C# Discussion Boards - CodeProject

Re: Creating a Combo box that is active but can't be typed into

shaunAustin12-Jun-03 5:21

shaunAustin

12-Jun-03 5:21

myComboBox.DropDownStyle = ComboBoxStyle.DropDownList;

RTFMSDN *joking*

Big Grin | :-D

Shaun

[edit: I have posted the answer anyway as I had already started before you posted your second message]

-----------------------------------------------------------------------
Shaun Austin: .NET Specialist. Spreading the word of .NET to the world... well the UK... well my tiny corner of it!! Big Grin | :-D

Re: Creating a Combo box that is active but can't be typed into

kevinrc12-Jun-03 5:24

kevinrc

12-Jun-03 5:24

yah, I found it pretty much right after I clicked the submit button on the question.. 10 lashes with a wet noodle shall be my punishment for asking before thoroughly looking..

Thanks!

Re: Creating a Combo box that is active but can't be typed into

Anonymous13-Jun-03 1:54

Anonymous

13-Jun-03 1:54

its default property dont u know it

Linking combo box to list box

totig12-Jun-03 3:31

totig

12-Jun-03 3:31

How would you link a combo box to a list box. I have a table of products, and a table of categories, and these are linked the standard way. My combo box has a dropdown of the categories. I want the listbox to be populated with all items that have the same category as the one selected.

Any ideas?

Re: Linking combo box to list box

kevinrc12-Jun-03 5:07

kevinrc

12-Jun-03 5:07

I would just attach a listener to the Combo box that calls a function that can populate the listbox with the correct items based on the selected index or item. Is this what you were looking for, or do you need some more detail?

Re: Linking combo box to list box

totig12-Jun-03 5:49

totig

12-Jun-03 5:49

A bit more detail if that would be possible.

Re: Linking combo box to list box

kevinrc12-Jun-03 6:40

kevinrc

12-Jun-03 6:40

ok, this is just off the top of my head but it should be close enough to get you going.

myCombo.SelectionChanged += new System.EventHandler(this.SelectionChanged);

private void SelectionChanged(object sender, System.EventArgs e) {
switch(((ComboBox)sender).SelectedIndex) {
case 1: //populate listbox for index 1
break;
case ..
}
}

This should get you going..

Good Luck,
-=- Kevin

Datagrid data entry problem in WinForm

Chris#12-Jun-03 3:31

Chris#

12-Jun-03 3:31

In a number column in Datagrid, I want to enter a negative number by using the NumPad "-" key. It does not work at all, but if I use "-" key in number row in the main key board, it works fine. After a further research, it seems that NumbPad "-" or "+" key does not fire a key_down or key_press event,(means no way to capture these two keys). Anyone knows how to solve it?

Re: Yes, the NumLock light is on

Chris#12-Jun-03 5:25

Chris#

12-Jun-03 5:25

other keys are all working except "-" and "+".

Re: Datagrid data entry problem in WinForm

A.Wegierski12-Jun-03 19:50

A.Wegierski

12-Jun-03 19:50

See:
protected override bool ProcessKeyPreview(ref Message m)
protected override bool ProcessDialogKey(Keys keyData)
or other methods with Key in names.

Hi,
AW

Databinder question

Peter Cresswell12-Jun-03 2:36

Peter Cresswell

12-Jun-03 2:36

Hi,

Should I be able to bind to a sub-property of a DataItem in a data grid?
i.e:

<br />
<%# DataBinder.Eval(Container.DataItem, "Product.Title") %><br />

It doesn't work for me. I get this message:

<br />
Exception Details: System.Web.HttpException: DataBinder.Eval:<br />
'POM.ProductDetails' does not contain a property with the name Title.<br />

But POM.ProductDetails does contain a Title Property!

The only way I can get it to work is to use a helper i.e.:

<br />
public string GetProductTitle(object Product)<br />
{<br />
     POM.ProductDetails product = (POM.ProductDetails)Product;<br />
     return product.Title;<br />
}<br />

This seems to be a very long way of doing it, especially if I have to do it
for every property!

Any ideas?

Memory leak woes.

EvilDingo12-Jun-03 2:28

EvilDingo

12-Jun-03 2:28

Hey everyone,

I'm still chugging away on my little game. Right now you can connect to a server and play across the internet. The 'game' works, but I'm having some serious issues with memory leaks.

I don't know when I should implement the IDisposable interface. Even when I implement it, it doesn't seem to make any difference at all. It seems the source of my problem are arrays and their values.

For example: I had an array of bullets. Whenever one bullet was spent and no longer being used, I would just simply call: bulletArray[i] = new Bullet(); and replace the old version of the object with a new one. This caused a very unwelcome memory leak that took me hours to track down. I thought I could just overwrite the old object but it turns out the system holds on to it indefinitely.

My next problem. I've recently started using ArrayLists. Whenever something was no longer needed, I would .Remove(ObjectNoLongerNeeded). Wouldn't removing the object also set it up for garbage collection? It doesn't seem to. What do I need to do to get rid of the old object and reclaim the memory?

