Re: Hashtable problem... - C# Discussion Boards

17-Jan-06 6:51

Current issue is making me crazy at the moment, there must be something I missed, 'cause it's not working as expected...

I like to access a hash table key either by it's name or a class instance. To achieve this I create a new class (HashKey) which internally has a string called _name. When the hashtable calls HashKey.GetHashCode() it returns the HashCode of the internal wrapped string _name. Should be pretty much the same like I would use a literal string value key directly, right?
so it must the be same if I add my value by a string key

HashTable myHashTable = new HashTable();
myHashTable.Add("keyName", 4);

or I add my value by a string key wrapped in HashKey class.

HashKey myHashKey = new HashKey("keyName");
myHashTable.Add(myHashKey, 4);

Now I should/wanna be able to read the value by literal string or by the HashKey instance.

object value = myHashTable["keyName"];
//
value = myHashTable[myHashKey];

This doesn't work, but WHY?

Here is the implemenation of HashKey class, which wraps the string and overrides GetHashCode and Equals methods.

public class HashKey
{
	private string _name;
	
	public HashKey(string name)
	{
		_name = name;
	}
	public override string ToString()
	{
		return _name;
	}

	public override int GetHashCode()
	{
		return  _name.GetHashCode();
	}
	public override bool Equals(object obj)
	{
		return _name.Equals (obj);
	}


}

User 665817-Jan-06 7:39

17-Jan-06 7:39

I copied your code and stepped through the debugger, and this is the solution, it works:

public override bool Equals(object obj)
{
    if (obj is HashKey)
        return _name.Equals(((HashKey)obj)._name);
    else
        return _name.Equals(obj);
}

You need to cast the object when necessary and access the _name attribute directly.

regards

modified 12-Sep-18 21:01pm.

Chris Richner17-Jan-06 7:54

17-Jan-06 7:54

Hi Greeeg,

Thanks for your fast reply, just added your code.

Now it works to access the key with the HashKey instance

c#"

value = myHashTable[myHashKey];

but this scenario still doesn't work here

c#"

object value = myHashTable["keyName"];

Any other changes you made to the code, any ideas?

myMsg.BehindDaKeys = "Jerry Maguire";

User 665817-Jan-06 8:00

17-Jan-06 8:00

Strange, both work for me

Hashtable myHashTable = new Hashtable();
HashKey myHashKey = new HashKey("keyName");
myHashTable.Add(myHashKey, 4);

value = myHashTable["keyName"];
value = null;
value = myHashTable[myHashKey];

after both calls "value" is 4. I inserted the "value = null" to see whether the second call will change "value" at all.
You might want to add another if-clause like else if(obj is String) return _name.Equals((String)obj) into the Equals method.

regards

modified 12-Sep-18 21:01pm.

Chris Richner17-Jan-06 23:12

17-Jan-06 23:12

It doesn't work for me. I think it can't work because in case of asking

value = myHashTable["keyName"];

string.Equals() is called which is can never returns true when asked about equality with HashKey instance, right?

myMsg.BehindDaKeys = "Jerry Maguire";

User 665818-Jan-06 2:14

18-Jan-06 2:14

But you do an object comparison with the _name-string of your hashkey instance, so you compare two strings in case object is a string.

modified 12-Sep-18 21:01pm.

Chris Richner18-Jan-06 5:46

custom attribute serialization in C#

18-Jan-06 5:46

Yep, but I guess the problem is that in case of the string hashtable key not the Hashkey.Equals() method is called. Instead it calls the string "keyName".Equals(hashKeyInstance) which returns false.

So in case of asking the value with the string key, it works the other way round with calling Equals(). Is this correct?

Thank you very much for your efforts.

myMsg.BehindDaKeys = "Jerry Maguire";

softplanner17-Jan-06 6:49

softplanner

17-Jan-06 6:49

I am trying to serialize and deserialize C# objects to an SVG file. I need to specify some custom types and have these serialized as attributes (e.g. fill = '#CCFF00'). However I cannot figure out how to serialize types other than the built-in types (string, int etc).

Right now my code looks like this (and it works):

<br />
private SVGColor m_Fill = new SVGColor(Color.White);<br />
[XmlAttribute("fill")]<br />
public string svg_fill {<br />
	get {<br />
		return m_Fill.ToString();<br />
	}<br />
	set {<br />
		m_Fill = SVGColor.Parse(value);<br />
	}<br />
}<br />
[XmlIgnore]<br />
public Color Fill {<br />
	get {<br />
		return m_Fill.Colour;<br />
	}<br />
	set {<br />
		m_Fill.Colour = value;<br />
	}<br />
}<br />

But it seems as though there should be a way to implement an interface for SVGColor that would allow the parser to automatically serialize & deserialize it based on its ToString & Parse methods. Then one could replace all this code with:

[XmlAttribute("fill")] public SVGColor Fill;

Is this possible??

Serial Port Status Reader

kinder202317-Jan-06 6:33

kinder2023

17-Jan-06 6:33

I am new to programming in C# so please be patient. How do i read (in C#) the status of a port to trigger an event. For example.... when door opens, trigger switch high, (or low) through optio-coupler device via serial port to control stereo power on, or answering machine play, etc.

