foreach with Generic Dictionary

I decided to write this post because few people approached me with the question:  “Is there a way to use foreach iteration statement with Dictionary<TKey, TValue> object?”

The quick response is: “Yes, use KeyValuePair.”

However, it wasn’t enough and I had to show an example.

Before I will show an example here, I want to remind you that Dictionary<TKey, TValue> class implements IDictionary<TKey, TValue> interface that extends ICollection<KeyValuePair<TKey, TValue> which in it turn is derived from IEnumerable<KeyValuePair<TKey, TValue>.  As we know every class that implements IEnumerable interface must implement the GetEnumerator method.  And that is the reason why we can use foreach iteration statement.

Here’s the promised example.

   1: // Create a Dictionary object and load it with values.

   2: Dictionary<string, double> employeesWage = new Dictionary<string, double>();

   3: employeesWage.Add("Tom", 20000);

   4: employeesWage.Add("John", 15200);

   5: employeesWage.Add("Chris", 35000);

   6: employeesWage.Add("Brian", 38000);

   7:  

   8: // Enumerate and display

   9: foreach (KeyValuePair<string, double> pair in employeesWage)

  10:   Console.WriteLine("{0} makes {1:C}", pair.Key, pair.Value);

GetAttribute Generics way.

As developers we often need to work with Xml.  In my case I found myself writing code like this one:

   1: public void Main()

   2: {

   3:   string name;

   4:   bool required;

   5:   XmlDocument _xmlDoc = new XmlDocument();

   6:   _xmlDoc.LoadXml("<column name=\"colName\" required=\"true\"/>");

   7:   if (_xmlDoc.DocumentElement.HasAttribute("name"))

   8:     name = _xmlDoc.DocumentElement.GetAttribute("name");

   9:   if (_xmlDoc.DocumentElement.HasAttribute("required"))

  10:     required = Convert.ToBoolean(_xmlDoc.DocumentElement.GetAttribute("required"));

  11: }

I hated the fact that I have to for every attribute use two lines in my Main function.  Below you can see refactored code.

 

Note: You will need to pass XmlNamespaceManager if you’re using namespaces.

   1: public void Main()

   2: {

   3:   XmlDocument _xmlDoc = new XmlDocument();

   4:   _xmlDoc.LoadXml("<column name=\"colName\" required=\"true\"/>");

   5:   string name = GetAttribute<string>(_xmlDoc.DocumentElement, "name");

   6:   bool required = GetAttribute<bool>(_xmlDoc.DocumentElement, "required");

   7: }

   1: private T GetAttribute<T>(XmlElement columnElement, string attributeName)

   2:   where T : IConvertible

   3: {

   4:   if (columnElement.HasAttribute(attributeName))

   5:     return (T) Convert.ChangeType(columnElement.GetAttribute(attributeName), typeof (T));

   6:   return default(T);

   7: }

I hope you’ll find it useful.