IT Weblog

Quotation of the day! 2012-02-20

klimmass — Mon, 20 Feb 2012 09:00:18 +0000

Never trust a programmer in a suit.

Quotation of the day! 2012-02-10

klimmass — Fri, 10 Feb 2012 10:34:29 +0000

In the future, programming will be a basic course alongside reading and math.

The Cult of Done Manifesto

klimmass — Sun, 05 Feb 2012 18:03:57 +0000

I hope this image is self-explaining

Quotation of the day!

klimmass — Fri, 03 Feb 2012 12:53:20 +0000

Programming is like sex… one mistake and you support it forever!

[Programming Rules] Describe summited bugs in details

klimmass — Tue, 27 Sep 2011 13:11:38 +0000

“Some fields should be read-only”… Is this a good description? If you can read in other minds, then it’s ok….. otherwise be more precise when submitting a bug report!
The rule is: Describe the bug in as many details as needed to be reproduced by software engineer. Attach some crash reports if possible.

Showing IDataErrorInfo for NULL objects

klimmass — Sat, 24 Sep 2011 11:50:04 +0000

WPF provides, fairly easy to implement, possibility to validate entered data and notify user when something is incorrect. An example is available in MSDN, so I will skip further explanation how does this work…

Everything works like a charm till you validate data bounded to main object. For instance let’s examine code below:

public abstract class AbstractCity : ICity
{
    private string name;
    private Country country;
 
    public string Name
    {
        get { return name; }
        set
        {
            if (name != value)
            {
                name = value;
                if (PropertyChanged != null)
                    PropertyChanged(this, new PropertyChangedEventArgs("Name"));
            }
        }
    }
    public virtual Country Country
    {
        get
        {
           return country;
        }
        set
        {
            if (country != value)
            {
               country = value;
               ExecutePropertyChanged("Country");
            }
        }
    }
    public string this[string columnName]
    {
        get
        {
            switch (columnName)
            {
                case "Name":
                    return String.IsNullOrWhiteSpace(Name) ? "City name must be set" : String.Empty;
                case "Country":
                    return Country == null ? "Country must be set" : String.Empty;
                default:
                    return String.Empty;
            }
        }
    }
 
    public string Error
    {
        get { return this["Name"]; }
    }
 
    protected void ExecutePropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }
 
    public event PropertyChangedEventHandler PropertyChanged;
}
 
public class CityNullCountry : AbstractCity { }

and binding in XAML:

<TextBox  Grid.Column="1" Grid.Row="0" Text="{Binding Path=City.Name, ValidatesOnDataErrors=True, NotifyOnValidationError=True, UpdateSourceTrigger=PropertyChanged}"/>
<TextBox  Grid.Column="1" Grid.Row="1" HorizontalAlignment="Left" Width="250" Text="{Binding Path=City.Country.Code, Mode=OneWay, ValidatesOnDataErrors=True, NotifyOnValidationError=True}" IsReadOnly="True"/>
<ComboBox Grid.Column="1" Grid.Row="1" HorizontalAlignment="Right" Width="100" SelectedItem="{Binding Path=City.Country}" ItemsSource="{Binding Path=Countries}" DisplayMemberPath="Code"/>
<TextBox  Grid.Column="1" Grid.Row="2" Text="{Binding Path=City.Country.Name, ValidatesOnDataErrors=True, NotifyOnValidationError=True, Mode=OneWay}" IsReadOnly="True"/>

in this code it is very easy validate and notify user when Name property in CityNullCountry object is NULL or empty. But there is no easy solution to validate City.Country.Name property. The reason is that Country object may not exists when City object is created.

So as up now we know that WPF needs Country class instance in order to validate it (using IDataErrorInfo in that class) and notify user when something is wrong. Some of you may ask, why I don’t check Country object in City class. The answer is simple. WPF validates bounded object and in that case it is Country object and it’s Name property. Text=”{Binding Path=City.Country.Name, ValidatesOnDataErrors=True, NotifyOnValidationError=True, Mode=OneWay}”. TextBox with such binding will check for IDataErrorInfo interface in Country class…. but Country object may be empty and nothing will be validated. User will be not aware of any errors at all.

So, my solution is fairly easy. I will simply provide an fake Country object when real object is NULL. Validation will run against my fake object and errors will popup in the user interface. One way to achieve that is to use Activator.CreateInstance() method. The whole mechanism implementation is showed below:

public class CityNullIsDefaultCountry : AbstractCity
{
    private Country country;
 
    protected DefaultsTable defaults = new DefaultsTable();
 
    public override Country Country
    {
        get
        {
            return defaults.GetObjectOrDefault(country, "Country");
        }
        set
        {
            if (country != value)
            {
                country = value;
                ExecutePropertyChanged("Country");
            }
        }
    }
}
 
public class DefaultsTable
{
    readonly Dictionary<string, object> defaults = new Dictionary<string, object>();
 
    public T GetObjectOrDefault<T>(T obj,  string propName) where T : class
    {
        if (obj != null)
            return obj;
 
        if (defaults.ContainsKey(propName))
            return (T)defaults[propName];
 
        T defaultObject = (T)Activator.CreateInstance(typeof(T));
 
        defaults.Add(propName, defaultObject);
 
        return defaultObject;
    }
}

DefaultsTable defaults = new DefaultsTable(); is responsible for providing fake object if it is NULL. When we set the Country property to some value, this value will be returned.

