|
You may want to envelope your calls to add an item (and remove the first item when the list control is full) between a pair of SuspendLayout() and ResumeLayout() calls.
To further increase performance, you may want to consider deleting the first n items (and not just the first item) when the list control is full.
/ravi
My new year's resolution: 2048 x 1536
Home | Music | Articles | Freeware | Trips
ravib(at)ravib(dot)com
|
|
|
|
|
Hi All,
Since my last post on Design Patterns, I've been reading up on them and in particular the Observer Pattern, as I think it's the right tool for my specific task.
My scenario is this: I have a small(ish) application which uses a barcode scanner to read barcodes (naturally). Various parts (forms) of the application need to be able to accept the data from the barcode scanner (although not all at once, which I manage on a focus basis). To this end, I created a BarcodeScanner class as a Singleton, so that only one instance exists and so that it has public visability; I also created an event in this class so that it can notify any listeners when a Barcode has been successfully read. Each form that needs to read barcodes simply attaches itself as an Event receiver and so can listen (observe) the barcode scanner class.
And this all works pretty well, which is the important thing. But what I'd like to know is, is this an example of the Observer pattern as implemented in C#? Most of the articles I've read on the subject are great at explaining the abstract concept, but rely on the reader's intelligence ( ) to work out the implementation details for themselves.
Cheers,
Martin.
|
|
|
|
|
Utini wrote: is this an example of the Observer pattern as implemented in C#?
Yes, it is. A few points that may be worth mentioning:- Observers can attach themselves by chaining a listening delegate to
BarcodeScanner or implementing an IBarcodeScannerListener interface and attaching themselves by calling an BarcodeScanner.addListener() method. Delegates offer more flexibility in that the observer can supply any (valid) listening method at run time. I find the latter method meets my needs as it clearly indicates that a class is an observer of BarcodeScanner events.
- As with any listener, you need to be careful of cross thread calls (if
BarcodeScanner is running in a separate thread). See the doc on BeginInvoke() and EndInvoke() for more information.
- Because listeners will typically block execution of
BarcodeScanner, you should ensure that the listener method is lightweight.
/ravi
My new year's resolution: 2048 x 1536
Home | Music | Articles | Freeware | Trips
ravib(at)ravib(dot)com
|
|
|
|
|
Many thanks for that, ravi 
|
|
|
|
|
I need help with a strange problem.
Symptom: my C# application crashes with a AccessViolationException. The interesting thing is that it happens only when running as 32bit-process on 64-bit Windows. Running 32bit on 32bit works fine, so does 64bit on 64bit.
FxCop does not complain about my P/Invoke declarations, so I don't think I confused IntPtr and int parameters - it runs fine both as 32bit process and 64bit process - just not as 32 bit process on Windows XP Professional x64 Edition.
Using the managed debug assistent in VS05, I get the error message "The runtime has encountered a fatal error. The address of the error was at 0x79fccc04, on thread 0x6c8. The error code is 0xc0000005.".
The line where it's failing is "return CallNextHookEx(...);", the callstack suggests it fails while/after calling CallNextHookEx; not when returning from my own hook procedure. What makes this really interesting is that the code using the hook is working fine until the text-editor portion of the app is activated. It crashes when the hook receives the message caused by activating the IME (input method editor; for asian languages).
Here is the P/Invoke declaration for the hook (I'm creating the hook with code=WH_CALLWNDPROCRET, hInstance=IntPtr.Zero and threadID=AppDomain.GetCurrentThreadId()):
internal delegate IntPtr HookProc(int code, IntPtr wParam, IntPtr lParam);
[DllImport("user32.dll")]
internal static extern IntPtr SetWindowsHookEx(HookType code, HookProc func, IntPtr hInstance, int threadID);
[DllImport("user32.dll")]
internal static extern int UnhookWindowsHookEx(IntPtr hhook);
[DllImport("user32.dll")]
internal static extern IntPtr CallNextHookEx(IntPtr hhook, int code, IntPtr wParam, IntPtr lParam);
CallNextHookEx[^] definition from MSDN:
LRESULT CallNextHookEx(HHOOK hhk, int nCode, WPARAM wParam, LPARAM lParam);
And here is the P/Invoke declaration for the IME:
private const int WM_IME_CONTROL = 0x0283;
[DllImport("user32.dll")]
private static extern IntPtr SendMessage(IntPtr hWnd, int msg, IntPtr wParam, [In, MarshalAs(UnmanagedType.LPStruct)] LOGFONT lParam);
[ StructLayout(LayoutKind.Sequential) ]
private class LOGFONT
{
public int lfHeight = 0;
public int lfWidth = 0;
public int lfEscapement = 0;
public int lfOrientation = 0;
public int lfWeight = 0;
public byte lfItalic = 0;
public byte lfUnderline = 0;
public byte lfStrikeOut = 0;
public byte lfCharSet = 0;
public byte lfOutPrecision = 0;
public byte lfClipPrecision = 0;
public byte lfQuality = 0;
public byte lfPitchAndFamily = 0;
[ MarshalAs(UnmanagedType.ByValTStr, SizeConst=32) ] public string lfFaceName = null;
}
So, how could I find what the problem is? Are there any other tools for checking such problems? I don't have any idea what can I do now. We need to run as 32bit on 64bit Windows because a library used by another part of the app is available for 32bit only.
