Category: .NET

Five common mistakes for ASP.NET MVC accesing resources : css, js, images, ajax

This is a Razor /MVC5 variant of older post
http://msprogrammer.serviciipeweb.ro/2010/10/09/five-common-mistakes-for-asp-net-mvc-accesing-resources-css-js-images-ajax/

To have once for all the link to show to people, because too much makes the same error again and again. (From here – you can use ResolveUrl or Url.Content – it’s the same for me. I use ResolveUrl because I used first …)

Case 1 The image does not display

Please check you have the following :

 <img src="@Url.Content("~/Content/images/YOURIMAGE.jpg" )" alt="image" style="border:0" /> or 
 
<img src="~/Content/images/YOURIMAGE.jpg" alt="image" style="border:0" /> 

Case 2 The css does not show

Please check you have the following :

 @string.Format("<link href="{0}" type="text/css" rel="stylesheet" />", Url.Content("~/Content/your.css"))  

or

 <style type="text/css">
@import '@Url.Content("~/Content/your.css")';

</style>  
  <style type="text/css">
<link href='~/Content/your.css' type='text/css' rel='stylesheet' />

</style>  

Case 3 The js does not execute (undefined error)

3.1 Please check you have the following :

 <script type="text/javascript" src="@Url.Content("~/Scripts/yourjs.js")"></script> 

or

 <script type="text/javascript" src="~/Scripts/yourjs.js"></script> 

This should be either in _Layout.cshtml, or in the scripts section

 @section scripts {   } 

in your .cshtml file.
3.2 please check in browser console ( press F12 ) for any javascript error that code may have

Case 4 The js does execute in .cshtml page, but did not execute under js file

Please check you DO NOT have the following @something in the js file. The js file is not interpreted by the same engine as cshtml, so can not interpret asp.net tags. Instead , add a parameter to your function for each @ variable that you have. Simple example : Let’s say in cshtml you have :

 <script type=”text/javascript”>

function Generate(){

window.open('@Url.Action(“About”)’);
}

</script> 

and you call Generate() from .cshtml file. Now you want the same in a .js file. The function Generate will have a parameter instead of Razor variable

 function Generate(url){  window.open(url); } 

and call like this from .cshtml file:

 Generate('@Url.Action("About")'); 

Case 5 The ajax request gives you a 404 error.

Please ensure that you have

 @Url.Content("~/path”) 

and not

 /path 

when you call the Ajax URL

Bonus 1: T4MVC , http://mvccontrib.codeplex.com/releases

Bonus 2: Edit the project file and put <MvcBuildViews>true</MvcBuildViews>

( short url: http://bit.ly/asp5Mistakes)

Async + sync completion + lock

Let’s suppose that you have 2 functions = one true sync and one true async . Let’s suppose more that the sync one can must finish before calling next time ( think about some weird COM component or , in our days, SqlConnection )

If we look just at the async function , we could wait for all. However, the sync function must be called sync

One solution is to make different calls:


var list = new List<Task<int>>(nr);
//add async to list

await Task.WhenAll(list)

//call each sync



But I want to make really async – and one solution is lock

We could wrote the sync function in async manner like this:


//SemaphoreSlim sem = new SemaphoreSlim(1);
static object myObject = new object();
async Task<int> syncTask(int i)         {             
lock (myObject)             
//try{                 
//await sem.WaitAsync();                                 
CallSyncFunction();                             
//}             
//finally             
//{                 
//sem.Release();             
//}                                   
}

The trick that I  used is lock, because the syntax is easier than SemaphoreSlim (BTW: if you want to learn about threading, jump directly to http://www.albahari.com/threading/)
In this manner, the sync function is modified in async -and, more, it waits for completion before entering the second time.

The code is on github on

More details in the Wiki https://github.com/ignatandrei/AsyncSyncLock/wiki or in the code https://github.com/ignatandrei/AsyncSyncLock/

spot errors in VB

Please spot the errors in the following code in VB.NET:

Dim Diff As String = con.ExecuteCommand(“SELECT DATEDIFF(Day, (select [date] from table where Username = ‘” + txtUserName.Text + “‘), ‘” & DateTime.Now.ToString() & “‘)”)
If (Diff > 30) Then
Response.Redirect(“PleaseChangeMyPassword.aspx”)
End If

 

( find at least 3…)

Side note:

No wonder Visual Basic has died ( more or less). Guess future of server javascript ….

