Re: basic questions about enum - C# Discussion Boards

13-May-08 3:29

Hello everyone,

I have 3 basic questions about Enum, from MSDN,

http://msdn.microsoft.com/en-us/library/sbbt4032(VS.80).aspx

1.

It is mentioned "A variable of type Days can be assigned any value in the range of the underlying type;" -- I think it is not correct to say any value in the range of the underlying type, like integer, but in the range from Sat to Fri.

For example, you can not write Days d = 65535;

2.

"and if additional elements have been added to the enum type, the test for default values can return true unexpectedly." I do not quite understand this scenario, could anyone show me some code please?

3.

"You can notice these changes when using tools such as the Console class methods, the Expression Evaluator, and so forth. (See example 3).", I have tried example 3. But what are the rules for the changes when we add System.FlagsAttribute? The document only says there will be some changes, but not clearly states what will be the changes. Any ideas?

thanks in advance,
George

Nissim Salomon13-May-08 4:29

Nissim Salomon

13-May-08 4:29

Hi
In the MSDN enum was declare as follow "The enum keyword is used to declare an enumeration, a distinct type consisting of a set of named constants called the enumerator list"
1.
you need to understand that at the bottem line there is a native variable like int or short that can hold other values.
for example:
Days d = (Days)int.MaxValue;
2.
"Assigning additional values new versions of enums, or changing the values of the enum members in a new version, can cause problems for dependant source code. It is often the case that enum values are used in switch statements, and if additional elements have been added to the enum type, the test for default values can return true unexpectedly."
in case that you are using flags for bitwaise operation,
if one or more enum value was changed you need to update your program
to prevent unwanted if results

George_George13-May-08 4:42

13-May-08 4:42

Thanks nissims,

Some further questions/comments.

1.

If we write an Enum variable like d in my code, and assign it beyond the related int range from Sat to Fri, does such code have any practical usage? I think people always use the values in the range and treat the ones beyond the range as invalid values.

2.

I do not quite understand what do you mean "in case that you are using flags for bitwaise operation", could you show me some pseudo code please?

regards,
George

Nissim Salomon13-May-08 4:56

Nissim Salomon

13-May-08 4:56

1.you are right the all purpose of enum is to give
you the ability to use some logical const names insetd of numbers
for example
enum Days { Sat = 1, Sun, Mon, Tue, Wed, Thu, Fri }
vs
1,2,3,4,5,6,7
there for it is not wise to override the enum consts using numbers
if the enum was declared use it, specially if you need to cast it in order to use numbers.

2.Please read the "using flags attribute" in the msdn article.

George_George14-May-08 1:39

14-May-08 1:39

Thanks nissims,

1.

nissims wrote:
if the enum was declared use it, specially if you need to cast it in order to use numbers.

I do not quite understand your above comments, could you show some pseudo code please?

2. Any comments to?

http://www.codeproject.com/script/Forums/View.aspx?fid=1649&msg=2552145[^]

regards,
George

Anthony Mushrow13-May-08 5:00

Anthony Mushrow

13-May-08 5:00

Any practical usage? There's probably something, but i can't think of anything.

And on to flags:

[Flags]
public enum MyKeys : int
{
  Null	= 0,
  Up	= 0x01,
  Down	= 0x02,
  Left	= 0x04,
  Right	= 0x08
}

...
MyKeys keys = MyKeys.Up | MyKeys.Right;

if((keys&MyKeys.Right) == MyKeys.Right)
  MessageBox.Show("keys contains MyKeys.Right!");

Each value in the enum represents 1 bit:

0x01 = 0001
0x02 = 0010
0x04 = 0100
0x08 = 1000

So if we use the bitwise operators OR and AND we can add and check for these bits. In the above code:

MyKeys keys = MyKeys.Up | MyKeys.Right;
is the same as
MyKeys keys = 0001 | 1000;
keys is now 1001

keys&MyKeys.Right
is the same as
1001&1000 and the result is 1000

My current favourite word is: Bacon!

-SK Genius

Game Programming articles start -here[^]-

George_George14-May-08 1:34

How can I add two byte[1] + byte[2]?

14-May-08 1:34

Thanks SK Genius,

My current confusion is, when add or remove flags attribute, the result is always the same. So I am wondering the special usage of the attribute compared with the situation when we do not use it.

