Multiple message filters - C# Discussion Boards

22-Mar-04 11:44

I'm trying to build a 2-player game that uses the keyboard to control the game elements. I'd like certain keys to control player 1 and others to control player 2. I was thinking about doing this by having each player's game piece contain a controller object that is used to capture key events and then call back to the game piece to do things like set direction. The controller would implement IMessageFilter and the game piece would create it like: Application.AddMessageFilter( new Ctrl( this )). Wondering if it's possible to add multiple message filters like this.

Nick Parker22-Mar-04 16:02

Nick Parker

22-Mar-04 16:02

I don't really think that you would need two message filters to handle this process, one should do the trick. The key that is press gets packed into the WParam of the Message so once you evaluate what was hit you can simply dispatch control to the appropriate method.

private const int WM_KEYDOWN = 0x0100;
public bool PreFilterMessage(ref Message m)
{
    if(m.Msg == WM_KEYDOWN)
    {
        char c = (char)m.WParam;
        if(c == 'A')
            MessageBox.Show("A was hit");
    }
    return false;
}

- Nick Parker
My Blog | My Articles

bisquic22-Mar-04 16:16

22-Mar-04 16:16

Well, what I'm trying to do is have each controller be associated with a specific game piece. That way I don't have to keep track of what game pieces were created or hard code specific references. If I want to create 2 players, I can, but if I later decide to create 7 players, I don't have to change much code.

Heath Stewart23-Mar-04 4:21

Heath Stewart

23-Mar-04 4:21

Yes it's possible, which is why the related methods are called AddMessageFilter and RemoveMessageFilter. There is a reason to keep a consistent naming convention, and Microsoft has done that with 90% of their code.

You also could've just thrown together a quick example. Throwing together samples is a staple of development.

Microsoft MVP, Visual C#
My Articles

bisquic28-Mar-04 19:07

28-Mar-04 19:07

Sorry for the delayed response... been busy with school.

I had written an example, but it did not work. I have two instances of a class that each create their own controller (which derives from IMessageFilter) and passes it to Application.AddMessageFilter. However, only one of the controllers' PreFilterMessage functions is capturing input. The second one is never called. This is why I was wondering if it was possible to have two since it only seems to be working with one.

Heath Stewart29-Mar-04 3:06

Heath Stewart

29-Mar-04 3:06

Works fine for me. Internally, when you add an IMessageFilter implementation it gets added to an ArrayList, so it doesn't even matter if you add the same instance more than once. If you return true from your PreFilterMessage method (not "function", objects have "methods", btw), then the message does not get dispatched. I looked quickly and didn't find whether or not it is sent to remaining message filters or not right away. More than likely it is.

If you want, verify that things are working with my little test app which adds three message filters, 2 in the static entry point and another in one of the constructors, which makes 2 filters added using the same instance of a class:

using System;
using System.Windows.Forms;

public class Test : Form, IMessageFilter
{
  static void Main()
  {
    Test t = new Test();
    Application.AddMessageFilter(t);
    Application.AddMessageFilter(new MessageFilter());
    Application.Run(t);
  }

  public Test()
  {
    Application.AddMessageFilter(this);
    Text = "Test";
  }

  public bool PreFilterMessage(ref Message m)
  {
    Print(this, m);
    return false;
  }

  internal static void Print(object obj, Message m)
  {
    Console.WriteLine("[{0}] 0x{1:x2} -> 0x{2:x2}",
      obj.GetType().Name, m.Msg, m.HWnd);
  }
}

public class MessageFilter : IMessageFilter
{
  public bool PreFilterMessage(ref Message m)
  {
    Test.Print(this, m);
    return false;
  }
}

Like me, you should get three lines with each message sent to the application pump, like so:

[Test] Message.Msg -> Message.HWnd
[MessageFilter] Message.Msg -> Message.HWnd
[Test] Message.Msg -> Message.HWnd

Microsoft MVP, Visual C#
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bisquic29-Mar-04 3:14

Datagrid to text (values only)

29-Mar-04 3:14

Yep, found the problem within seconds of reading your email. I was returning true and the message was not making it any further. Duh. Thanks so much for the help, this is all a lot clearer to me now.

