development

Using a Canvas Element in XUL / Mozilla-Extensions

It's actually pretty simple, but many small things can go wrong. So, here is your small boilerplate code for a XUL overlay which renders a small canvas area in the status bar:

  1. <?xml version="1.0"?>
  2.  
  3. <overlay id="myOverlay"
  4. xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
  5. xmlns:html="http://www.w3.org/1999/xhtml">
  6.  
  7. <statusbar id="status-bar">
  8. <statusbarpanel>
  9. <box>
  10. <html:canvas id="myCanvas" width="15" height="15" style="border:1px solid black;"/>
  11. </box>
  12. </statusbarpanel>
  13. </statusbar>
  14. </overlay>

and some simple painting in JS:

  1. var canvas = window.document.getElementById("myCanvas");
  2. var ctx = canvas.getContext("2d");
  3. ctx.fillStyle = "red";
  4. ctx.fillRect(5,5,5,5);

If done right, you will get a result like this

CANVAS in XULCANVAS in XUL

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Using .NET reflection to determine if a Class implements a generic interface.

Reflection and me? Big friends. With all the love and hate a good friendship should have. A few days ago it was all about hate again. I had a bunch of service classes, some of them would implement a generic interface... Let's call it IHasAdorable - so a Service-Implementation could look like this:

  1. public class MarketMerchant : IHasAdorable<CheeseBurger>, IProductSeller
  2. {
  3. // defined in IHasAdorable
  4. CheeseBurger BuyAdorable()
  5. {
  6. return new AdorableCheeseburger();
  7. }
  8.  
  9. // defined in IProductSeller
  10. IProduct Buy(String eanCode)
  11. {
  12. if (eanCode.equals("12345"))
  13. return this.bigStackOfSmellyFishburgers.Pop();
  14. else
  15. throw new IAmSoSorryException("We don't have any of these!");
  16. }
  17. }

Now lets assume we want to browse through ALL market merchants and have a look if they have any adorable products. Let's skip the iteration process and pay attention to the probing of all market merchants in order to buy a adorable product from each of them. First attempt might be to use "is":

  1. IProductSeller merchant;
  2. // iteration goes here
  3. if (merchant is IHasAdorable<object>)
  4. {
  5. // this wont work. We are selling something very special, not just a stupid object!
  6. // Casting to IHasAdorable<> won't even compile.
  7. }

This one would not work either, although it makes sense to me:
  1. typeof(IHasAdorable<object>).IsAssignableFrom(merchant)

It seems we need to know what kind of objects a unknown merchant sells before we can "see" if those are also adorable. So here is how I got it working. Let me know if you do know a better solution:
  1. // `1 means there is 1 Generic parameter
  2. Type adorableInterfaceType = merchant.GetType().GetInterface("IHasAdorable`1");
  3.  
  4. if (adorableInterfaceType != null)
  5. {
  6. // yay, the merchant has adorable products, what whould those be!?
  7. Type adorableProductType = adorableInterfaceType.GetGenericArguments()[0];
  8.  
  9. // here is the magic we need to get the correct IHasAdorable Type
  10. // with "filled in" generic type.
  11. Type genericAdorableInterfaceType =
  12. typeof(IHasAdorable<>).MakeGenericType(adorableProductType);
  13. MethodInfo mi = genericAdorableInterfaceType.GetMethod("BuyAdorable");
  14. myBagOfAdorableProducts.Add(mi.invoke(merchant,null));
  15. }

Bon Appétit

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"Jar-Hell" - or how do I find a Java-Class in a folder full of Jar-Archives

There you go

  1. #!/bin/sh
  2.  
  3. ########################################################################
  4. ## Scans all jar files within a directory (recursively) for a class
  5. ## name
  6. ## Usage: findClass /tmp/ MyFunnyClass
  7. ########################################################################
  8.  
  9. black='\E[30;47m'
  10. red='\E[31;40m\033[1m'
  11. green='\E[32;47m'
  12. yellow='\E[33;40m'
  13. blue='\E[34;40m\033[1m'
  14. magenta='\E[35;47m'
  15. cyan='\E[36;47m'
  16. white='\E[37;47m'
  17. alias Reset="tput sgr0"
  18.  
  19. cecho ()
  20. {
  21. local default_msg=" "
  22. message=${1:-$default_msg} # Defaults to default message.
  23. color=${2:-$black} # Defaults to black, if not specified.
  24. echo -e -n "$color"
  25. echo -n "$message"
  26. Reset # Reset to normal.
  27. return
  28. }
  29.  
  30. clsln()
  31. {
  32. fillLine " ";
  33. }
  34.  
  35. fillLine()
  36. {
  37. let tw=$(tput cols)-1;
  38. for (( c=0 ; c < $tw; c++))
  39. do
  40. echo -n "$1";
  41. done
  42. echo -e -n '\r'
  43. }
  44.  
  45. echo
  46. echo -n Scanning Folder:
  47. cecho "$1" $yellow
  48. echo -n for Class:
  49. cecho "$2" $yellow
  50. echo
  51.  
  52. fillLine "."
  53. echo
  54. for i in $(find $1 -name '*jar');
  55. do
  56. clsln;
  57. echo -n -e "Scanning :";
  58. cecho $i $blue
  59. echo -n -e '\r';
  60.  
  61. out=$(jar vft $i | egrep $2);
  62.  
  63. if [ "$out" ]
  64. then
  65. clsln;
  66. fillLine "*"
  67. echo
  68. echo -n -e 'Possble hit in file:'
  69. cecho $i $blue
  70. echo
  71. echo "$out" $red
  72. echo
  73. fillLine "*"
  74. echo
  75. echo
  76. fi
  77. done;
  78. clsln;
  79. echo;

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Tweet-Feed: soapUI

_pulsar_: did I mention me being in love with soapUI - http://www.soapui.org/? #java #dotnet #webservice

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(Unix) Timestamp to .NET DateTime ?