Here is my test code, any comments?

using System;

class Test
{
    enum Days
    {
        Mon = 1,
        Tue = 2
    };

    [Flags]
    enum DaysFlag
    {
        Mon = 1,
        Tue = 2
    };

    static void Main()
    {
        int a = (int) (Days.Mon | Days.Tue);
        int b = (int)(DaysFlag.Mon | DaysFlag.Tue);

        return;
    }
}

regards,
George

merh13-May-08 3:26

13-May-08 3:26

Hi,
I have two bytes which I need to obtain the sum of them.
I have done like this but the result is wrong.
int result = byte[1] + byte[2];
How can I do that?

Thanks in advanced
Merh

CPallini13-May-08 3:48

CPallini

13-May-08 3:48

merh wrote:
I have done like this but the result is wrong.

Sure? How did you check the result?
Please post code, inputs and ouput.
Smile | :)

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

merh13-May-08 3:56

13-May-08 3:56

I have an array of bytes. s below is my array and I try to read byte nr 0 and add to nr 1.

for(int i=0; i<=1; i++)
int result += s[i];

Thanks
Merh

Dan Neely13-May-08 4:13

Dan Neely

13-May-08 4:13

What are the values of s[0] and s[1]? What is the value of result produced by the code? What are you expecting result to be?

You know, every time I tried to win a bar-bet about being able to count to 1000 using my fingers I always got punched out when I reached 4....
-- El Corazon

CPallini13-May-08 4:16

CPallini

13-May-08 4:16

do you mean something similar to:

int i;
byte[] s ={ 10, 20 };
int result=0;
for (i = 0; i <= 1; i++)
  result += s[i];

though inelegant, I see no error in the above.

On the other hand, your code, ss it stands, doesn't even compile.

Smile | :)

merh13-May-08 4:27

13-May-08 4:27

Yes, I mean something like this
int i;
byte[] s ={ 10, 20 };
int result=0;
for (i = 0; i <= 1; i++)
result += s[i];

CPallini13-May-08 4:32

CPallini

13-May-08 4:32

Well it works fine on my system and since you have provided no inputs and no output I can only guess what is happening on yours.
Should I turn ON my Code Project Mind Reader Unit?

merh13-May-08 5:53

how to make a service automatic

13-May-08 5:53

Thanks it works now on my system too.
/Mehran

prasadbuddhika13-May-08 2:59

prasadbuddhika

13-May-08 2:59

i created a sevice by using c#.net. and installed it in the client machine.I want the service to be started automatically.(default it is manual).

Re: how to make a service automatic

dan!sh 13-May-08 3:02

dan!sh

13-May-08 3:02

this.serviceInstaller1.StartType = System.ServiceProcess.ServiceStartMode.Automatic;

Avoid Google. Use Blackle[^]

Disassmble GAC-installed assembly

ctoma200513-May-08 2:45

ctoma2005

13-May-08 2:45

Hy there, I have a problem. i want to see how winforms made the ResourcePickerDialog (the one that appears when you set an Image at design-time). I found out that the class is in the assembly Microsoft.VisualStudio.Windows.Forms, but i can't seem to find the assembly anywhere, except GAC.

Does anyone know how can I disassemble an assembly installed there? I have reflector and ildasm, but they can't open assemblies from GAC.

Thanks very much.

Flicker Problem in GDI+

hdv21213-May-08 2:12

hdv212

13-May-08 2:12

hi i have a panel and timer in my form, in timer.tick event handler, i want to draw a circle and increase pos.X in every timer interval, but when i run app and start animation, it has a flicker and not smoothing animation, also in constructor of my form, i write this code :
this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.OptimizedDoubleBuffer, true);
and set Form.DoubleBuffered to true, but still my problem was not solve, how to remove flicker correctly ?
here is all of my code :

int lastX;<br />
        int lastY;<br />
        bool reverse = false;<br />
        Pen pen = new Pen(Brushes.Red, 2);<br />
<br />
        public Form1()<br />
        {<br />
            InitializeComponent();<br />
            this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.OptimizedDoubleBuffer, true);<br />
        }        <br />
<br />
        private void button1_Click(object sender, EventArgs e)<br />
        {            <br />
            this.timer1.Start();<br />
        }<br />
<br />
        private void Paint(Graphics g,int x,int y)<br />
        {<br />
            g.Clear(Color.White);<br />
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighSpeed;<br />
            g.DrawEllipse(this.pen, new Rectangle(x, y, 100, 100));<br />
        }<br />
<br />
        private void timer1_Tick(object sender, EventArgs e)<br />
        {<br />
            if (!this.reverse)<br />
            {<br />
                if ((this.lastX + 102) <= this.panel1.Width)<br />
                {<br />
                    this.lastX += 2;<br />
                }<br />
                else<br />
                {<br />
                    this.reverse = true;<br />
                }<br />
            }<br />
            else<br />
            {<br />
                if (this.lastX >= 0)<br />
                {<br />
                    this.lastX -= 2;<br />
                }<br />
                else<br />
                {<br />
                    this.reverse = false;<br />
                }<br />
            }<br />
            this.Paint(this.panel1.CreateGraphics(), this.lastX, this.lastY);<br />
        }