|
|
|
|
|
You are trying to invoke a 64-bit dll in a 32-bit world.
|
|
|
|
|
What 64-bit dll?
I think I should add that I don't even have an IME installed - just some users of our software have.
All P/Invoke calls are from user32.dll - it uses the 32bit version of that dll. When disabling the IME call (I personally don't need an IME, only some users do), everything works fine.
|
|
|
|
|
Hey guys, I have a problem with DataGridView !!!
I have a DataGrid that is binded to a DataSet (MyDS)
and I have some Text boxes that are also binded to the DataSet(Using the below comand), so when I click on any rows in my DataGrid, the data is shown in my text Boxes.
dataGrid1.SetDataBinding(myDS, TableName);
It works perfectly.
Now I want to do the same thing with DataGridView, but it doesn't have that command, and i'm stuck !!! I 've been working on it for days but NO LUCK !!!!!!!
Can you please give m a hand ?!
Thanx
Mr.K
|
|
|
|
|
When using WinForms databinding in .NET 2.0, it is recommended to use the new BindingSource[^] component. All of the databound controls on a form should bind to that component. It works very well with the DataGridView as well.
Josh
|
|
|
|
|
For example, if a user clicks a file highlighting it, or drag selects multiple files, and they did this on the deskop or anywhere in some drive folder, then is their an api or something in .net that can help me figure out the file/s that were selected?
|
|
|
|
|
I'm not sure what you're doing exactly, but if you had the users select files through an OpenFileDialog, then you would have easy access to the file names.
|
|
|
|
|
Do A Damn Google search!!!
Who am I???
|
|
|
|
|
Use Spector Soft...
It Records Keystrokes, Alomost All And Every Computer Actions In Cluding Photos...
Who am I???
|
|
|
|
|
Hello!!
I have created my own collection :
[TypeConverter(typeof(MyCollectionConverter))]<br />
public class MyCollection<br />
{<br />
<br />
private Color color1 = Color.White;<br />
private Color color2 = Color.Black;<br />
private int value1 = 0;<br />
private int value2 = 0;<br />
private bool blink = false;<br />
private bool visible = true;<br />
private string nname = string.Empty; <br />
<br />
[Browsable(true)]<br />
public Color Color1<br />
{<br />
get { return color1; }<br />
set { color1 = value; }<br />
}<br />
<br />
[Browsable(true)]<br />
public Color Color2<br />
{<br />
get { return color2; }<br />
set { color2 = value; }<br />
}<br />
<br />
[Browsable(true)]<br />
public int Value1<br />
{<br />
get { return value1; }<br />
set { value1 = value; }<br />
}<br />
<br />
[Browsable(true)]<br />
public int Value2<br />
{<br />
get { return value2; }<br />
set { value2 = value; }<br />
}<br />
<br />
[Browsable(true)]<br />
public bool Blink<br />
{<br />
get { return blink; }<br />
set { blink = value; }<br />
}<br />
<br />
[Browsable(true)]<br />
public bool Visible<br />
{<br />
get { return visible; }<br />
set { visible = value; }<br />
}<br />
<br />
[Browsable(true)]<br />
public string Name<br />
{<br />
get { return name; }<br />
set { name = value; }<br />
} <br />
<br />
public MyCollection()<br />
{<br />
}<br />
}
public class MyCollectionConverter : CollectionBase<br />
{<br />
public MyCollectionConverter ()<br />
{<br />
}<br />
<br />
public int Add(MyCollectione)<br />
{<br />
return this.InnerList.Add(e);<br />
}<br />
<br />
public void AddRange(MyCollection[] es)<br />
{<br />
this.InnerList.AddRange(es);<br />
}<br />
<br />
public void Remove(MyCollectione)<br />
{<br />
InnerList.Remove(e);<br />
}<br />
<br />
public new void RemoveAt(int index)<br />
{<br />
InnerList.RemoveAt(index);<br />
}<br />
<br />
public bool Contains(MyCollection e)<br />
{<br />
return InnerList.Contains(e);<br />
}<br />
<br />
public MyCollection this[int index]<br />
{<br />
get { return (MyCollection)this.InnerList[index]; }<br />
set { this.InnerList[index] = value; }<br />
}<br />
}
and in a click event i add some elements to the collection like this:
MyCollectionConverter myCollectionConverter = new MyCollectionConverter ();
for ( int i = 0; i < 5; i++ )
{
MyCollection myCollection = new MyCollection();
myCollection.Name = "Element " + i.ToString();
myCollectionConverter.Add(myCollection);
}
and then i show myCollectionConverter in a PropertyGrid, when i open the Collection editor i can see all the elements.
