C# Discussion Boards - CodeProject

Changing whats displyed on a page in a Webbrowser Control. [modified]

Beijer21-Jun-09 6:52

21-Jun-09 6:52

Hi,
I'm currently working on a project were I want to be able to extract information from the currently displayed page in a browser control, and also be able to change whats displayed on the page, or add information by my self.

Is there anyone that can point me in the right direction were to start if I want to be able to manipulate the content on the page?
I know HTML and some DOM, now it's just how i can access the code behind to collect data and to change it on the page.

Thanks in advanced.

modified on Tuesday, June 23, 2009 9:42 AM

Equality of floating point numbers

Wags21-Jun-09 5:52

Wags

21-Jun-09 5:52

Okay, I think that I understand the issues affecting C# equality testing (including numerical precision, type conversions, boxing etc) - e.g. http://blogs.msdn.com/jmstall/archive/2005/03/09/390135.aspx[^] - but I don't understand the statement in MSDN (http://msdn.microsoft.com/en-gb/library/bsc2ak47.aspx[^]):

x.Equals(x) returns true, except in cases that involve floating-point types. See IEC 60559:1989, Binary Floating-point Arithmetic for Microprocessor Systems.

Can anyone please explain? How can this sometimes evaluate to false?
(I couldn't find anything interesting re: IEC 60559:1989 - still Googling though.)

P.S.

double d = Double.NaN;
d.Equals(d); // is still true - although it doesn't have to be under the standard

"...there's what people want to hear, there's what people want to believe, there's everything else, THEN there's the truth!" - New York D.A., The International

Re: Equality of floating point numbers

Luc Pattyn21-Jun-09 6:24

Luc Pattyn

21-Jun-09 6:24

Hi,

the MSDN documentation on Object.Equals says:

This method can be overridden by a derived class.... The following statements must be true for all implementations of the Equals method...
x.Equals(x) returns true, except in cases that involve floating-point types. See IEC 60559:1989, Binary Floating-point Arithmetic for Microprocessor Systems.

so all it says is xfloat.Equals(xfloat) is ALLOWED to return false; it just leaves the Equals() result for floats undefined.

The IEC standard isn't available for free, so I can't check this, however I assume they call the result of x==x undefined, hence hardware that implements IEC 60559:1989, and software running on such hardware, would find it difficult to enforce x.Equals(x) returns true.

The fundamental reason is it does not make sense at all to test two floats for equality; by their very nature, float values are either close to each other (difference less than epsilon), or they are not. Zero does not exist in nature.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.

Re: Equality of floating point numbers

CPallini21-Jun-09 7:01

CPallini

21-Jun-09 7:01

Luc Pattyn wrote:
Zero does not exist in nature.

Shhhhhhhhhhhhhh, please don't tell it to Zero. It assumes its existance having the same dignity of 1, 2, pi and so on.
Roll eyes | :rolleyes:

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Re: Equality of floating point numbers

Eddy Vluggen21-Jun-09 7:08

Eddy Vluggen

21-Jun-09 7:08

Hmmmm, pie Poke tongue | ;-P

I are troll Smile | :)

Re: Equality of floating point numbers

Wags21-Jun-09 7:55

Wags

21-Jun-09 7:55

I think that the standard states that NaN may be treated as not being equal to NaN - which seems fair as operations resulting in NaN are NOT returning an an actual numerical value. .NET does however treat them as equal when using Equals() but not when using ==.

I can't see how x.Equals(x) can evaluate to false for real numbers (whatever the implementation) when the 2 operands are references to the same object.

Do you think that MSDN is really just saying not to rely on it - even when referencing the same object? (If so it would be useful if they stated thay some other comparison should be used with reference to Epsilon.)

"...there's what people want to hear, there's what people want to believe, there's everything else, THEN there's the truth!" - New York D.A., The International

Re: Equality of floating point numbers [modified]

Luc Pattyn21-Jun-09 8:08

Luc Pattyn

21-Jun-09 8:08

As I said, MSDN requires an inherited Equals to return true for x.Equals(x) unless x is of type float/double, in which case there is no such requirement at all.

Your point on one NaN not being equal to another NaN is absolutely valid; anyway, x.Equals(y) is not supposed to first check if x and y refer to the same object. So if they both refer to the same float variable and that happens to be NaN, then is really ~~should return~~ wouldn't be wrong to return false!

AFAIK the same argument applies to plus and minus infinity, one infinity does not equal another.