jazzle22-Mar-04 10:42

jazzle

22-Mar-04 10:42

Hi all,
I have a datagrid populated from an XML file like the following:

<?xml version="1.0" standalone="yes"?>
<pairs xmlns="http://tempuri.org/Data.xsd">
<pair>
<x>3</x>
<y>10</y>
</pair>
<pair>
<x>4</x>
<y>17</y>
</pair>
...
</pairs>

and would like to convert this to a string of the values like this:
3 10 4 17 ...
(to create input for an old C++ app, just the values in one long string - nothing but numbers and spaces)

I hoped this would be fairly straightforward, but I haven't found how to do it.
(I could transform the XML file if necessary)

Any help much appreciated.

---
J Eek! | :eek:

Re: Datagrid to text (values only)

Nick Parker22-Mar-04 18:02

Nick Parker

22-Mar-04 18:02

With the below XML, I wrote this quick method to return a string value as you have requested.

<?xml version="1.0" standalone="yes"?>
<pairs>
  <pair>
    <x>3</x>
    <y>10</y>
  </pair>
  <pair>
    <x>4</x>
    <y>17</y>
  </pair>
</pairs>

private string GetInput()
{
	XmlDocument doc = new XmlDocument();
	StringBuilder sb = new StringBuilder();
	XmlNode buffer = null;
	doc.Load("../../data.xml");
	XmlNodeList nodes = doc.SelectNodes("//pairs/pair");
	if(nodes != null)
	{
		foreach(XmlNode node in nodes)
		{
			buffer = node.SelectSingleNode("x");
			if(buffer != null)
				sb.Append(buffer.InnerXml + " ");
			buffer = node.SelectSingleNode("y");
			if(buffer != null)
				sb.Append(buffer.InnerXml + " ");
		}
	}
	return(sb.ToString());
}

- Nick Parker
My Blog | My Articles

Re: Datagrid to text (values only)

jazzle22-Mar-04 21:37

jazzle

22-Mar-04 21:37

excellent, thank you.
hadn't come across string builder before, am sure it will be useful.

---
Eek! | :eek:

Re: Datagrid to text (values only)

Heath Stewart23-Mar-04 4:24

Heath Stewart

23-Mar-04 4:24

It's very useful - especially when formatting unknown lengths of strings. The String class is immutable - any changes to it force another string to be created and the chars within the original string to be copied to the new string merged with the changes you've made. Do this several hundred times and you're app is slow. The StringBuilder is a mutable string and eliminates these problems and should be used when appending strings like Nick pointed out. The StringBuilder is also used internally in many methods like String.Format.

Microsoft MVP, Visual C#
My Articles

Converting strings to DateTime structs

profoundwhispers22-Mar-04 10:38

profoundwhispers

22-Mar-04 10:38

I get dates in the following format:

Mar-07 13:45

How can I feed this to a ConvertTo.DateTime expression without getting an exception?

Sammy

"A good friend, is like a good book: the inside is better than the cover..."

Edbert P22-Mar-04 12:19

Edbert P

22-Mar-04 12:19

Tough luck. I think you need to write your own function to read it and convert it to ISO format.
Check if the format is always mmm-dd hh:nn. If it is, it will be simpler for you to write the function.
I might be wrong though, so if anyone knows about this, feel free to answer. Smile | :)

Edbert P.
Sydney, Australia.

profoundwhispers22-Mar-04 12:39

profoundwhispers

22-Mar-04 12:39

Yes in fact, it is always in this format.
How should I write this function?

Sammy

"A good friend, is like a good book: the inside is better than the cover..."

Edbert P22-Mar-04 13:18

Edbert P

22-Mar-04 13:18

I've checked that in your case you only need to add the year value to the string.
Here's what I would do:

string dateValue = "Mar-07 13:45";
string[] dateParts = dateValue.Split(' ');
dateValue = String.Concat(dateParts[0], "-", DateTime.Now.Year, " ", dateParts[1]);

You can use the final string as input for any DateTime functions.

Edbert P.
Sydney, Australia.