get value from Hashtable for a given key RSS

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  Charles Bai

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  get value from Hashtable for a given key

  Jul 14, 2004 11:32 PM|LINK

  Hashtable myHash = new Hashtable(); myHash.Add(1, "word1"); myHash.Add(2, "word2"); Now I want to get the value for a given key, for example the first key is given. How could I do this? I tried string test = myHash.Item(1); // but this line failed to compile I can not find other appropriate methods that I can call to retrieve my value for a given key.
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  SreedharK

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  Re: get value from Hashtable for a given key

  Jul 14, 2004 11:48 PM|LINK

  One small mistake Below code should work! myHash[1].ToString();
  Sreedhar
  http://www.w3coder.org
  weblog http://weblogs.asp.net/skoganti
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  Charles Bai

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  Re: get value from Hashtable for a given key

  Jul 15, 2004 01:10 AM|LINK

  Unfortunately, it is not working. An exception was thrown saying "the object referrenced is not instantiated". I tried also int n = 1; string test = myHash[n].ToString(); Same thing happens. Any idea?
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  SreedharK

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  Re: get value from Hashtable for a given key

  Jul 15, 2004 01:40 AM|LINK

  OK, just now I tried below code in page_load it worked

  Hashtable myHash = new Hashtable();
          myHash.Add(1, "word1");
          myHash.Add(2, "word2");
  
  
          int n = 1;
          string test = myHash[n].ToString();
  
  
          Response.Write(test);

  Can you please let me know on which line you got the problem!! Also you are immidiately using myHash after Add or you are using in different place???
  Sreedhar
  http://www.w3coder.org
  weblog http://weblogs.asp.net/skoganti
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  Charles Bai

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  Re: get value from Hashtable for a given key

  Jul 15, 2004 02:26 AM|LINK

  Thanks for your test out the code. Let me be more specific I created a class called Constants that holds a Hashtable public variable. public class Constants { public Hashtable poStates; public Constants() { // init poStates = new Hashtable(); poStates.Add (1 , "word1"); poStates.Add (2, "word2"); } } In a page's code behind I call it this way: Constants con = new Constants (); int n = 1 string test = con.poStates[n].ToString (); It crashed on the line of the caller code. Don't know why, I called the constructor of the Constants and the Hashtable should be populated correctly. Any ideas?
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  SreedharK

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  Re: get value from Hashtable for a given key

  Jul 15, 2004 10:12 AM|LINK

  OK, Code seems fine, I had copied your code and tested, it worked for me! I would think only one thing, if you are not able to access Constants and if you are using Constants in your page, you will get the error in Constants con = new Constants (); line. Also remember to keep ; in the line int n = 1 , because, when I copy your code, I got the error in only that line, if I added semicolan, everything worked fine to me. All you have to look into is, is Constants is the scope of used codebehind page.
  Sreedhar
  http://www.w3coder.org
  weblog http://weblogs.asp.net/skoganti
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  Charles Bai

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  Re: get value from Hashtable for a given key

  Jul 15, 2004 02:06 PM|LINK

  Omitting ';" for n = 1 is a typo. The code still does not work for me. I added the following line Constants con = new Constants (); int nCount = con.poStates.Count; int nKey = 1; string test = con.poStates[nKey].ToString (); I debug it and found nCount has correct value, so that the Hashtable itself is OK, but it still crash on the last line. On another test, I tried to transfer all the code in Constants class into my code behind, but compiler does not recognise HastTable keyword even though I have added System.Collection namespace to the page. I do not know why? Could this be the problem?
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  Charles Bai

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  Re: get value from Hashtable for a given key

  Jul 15, 2004 02:45 PM|LINK

  Not recognising Hashtable is because I typed "HashTable", I forgot this is c# world, case sensitive world. The code became working after I transfer all the Hashtable code from Constants to the page's code behind. MyHashtable[nKey] did get the value. So, the problem lies in the usage of Constants class, which I do not know what I did wrong.