Throw me a line and we'll help each other.

Re: Serial Port Status Reader

Dave Kreskowiak17-Jan-06 8:16

Dave Kreskowiak

17-Jan-06 8:16

You might want to have a look at this[^] series on Coding4Fun.

It'll save you having to write device drivers to get at the low-level details of a serial port, something that is abstracted from your code by Windows.

RageInTheMachine9532
"...a pungent, ghastly, stinky piece of cheese!" -- The Roaming Gnome

session management using sql server

mevir17-Jan-06 6:10

mevir

17-Jan-06 6:10

I am trying to set sessions on the sql server in my web services. After running some scripts on sql server and setting the config files, how do I actually populate the sql server session tables? I would also like to save the data (from the user's search results) from several sessions in the session tables. Can somebody help me with this. Thanks.

Mina

Update the dataset into the original database

Sasuko17-Jan-06 5:05

17-Jan-06 5:05

i've selected some rows from the database and populate my DataSet.
After i've deleted some rows and update them.
Now i want to update the original Database with changed on the dataset.
i've used this code, but it is not good becouse it need an insert comand:

conn = new OleDbConnection(conn_string);
string selction_string = "Select * FROM myTable";
OleDbDataAdapter adapter = new OleDbDataAdapter(selction_string, conn);
conn.Open();
adapter.Update(mydataSet); <-----
conn.Close();

Christian Graus17-Jan-06 9:21

17-Jan-06 9:21

Yes, you need to provide the SQL to do the insert. What's wrong with that ?

Christian Graus - Microsoft MVP - C++

Sasuko17-Jan-06 9:28

17-Jan-06 9:28

so the dataAdapter doesn't understand automatically what is changed and make the correct update automatically?
If so, what is a possible SQL statement to do that (how have i to change the code)?

Christian Graus17-Jan-06 9:37

17-Jan-06 9:37

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemdatacommondbdataadapterclassupdatetopic.asp[^]

It looks to me like it can work out the update statement for you. I have to admit I never use this crap - I write my own SQL and call it myself.

I can't tell you how to write the update SQL because I have no idea what's in the table, you did a select *.

Christian Graus - Microsoft MVP - C++

Sasuko17-Jan-06 9:53

17-Jan-06 9:53

Honestly i don't wanted you to write code for me, but i want to know what is the correct InsertCommand i've to indicate for the dataAdapter.
I don't think it can be a: "INSERT INTO ..." becouse i don't know what are new rows inserted.
Then also rows deleted or modified.

Christian Graus17-Jan-06 9:56

17-Jan-06 9:56

Sasuko wrote:
I don't think it can be a: "INSERT INTO ..." becouse i don't know what are new rows inserted.

It *has* to be INSERT INTO, what else would work ? The rows are marked in the dataset as being changed/added/deleted. I suspect if you provided SQL that selected specific columns, what you're doing may work, but like I said, I would iterate through the dataset myself and write a stored proc that takes XML and uses OPENXML to do bulk deleting/updating/inserting.

Christian Graus - Microsoft MVP - C++

Sasuko17-Jan-06 10:19

17-Jan-06 10:19

so i've get all the row added to the datase then creating a SQL insert statement and past it to the datadapter?

Christian Graus17-Jan-06 10:22

17-Jan-06 10:22

You need to do what Wjousts said. I thought you did, but the sample I linked to didn't seem to have that bit, so I figured it could be inferred ( which makes sense, the table knows the columns, and it knows which rows are new ).

If the dataadapter works, then you wouldn't need to work out for yourself what rows are changed/new. I'm saying I don't use the dataadapter.

Christian Graus - Microsoft MVP - C++

Re: Detecting Video format

Wjousts17-Jan-06 10:20

Wjousts

17-Jan-06 10:20

Of course it's INSERT INTO...
You need something like this:

MyDataAdapter.InsertCommand = new OleDbCommand("INSERT INTO MyTable (MyField1, MyField2, ....) VALUES (?, ?, ...)",MyConnection);
MyDataAdapter.InsertCommand.Parameters.Add(new OleDbParameter("MyField1",int,0,"MyDataTableField1");
...

And so on. When you do the update the DataAdapter knows which rows are new and substitutes the parameters (the ? in the SQL statement) with the real values in your DataTable according to the mappings in the InsertCommands Parameters.
You might also want to do the Update and Delete commands as well if you actually want updates and deletes to be possible.

Detecting Video format

amitmores17-Jan-06 3:57

amitmores

17-Jan-06 3:57

Hi All,

I want to developed application for automatically detecting Video format .can any one help regrding above problem.Pls do reply on frum or personally mail me .

Thanks & Regards,
Amit More
amit.more@pictureal.net

User 665817-Jan-06 4:17

avoid having this drawing bad effect

17-Jan-06 4:17

Reading the FOURCC-code from the header of the video will you give you a lot of information. You can then use a lookup-table to check agains the correct format.

regards

modified 12-Sep-18 21:01pm.

Sasuko17-Jan-06 3:51