oleDbDataAdapter and dataSet - C# Discussion Boards

Re: How to use SortedList.Item Property

5-Apr-04 17:42

If you look at the documentation for the Items property, it says that it's the indexer in C# (the same as other lists' Items properties). This means you use it like this:

myList[key] = value;
value = myList[key];

You can use a key because a SortedList implement IDictionary, an interface for key/value collections. Mosts lists in the .NET FCL simply take an index (0-based, as with all .NET languages) in their indexer.

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Member 9576656-Apr-04 5:57

Member 957665

6-Apr-04 5:57

Thanks for your reply. I am new to .Net. Trying to understand these properties. DO I have to override this property.

I am doing like this, but it doesn't work. In my Sorted list keys are of type string and value is of type int.

public override int Item(string myKey)
{
get
{
return mySrotedList[myKey];

}
set
{
mySortedList[myKey] = value;

}

}

Thanks for your help and time.

Raj

Re: How to use SortedList.Item Property

Heath Stewart6-Apr-04 6:07

SuspendLayout() - Does this work?

6-Apr-04 6:07

Why are you trying to override this? If you're just using a SortedList, you just use it like the code example I gave. If you do want to extend a class, you only have to override abstract methods, and override other methods and properties as you need to. In this case, though, it's seems like you don't need to.

Besides, when you declare an indexer for a class in C#, you use the following syntax:

public object this[int index]
{
  get { return internalList[index]; }
  set { internalList[index] = value; }
}

Read the .NET Framework SDK for more information, especially since your new. Specifically, see the Visual C# Language[^] topic.

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Tristan Rhodes5-Apr-04 13:56

Tristan Rhodes

5-Apr-04 13:56

I've played around with suspendlayout.

I believe it's there to stop changes to layout being applied before you have done all the changes that you need.

However, i've used the two following pieces of code, and they produce dramaticaly different effects in terms of rendering:

Code one: Low Flicker, Pretty neat solution

<br />
			//Apply Changes<br />
			this.SuspendLayout();<br />
			this.Size = new Size(newWidth,newHeight);<br />
			this.Location = new Point(newXLoc, newYLoc);	<br />
		this.ResumeLayout(true);

Code two: High Flicker, massive jerking to either side of resize points.

<br />
			//Apply Changes<br />
			this.SuspendLayout();<br />
			this.Location = new Point(newXLoc, newYLoc);<br />
			this.Size = new Size(newWidth,newHeight);	<br />
		this.ResumeLayout(true);

Any ideas why this is if they are only applied after ResumeLayout is run?

Cata

Re: SuspendLayout() - Does this work?

Heath Stewart5-Apr-04 17:37

Re: SuspendLayout() - Does this work?

5-Apr-04 17:37

Read the documentation for SuspendLayout and ResumeLayout if you're wondering what they do. It pretty much states what you already suspect. If you have the documentation installed locally for VS.NET (and any decent developer should), it's a heck of a lot quicker than waiting for a reply.

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Tristan Rhodes5-Apr-04 22:32

Tristan Rhodes

5-Apr-04 22:32

I know what it does, but I was wondering why it displayed different behavior depending on layout if it was executed at the same time.
All i did was switch the two middle lines around, and it looks hideous.

oleDbDataAdapter and dataSet

DougW485-Apr-04 13:10

DougW48

5-Apr-04 13:10

I've got a C# application that connects to a database, and does various things with it. My question is this: When designing an application that uses a database, what is the best programming practices to ensure speed and reliability? Should I have just one dataset with many adapters, or multiple datasets and multiple adapters? Will having many adapters cause my form to take longer to load? I'm able to use these things fine, but I don't want an inefficient application in case I am doing something wrong. Thanks..

Also, I notice that if I set the source of a comboBox to a column in a table, that the comboBox takes the liberty of setting the text to the first item in that column. I've tried various things, like setting the comboBox.Text = "", or setting the selectedItem to -1. So far nothing has seemed to work...I want the comboBox text to start out empty...any suggestions? Big Grin | :-D

Re: oleDbDataAdapter and dataSet

Heath Stewart5-Apr-04 17:29

Re: oleDbDataAdapter and dataSet

5-Apr-04 17:29

The time to initialize a DataAdapter is negligible compared to the time to execute its Fill or Update methods which opens the connection and executes the appropriate commands based on the DiffGram (DataSet which change-tracking information). Set up your DataAdapters either upon initialization or use a provider pattern that initializes them only when needed (leaving the instances alive for future use).

Also, it's good to use typed DataSets. Typed columns refer to the columns in your tables directly, where referring to them by index - or worse, by name - requires several lookups. You can create typed DataSets in VS.NET by adding a new DataSet class to your project (Add->Add New Item) or using xsd.exe. The Solution Explorer can also help if you create a new DataSet class and drag-n-drop tables, views, or stored procs from a database connection to your design surface.

Finally, you really should read about the <cdoe>ComboBox.Text property. For one, it's only effective in some cases depending upon the value assigned to ComboBox.DropDownStyle. If you want to insert an empty element, after setting the DataSource property call Items.Insert(0, ""); or something similar. Take care, however, since this screw up your data binding (by inserting a null/empty column in your tables, which may violate a key constraint).

