember=”Name” YValueMembers=”People”>
</asp:Series>

</series>
<chartareas>

<asp:ChartArea AlignmentOrientation=”Horizontal” Name=”ChartArea1″>

<Area3DStyle Enable3D=”True” />

</asp:ChartArea>
<asp:ChartArea Name=”ChartArea2″>

<area3dstyle enable3d=”True” />

</asp:ChartArea>

</chartareas>

</asp:Chart>

Depending on your data this should give you something like this…

This is just a simple example of what you can do, but if you download the Chart Samples Project and have a look through there is no end to the possibilites with everything from different styles of charts to adding ajax functionality even with the ability to click of different parts of the carts to trigger events.

System.Lazy

Lazy loading isn’t a new concept, it’s a pattern that been around for a while to improve the performance of your apps by only loading objects when they are going to be used. For example if you have an object that contains a property of a list of customers then you only really need to populate it when you access the property not when the object was initially created, as it may never be used. At the same time though you don’t want to be going off to the database every time access the property. So the simple solution is to have another private variable that stores if the customers property is populated or not and then check that in the property’s get to determine if the data needs to be loaded or not.

Well now in .NET 4, lazy loading has been built into the framework with System.Lazy. Instead of the above all you need to do now is write something like this…

Lazy<Customers> _customers = new Lazy<Customers>();

What this will do is create you a customers object but only run the constructor when you actually access the objects Value property which will be of type Customers. e.g.

_customers.Value.CustomerData 

It’s that simple, but can get even better. The constructor may not be the only thing you want to run when you access the property the first time. In this case you would write something like…

_customers = new Lazy<Customers>(() =>
        {
            // Write any other initialization stuff in here
            return new Customers();
        });

I must point out though while as great as this is, it does have some limitations so you probably won’t want to use it in all scenarios.

For more information check out the Lazy initialization page on MSDN

Doloto

Doloto

Meant for Web 2.0 Apps that use a lot of JavaScript, Doloto will speed up the download time of all the JavaScript by basically removing anything that isn’t initially needed and replacing it with stubs. It will then download in the background or wait until it is first called. The result, a seemingly much faster Web App for the user.

For more info have a look at the Doloto page on Microsofts Research site or head over to the download page on MSDN.

Introduction to Real Time Search

The Real Time Search this article relates to is a dll that comes included in the Web Client Software Factory one of Microsoft’s patterns and practices downloads. What it can do and what this example will demonstrate is adding the ability cause a post back that will refresh an update panel as the users types into a search box. This can give a great effect and make a web app really user friendly in scenarios like searching photo’s, emails or any general list.

First late me state though that this is in no way the most optimal way program. In most scenarios you could built a better result using something like JSON as their will be a lot less data transfer, which is also a general reason to avoid update panels. However this is also very quick and very easy to implement, not to mention if you’ve ever used update panels before you already know 90% of what’s needed. This can also only work in situations where you have a good search that is going to return the result quickly, rather than leaving the user sitting there trying to work out why nothing’s happening and where the search button has gone.

Implementing Real Time Search

For this example I will be filtering a table from a DB based on the search criteria and refreshing a Grid View with the results. I will be using a normal C# Web Site project with the Adventure Works sample DB from Microsoft. DB connection will be done using LINQ to EntityFramework, however there is no need to use this it is just my preference for the example.

First off set up you’re website and db and make sure both are working with no problems. As results will be displayed in an Update Panel, get one of these along with a script manager added to your page, so it looks something like this:

<form id=”form1″ runat=”server”>
<div>
<asp:ScriptManager ID=”ScriptManager1″ runat=”server”>
</asp:ScriptManager>
<asp:UpdatePanel ID=”UpdatePanel1″ runat=”server”>
<ContentTemplate></ContentTemplate>
</asp:UpdatePanel>
</div>
</form>

Next let’s get the search working in the normal method, so I’m going to create my Entity Model and add a textbox and gridview to show the results. Again you can connect and show your results however you want. You should now have something like this in your aspx file:

<form id=”form1″ runat=”server”>
<div>
<asp:ScriptManager ID=”ScriptManager1″ runat=”server”>
</asp:ScriptManager>

<
asp:TextBox ID=”txtSearch” runat=”server” OnTextChanged=”TextChanged” Text=””></asp:TextBox>

<
asp:UpdatePanel ID=”UpdatePanel1″ runat=”server”>
<ContentTemplate>

<
asp:LinqDataSource ID=”LinqDataSource1″ runat=”server” onselecting=”LinqDataSource1_Selecting”>
</asp:LinqDataSource>

<
asp:GridView ID=”GridView1″ runat=”server” AutoGenerateColumns=”False” DataSourceID=”LinqDataSource1″>
<Columns>
<asp:BoundField DataField=”ProductID” HeaderText=”ProductID”
ReadOnly=”True” SortExpression=”ProductID” />
<asp:BoundField DataField=”Name” HeaderText=”Name”
ReadOnly=”True” SortExpression=”Name” />
<asp:BoundField DataField=”ProductNumber” HeaderText=”ProductNumber” ReadOnly=”True” SortExpression=”ProductNumber” />
<asp:BoundField DataField=”Color” HeaderText=”Color”
ReadOnly=”True” SortExpression=”Color” />
<asp:BoundField DataField=”SafetyStockLevel” HeaderText=”SafetyStockLevel”
ReadOnly=”True” SortExpression=”SafetyStockLevel” />
<asp:BoundField DataField=”ReorderPoint” HeaderText=”ReorderPoint”
ReadOnly=”True” SortExpression=”ReorderPoint” />
</Columns>
</asp:GridView>
</ContentTemplate>

</asp:UpdatePanel>
</div>
</form>

And this in your code behind:


protected void LinqDataSource1_Selecting(object sender, LinqDataSourceSelectEventArgs e)
{
Model.AdventureWorks2008Entities AdventureWorkds = new Model.AdventureWorks2008Entities();
var products = from p in AdventureWorkds.Product
where p.Name.Contains(txtSearch.Text)
select p;
e.Result = products;
}

Next its time to add the Real Time Search. Make sure you have the dll downloaded (you may need to compile the download to get it) and add it to your bin folder. Add the following to your page in the relevant places:

<%@ Register Assembly=”RealTimeSearch” Namespace=”RealTimeSearch” TagPrefix=”cc1″ %>

<cc1:RealTimeSearchMonitor ID=”RealTimeSearchMonitor1″ runat=”server” AssociatedUpdatePanelID=”UpdatePanel1″>
<ControlsToMonitor>
<cc1:ControlMonitorParameter EventName=”TextChanged” TargetID=”txtSearch” />
</ControlsToMonitor>
</cc1:RealTimeSearchMonitor>

Important things to notice here are the AssociatedUpdatePanelId which tells the control what it has to refresh and the controls to monitor section which sets what the control to watch is called and the event name that will be fired when the post back is created. You will now need to corresponding control in your code behind like so:

protected void TextChanged(object sender, EventArgs e)
{
GridView1.DataBind();
}

Run the site and  you should find that the grid view now updates as you type (all be it with a slight delay).

To improve you can add other controls like update progress to show something happening which will help with any delays in displaying the results.