On of the challenges now is to determine what kind of object is returned when we access Country property on City class… I will discuss that somewhere in the future. In short: this can be determined by adding IsDefault flag and checking it.

Sample code for this example can by found here

[Programming Rules] Consider writing Unit Test for the bug you have fixed

klimmass — Sun, 18 Sep 2011 17:54:30 +0000

Remember!
When you fix a bug and you feel that it may occur in the future, don’t waste time and write at least one Unit Test to check code against that bug.

Logging Exception with StackTrace

klimmass — Thu, 15 Sep 2011 08:48:10 +0000

C# language has a great Exception Handling mechanism build-in. If something in not predictable during compile time developer can easily embed that piece of code in try{ (...) } catch{ (...) } and say “case closed”. Sample code taken from MSDN:

class ExceptionTest
{
    static double SafeDivision(double x, double y)
    {
        if (y == 0)
            throw new System.DivideByZeroException();
        return x / y;
    }
    static void Main()
    {
        // Input for test purposes. Change the values to see
        // exception handling behavior.
        double a = 98, b = 0;
        double result = 0;
 
        try
        {
            result = SafeDivision(a, b);
            Console.WriteLine("{0} divided by {1} = {2}", a, b, result);
        }
        catch (DivideByZeroException e)
        {
            Console.WriteLine("Attempted divide by zero.");
            //Logger.Error("Attempted divide by zero.")
        }
    }
}

Works like a charm…. but this was very simple scenario. In more advanced scenarios we – developers – would like to get some more feedback, then just a logged information like:Attempted divide by zero. In business application a lot of other factors in involved. So it is necessary to have proper feedback information when something goes wrong. I’ve also faced that problem. Not sufficient information was provided with the bug description and we were unable to reproduce and fix the bug.

At that moment I’ve decided to do the obvious step. Serialize Exception object and save in separate log file

Code that realizes my idea is showed below:

public class ExceptionXElement : XElement
    {
        public ExceptionXElement(Exception exception)
            : base(new Func<XElement>(() =>
            {
                if (exception == null)
                {
                    throw new ArgumentNullException("exception");
                }
                XElement root = new XElement
                  (exception.GetType().ToString());
 
                if (exception.Message != null)
                {
                    root.Add(new XElement("Message", exception.Message));
                }
 
                if (exception.StackTrace != null)
                {
                    root.Add
                    (
                      new XElement("StackTrace",
                        from frame in exception.StackTrace.Split('n')
                        let prettierFrame = frame.Substring(6).Trim()
                        select new XElement("Frame", prettierFrame))
                    );
                }
 
                if (exception.Data.Count > 0)
                {
                    root.Add
                    (
                      new XElement("Data",
                        from entry in
                            exception.Data.Cast<DictionaryEntry>()
                        let key = entry.Key.ToString()
                        let value = (entry.Value == null) ?
                          "null" : entry.Value.ToString()
                        select new XElement(key, value))
                    );
                }
 
                if (exception.InnerException != null)
                {
                    root.Add
                    (
                      new ExceptionXElement
                        (exception.InnerException)
                    );
                }
 
                return root;
            })())
        { }
    }

Code above is nicely wrapped in a function that saves XElement into single file.

iphone.klimczyk.pl website launch

klimmass — Wed, 03 Aug 2011 09:29:51 +0000

I’m proudly to announce launch of my iphone games website. Website is located under: http://iphone.klimczyk.pl.
We run this website together with my wife.

If you are interested in some iphone games and apps please visit us there

Using different .config file in .NET application

klimmass — Wed, 01 Jun 2011 08:03:15 +0000

In .NET world executable files using by default configuration file with special name. Microsoft has implemented following pattern: executable: program.exe and corresponding configuration file program.exe.config. In many scenarios this pattern is fitting well, but there are some cases when something else necessary. In my situation common configuration file was desirable! One configuration file with shared app settings, configuration strings, etc.

First solution I found was sharing AppSettings section between configuration files. This can be easily achieved by adding file attribute in appSettings tag. Like this:

<appSettings file=”commonSettings.config”>

But this doesn’t solve problem with connections string and custom sections… damn…

The solution that I end up with is:

AppDomain.CurrentDomain.SetData("APP_CONFIG_FILE", @"commonConfig.config");
 
FieldInfo fiInit = typeof(ConfigurationManager).GetField("s_initState", BindingFlags.NonPublic | BindingFlags.Static);
 
if (fiInit != null)
{
fiInit.SetValue(null, null);
}
 
ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);

The AppDomain.CurrentDomain.SetData() method changes properties for current domain. So I simply change the APP_CONFIG_FILE property value to point to another config file. Rest of the code is necessary to re-read the configuration. With this solution I able to force .NET to use one configuration file between multiple executables.