Generating Visual Studio solution( or project) references

A Visual Studio pacakge is a plugin of Visual Studio that can do (almost) anything inside Visual Studio

I have made a small project that generates a list of all solution ( or project) references from VS:

 

            foreach (var project in dte.Solution.Projects)
            {
                var p = project as Project;
                if (p == null)
                {
                    continue;
                }

                var vsproject = p.Object as VSLangProj.VSProject;
                if (vsproject == null)
                    continue;

                string nameProject = p.Name;
                foreach (var reference in vsproject.References)
                {
                    var r = reference as Reference;
                    if (r == null)
                        continue;

                    var pathRef = r.Path;

                    //this is a package                    
                    var pa = new PackageAdd();
                  
                    pa.ProjectName = p.Name;
                    pa.IdentifierPackage = r.Identity;
                    pa.VersionPackage = r.Version;
                    pa.NamePackage = r.Name;

                  



                    if (r.SourceProject != null)
                    {
                        
                        pa.NamePackage = r.SourceProject.Name;
                    }
                    sb.AppendLine(pa.ToString());
                }
            }

You can find the solution at https://github.com/ignatandrei/ToolsAndUtilities/tree/master/VS2015/FindReferencesVS

Also the video is at https://youtu.be/a3YHVjJ9fm4

Enjoy!

Thank you for all the API

In our days it is simpler to make an application by putting together some API . I wanted to make a list of all my 5 Minutes .NET playlist videos . First, I have tried to find an application(nothing). Then I have read  You Tube API from https://console.developers.google.com/apis/library . With 2 http requests( one for retrieving all videos from a playlist, the other to find video details) and a NuGet package to export to Excel/Word/PDF/HTML it was simple. You can find the whole project at https://github.com/ignatandrei/YouTube . A video demo at https://www.youtube.com/watch?v=wNHDsHtLBq4 . And the whole list at https://github.com/ignatandrei/ToolsAndUtilities/tree/gh-pages

IDisposable and Marshal.ReleaseCOMObject and dynamic in C#

 

If you have worked with COM, you know that for every COM object that you access is not only necessary to null the reference, but also call Marshall.ReleaseCOMObject .

This is a very error prone task, because you have all try / finally blocks

 
// declare a, ws, w 
try{ 
a=new Application(); 
ws = a.Workbooks; 
w = ws.Add(); 
//code 
}
 catch(...) {
 if( w != null){ 
Marshal.ReleaseComObject(w); 
w = null; 
}
 if(ws !=null){ 
Marshal.ReleaseComObject(ws); 
ws = null; 
} 
if( a!= null) { 
Marshal.ReleaseComObject(a); a= null; 
} 
} 

All of this could be done easy with IDisposable, if

1. IDisposable calls the Marshal.ReleaseCOMObject

2. Find a way to call methods / properties on the COM object from the class that implements IDisposable

 

I have done this and the result is like this:

 
using (dynamic a = new ComDisposable(new Application())) { 
using (dynamic ws = a.Workbooks) { 
using (dynamic w = ws.Add()) { 
using (var shs = w.Sheets) { 
using (var s = shs[1]) { 
//Worksheet a; 
using (var r = a.Range("A1")) { 
r.Value2 = "http://ignatandrei.github.io/ToolsAndUtilities/";; 
using (var f = r.Font) { 
f.Bold = true; 
}
 }
 }
 }
 w.SaveAs(fileName); 
w.Close(); 
} 
}
 a.Quit(); } 

 

Video at https://youtu.be/2qbAcSjL1gU

NuGet package at https://www.nuget.org/packages/ReleaseComObjectDisposable/

AppContext

AppContext is like Application in ASP.NET (MVC). You can see the value all over the application

AppContext.SetSwitch("OCR", true);

And we can have the result in all dll’s by

 public bool IsOCREnabled()
        {
            bool test;
            if (!AppContext.TryGetSwitch("OCR", out test))
                return false;

            return test;
        }

Video demo at https://youtu.be/GMgn4o3yPqw

Instrumentation in C# / .NET

For many programmers a try/catch with stack trace it is enough

try
{
var p = new Person();
p.DateOfBirth = DateTime.Now.AddYears(-10);
p.Drink(10, 2);
}
catch (Exception ex)
{
Console.WriteLine("ERROR OCCURED " + ex.StackTrace);
}

