.NET/ASP.NET/C#/VB.NET PDF Document SDK

Just as printed dictionaries vary in what you get when you look up a word, so can .NET dictionaries. The Dictionary type in the System.Collections.Generic namespace is a generic type, letting you choose the type for both the key the value used for the index and the value associated with the index. (Note that there are some restrictions regarding the key type see the sidebar on the next page.) Example 9-1, which models

10 11

ssrs ean 128, ssrs ean 13, ssrs pdf 417, ssrs code 128 barcode font, ssrs code 39, ssrs data matrix, c# remove text from pdf, pdfsharp replace text c#, winforms upc-a reader, c# remove text from pdf,

a traditional printed dictionary, uses strings for the index, and expects a string as the result, so myDictionary in that example would be defined as shown in Example 9-2.

Dictionary<string, string> myDictionary = new Dictionary<string, string>();

Table B-1 explains the Drush commands that I use on a frequent basis. Navigate http://drupal.org/node/477684 to see the full list of Drush commands. to

To be able to look up entries quickly, dictionaries impose a couple of requirements on keys First, a dictionary entry s key must not change in a way that affects comparisons (This often just means that you should never change a key However, it s technically possible to build a type for which certain kinds of changes have no impact on comparisons performed by the Equals methods Such changes are invisible to the dictionary) Second, it should provide a good hash function To understand the first requirement that for comparison purposes, keys must not change consider what changing a key would mean in a printed dictionary Suppose you look up the entry for bug in your dictionary, and then you cross out the word bug and write feature in its place.

We can now navigate to our website with pretty URLs in the form http://localhost:84/ product/show/4.

The usual way of looking up words will now fail for this entry the entry was positioned in exactly the right place for when the key was bug Anyone looking up feature will not think to look in the location for your amended item And it s the same with a dictionary collection to enable fast lookup, dictionaries create an internal structure based on the keys items had when they were added to the dictionary It has no way of knowing when you ve changed a key value If you really need to do this, you should remove the entry, and then add it back with the new key this gives the dictionary a chance to rebuild its internal lookup data structures This requirement is most easily met by using an immutable type, such as string, or any of the built-in numeric types.

The second requirement that key types should have a good hash function is a bit less obvious, and has to do with how dictionary collections implement fast lookup The base SystemObject class defines a virtual method called GetHashCode, whose job is to return an int whose value loosely represents the value of the object GetHashCode is required to be consistent with the Equals method (also defined by SystemObject) two objects or values that are equal according to Equals are required to return the same hash code Those are the rules, and dictionaries will not work if you break them This means that if you override Equals, you are required to override GetHashCode, and vice versa The rules about hash codes for items that are not equal are more flexible.

For more detailed configuration options, consult the readme included with the download from CodePlex. The download includes configuration examples, as well as instructions for enabling logging and other advanced features.

Ideally, nonequal items should return nonequal hash codes, but clearly that s not always possible: a long can have any of several quintillion distinct values, but a hash code is an int, which has merely a few billion possible values So inevitably there will be hash collisions nonequal values that happen to have equal hash codes For example, long returns the same hash code for the values 4,294,967,296 and 1..