Well, this is rather a note to myself:

for Javascript new Date().getTime() value (miliseconds, hence / 1000)

  1. new System.DateTime(1970, 1, 1, 0, 0, 0, 0)
  2. .AddSeconds(ajaxRequest.RequestDate / 1000)

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One more reason why I love local initializers

  1. public static IDictionary<RequestTypeEnum, RequestGroupEnum>
  2. RequestTypeToGroup= new Dictionary<RequestTypeEnum, RequestGroupEnum>()
  3. {
  4. {RequestTypeEnum.RegisterAccount, RequestGroupEnum.Account},
  5. {RequestTypeEnum.UnregisterAccount, RequestGroupEnum.Account},
  6. {RequestTypeEnum.RegisterInetAccess, RequestGroupEnum.InetAccess},
  7. {RequestTypeEnum.UnregisterInetAccess, RequestGroupEnum.InetAccess},
  8. {RequestTypeEnum.RegisterMailbox, RequestGroupEnum.Mailbox},
  9. {RequestTypeEnum.UnregisterMailbox, RequestGroupEnum.Mailbox},
  10. {RequestTypeEnum.RegisterRLA, RequestGroupEnum.RLA},
  11. {RequestTypeEnum.UnregisterRLA, RequestGroupEnum.RLA}
  12. };
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Unexpected Consequences


Ooops! That was quite unexpected

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Accessing Arrays in .NET/c# via Reflection

Yesterday I was implementing a generic serializer (for logging purposes). While there is a good number of XML serializers available for .NET - none of them was meant to be used for only the purpose of reading. That means, I would not need deserialization but only some nice human readable output.

Anyway, thats not the point here. What took me about an hour to figure out is how to handle arrays (of natives) via reflection. I kinda feel stupid, but let me show you what i tired:

  1. Object propertyValue = prop.GetValue(o, null);
  2. if (propertyValue != null &amp;&amp; propertyValue.GetType().IsArray)
  3. {
  4. //if you need the type, here is how we get it, it's not used
  5. //in this example.
  6. Type arrayType = propertyValue.GetType().GetElementType();
  7. object[] arr = propertyValue as object[];
  8. for (int i = 0; i &lt; arr.Length; i++)
  9. {
  10. // serialization logic goes here
  11. }
  12. }
  13. ...

While this might work perfectly for arrays of "real" objects such as string[] - it will fail when your array is composed of native objects such as long[]. The cast to object[] will get you a nice null reference. Yummy.

After that I've been looking for Array.ForEach() which was pretty interesting, but did not really help due to it's generic nature. The solution was much simpler in the end, it just did not cross my mind to cast the propertyValue to Array - sometimes .NET can be pretty mysterious in terms of Autoboxing. Here is how it should be done:

  1. Object propertyValue = prop.GetValue(o, null);
  2. if (propertyValue != null &amp;&amp; propertyValue.GetType().IsArray)
  3. {
  4. Array array = propertyValue as Array;
  5. foreach (var arrElement in array)
  6. {
  7. // serialization logic goes here
  8. }
  9. }
  10. ...

Straight forward, simple - makes me feel stupid.

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Project Euler

So, you want to give your programming skills some training? Or just want to get familiar with a programming language and all test-projects you can come up with are pretty large and have been done 1000 times before? Yes, I know, your blogging software will be badass but will it be ever ready?

Anyway, If you are looking for some nice exercises which will also improve your math skills dramatically - head over to Project Euler and practice!

It contains a lot of math problems which can only be solved using a computer and won't knock out you right away, the challenges will guide you through ascending difficulty levels and should always give you an idea about the math you should use. 

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Why I Love Local Initializers...

  1. layoutTable.Rows.Add
  2. (
  3. ControlUtils.CreateRow
  4. (
  5. EmployeeFieldLabels.ExternalCompanyName,
  6. new ExtCompanyPickerControl(CreateChildID(&quot;ExternalCompanyName&quot;))
  7. {
  8. Customizer = new ExtCompanyCustomizer(MedaSession),
  9. AllowMultipleSelection = false,
  10. RenderListHeader = false,
  11. CountryProviderId = locationPickerControl.ID,
  12. CountryProviderProperty = &quot;SelectedCountryIsoCode&quot;;
  13. },
  14. false,
  15. EmployeeFieldTooltips.ExternalCompanyName,
  16. Page,
  17. CreateChildID(&quot;ExternalCompanyLabel&quot;),
  18. (
  19. externalCompanyValidator = new CompareValidator
  20. {
  21. ControlToValidate = CreateChildID(&quot;ExternalCompanyName&quot;),
  22. Operator = ValidationCompareOperator.Equal,
  23. Type = ValidationDataType.Integer,
  24. ValueToCompare = &quot;1&quot;,
  25. EnableClientScript = false,
  26. Display = ValidatorDisplay.Dynamic,
  27. ErrorMessage = string.Format(EmployeeManagerControlRes.ErrorValueRequired, EmployeeFieldLabels.ExternalCompanyName)
  28. }
  29. )
  30. )
  31. );

Check them out! http://msdn.microsoft.com/en-us/library/bb384062.aspx

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