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1)
public List<string> GetList()
{
List<string> list = new List<string>();
return list;
}
But as per msdn we should not expose the generic list.
How to return a list from a method.
2)
Simillarly I have a method which has dictionary as a return type
How to return a dictionary from a method.
3) In my code I have craeted a dictionary as
Dictionary < int , Some Str> .
Now I need a colletion of keys avaialble in the dictionary.
How to do this.??
Do I need to retrive one by on from dictionary. ??
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Hi,
1.
there is nothing that prevents you from returning a List (or any other collection) like that.
There may be "good practice" or "OO" reasons not to do so under certain circumstances, but it is perfect C#.
2.
see 1.
3.
if you look through the MSDN documentation, more particularly the properties of Dictionary<Tkey, Tvalue>, you will notice it is all there.
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read formatted code with indentation, so please use PRE tags for code snippets.
I'm not participating in frackin' Q&A, so if you want my opinion, ask away in a real forum (or on my profile page).
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FxCop will recommend using ReadOnlyCollection[^]
I know the language. I've read a book. - _Madmatt
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That seems kind of inefficient. Does that mean there are now two copies of the same data in memory? (Actually, with their crappy sample, the array at the end of the Main() method makes a 3rd copy).
.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
modified on Wednesday, June 9, 2010 1:50 PM
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 You're not supposed to actually read or use the examples 
I know the language. I've read a book. - _Madmatt
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John Simmons / outlaw programmer wrote: Does that mean there are now two copies
No. The way I understand it the ReadOnlyThingy is just a wrapper; it holds a reference to the original collection (and that explains how it tracks the changes to the original collection, see the example), but offers fewer valid operations on that collection. So nothing gets copied.
I haven't used it ever yet, as I see not much point in making the collection read-only, while the items in the collection remain as they were, modifiable at will (except for the silly example that used strings of course).
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read formatted code with indentation, so please use PRE tags for code snippets.
I'm not participating in frackin' Q&A, so if you want my opinion, ask away in a real forum (or on my profile page).
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I use them quite a lot. Many times I want a collection to be exposed but not have add and remove methods etc as I don't want the collection itself to be modified. I find it very useful!
DaveIf this helped, please vote & accept answer!
Binging is like googling, it just feels dirtier. (Pete O'Hanlon)
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
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You're probably right, I still have to get used to them...
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read formatted code with indentation, so please use PRE tags for code snippets.
I'm not participating in frackin' Q&A, so if you want my opinion, ask away in a real forum (or on my profile page).
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Try using a custom iterator. Passing back a generic list is wasteful in some cases anyway.
public IEnumerable<String> GetStrings(){
foreach(var str in stringList){
yield return str;
}
}
"Simplicity carried to the extreme becomes elegance."
-Jon Franklin
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You can do it that way (and IMHO, if the compiler lets you do it, nobody else has the right to complain, coding style guidelines in force not withstanding), but to ease typing, I create a class derived from the desired collection type:
public class ListOfThings : List<Thing>{}
That way, I can pass/return a ListOfThings object instead of having to type all that crap over and over again.
public ListOfThings GetListOfThings() { get; set; }
I can also add custom methods to the class that perform Thing-specific functionality.
.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
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John Simmons / outlaw programmer wrote: You can do it that way ...
But you end up actually typing MORE 'things':
ListOfThings
List<thing>
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List<thing> - a little shorter
ListOfThings - a little eaiser to read
ThingsList - even shorter and still easier to read - WINNER!
.45 ACP - because shooting twice is just silly
-----
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
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It is code analysis that tells to return collections in stead of List. You can make use of a global suppression file in your code to get rid of it.
For dictionary, it would be suggesting a read only collection. Suppress that too if you do not want another object to be returned.
It is up to you to decide till when you are going to follow MS code analysis. I personally follow everything it tells.
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Regarding Geneneric list as return type :
If you send/return the generic list outside, your collection can be very easily changed
from outside of your class without your permission and you lose total control on the same.
that is why , one should not expose or return generic list and use ReadOnlyCollection instead.
Dot net does not force you to do so but generally its not good programming practice!
