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First, you need to understand the difference between value types and reference types.
All structures and primitives (such as int, long, float) are value types. Value types exist in the stack and are always copied. For example:
int a = 1;
int b = a;
All classes are reference types and their objects exist in the heap. Variables used to access class objects really only store addresses (so to speak) to their objects. Keyword "new" creates an object and returns a reference to that object. For example:
ArrayList a = new ArrayList();
ArrayList b = a;
Now, a shallow copy means that only an object's member variables are copied. This means the value types and references are copied, but the referenced objects themselves are not copied/cloned. A deep copy is when you clone the referenced objects too. You can do this by overriding your class' Clone() method and explicitly clone your reference member variables.
In the case of your ArrayList example, it's storing integers which are value types. So, changing the cloned ArrayList's items will not effect the original ArrayList. However, if the original ArrayList stored reference types instead, then that would be another story.
Phew! That was a bit long winded, but I hope that made sense.
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the example you shown is shallow copy.
To achieved deep copy you need to create an object for arraylist and not a reference to it
ArrayList b = new ArrayList().
int i = 0
while (i < b.count)
{
a[i] = b[i];
i++;
}
shallow copy mean two pointers pointing at the same piece of memory.
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hello. i have a menu, when a user clicks an item in it, the program calls a function, which calls another function based on the value of a combobox. the combobox isnt visible until the first function is called, how can i make the program 'wait' until an item is selected in the combobox? i try this, but it returns 1 right away.
while(clientlist.SelectedText == "Choose Client #")
continue;
clientlist.Visible = false;
return (System.Convert.ToInt32(clientlist.SelectedItem) + 1);
any suggestions?
thanks in advance,
sam kline
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Correct me if wrong ;(
below is my idea....
1. set the combobox to be invisible
2. in the first func: set the combo box to be visible
3. In the event handler for the combo box, call the second func when user selects the item from the combo box
<< >>
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HI,
Why don't you use selected item change event of the menu to show the combobox and execute the combobox selected Index change function.
regards
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I'm trying to write a wrapper for this mfc dll to call from c# via p/invoke
Code128BarcodeToClipboard
[^]
I get the win32 error code 203: The system could not find the environment option that was entered.
Has anyone had any luck calling these methods from c#? I need to generate the barcode images(code 128) from an aspx page...any help would be appreciated.
Thanks
Graham
Graham
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I thought there was C# code to generate bar codes on CP somewhere ?
Christian Graus - Microsoft MVP - C++
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There is...but unfortunately they aren't the type I require...i've found codabar and several others in c# but only an mfc version for the code 128.
I created an active x control wrapper for the mfc dll, but get a COMException "catastrophic error" when i try to invoke a function from c#.
I'm experienced in writing and calling native win32 dll's...but having a lot of trouble trying to use the MFC component. I can get the code to run from adding the method to the contstructor, but can't pass any parameters that way, and still get the error when i try to call a function.
I used aximp.exe to generate a slightly different interface to the component, but still get an ActiveXException when I try to invoke a member.
Graham
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I am getting a id from a datagrid in a aspx page and then I want another page to display de pdf file file corresponding to the id, with the path in a sql2000 file. Can anyone help me.
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Hi there,
Just open a window with the url pointing to the pdf file on ur web server, and you dont have to worry anything becoz IE will do it for u.
<< >>
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I'm writting an app that receives and sends a data packet via TCP/IP
I'm wondering what would be the easiest way to parse out the data packet I receive, since there are no delimiters seperating the information.
Here is the break down of the data packet
four-byte start pattern
two-byte binary
20-byte fixed length
variable length data
four-byte end pattern
Thanks for your thoughts
Tom Wright
tawright915@yahoo.com
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It appears to me that you answered your own question.
You know that the first 4 bytes are the start pattern
You know that the next 2 bytes are binary
So on and so forth,
.....
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okay so maybe I'm over thinking this, but I can do something like
coutn over 6 (total bytes) to the data that I'm looking for.
I guess I'm wondering is how do I tell my app to go to this spot in the data stream, and grab the data from here to there and copy it to the string variable?
Thanks
Tom Wright
tawright915@yahoo.com
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How can i add a new string to the array?