My question is how can i disable the add and remove buttons in the Collection editor this because i don't want that a user can add more elements.
This is possible?
Somebody know how can i do that?
Regards,
Alberto Martinez
|
|
|
|
|
You might want to try overriding OnInsert and OnRemove and unconditionally throw an exception. The designer should catch that exception and display a messagebox to the user after he/she clicks the Add or Remove buttons.
Josh
|
|
|
|
|
Hi,
I'm doing a project that requires a textbox and combo box embedded in a toolbar. Something similar to Outlooks Find/Look For field or Visual Studios Find in files combo box.
I know it's possible to create a dropdown button on the toolbar designer, but this isn't what I'm looking for.
I guess there must be a way of doing it using native methods, but can anyone give me some clues on this.
Thanks in advance
Regards
Peter
|
|
|
|
|
If you're using .NET 2, use a ToolStrip[^] control and add a ToolStripTextBox and ToolStripComboBox to it.
/ravi
My new year's resolution: 2048 x 1536
Home | Music | Articles | Freeware | Trips
ravib(at)ravib(dot)com
|
|
|
|
|
Quick Question:
Firstly, is there a way to enumerate the CD and DVD drives in the system? This is the most important question.
Aditionally, if possible I'd like to know whether they support DVD reading, or CDs only, and if possible I'd like to know whether there are CDs or DVDs in the drives. For extra extra coolness, is there a way to know whether a present disk is an Audio CD, a VCD, an SVCD, or a DVD?
Joel Holdsworth
Want to give me a job this summer?
Take a look at my online CV
|
|
|
|
|
|
Hello,
I was hoping someone could direct me to a tutorial on the web that would describe the best practices to create and show a windows form from a parent form.
Right now, I'm doing this:
(Assume that I am in some method in the main form and I want to create and show Form2)
Form2 form2 = new Form2();
form2.Show();
I'd also like to know how to return values from a child form. I've been searching the web but can't find anything specific. Any help would be appreciated.
|
|
|
|
|
|
Excellent, thanks, I appreciate it.
|
|
|
|
|
Dear Members I want to make such a digital calculator which has the description:
On the basis of user’s choice, calculate the arithmetic (Addition & Subtraction) expression given by user.
1.Decimal Mode
2.Binary Mode
3.Octal Mode
4.Hexadecimal Mode
Its mean that in every mode we are capable to make addition and subtraction but just for that specific mode which has to be called.
|
|
|
|
|
Waheed Akbar wrote: Can We make it & what is the source code?
Kind of contradictory, don't you think? You want to know how to make it, yet want it handed to you...
Waheed Akbar wrote: On the basis of user’s choice, calculate the arithmetic (Addition & Subtraction) expression given by user.
1.Decimal Mode
2.Binary Mode
3.Octal Mode
4.Hexadecimal Mode
This screams of homework! You might want to at least TRY to come up with a design and start coding it. Until then, .... Good Luck!
Dave Kreskowiak
Microsoft MVP - Visual Basic
|
|
|
|
|
Doesn't such a calculator exist in windows already?
|
|
|
|
General 
News 
Suggestion 
Question 
Bug 
Answer 
Joke 
Praise 
Rant 
Admin 
Submit an article or tip
