c# generate barcode from string Lesson Review in C#

Drawer QR in C# Lesson Review

Lesson Review
Encode QR-Code In C#
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QR Decoder In Visual C#.NET
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You can use the following questions to test your knowledge of the information in Lesson 2, Working with Sequential Lists. The questions are also available on the companion CD if you prefer to review them in electronic form.
Paint Bar Code In C#.NET
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Read Barcode In C#.NET
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NOTE Answers
QR Encoder In .NET
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Encode QR Code ISO/IEC18004 In .NET Framework
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Answers to these questions and explanations of why each answer choice is right or wrong are located in the Answers section at the end of the book.
QR-Code Maker In Visual Basic .NET
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2D Barcode Drawer In Visual C#.NET
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1. What does the Dequeue method of the Queue class do (Choose all that apply.) A. Retrieves an item from the front of the collection B. Adds an item to the collection C. Removes the first item from the collection D. Clears the collection 2. In what order does a Stack retrieve items as you use its Pop method A. Random order B. First-in, first-out C. Last-in, first-out D. Last-in, last-out
UCC-128 Drawer In C#.NET
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Making ANSI/AIM Code 128 In C#
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Lesson 3: Working with Dictionaries
Paint Data Matrix ECC200 In Visual C#.NET
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USPS PLANET Barcode Encoder In C#.NET
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Lesson 3: Working with Dictionaries
Draw UPCA In Java
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Print EAN 128 In None
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At the other end of the spectrum from sequential lists are dictionaries. Dictionaries are collections that are meant to store lists of key/value pairs to allow lookup of values based on a key.
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Create PDF 417 In None
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After this lesson, you will be able to:
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Barcode Scanner In None
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Use a Hashtable to create a simple list of unique items. Use a SortedList to sort a list of objects. Work with DictionaryEntry objects to store name/value pairs. Enumerate dictionaries and know how to use DictionaryEntries. Understand the IEqualityComparison interface to provide uniqueness to Hashtables. Use the HybridDictionary to store name/value pairs in a very efficient way. Use the OrderedDictionary to store name/value pairs in a way that preserves the order of adding them to the collection.
Paint PDF417 In Java
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Barcode Creator In None
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Estimated lesson time: 30 minutes
Using a Dictionary
The Dictionary classes supported by the .NET Framework are used to map a key to a value. Essentially, they exist to allow you to create lookup tables that can map arbitrary keys to arbitrary values. In the most basic case, the Hashtable class is used to do this mapping of key/value pairs. For example, assume that you needed to map e-mail addresses to the full name of some user. You could use a Hashtable to store this mapping, as seen in this code snippet:
' VB Dim emailLookup As New Hashtable() ' Add method takes a key (first parameter) ' and a value (second parameter) emailLookup.Add("sbishop@contoso.com", "Bishop, Scott") ' The indexer is functionally equivalent to Add emailLookup("sbishop@contoso.com") = "Bishop, Scott" // C# Hashtable emailLookup = new Hashtable();
4
Collections and Generics
// Add method takes a key (first parameter) // and a value (second parameter) emailLookup.Add("sbishop@contoso.com", "Bishop, Scott"); // The indexer is functionally equivalent to Add emailLookup["sbishop@contoso.com"] = "Bishop, Scott";
Unlike the previous types of collections, dictionaries always expect two pieces of information to add them to the collection: a key and a value. This example shows us two ways to add items to our collection. First the Add method will allow us to add an item by specifying the key/value pair. In addition, you can use the indexer to specify a key/value pair by specifying the key in the indexer and assigning to it the value that you want the key to point to. Retrieving objects from a dictionary is simple as well. To access data once it has been added to the dictionary (here, a Hashtable), you simply call the indexer with the key you are looking for:
' VB Console.WriteLine(emailLookup["sbishop@contoso.com"]) // C# Console.WriteLine(emailLookup["sbishop@contoso.com"]);
Because dictionaries are made for looking up key/value pairs, it is not a surprise that iterating through the objects in a dictionary is not all that straightforward. For example, assume that you ve created a Hashtable and want to iterate over all the values. The code for accomplishing this task might look like this:
' VB Dim emailLookup As New Hashtable() emailLookup("sbishop@contoso.com") = "Bishop, Scott" emailLookup("chess@contoso.com") = "Hess, Christian" emailLookup("djump@contoso.com") = "Jump, Dan" For Each name as Object In emailLookup Console.WriteLine(name) Next name // C# Hashtable emailLookup = new Hashtable(); emailLookup["sbishop@contoso.com"] = "Bishop, Scott"; emailLookup["chess@contoso.com"] = "Hess, Christian"; emailLookup["djump@contoso.com"] = "Jump, Dan";
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