Smile | :)

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DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.

modified on Sunday, June 21, 2009 2:14 PM

Crystal report field strange behaviour

Muammar©21-Jun-09 5:35

Muammar©

21-Jun-09 5:35

Hey everyone,
Any idea why one of my fields in a crystal report totally disappear from the report during runtime?? Everything related to that field, the header lable, the data field, and even the summary field!! All the other fields are just fine and were created just like this one by dragging them from the database field tree.

Many thanks!

All generalizations are wrong, including this one!
(\ /)
(O.o)
(><)

Solved!

Muammar©21-Jun-09 6:19

Muammar©

21-Jun-09 6:19

Hey,
Just found the answer and it was stupid.. I accidentally misspelled the field name when filling the dataset that it was never filled with the other fields, now it's fine!

Thanks for reading.

All generalizations are wrong, including this one!
(\ /)
(O.o)
(><)

Deleted VS component

Hans Ruck21-Jun-09 4:01

Hans Ruck

21-Jun-09 4:01

Hi,

Is there a way to determine that a custom Visual Studio component has been deleted from a form at design time?
I am currently working on such a component.

online

Re: Deleted VS component

Henry Minute21-Jun-09 8:00

Henry Minute

21-Jun-09 8:00

The only two things that occur to me are:

1) It might (that's a very big might) be possible to override the OnControlRemoved method of your Form, test for DesignMode and then check if the ControlEventArgs.Control is your control. I'm not even sure that the method gets called at Design time, you'd have to check that for yourself. You would also conceivably have to do this for every container control on the Form.

2) Another possibility is to override the Dispose method of your control, or write a Destructor, and handle things there. Again, you'd have to test for DesignMode.

These two options may be either impossible or unfeasable. I'm pretty sure that others will tell me if I have it totally wrong, but that is where I would start investigating if it were my project.

Henry Minute

Do not read medical books! You could die of a misprint. - Mark Twain
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Re: Deleted VS component

Hans Ruck21-Jun-09 8:59

Hans Ruck

21-Jun-09 8:59

Thank you for the reply.

I need a design time solution, independent of the container form.
Trying the second solution didn't work. The Dispose is called also when the form is closed during the design time.

Bogdan.

Reuseability of controls

Rafone21-Jun-09 3:29

Rafone

21-Jun-09 3:29

Good Morning Fellow Coders;
I have a treeView that I have developed over the years. It has all the things that I need it to do in most of my apps including the ability for the user to persist it to a file on the hard drive.
The problem is that I use it in many apps that I write but, as I adapt it to different apps it can only open files for a the app it was compiled in.
My questions is this.
How do I re-use it and keep the ability to open any of these files from any app I use it in?

Do I create a stand-alone project for just the tree then change the namespace or do I have to make a control out of it?

Any thoughts will be appreciated...

tia
rafone

Statistics are like bikini's...
What they reveal is astonishing ...
But what they hide is vital ...

Re: Reuseability of controls

Colin Angus Mackay21-Jun-09 4:12

Colin Angus Mackay

21-Jun-09 4:12

Rafone wrote:
How do I re-use it and keep the ability to open any of these files from any app I use it in?

You redesign it with extensibility points.

In your example, saving and retrieving the tree state from a file and you having different file formats for various applications, you would add the ability of being able to query in all ways necessary the state and structure of the tree. Another class is responsible for persisting this to where ever you need it (file, database, whereever). If you have multiple ways of storing it you have multiple classes responsible for persisting the information. Single responsiblity principle.

Re: Reuseability of controls

Rafone21-Jun-09 5:08

Rafone

21-Jun-09 5:08

Let me see if I can clarify.

Right now I use it in a couple of apps. If I try to open one of the files made from myApp in myApp2 I get an exception...

"Unable to find assembly 'myApp, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'."}

All I have done was to copy my tree.cs file from myApp to myApp2 and changed the namespace so it will work in myApp2.

So...is this because the namespace's are different? If so can I just reference the myApp namespace in myApp2 and use the tree components from myApp?

tia
rafone

Statistics are like bikini's...
What they reveal is astonishing ...
But what they hide is vital ...

Re: Reuseability of controls

Luc Pattyn21-Jun-09 5:25

Luc Pattyn

21-Jun-09 5:25

Hi,

as long as you included a reference to your DLL, you can refer to its public types, either using the full name (mySpace.mySubspace...MyClass) or using a using statement (using mySpace.mySubspace; ) and a short name (MyClass instance=new MyClass()).

There is no need to modify namespace names, they exist to help you keep things apart (avoid name clashes), not to make your job more difficult.

PS: the types need to be public, VS often creates classes without attributes, just prefix "public".

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.

Re: Reuseability of controls

Rafone21-Jun-09 7:58

Rafone

21-Jun-09 7:58

Excellent!

