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I tried with minimum height. Its not solving my issue.
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Hi all,
I am in the process of coding a generic wrapper class that adds some metadata and functionality to a generic value (unconstrained). I would prefer the equality of this wrapper to simply pass through to the underlying value.
As a result the equals and getHashCode overrides are as follows
public override bool Equals(object obj)
{
return _value.Equals(obj);
}
public override int GetHshCode()
{
return _value.GetHashCode();
}
My concern here is that, as _value is not read-only, we now have a hash code that could potentially change.
Am i right to be concerned about this with regard to housing the class within collections or using it within LINQ statements? (IIRC they make use of hashtables behind the scenes)
Is there a better/safer approach?
Thanks in advance
Pedis ex oris
Quidquid latine dictum sit, altum sonatur
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This could, I think, potentially cause problems if you're using instances of this class in the key of dictionaries. But no more so than if you put _value in there instead, and there's not really a way to avoid it with mutable types.
I think that you are only going to be sacrificing a bit of performance, not creating subtle bugs, because the .Net hashtable will look through all the items if it doesn't get a hash hit. Generally, you wouldn't put mutable things into collections as a key anyway.
There are only two 'golden rules' of GetHashCode, to quote the documentation[^]:
If two objects compare as equal, the GetHashCode method for each object must return the same value. However, if two objects do not compare as equal, the GetHashCode methods for the two object do not have to return different values.
The GetHashCode method for an object must consistently return the same hash code as long as there is no modification to the object state that determines the return value of the object's Equals method. Note that this is true only for the current execution of an application, and that a different hash code can be returned if the application is run again.
You generally want to use as much of the state (which you compare within an Equals override) as possible to make the hash code uniqueness work well, and that means that if you mutate the object you change its hash code, which could cause a minor slowdown next time you look 'it' (i.e. something that matches it by Equals) up.
So in conclusion, you're okay, but good question, and it's good practice not to mutate things (at least, not to mutate the parts of them which are part of their equality semantics) if they're being used as dictionary keys.
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Excellent explanation.
Thanks for putting my mind at ease 
Pedis ex oris
Quidquid latine dictum sit, altum sonatur
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BobJanova wrote: I think that you are only going to be sacrificing a bit of performance, not creating subtle bugs, because the .Net hashtable will look through all the items if it doesn't get a hash hit.
No, it won't. Mutating an object that is used as a dictionary key will cause bugs.
The correct solution is to remove the object from the dictionary, then mutate the key, then re-add it. Or better, just make the key immutable, remove the object from the dictionary, and re-add it using another key.
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Then make it immutable / readonly; it probably should be anyway.
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can't make it readonly im afraid.
The class is providing a solution to firing off propertyChanged notifications without having to rely on hardcoded property name strings (it provides a 'single run per property' means by which property names are programatically derived)
As a result the wrapper class is being used in place of a basic property backing field and therefore must be able to have its value changed as and when required.
hope that makes sense
Pedis ex oris
Quidquid latine dictum sit, altum sonatur
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Hi All,
I would like to develop a windows desktop application in C# which would display the video from a Raysharp DVR sitting in my network. I would like to know if there is any SDK available (compatible with raysharp dvr) which can be useful. Raysharp is using H264 encoding to stream the video.
If anyone can direct me to any site or could help with some idea, will be very much helpful.
Thanks in Advance
Jayesh
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Ask these guys[^] for an SDK.
I would suspect that you cannot play the video because, at least on the security system I worked with, the video stream was encrypted. This would be for legal reasons as surveilence video is admissable as evidence. Any files saved from the system would need to be played in the player supplied by the vendor because of the encryption.
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Hi,
But i can see the video in my iPhone using a couple of third party applications. This will raise two options, either the suppliers have access to the encryption (which seems to be very less) or there is no encryption at all..
please let me know your thoughts on the same.
Thanks
jayesh
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I have a question if someone can kindly refer me to a good source, on how to make a visual c # dictionary.
For example using a simple list box and text box, where all data are recalled from a database.
So the words would be displayed in the list box, and as you click on that particular word, you may get the meaning in the text box, or label, also how to include a search system.
It is simple to do this using the basic of assigning the list box to the text box, but that requires repeating the same code for different words over and over again.
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can you post some sample code? I'm not 100% clear on what the problem is.
V.
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csshtml wrote: I have a question if someone can kindly refer me to a good source, on how to make a visual c # dictionary.
We don't have tutorials on each type of application. MSDN holds various tutorials[^], and has a topic on connecting to a database[^]. There's also a topic on manipulating data[^].
Both the TextBox[^] and the ListBox[^] are documented on MSDN.