Regarding point 2 :
Here also, A ReadOnlyCollection is recommanded.
Regarding point 3 :
You can create your customDictionary in which you can maintain and return the colelction of keys and/or
collection of values as per request.
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Hi,
I have a web app that talks to a web service using binary remoting. I've been asked to change the solution so that the objects are transported in XML format to allow the data to be audited more easily and to prevent firewall problems.
I have read this article .NET Remoting with an easy example[^] which is great but I'm not clear on how to change my current binary implementation which use TcpClientChannels to a XML Marshal by Value solution.
Is this simple? If so, I would appreciate a work example if possible. Also is it going to provide the customer with what they want? How would you trace the XML objects while the application is running
Many Thanks for your time,
Andy
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Hi,
You should be using an IChannel, rendering the channel type meaningless (use the HttpChannel instead of a TcpChannel).
Note!
The xml serializer is different than the binary one and it blindly places values for all public members and properties.
One more thing that may be causing you problems is that there are no back channel tricks like in tcp for passing events or data back to the client.
I am the developer of a bingo card software named The Bingo Maker
I have been developing in .NET since 2003
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I started with a generic class which has a delegate. The consumer of this class could set a method callback which requires invoking but they may not also. To address this I check if the callback is ISyncronizeInvoke, if it is then I will call BeginInvoke. This works great as long as the class is a generic class:
public class TestClassGeneric<T>
{
public delegate void GetMe();
private GetMe _call;
public TestClassGeneric(GetMe theCall)
{
_call = theCall;
System.ComponentModel.ISynchronizeInvoke si =
_call as System.ComponentModel.ISynchronizeInvoke;
}
}
Since I don't need the class to be generic I want to make it just a standard class:
public class TestClassGeneric
{
public delegate void GetMe();
private GetMe _call;
public TestClassGeneric(GetMe theCall)
{
_call = theCall;
System.ComponentModel.ISynchronizeInvoke si =
_call as System.ComponentModel.ISynchronizeInvoke;
}
}
But then I get a compile error:
"Cannot convert type 'PureLibrary.TestClassGeneric.GetMe' to 'System.ComponentModel.ISynchronizeInvoke' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion"
Could someone please help me understand why this makes such a difference? Since the delegate signature didn't change it seems the casting would be the same.
Thank you.
- Kalvin
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Very interesting question.
I have an idea why this might happen.
1. Generic class: TestClassGeneric<T>.
GetMe is unknown during the compile-time, because it's defined inside a generic class and the typeparam T may vary at run-time (actually, GetMe in this case will be TestClassGeneric<T>.GetMe).
2. Non-ceneric class: TestClassGeneric.
GetMe is non-generic too, and the compiler may "guess" that the conversion will fail.
Some facts:
System.Action is built-in delegate, it's defined as
public delegate void Action()
If you replace GetMe with Action, you will get an error in two cases.
- At the run-time, the conversion will fail, and
si will be null.
- If you replace
si = _call as System.ComponentModel.ISynchronizeInvoke;
with
si = (System.ComponentModel.ISynchronizeInvoke)_call;,
both generic and non-generic will fail.
Thanks! I'll remember this - it's a very good task and needs understanding of generics in .NET Framework 
Die Energie der Welt ist konstant. Die Entropie der Welt strebt einem Maximum zu.
modified on Wednesday, June 9, 2010 2:13 PM
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Hi ,
Might be a simple fix, but struggling for a long time.
I have built a new site and configured that in IIS, whenever I login to the server I get the "Connect to" windows login dialog. However on pressing cancel in this dialog, te screen loads without any issues.
Any idea how i can get rid of this?
Jack Sparrow
--------------------------------------
Defeat is not the worst of failures. Not to have tried is the true failure.
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Hi,
I have a datagridview with 8 Cells. and now i wanna to do this:
When i am in cell[2] and i finished editing leaving cell with {Tab} I want cell[4] be selected and i be able to enter the data in it.
so please help.
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I am not 100% sure that this will work, since I have not tried it but if cell[3] will never ever ever be editable, set it to readonly.
dataGridView1.Columns[3].ReadOnly = true;
You should be aware that, even if this works for your situation, there are reports of problems with the DataGridViewColumn/Cell Readonly property. It seems from some reading that it does not prevent pasting of data. Once again I cannot confirm this as I have not tried it.