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MeterMan5-Apr-04 23:14

MeterMan

5-Apr-04 23:14

Doug:
I had the same problem with this in my program as far the the combobox is concerned. What i did was the following after a search.

dataset.Movie.Clear(); //clear your dataset
oleDbDataAdapter1.Fill(dataset); //refill your dataset
if ( dataset.Movie.Count>0) // check to see if the dataset is empty
{
 comboBox1.Text=dataset.Movie[0].Title; // I have just titles in my combobox
}
else
{
 comboBox1.Text="Sorry Jack No Data is in the Database!";
 comboBox1.Enabled=false; // you can later enable it when you have data
}

Hope this helps ya

Win32newb
"Making windows programs worse than they already are"

assembly's dll extension

Anonymous5-Apr-04 11:09

Anonymous

5-Apr-04 11:09

I am using multiple projects and I am trying to add project refernece to another project and I get the following error message:

A reference to NDMUI could not be added. An assembly must have a "dll" extension in order to be referenced.

I have these AssemblyIfo.cs file and i tried to sign the assembly, but i didn't write the KeyFile atribute because i can't find the CPS that is installed on my machine. Could this be the problem??? Please help where you can.

Dave Kreskowiak5-Apr-04 11:25

Dave Kreskowiak

5-Apr-04 11:25

Just like it says... Are you trying to add a reference to an .EXE file? If yes, then it won't work. Signing it won't help the situation...

RageInTheMachine9532

Heath Stewart5-Apr-04 11:34

5-Apr-04 11:34

As I mentioned to someone the other day, you CAN reference a .EXE if you use the command-line compilers. VS.NET won't let you, but the C# command-line compiler (csc.exe) and the CLR itself, for that matter, will. Don't ask me why VS.NET won't then - I wonder that myself.

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Anonymous5-Apr-04 13:16

Anonymous

5-Apr-04 13:16

I tried to use the C# command-line compiler, but the error message is still there.....what i actually was to compile my NDMUI.cs file.....i'm wondering if that is what you suggested??

Heath Stewart5-Apr-04 17:18

5-Apr-04 17:18

Yeah, and what error message would that be? Do you tell your doctor that you have a pain and not tell him where?

You can reference a .EXE assembly using the /r switch just like you do a .DLL. I've done it before and there's nothing in the CIL specs that says you can't. A simple example:

csc.exe /t:exe /r:MyAsm.dll /r:MyApp.exe /out:Test.exe Test.cs

Type /? as the switch to csc.exe for more information. If you get an error - which you didn't mention what error - still in your .cs source file, then it's something else. The error message will explain the problem.

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CWIZO6-Apr-04 2:47

CWIZO

6-Apr-04 2:47

I may have got thsi wrong, but are you trying to refrence an uncompiled CS file?

Q:What does the derived class in C# tell to it's parent?
A:All your base are belong to us!

Heath Stewart6-Apr-04 2:52

Catch Windows KeyPress Events?

6-Apr-04 2:52

No, the command line is compiling the Test.cs file, referencing two assemblies, MyAsm.dll and MyApp.exe. See the documentation for csc.exe in the .NET Framework SDK or type csc.exe /? for more information.

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Verdant1235-Apr-04 9:32

Verdant123

5-Apr-04 9:32

is there anyway to get my C# winforms app to handle a keyboard keypress event in windows, whether or not the form is the active window?

i want to be able to detect caps lock, num lock and scroll lock presses without out polling the keyboard state

LongRange.Shooter5-Apr-04 9:43

LongRange.Shooter

5-Apr-04 9:43

You would not be able to do this at any form level. I would imagine you'd have to write a service and have it hook into the OS (if NT even allows that type of hook)

___________________
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Heath Stewart5-Apr-04 9:50

5-Apr-04 9:50

There are basically three types of hooks you can use. One is that you override WndProc and handle all messages sent to your form whether its active or not. In the case of keyboard events, your application must be active to recieve them (except when using the other two hooks to be mentioned...).

You can use an IMessageFilter along with Application.AddMessageFilter and Application.RemoveMessageFilter to add a message filter that applies to all windows (that includes controls) in your application so that you can handle keyboard events (or any other events) no matter which form is active.

Finally, there's system hooks. These should be used as little as often as they hook every message of a certain type in the OS. Inefficient or buggy code can degrade performance of the OS and all applications seriously, or even cause crashes if you don't handle errors correctly. You can find more information about using system hooks in C# by reading Using Hooks from C#[^].

In any case, you'll be using Windows messaging and catching notification messages like NM_KEYDOWN, which you can find the constants for in winuser.h in the Platform SDK. Experience with Windows messaging will be helpful.

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Verdant1235-Apr-04 10:27

Verdant123

5-Apr-04 10:27

many thanks

i think i will try the IMessageFilter interface method.

for now i guess i will leave it polling every few seconds

Heath Stewart5-Apr-04 10:43

5-Apr-04 10:43

Verdant123 wrote:
for now i guess i will leave it polling every few seconds

Confused | :confused:

Why are you polling? Every message posted to the message queue for your application is filtered through the IMessageFilter implementation you added to your application using Application.AddMessageFilter. There's no polling necessary. For example, lets say I want to write a message to the console every time a key is pressed anywhere in my application:

public class KeyboardFilter : IMessageFilter
{
  public bool PreFilterMessage(ref Message m)
  {
    if (m.Msg == 0x0100) // WM_KEYDOWN
      Console.WriteLine("Key down: " + m.WParam.ToString());
    return false;
  }
}

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