I've never actually used an array before  , yes i know, incredible isn't it.
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Hi there,
Just create a new array with it's length is increased one. Then, copy all the values from names array to the new one and add a new string to the new one.
For me, it's easier if using ArrayList object.
<< >>
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Don't use array any longer.
You should use System.Collections.ArrayList instead or in .NET 2.0 generics: List<Type>.
André
'A programmer ist just a tool which converts caffeine into code'
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I have an old C++ thread unsafe library that I must use for a new multithreaded C# project. I was hoping that I could use AppDomains to load mulitple instances of the library so that I could use multiple threads yet keep segregate the data. This seems to work for managed code, but not for old unmanaged libraries. Can anyone explain why? Does anyone have suggestions on other ways to use the library in a multithreaded environment?
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I'm sure this is a common question but my choice of search criteria isnt yielding me an answer....
I have a class like this:
[Serializable]
public class MyClass
{
public string Name
{
public string HiddenName
{
}
If I attempt to serialize that class both the Name and HiddenName field get serialized. I dont want to serialize HiddenName. So how can I do that?
I have tried adding the [NonSerialized] attribute to HiddenName but that doesnt compile.
Thanks for the help
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If you are referring to xmlserialzation then according to the MSDN:
Preventing Serialization with the XmlIgnoreAttribute
There might be situations when a public property or field does not need to be serialized. For example, a field or property could be used to contain metadata. In such cases, apply the XmlIgnoreAttribute to the field or property and the XmlSerializer will skip over it.
Other wise try this from the MSDN:
A class often contains fields that should not be serialized. For example, assume a class stores a thread ID in a member variable. When the class is deserialized, the thread stored the ID for when the class was serialized might no longer be running; so serializing this value does not make sense. You can prevent member variables from being serialized by marking them with the NonSerialized attribute as follows.
[Serializable]<br />
public class MyObject <br />
{<br />
public int n1;<br />
[NonSerialized] public int n2;<br />
public String str;<br />
}If possible, make an object that could contain security-sensitive data nonserializable. If the object must be serialized, apply the NonSerialized attribute to specific fields that store sensitive data. If you do not exclude these fields from serialization, be aware that the data they store will be exposed to any code that has permission to serialize. For more information about writing secure serialization code, see Security and Serialization.
Tom Wright
tawright915@yahoo.com
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But you cannot apply [NonSerialized] to properties only fields. I can change the code to use a field rather than a property but that doesnt seem right either.
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You could implement the ISerializable interface and take control of your object's serialization. Admittedly, it's a little more work, but you won't have to worry about what does and does not get into the persitent area since you are the one that puts it in there.
"we must lose precision to make significant statements about complex systems."
-deKorvin on uncertainty
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reading about interfaces, i understand that its a contract and you have to implement all methods/properties/events...etc once you inherit an interface, what i dont understand is why this example casts back to an interface to execute the method
interface IVehicle
{
void Start();
}
class Car : IVehicle
{
public Car() { }
public void Start() { Console.WriteLine("starting..."); }
}
--test class--
void Main()
{
Car myCar = new Car();
IVehicle vehicle = (IVehicle)myCar;
vehicle.Start();
}
anyone can give me some real world examples as to when/why you would cast back to an interface to access methods/properties?
thanks
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What about just expanding your sample here.....
<code>interface IVehicle
{
void Start();
}
class Car : IVehicle
{
public Car() { }
public void Start() { Console.WriteLine("starting Car..."); }
}
class Truck : IVehicle
{
public Truck() { }
public void Start() { Console.WriteLine("starting Truck..."); }
}
--test class--
void StartVehicle(IVehicle vehicle)
{
vehicle.Start();
}
void Main()
{
Car myCar = new Car();
IVehicle vehicle = (IVehicle)myCar;
Truck myTruck = new Truck();
IVehicle vehicle2 = (IVehicle)myTruck;
StartVehicle(vehicle);
StartVehicle(vehicle2);
}</code>
This way a function that can take any type of vehicle can be used on either a Car or a Truck.
Steve Maier, MCSD MCAD
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ahh that makes sense.
Thanks Steve
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