thanks

Anthony Mushrow13-May-08 2:35

Anthony Mushrow

13-May-08 2:35

You should really only draw in the OnPaint event (or override), so if you want to redraw the circle then you need to have it drawn in OnPaint and call this.Invalidate(); to update the screen.

My current favourite word is: Bacon!

-SK Genius

Game Programming articles start -here[^]-

hdv21213-May-08 5:58

hdv212

13-May-08 5:58

Thanks SK Genius
i modify my code as follow :

public partial class Form1 : Form<br />
    {<br />
        int lastX;<br />
        int lastY;<br />
        bool reverse = false;<br />
        Pen pen = new Pen(Brushes.Red, 2);<br />
<br />
        public Form1()<br />
        {<br />
            InitializeComponent();<br />
            this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.OptimizedDoubleBuffer, true);<br />
        }        <br />
<br />
        private void panel1_Paint(object sender, PaintEventArgs e)<br />
        {<br />
            this.timer1.Start();<br />
            this.panel1.Invalidate();<br />
        }<br />
<br />
        private void Paint(Graphics g,int x,int y)<br />
        {<br />
            g.Clear(Color.White);<br />
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighSpeed;<br />
            g.DrawEllipse(this.pen, new Rectangle(x, y, 100, 100));<br />
            this.panel1.Invalidate();<br />
        }<br />
<br />
        private void timer1_Tick(object sender, EventArgs e)<br />
        {<br />
            if (!this.reverse)<br />
            {<br />
                if ((this.lastX + 102) <= this.panel1.Width)<br />
                {<br />
                    this.lastX += 2;<br />
                }<br />
                else<br />
                {<br />
                    this.reverse = true;<br />
                }<br />
            }<br />
            else<br />
            {<br />
                if (this.lastX >= 0)<br />
                {<br />
                    this.lastX -= 2;<br />
                }<br />
                else<br />
                {<br />
                    this.reverse = false;<br />
                }<br />
            }<br />
            this.Paint(this.panel1.CreateGraphics(), this.lastX, this.lastY);<br />
        }        <br />
    }

but result was very bad and my problem was not solve, can u wite your suggestion code ?
thanks

Anthony Mushrow13-May-08 6:07

Anthony Mushrow

13-May-08 6:07

You need to put this.timer1.Start() somewhere else (like, wherever you had it before) and move this.panel1.Invalidate() into your timer.

Then, call your draw method from within the onPaint event:

private void panel1_Paint(object sender, PaintEventArgs e)
{
  this.Paint(e.Graphics, this.lastX, this.lastY);
}

Don't forget to remove this.Paint(...) from your timer.

int lastX;
int lastY;
bool reverse = false;
Pen pen = new Pen(Brushes.Red, 2);

public Form1()
{
  InitializeComponent();
  this.SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.UserPaint | ControlStyles.OptimizedDoubleBuffer, true);
  this.timer1.Start();
} 

private void panel1_Paint(object sender, PaintEventArgs e)
{
  this.Paint(e.Graphics, this.lastX, this.lastY);
}

private void Paint(Graphics g,int x,int y)
{
  g.Clear(Color.White);
  g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighSpeed;
  g.DrawEllipse(this.pen, new Rectangle(x, y, 100, 100));
  this.panel1.Invalidate();
}

private void timer1_Tick(object sender, EventArgs e)
{
  if (!this.reverse)
  {
    if ((this.lastX + 102) <= this.panel1.Width)
    {
      this.lastX += 2;
    }
    else
    {
      this.reverse = true;
    }
  }
  else
  {
    if (this.lastX >= 0)
    {
      this.lastX -= 2;
    }
    else
    {
      this.reverse = false;
    }
  }
  this.panel1.Invalidate();
}

My current favourite word is: Bacon!

-SK Genius

Game Programming articles start -here[^]-