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Hi, I am just beginner in .NET with C#. In my study, I have learned that when an instance of a class created in the heap is not owned by reference (a variable of that class) , the Garbage Collector (GC) removes this instance from the memory after a while. In my first small application in .NET, I hasitate in a point that When I am testing a click event of a button control of my Form1 class, I declared a variable of type a Form class (let's say Form2). The View is like this:
private void button1_click(....)
{
Form2 myForm2 = new Form2();
myForm2.Show();
}
Here when the execution gets out of the click event, then I expect that the local "myForm2" becomes out of scope for availibility. But my new form (Form2) still apears on my screen. Why? Cause no availiable reference to this Form2 instance anymore, immediately after the button click event routine. Anything I need to know more about "scopes" and GC ?
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As u have created reference of form2 from form1's button click event so this reference of form2 will remain in scope till the form1 is in scope and as soon u will close the form1 the reference of form2 will also be lost and GC will reclaim the memory back and will close the form2 also.
rahul
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First, I'd really like to thanks to you rah_sin for your answer..
I need one more point: What you explain is valid for only class of Form or those inherited from Form class? Cause as you hv seen in my example the refernce "myForm2" is not a direct member of Form1 class but a local declaration in button click event. Or should I understand that Show() method of Form class, saves or register its reference into a global collection internally or somewhere in caller form ?
In other words, what if my locally declared variable was of simple class like:
class Sample
{
private string sName;
private int nIdNumber;
public Sample()
{
//...
}
public string Name
{
get {...}
set {...}
}
//...
}
private button_click(....)
{
Sample mySample = new Sample();
mySample.Name = "Testing Name";
}
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Hi!
I'm using a dataGridView (dgv) bound to dataSet through bindingSource.
one method (fired by button.click) fills the dataSet using dataAdapter.
the dgv displays loaded rows.
now what my goal is: when a row is displayed additional data for it is loaded in a background thread, and the row is refreshed (i'm using grid's overriden paint event to display the additional data) the reason for this is that I want to get and display the additional data only if the row is ever displayed, to avoid downloading (from sqldb) data that is not needed..
my current solution is:
<br />
public void GetPricesForRow(DataGridViewRow row) {<br />
if(backgroundThread != null)<br />
while(backgroundThread.ThreadState == System.Threading.ThreadState.Running)<br />
Thread.Sleep(3);<br />
<br />
backgroundThread = new Thread(new ThreadStart(delegate() {<br />
try {<br />
int colCt = row.DataGridView.Columns.Count;<br />
<br />
string[] vals = GetAdditionalData(row.Cells[1].Value.ToString().Trim());<br />
row.Cells[colCt - 2].Value = vals[0];<br />
row.Cells[colCt - 1].Value = vals[1];<br />
row.Refresh();<br />
} catch { }<br />
}));<br />
<br />
backgroundThread.Start();<br />
}<br />
row.Refresh(); fires:
<br />
public void Refresh() {<br />
this.DataGridView.InvalidateRow(this.Index);<br />
} <br />
well it works.. but pretty slow.. when i set backgroundThread.IsBackground to true the row doesn't refresh (at least not always)
anybody knows a better solution?
life is study!!!
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Hi,
Use VirtualMode option of the datagridview. U can find examples in the MSDN
HTH.
Hayder Marzouk
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ok. i got it..
<br />
public bool GetPricesForRow(DataGridViewRow row) {<br />
ManualResetEvent doneEvent = new ManualResetEvent(false);<br />
PricesForRow pfr = new PricesForRow(row.Cells[1].Value.ToString().Trim(), doneEvent);<br />
<br />
bool x = ThreadPool.QueueUserWorkItem(pfr.ThreadPoolCallback);<br />
WaitHandle.WaitAll(new WaitHandle[] { doneEvent });<br />
int colCt = row.DataGridView.Columns.Count;<br />
row.Cells[colCt - 2].Value = pfr.OutBold;<br />
row.Cells[colCt - 1].Value = pfr.OutNormal;<br />
row.Refresh();<br />
<br />
return x;<br />
}<br />
and an additional class:
<br />
class PricesForRow {<br />
ManualResetEvent _doneEvent;<br />
string _param;<br />
<br />
string _outBold;<br />
public string OutBold {<br />
get { return _outBold; }<br />
set { _outBold = value; }<br />
}<br />
<br />
string _outNormal;<br />
public string OutNormal {<br />
get { return _outNormal; }<br />
set { _outNormal = value; }<br />
}<br />
<br />
public PricesForRow(string param, ManualResetEvent doneEvent) {<br />
_param = param;<br />
_doneEvent = doneEvent; <br />
}<br />
<br />
public void ThreadPoolCallback(Object threadContext) {<br />
try { <br />
string[] vals = DataBase.Instance.GetKtmsPrices(_param);<br />
_outBold = vals[0];<br />
_outNormal = vals[1];<br />
_doneEvent.Set();<br />
} catch { }<br />
}<br />
}<br />
this works just fine!! doesn't slowdown the grid or anything..
life is study!!!