Bastard Programmer from Hell 
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I doubt you'd want to have a whole dictionary in memory, but if it's just a small dictionary, something like this might be what you want (once you have the DataTable populated):
System.Data.DataTable dt = new System.Data.DataTable() ;
dt.Columns.Add ( new System.Data.DataColumn ( "Word" ) ) ;
dt.Columns.Add ( new System.Data.DataColumn ( "Definition" ) ) ;
System.Data.DataRow dr ;
dr = dt.NewRow() ;
dr [ 0 ] = "CAT" ;
dr [ 1 ] = "Man's worst enemy" ;
dt.Rows.Add ( dr ) ;
dr = dt.NewRow() ;
dr [ 0 ] = "CART" ;
dr [ 1 ] = "Don't put it before the horse" ;
dt.Rows.Add ( dr ) ;
dr = dt.NewRow() ;
dr [ 0 ] = "COT" ;
dr [ 1 ] = "A place to rest at work" ;
dt.Rows.Add ( dr ) ;
this.comboBox1.DataSource = dt.DefaultView ;
this.comboBox1.DisplayMember = "Word" ;
this.comboBox1.AutoCompleteMode = System.Windows.Forms.AutoCompleteMode.SuggestAppend ;
this.comboBox1.AutoCompleteSource = System.Windows.Forms.AutoCompleteSource.ListItems ;
this.comboBox1.SelectedIndexChanged += delegate ( object sender , System.EventArgs e )
{
this.textBox1.Text = (string) ((System.Data.DataRowView) this.comboBox1.SelectedItem) [ 1 ] ;
} ;
This may not provide all the searching you want. If not, another similar possibility is to have a TextBox for the search pattern. When the Text is changed, you set the .Filter property of the DataTable's DefaultView -- but you have to catch Exceptions and let the user know that the pattern has a problem.
Here's one (untested) way to do that:
System.Data.DataView dv = this.cbItemName.DataSource as System.Data.DataView ;
if ( dv != null )
{
try
{
dv.RowFilter = System.String.Format ( "Name LIKE '%{0}%'" , this.tbSearchText.Text ) ;
this.tbSearchText.BackColor = System.Drawing.SystemColors.Window ;
}
catch
{
this.tbSearchText.BackColor = System.Drawing.Color.LightPink ;
}
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I would like to thank you all for your kind reply on this topic. As PIEBALDconsult said I don’t want to store data in memory.
What I was thinking of was the following:
1- Suppose you have an English – French dictionary, and assume they are all stored on a database, i.e. SQL, Access…etc.
2- The 2nd step would be, to create a simple user interface, which has a list box, and a text box.
3- All the English words for example would go into the list box, by calling them from the database.
4- As you click on a word, you must be able to display the meaning of that word in the text box, which would be the French meaning of that English word. And if you click on a different word you would get the meaning of that word and so on.
I hope i managed to explain the idea in the simplest form possible.
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hi,
i want to lock a folder contains a encrypted video file. Along with this i want to play this file using windows application. But no one can copy or cut this file while playing. Is there any method to develop this?
please help me
thanks in advance.
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Hi, can I make my .net service non disable by changing registry values? Like when a user from administrator group tries to disable service it will give an acess is denied message like Eset Service? Thanks.
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Are we talking a Web or WCF Service or a windows service?
V.
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It is a windows service. I tried this
I opened regedit -> Local Machine -> CurrentControlSet -> services ->[My Service name] right click -> permissions and I edited some of the permissions from there finally it's done! When I try to disable the service it gives Access is denied! but I wonder if there is another way to do this? thanks.
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Don't think so. You might be able to use something like run as... or impersonate through code when the application is launched so you don't have to do that manually, but I have never tried it.
Note that if you run the service as a certain user, that user needs to have access to the resources (if there are resources used). A common mistake eg. is folder access rights.
V.
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You can't. As an admin, I have full control of the machine.
I know that you're not going to accept this as an answer, and you won't believe me. Raymond Chen says the same[^], pointing out how you can "kill" an unkillable proces.
Your house, your rules. My machine, my rules.
Bastard Programmer from Hell
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Yeah I understand, I don't want to restrict administrators from doing nothing but in our company we give our users admin rights and this is a mistake I know that. We'll get back admin rights from users soon but until that holy day, I made a service that is not non killable but it's really hard to kill or disable or stop it!!! I understand all of u who don't want programmers to restrict administrators from doing something but in some cases like mine I should. Thank all of u for your answers. 
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Please let me know how to get dimensions values from dwg images after upload.what are the libraries included...
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You're going to have to explain what a "dwg image" is. I've never heard of it.
The only thing I know of is DWG is an AutoCAD file format, but it's not an image and the .NET Framework has no class that handles them natively.
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