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For a generic return type the type has to be part of the generic type arguments of the method:
public static IObservable<T> Observes<TSource, T>(this TSource MyObject) where TSource : object, T: object
So this would just move the neccessity to write a different method name to having to write a different type name.
However, if you merged the methods for creating the observable and subscribing to it into one, you wouldn't have to return the generic IObservable but just the non-generic IDisposable subscription object instead.
But: Lifting the type constraint for TSource from IPropertyChanged / INotifyCollectionChanged to Object for the sake of having one method is rather "dirty" 
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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Sascha Lefèvre wrote: But: Lifting the type constraint for TSource from IPropertyChanged / INotifyCollectionChanged to Object for the sake of having one method is rather "dirty"
Oh yes indeed  What I really wanted was a way to write a little more complex where clause, and I thought I might have missed something. I could write where T : INotifyPropertyChange,INotifyCollectionChanged but not a clause that said that it cound not implement some interface.
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Kenneth Haugland wrote: I could write where T : INotifyPropertyChange,INotifyCollectionChanged but not a clause that said that it cound not implement some interface.
Yes, that's not possible.
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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As it turns out, I was asking the wrong question, thus looking for solutions in the wrong place.
The trick I used was that I created a generic SubscribeWeakly, and it was this method that I really needed:
Weak events in .NET using Reactive Extensions (Rx)[^]
Yeah, question is old now, but in case other people see it they should now be able to solve it 
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Thank you, Kenneth, I'll take a look at it
If the brain were so simple we could understand it, we would be so simple we couldn't. — Lyall Watson
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Hi C# Developers,
Question 1:
How do I suppress Cancel button click event of Save As dialog box to make sure that my users click save button only?
Question 2:
How do I prevent users from creating New folder while Save As dialog box is open?
Question 3:
How do I prevent users from changing the current folders path while Save As dialog box is open?
Your help is much appreciated in advance
Kindest Regards
Lucky Khoza
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1) You can't.
2) You can't.
3) You can't.
It's a system dialog, and as such it exposes system facilities. If you want to restrict what it can do that heavily - and you'll annoy a lot of people if you do - then you need to write your own custom "Save As" dialog and use that instead of the system one.
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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Issues with customizing the built-in WinForms 'FileDialogs ('Open, 'Save) are discussed thoroughly in these CodeProject articles: [^], [^], [^].
I think it's a mistake to try and alter the appearance (the UI) of these Dialogs; Win users are socialized to expect these dialogs to behave in standard ways, and its tricky coding that will entail things like hooking the underlying Window of a Button, using Win API's, etc.
But, you can certainly exert a strong degree of control by creating a custom 'Filter setting restricting the viewed locations.
If you really want total control of where the user can save a file, why not create a ComboBox with all the valid locations in it; idea: use the 'DisplayMember and 'DisplayMember property to display whatever "friendly" name you think is meaningful to the user, and, perhaps, use the 'ValueMember property to hold the DirectoryInfo, or FileInfo you want associated with the "friendly" name. Put the ComboBox in a UserControl and then 'Show/Hide it as necessary.
In short, if you want the user to have fewer options: give them fewer options.
«In art as in science there is no delight without the detail ... Let me repeat that unless these are thoroughly understood and remembered, all “general ideas” (so easily acquired, so profitably resold) must necessarily remain but worn passports allowing their bearers short cuts from one area of ignorance to another.» Vladimir Nabokov, commentary on translation of “Eugene Onegin.”
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You can't do any of that stuff with the stock SaveDialog.
But, with all those restrictions, you've pretty much limited the user to entering a filename in a TextBox so why even use a SaveDialog at all?
Also, what if the user accidentally click the SaveAs menu item? How are you giving them a way out without performing the Save operation?
modified 2-Feb-16 9:51am.
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Dave Kreskowiak wrote: Also, what if the use accidentally click SaveAs? How are you giving them a way out without performing the Save operation?