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well once again i am posting the question with bit more elaboration.I need to create MS project file using "MS Project Object Modal 11.0" within C# .All examples ,that I searched on internet, were written in VB.Net .I wonder if this could not be done in C# ... I am not getting any documentation on msdn either about Microsoft.Office.Interop.MSProject namespace .Is there any need to install MS Project 2003 SDK as well ???
Regards,
LinkinP
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Hello, I need to use an unmanaged dll written in c in a program written in c#.
This dll uses linked list and I use PInvoke in my c# code.
Dll code:
typedef struct payload{
char name[NAME_SIZE];
int release;
char info[INFO_SIZE]; //this info is related to the type of msg: {app url, log url, command-line arguments}
payload *next;
}payload;
C# Code:
[StructLayout(LayoutKind.Sequential)]
public struct payload
{
public string name;
public int release;
public string info;
ref payload next; //Compiler error
}
I can't make it work because the compiler prompts me an error for the pointer in the struct, any suggestions?
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what is the error, it might need a sizeof check out in the api
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mephy83 wrote: [StructLayout(LayoutKind.Sequential)]
public struct payload
{
public string name;
public int release;
public string info;
ref payload next; //Compiler error
}
Use IntPtr for the pointer to the next structure:
[StructLayout(LayoutKind.Sequential)]
public struct payload
{
public string name;
public int release;
public string info;
public IntPtr next;
}
Check this reference[^] for more details. Specifically, look at the "MYPERSON2" example.
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I want to use an enum of strings in my program, but as I found out, the default underlying type for enums is int
So how do you set the underlying type of an enum to string??
Thanks.
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I guess I'll use string constants instead...
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Depending on what your trying to solve it may be best. Enums were introduced to give meaning to magic numbers, it allows you to work with a meaningful name rather than some meaningless number.
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The names of the enum values are strings, can't you use that?
public enum Animal { Dog, Cat, Mouse, Hippopotamus }<br />
Animal spot = Animal.Dog;<br />
string spotIs = spot.ToString();<br />
Console.WriteLine("Spot is: " + spotIs);
Output:
Spot is: Dog
---
single minded; short sighted; long gone;
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Hi!
I have a windows-app, that should perform normally when started with double-click.
If it is being started from an console/Dos-Box with more than 0 arguments it shall do a specific operation.
My problem is, that i cannot write console-output with Systen.Console.WriteLine("..."), because the application is set to be a windowsapplication. If i changed this to console-application i get an DOS-Box everytime i start the app with double-click (which looks stupid).
How can i make a windows application write it´s output to my DOS-Box or make the console-app not to open an DOS-box?
Help would be great!
Thanx a lot!
Greetings
J.
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Hi,
Has anybody tried out creating an out of proc .NET component exposing
COM interface? We need to create component which would interact with Windows
powershell hence a .NET component and since it has to run on 64 bit system (Server)
but the client would be 32 bit thus a out of proc component which would
expose COM Interface.
Any pointers?
Thanks
Learning is a never ending process of Life.
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Hi,
How to check if one type it is .Net type??
i have one list: Type[] list with many type. How can i know if one type it is .net type or one new type???
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darkcalin wrote: Type[] list with many type. How can i know if one type it is .net type or one new type???
What do you mean by that? Surely they are all .NET types.
Do you mean, does the type belong to the .NET framework? If so, then I'm curious about why you would want to know that.
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I want to find one solution for a big nonsolution  ))
I want to know if it is System type
for example i have
Class class1
{
class2 bubu; // this is not a System type
int unu; //this is a simple type
int doi; //this is a simple type
}
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darkcalin wrote: I want to know if it is System type
Then the full class name (the bit that includes the namespace) will start with System
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is a god solution but i want to no make the string compare ...if is possible
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How do I add and retrieve an image from MS Access
and then display it in a C# Form
Logically Onpoint
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