Exactly what I needed.

Thanks Luc

rafone

Statistics are like bikini's...
What they reveal is astonishing ...
But what they hide is vital ...

Re: Reuseability of controls

Luc Pattyn21-Jun-09 8:10

Luc Pattyn

21-Jun-09 8:10

You're welcome.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.

Event handling in a custom control.

Siddhartha S.21-Jun-09 1:26

Siddhartha S.

21-Jun-09 1:26

Hi All,

I have a composite(custom) control in which I have a button control (call it button1). In the control I have coded for the button click event. i.e. inside the method:

private void button1_Click(object sender, EventArgs e)
{
    //My functionality here
}

This control will be used by some other application developer.
The requirement demands the functionality that I have impelemented though my code in the button click event handler be overwritten by the developer who will be using my control in his application iff he wishes so or else the functionalty would persist.
The problem that I am facing is how to access the button click event handler in the cutom control from the application that is hosting the control. Making the event handling method public would be a bad work around. I believe I am missing on a concept.
Any guidance will be appreciated.

Best Regards,
Sid

Re: Event handling in a custom control.

Luc Pattyn21-Jun-09 1:58

Luc Pattyn

21-Jun-09 1:58

Hi,

you could offer a public event, and have your button handler check for it being null or not.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.

Re: Event handling in a custom control.

Siddhartha S.21-Jun-09 16:55

Siddhartha S.

21-Jun-09 16:55

Hi Luc,
Thanks for the reply.
But could you elaborate it a bit more. I mean a few lines of code will be fine.

Best Regards,
Sid

Re: Event handling in a custom control.

Luc Pattyn21-Jun-09 17:00

Luc Pattyn

21-Jun-09 17:00

Hi,

something along these lines, where another class may or may not add delegates to ButtonClicker:

public event EventHandler ButtonClicker;

private void button1_Click(object sender, EventArgs e) {
    if (ButtonClicker==null) {
        //My default functionality here
    } else {
        ButtonClicker(sender, e);
    }
}

Luc Pattyn [Forum Guidelines] [My Articles]

DISCLAIMER: this message may have been modified by others; it may no longer reflect what I intended, and may contain bad advice; use at your own risk and with extreme care.

Re: Event handling in a custom control.

Siddhartha S.21-Jun-09 17:04

Siddhartha S.

21-Jun-09 17:04

Hey thanks for the reply.
I will try this. Seems I need to get my concepts on events and delegates proper.

Best Regards,
Sid

Casting KeyValuePair -- eliminate else if blocks [modified]

devvvy21-Jun-09 0:48

devvvy

21-Jun-09 0:48

hello

Trying to write simpler code... how can I reduce the number of the else-if blocks below?

<br />
if (o is DictionaryEntry)<br />
{<br />
	DictionaryEntry oEntry = (DictionaryEntry)o;<br />
	object oKey = oEntry.Key;<br />
	object oValue = oEntry.Value;<br />
	<br />
	// In this case lstAnotherCollection is a Hashtable<br />
	lstAnotherCollection.Add(oKey, oValue);<br />
	... more ...<br />
}<br />
else if (o is KeyValuePair<string, System.Drawing.Bitmap>)<br />
{<br />
	// This would give error ...<br />
	// KeyValuePair<object, object> oEntry = (KeyValuePair<object, object>)o;<br />
	<br />
	// To resolve this, I resorted to else-elseif blocks (That's obviously undersirable)<br />
	KeyValuePair<string, System.Drawing.Bitmap> oEntry = (KeyValuePair<string, System.Drawing.Bitmap>)o;<br />
	string oKey = oEntry.Key;<br />
	System.Drawing.Bitmap oValue = oEntry.Value;<br />
	<br />
	// lstAnotherCollection = Dictionary<Object, Object><br />
	lstAnotherCollection.Add(oKey, oValue);<br />
	... more ...<br />
}<br />
... many more else-if blocks ...<br />

I suppose I cannot cast KeyValuePair<X,Y> into KeyValuePair<Object, Object> ... because it defeats purpose of Generics in the first place?

Thanks

dev

modified on Sunday, June 21, 2009 6:54 AM

Re: Casting KeyValuePair -- eliminate else if blocks

Colin Angus Mackay21-Jun-09 3:49

Colin Angus Mackay

21-Jun-09 3:49

I'd say you potenially have bigger problems that sorting out a bunch of if/else blocks.

How come you get to this code? Why can o end up being so many different things? There isn't event a common base class to tie it all together.

Excessive casting is a known "code smell" that indicates you are using the wrong types or the types are incorrectly defined.

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