Others want to see also functions arguments, like in


p.Drink(10, 2);

will produce the result

ERROR An exception occured in method InstrumentationPostSharp.Person.Drink with (beersNumber = 10 , vodkaNumber = 2)

For this you can install the package
https://www.nuget.org/packages/LoggerAspect.Nlog

that have full source code at
https://github.com/vnvizitiu/AOP/tree/master/PostSharpTutorial

and watch my video for more details
https://youtu.be/qe2kpuuWXkw

RavenDB embedabble

I have made an application with RavenDB embeddable.

The good part is that is embeddable and easy to work with – at least, at start.

What I have learned:

  • If you forgot to use using, then RavenDB will throw an exception complaining about multiple sessions. Code:
 using (var session = instanceDefault.OpenSession(DatabaseName()))
{

//code
}

 

  • If you use multiple instance of the same EmbeddableDocumentStore , even on different default databases , then will complain about “temp path already used by another database instance “ . And the generics do NOT share the same instance of a static variable. And when you dispose a static singleton instance ? At the final of the application ( do not forget , otherwise you may have again “temp path already used by another database instance ” !)

 

  • The most simple index for new databases is RavenDocumentsByEntityName . Code:
//static EmbeddableDocumentStore instanceDefault;
var dbc = instanceDefault.DatabaseCommands.ForDatabase(DatabaseName());
                var defIndex = new RavenDocumentsByEntityName();
                
                defIndex.Execute(dbc,new DocumentConvention()
                {
                    DefaultUseOptimisticConcurrency = true                    
                    
                } );

 

  • If you create an index, create in the Database that needs. Otherwise if will complain when you get the data.  ( see previous code)

 

  • To manage data / databases , there is RavenDB Management Studio – a fancy name for an application that you can access ( by default ) at http://localhost:8080 . Code:
            instanceDefault = new EmbeddableDocumentStore();
//I have put this in app.config/web.config
            //instanceDefault.Configuration.Settings.Add("Raven/MaxSecondsForTaskToWaitForDatabaseToLoad", "60");
/*
<connectionStrings>
		<add name="RavenDB" connectionString="DataDir = ~\App_Data\Database"/>
	</connectionStrings>
   <appSettings>
	<add key="Raven/MaxSecondsForTaskToWaitForDatabaseToLoad" value="60"/>
*/
            instanceDefault.ConnectionStringName = "RavenDB";
            instanceDefault.Conventions.FindIdentityPropertyNameFromEntityName = (entity) => "ID";

            try
            {
                //To try in debug mode
                NonAdminHttp.EnsureCanListenToWhenInNonAdminContext(8080);
                instanceDefault.UseEmbeddedHttpServer = true;
                instanceDefault.Initialize();

            }
            catch (ReflectionTypeLoadException ex)
            {
                string message = "LoaderExceptions:";
                ex.LoaderExceptions.ForEach(it => message += it.Message + ";");
                throw new Exception(message, ex);
            }


 

( do not let this into Web Application if you want to deploy to a third party host)

 

  • Copy / paste database do not work. You must backup and restore data( preferably with RavenDB Management Studio )

 

  • RavenDB documentation is ok – however, embeddable database is not so represented very well

 

If you want to see a sample ( not very good, though) repository, I have created one at https://github.com/ignatandrei/RomaniaOpenData/blob/master/ROP/ROPInfrastructure/Repository.cs

Bottom line: I think that is good enough.

Export to Excel,Word , Pdf, Html,CSV

I have made an application / package that exports data ( classes/datatable/csv/json) to Word/Excel/PDF.

I have made several tries in the past , however now is the definitive source for .NET 4.x It is FULL code source, with tests and tutorials..

 

The code is at https://github.com/ignatandrei/Exporter 

The NuGet package is at https://www.nuget.org/packages/ExporterWordExcelPDF

The demo online is at http://exporter.azurewebsites.net/ 

The documentation is at https://github.com/ignatandrei/Exporter/wiki 

You can help with the project – please read https://github.com/ignatandrei/Exporter/wiki/Help-the-project 

So if you need Excel / Word / PDF to export, please consider this open source project.

Andrei Ignat weekly software news(mostly .NET)

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