With a WinForms SaveFileDialog you can define a 'FileDialog.FileOk EventHandler, in which you can cancel the 'Save operation, and keep the dialog open.
private void saveFileDialog1_FileOk(object sender, CancelEventArgs e)
{
if (saveFileDialog1.FileName == @"C:\Users\SomeUser\Desktop\NoGo.xxx"
|| saveFileDialog1.FileName.ToLower().Contains("forbidden"))
{
e.Cancel = true;
}
}And, when the SaveFileDialog 'returns is closed: of course, you've got another chance to validate and do nothing based on the selected File. And, you've got the power to restrict files viewed by means of the 'Filter Property.
My preference is to never enable showing any kind of Dialog unless the pre-conditions for its valid use are met. So, yeah, that means disabled MenuItems, or Buttons, etc.
Unfortunately, the FolderBrowserDialog does not expose any Events.
«In art as in science there is no delight without the detail ... Let me repeat that unless these are thoroughly understood and remembered, all “general ideas” (so easily acquired, so profitably resold) must necessarily remain but worn passports allowing their bearers short cuts from one area of ignorance to another.» Vladimir Nabokov, commentary on translation of “Eugene Onegin.”
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Yeah, but that goes against how the standard dialog works from the users perspective and isn't intuitive. Clicking OK to Cancel? I don't think so.
I was referring to someone clicking something like a SaveAs menu item only to realize they clicked on the wrong item. The dialog is being shown now, but how does the user get back intuitively with a Cancel button? I know, the little X in the top right corner or double-clicking the top left corner or hitting Alt-F4 to close the dialog works to do this also but too many users don't know about them.
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More to the point, you can even have a default value that the user can use as the "file name" (probably somehow related to current day/time), so that the user can/will probably just click OK to save it.
And trust me, it's very likely the user will choose that default 95% of the time 
Best,
John
-- Log Wizard - a Log Viewer that is easy and fun to use!
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Write your own dialog.
If it's not broken, fix it until it is
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how are you all.
i am new to asp.net and c#. i need help.
well my question is, i have a textbox in which a user have to enter a float value in the webform.
and i want to manipulate that value in a calculation.
so have created a class for the calculation which is Sales class. in that class i have declared Price as a float value,the value which should be obtained from the textbox.ie public float Price {get;set;}
Now my problem is with binding/linking the Price variable with the textbox in the button_click method.
initially i had done it this way:
in my .aspx.cs file i have created an object of the class in this case :
Sales s = new Sales ();
protected void button_Click (object sender EventArgs e)
{
s.Price =Convert.ToInt32(Textbox1.Text);
s.Save();
}
i want the Price value to be saved in my database after a user clicks the SAVE button from the webform.
Now the problem is when i run the application there is an error (
Hide Copy Code
An exception of type 'System.FormatException occur but was not handred in the mscorlib.dll but was not handled in the user code
)
on the line :
s.Price = Convert.ToInt32(Textbox1.Text);
could i have done something wrong in the code?
modified 2-Feb-16 2:33am.
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You say you want the user to enter a 'float, but your code shows you try to convert what's in the TextBox to an integer.
You should be using float.TryParse to get/validate the user's input; example:
float result;
if (float.TryParse(tbUserName.Text, NumberStyles.Number, System.Globalization.NumberFormatInfo.InvariantInfo, out result))
{
}
else
{
}But, if you do use 'float, don't be surprised if when the user enters "0.123456789" in the TextBox that 'tryParse will return that as: 0.123456791.
'float is low precision.
«In art as in science there is no delight without the detail ... Let me repeat that unless these are thoroughly understood and remembered, all “general ideas” (so easily acquired, so profitably resold) must necessarily remain but worn passports allowing their bearers short cuts from one area of ignorance to another.» Vladimir Nabokov, commentary on translation of “Eugene Onegin.”
modified 2-Feb-16 3:04am.
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Yes - you have assumed that the user can type, and won't make any mistakes!
If the user types "Hello" or "1.1", then the Convert will fail and throw an exception.
Instead, use TryParse:
int price;
if (!int.TryParse(Texbox1.Text, out price))
{
... Report problem to user and ask him to re-enter
return;
}
s.Price = price;
s.Save();
BTW: Do yourself a favour, and stop using Visual Studio default names for everything - you may remember that "Textbox1" is the price today, but when you have to modify it in three weeks time, will you then? Use descriptive names - "tbPrice" for example - and your code becomes easier to read, more self documenting, easier to maintain - and surprisingly quicker to code because Intellisense can get to to "tbPRice" in three keystrokes, where "Textbox1" takes thinking about and 8 keystrokes...