Good luck!
Henry Minute
Do not read medical books! You could die of a misprint. - Mark Twain
Girl: (staring) "Why do you need an icy cucumber?"
“I want to report a fraud. The government is lying to us all.”
Why do programmers often confuse Halloween and Christmas?
Because 31 Oct = 25 Dec.
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No, You didnt understand my Question
you have to choose :you should enter data in Cell[2] Or Cell[3] (I mean the user will select and when one has data the onther one will be filled with data Automatically)
Thanks for reply
Please HELP !
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I have been looking at your problem since I got your message. I now understand what you require but unfortunately I cannot find a way to do it.
d@nish was quite right in saying that all you have to do is set CurrentCell to the value you want. Just put a Button on your Form and in its' Click event handler put the following:
private void button1_Click(object sender, EventArgs e)
{
dataGridView1.CurrentCell = dataGridView1[3, 0];
}
and regardless of where you select in the DGV, each time you click the button the [3, 0] cell is selected. No problem.
The problem is in finding an event to handle where you can both check the values for the two cells (that bit is relatively easy) and also set the CurrentCell without throwing an exception (that is where the problems occur).
It is now time for my cocoa and bed but I will keep thinking about this and will get back to you if I find an answer.
Henry Minute
Do not read medical books! You could die of a misprint. - Mark Twain
Girl: (staring) "Why do you need an icy cucumber?"
“I want to report a fraud. The government is lying to us all.”
Why do programmers often confuse Halloween and Christmas?
Because 31 Oct = 25 Dec.
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I have a (sort of) solution. It is not perfect and that bothers me but I cannot spend any more time on this.
I hope that it will at least give you a starting point for a solution of your own.
I tested this using a DataGridView with four text columns. The second column (columnIndex 1) should contain "Home" to be considered valid and cause a jump to the fourth column, and the third (columnIndex 2) should when editing reaches there should contain "Business" to be valid.
private bool IsValidColumn1Response(DataGridViewCell dgvCell)
{
return (dgvCell.Value == null) ? false : dgvCell.Value.ToString() == "Home";
}
private bool IsValidColumn2Response(DataGridViewCell dgvCell)
{
return (dgvCell.Value == null) ? false : dgvCell.Value.ToString() == "Business";
}
private void dataGridView1_SelectionChanged(object sender, EventArgs e)
{
DataGridView dgv = sender as DataGridView;
if (dgv != null)
{
DataGridViewCell currentCell = dgv.CurrentCell;
if ((currentCell != null) && (currentCell.ColumnIndex == 1))
{
int nextRow = currentCell.RowIndex;
int nextCol = currentCell.ColumnIndex;
if (this.IsValidColumn1Response(currentCell))
{
dgv[nextCol + 1, nextRow].Value = "N/A";
nextCol += 2;
}
DataGridViewCell nextCell = dgv.Rows[nextRow].Cells[nextCol];
if (nextCell != null && nextCell.Visible)
{
dgv.CurrentCell = nextCell;
}
}
else if ((currentCell != null) && (currentCell.ColumnIndex == 0))
{
int nextRow = currentCell.RowIndex;
int nextCol = currentCell.ColumnIndex;
if (this.IsValidColumn2Response(dgv[currentCell.ColumnIndex + 2, currentCell.RowIndex]))
{
nextCol++;
dgv[nextCol, nextRow].Value = "N/A";
}
DataGridViewCell nextCell = dgv.Rows[nextRow].Cells[nextCol];
if (nextCell != null && nextCell.Visible)
{
dgv.CurrentCell = nextCell;
}
}
}
}
As you will see, if you try this out, there are some problems particularly with going back and changing already entered text. It is, however, a start.
Good luck!
Henry Minute
Do not read medical books! You could die of a misprint. - Mark Twain
Girl: (staring) "Why do you need an icy cucumber?"
“I want to report a fraud. The government is lying to us all.”
Why do programmers often confuse Halloween and Christmas?
Because 31 Oct = 25 Dec.
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