A Panel object does not allow DoubleBuffered to be set.



Simply creating a new control as below allows one to set that property so it
isn't that it can't be done.

It's just a little harder.

So, why did they set the property (or any property) to Protected?

What's the rational?



Thanks





Class MyPanel

Inherits System.Windows.Forms.Panel

Public Sub New()

MyBase.New()

'The reason for this class:

'The following protected property needed to be set to reduce flicker

Me.DoubleBuffered = True

End Sub

Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)

MyBase.Dispose(disposing)

End Sub

End Class

I think this was an oversight.

Some would call it an unimplemented feature.

--
--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

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" active" <activeNOSPAM (AT) a-znet (DOT) com> wrote

I don't think I was clear.

The question is why set ANY property to Protected.

It's a little harder to change then Public - but only a little harder (as I
illustrated below)
If the class prohibits inheritance Protected has a real effect,
but otherwise Protected and Public are basically the same.






"Bob Powell [MVP]" <bob (AT) spamkillerbobpowell (DOT) net> wrote

Well, now you're getting into aspects of architecture, which I can yack on
about all day :-)

The protected access keyword enforces the rule that class wishing to change
or affect certain behaviours of an object must derive from the base class in
question.

This was obviously a desire of the original design team.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

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" active" <activeNOSPAM (AT) a-znet (DOT) com> wrote

Bob, I think that is the definition.
What I'm wondering is, why would you, for example, create a Protected
property.
You make it slightly more difficult for a user to change that property, but
you don't prevent it.
(As in my example I make a new class that changes it. I suppose I could make
a new class with a public property that sets the Protected one.)
There must (I hope) be a rational for doing that.
Have you ever created a Protected property? If so why?

Thanks


"Bob Powell [MVP]" <bob (AT) spamkillerbobpowell (DOT) net> wrote

Hi, Ok, Yes, a specific example.

Properties are not direct access to a variable such as a public or even
protected field. They are methods that can perform some task. In fact,
setting or getting the contents of a property may not even have a backing
variable or field associated with it.

In a specific control I wanted to be able to perform some initialisation
when a field changed so, I added a protected property that accessed a
private field. In this way I could ensure that derived classes would
automatically call the complex initialization routine when setting the field
value instead of having to set the value and then call the initialization
method explicitly or indeed, forget to do so causing some disaster
condition.

Another reason for having a protected property was in the case of a bit of
code that used the new TypeDescriptionProvider system. I wanted this object
to provide only those public properties defined by a special attribute. The
protected property never showed up in the course of simple reflection, such
as by the property grid. However, it could be accessed via reflection and
it, once again, called a complex reinitialization routine when the object
property changed.

I can't give you code or a more specific example because the work was for a
paying customer. I hope however that it helps.

--
--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

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" active" <activeNOSPAM (AT) a-znet (DOT) com> wrote

Bob

When I asked if you ever used Protected that was a mistake on my part since
that's not the best way to get the answer I want. (But look how you had to
reach to find a situation.)

What I'm wondering about, and there is no reason to expect you to be able to
get into someone elses mind, is why MS makes some Properties Protected??

Like:
Textbox.DefaultMargin
Panel.DoubleBuffered
Panel.FontHeight...

As I said before, I can create a control the inherits a control with
Protected properties and add a public property that changes a base control's
Protected property.

Would I be doing something that I shouldn't?


Thanks

Of course you'd be doing something you shouldn't. You'd be exposing
properties that have a design usage with a specific protection to
something else entirely.

Whatever approach to take you need to question the motives of the
original object and see why those properties were protected.

Take the example of Panel.DoubleBuffered; If this property were public,
you could turn on double buffering. However, as soon as you make a
control with a complexity that requires this operation you automatically
need to turn off OnPaintBackground so that you don't cause flashing or
multiple redraws of the back-buffer. As soon as you do this you need to
override but then you just bring along the baggage of Panel. You might
as well accept the fact of doing the job properly, creating an object
derived directly from Control or ScrollableControl and stop trying to
persuade Panel to do stuff it wasn't designed for.


--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

Find great Windows Forms articles in Windows Forms Tips and Tricks
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Answer those GDI+ questions with the GDI+ FAQ
http://www.bobpowell.net/faqmain.htm

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active wrote:

I think I understand now.
The answer to my question is that those properties can be changed, but
changing them may require more knowledge and care then changing the public
properties.


thanks



"Bob Powell [MVP]" <bob (AT) _spamkiller_bobpowell (DOT) net> wrote

I probably should have mentioned that I needed a drawing surface and was
using a picturebox but thought I could use a simpler scrollable control so I
tried a Panel which seemed to work OK except for some flashing.

So I created a control inherited from Panel with only the one change of
DoubleBuffered = True and that appeared to fix the flashing without and
adverse side effects. Maybe I just don't what to look for or maybe I'll get
hit latter.


Thanks for all the help






" active" <activeNOSPAM (AT) a-znet (DOT) com> wrote