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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note the OP talks about using a 'float, but the code used 'int
«In art as in science there is no delight without the detail ... Let me repeat that unless these are thoroughly understood and remembered, all “general ideas” (so easily acquired, so profitably resold) must necessarily remain but worn passports allowing their bearers short cuts from one area of ignorance to another.» Vladimir Nabokov, commentary on translation of “Eugene Onegin.”
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I see you fixed your code to reflect that - good idea!
A float is probably what he wanted - or better is probably Decimal given that it's a Price.
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
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OriginalGriff wrote: I see you fixed your code to reflect that
Nope, I wrote code using 'float from the git-go ... in a temporary loss of sanity where I assumed the OP meant what he wrote, rather than what he coded 
«In art as in science there is no delight without the detail ... Let me repeat that unless these are thoroughly understood and remembered, all “general ideas” (so easily acquired, so profitably resold) must necessarily remain but worn passports allowing their bearers short cuts from one area of ignorance to another.» Vladimir Nabokov, commentary on translation of “Eugene Onegin.”
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hi thank you it worked. for Textbox name i had t name it that way for my question to be understood but its named something else in my code.thanx .
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how are you all.
i am new to asp.net and c#. i need help.
well my question is, i have a textbox in which a user have to enter a float value in the webform.
and i want to manipulate that value in a calculation.
so have created a class for the calculation which is Sales class. in that class i have declared Price as a float value,the value which should be obtained from the textbox.ie public float Price {get;set;}
Now my problem is with binding/linking the Price variable with the textbox in the button_click method.
initially i had done it this way:
in my .aspx.cs file i have created an object of the class in this case :
Sales s = new Sales ();
protected void button_Click (object sender EventArgs e)
{
s.Price =Convert.ToInt32(Textbox1.Text);
s.Save();
}
i want the Price value to be saved in my database after a user clicks the SAVE button from the webform.
Now the problem is when i run the application there is an error (
Hide Copy Code
An exception of type 'System.NullReferenceException' occurred in Version1.dll but was not handled in user code
)
on the line :
s.Price = Convert.ToInt32(Textbox1.Text);
could i have done something wrong in the code?
|
|
|
|
|
how are you all.
i am new to asp.net and c#. i need help.
well my question is, i have a textbox in which a user have to enter a float value in the webform.
and i want to manipulate that value in a calculation.
so have created a class for the calculation which is Sales class. in that class i have declared Price as a float value,the value which should be obtained from the textbox.ie public float Price {get;set;}
Now my problem is with binding/linking the Price variable with the textbox in the button_click method.
initially i had done it this way:
in my .aspx.cs file i have created an object of the class in this case :
Sales s = new Sales ();
protected void button_Click (object sender EventArgs e)
{
s.Price =Convert.ToInt32(Textbox1.Text);
s.Save();
}
i want the Price value to be saved in my database after a user clicks the SAVE button from the webform.
Now the problem is when i run the application there is an error (
Hide Copy Code
An exception of type 'System.NullReferenceException' occurred in Version1.dll but was not handled in user code
)
on the line :
s.Price = Convert.ToInt32(Textbox1.Text);
could i have done something wrong in the code?
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I have a method something like this.
private void PrintSomething()
{
}
then calling this method like this
MethodInvoker mi = new MethodInvoker(PrintSomething);
mi.BeginInvoke(null, null);
This will work pretty well on win7 and up, but if running it on Win XP will cause a very high cpu usage and will it eat up the memory then the desktop will freeze.
but just calling the method synchronously everything is fine under win XP.
private void btn_click(object sender, EventArgs e)
{
PrintSomething();
}
Any thought about this?
I will appreciate for any advice will.
Thanks.
modified 2-Feb-16 1:03am.
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Suggestions:
1. Try debugging it. Or it's not possible?
2. If not debugging, do some logging within the PrintSomething method. By what you're saying, it looks like you might end up calling PrintSomething method too many times
3. You can also ask if IsInvokeRequired first.
4. A profiler? (dotTrace comes to mind)
Best,
John
-- Log Wizard - a Log Viewer that is easy and fun to use!
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