This is my first C# program and the first time using a OO language. It's wonderful to see my program working, but whenever anyone shoots while connected their program's memory requirement permanently increases. Whenever anyone explodes, memory requirement goes up. I know this has to do with my arrays, but damn, there are so many of them. How can I get around this?

If I have a class called MyClass() that implements IDisposable, what do I need in the Dispose function to actually 'dispose' it? How do you dispose integers, floats, and other primatives?

Thanks,
EvilDingo

Re: Memory leak woes.

Philip Fitzsimons12-Jun-03 3:34

Philip Fitzsimons

12-Jun-03 3:34

hmm, I know its a silly question but are you actually calling GC.Collect ?

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemGCClassCollectTopic.asp[^]

"When the only tool you have is a hammer, a sore thumb you will have."

Re: Memory leak woes.

CBoland12-Jun-03 6:35

CBoland

12-Jun-03 6:35

Interesting problem. You only need to implement IDisposable if you have either unmanaged resources (i.e. window or other object handles from the OS) or scarce managed resources (i.e. database connections). All other managed classes, including arrays, should be collected by GC periodically.

In fact, implementing IDisposable imposes a small performance penalty when it comes to garbage collection. Not that you should never do it, but only do it when necessary.

I have heard of other situations like this. I don't know if it was a problem with the Framework or simply sloppy programming. You may look into using structures instead of classes, if your classes are very simple and contain mostly primitives. Structures can have constructors, properties and methods. They are like light-weight objects, but are created on the stack instead of the heap.

HTH

Re: Memory leak woes.

totig12-Jun-03 22:17

totig

12-Jun-03 22:17

Hi
I know this does not answer your question, but I hope you know about the problems with ArrayLists. If you dont know these problems, these are what they are. Once you have set up an array to hold a certain number of items, it works fine. When you start increasing the size dynamically, speed drops bigtime, especially if you have large arrays or lots of them. The way it works, is if it can store 10 ints, and you add another 1, it will make a new array, and copy all the items into it, and hopefully delete the old one.

Creating an instance of type using string litteral

Venkatraman11-Jun-03 23:42

Venkatraman

11-Jun-03 23:42

Hey,

I have read this before it is possible to create an instance of a type
by specifying their string literal equivalent.

for example if i need to create an instance of Employee class

generally i will say Employee objEmployee = new Employee();

my question is i just know that the class which i need to instantiate is "Employee" how will i instantiate using the string "Employee"

hope i did not made the simple ques more complex.

Cheers,
Venkatraman Kalyanam
Chennai - India

"Being Excellent is not a skill, it is an attitude"

Reality is an illusion caused by caffeine deficiency(one Microsoft Research scholor)

Re: Creating an instance of type using string litteral

Rocky Moore12-Jun-03 0:05

Rocky Moore

12-Jun-03 0:05

Check out AppDomain.CreateInstance and AppDomain.CreateInstanceFrom

Rocky Moore <><

Re: Creating an instance of type using string litteral

shaunAustin12-Jun-03 0:12

shaunAustin

12-Jun-03 0:12

You can instantiate a class using a "partial" name... i.e. the type name as a string literal, one way is...

<br />
string path = "MyApp.MyAssembly"; // assembly name<br />
string class = "MyClass"; // class in the assembly <br />
<br />
object MyObj = Assembly.Load(path).CreateInstance(class);<br />

This is most useful when your class implements a known interface but you want to dynamically load the implementation because you can do the following.

<br />
IFooBar fooBar = Assembly.Load(path).CreateInstance(class) as IFooBar<br />

This stuff is my favourite thing about .net... Big Grin | :-D

HTH

Shaun Big Grin | :-D

-----------------------------------------------------------------------
Shaun Austin: .NET Specialist. Spreading the word of .NET to the world... well the UK... well my tiny corner of it!! Big Grin | :-D

Re: Creating an instance of type using string litteral

Venkatraman12-Jun-03 0:38

Venkatraman

12-Jun-03 0:38

thanks for your info

Cheers,
Venkatraman Kalyanam
Chennai - India

"Being Excellent is not a skill, it is an attitude"

Reality is an illusion caused by caffeine deficiency(one Microsoft Research scholor)

Re: Creating an instance of type using string litteral

Kannan Kalyanaraman12-Jun-03 0:12

Kannan Kalyanaraman

12-Jun-03 0:12

Venkat,

Have a look at CreateInstance and CreateInstanceAndUnwrap method, I think you can also do this using other reflection techniques.

Cheers,
Kannan

Re: Creating an instance of type using string litteral

Venkatraman12-Jun-03 0:19

Venkatraman

12-Jun-03 0:19

Re: Creating an instance of type using string litteral

CBoland12-Jun-03 6:43

CBoland

12-Jun-03 6:43

You could also use Activator.CreateInstance. This is much simpler that using AppDomain.CreateInstance, especially if the "Employee" class is in the same assembly. It also returns an Object instance instead of an ObjectHandle.

About loading an image from resource...

Weiye Chen11-Jun-03 23:22

Weiye Chen

11-Jun-03 23:22

How do i load an image from resource?? I found 2 ways :

1) Using class Bitmap's constructor as shown below

public Bitmap(
   Type type,
   string resource
);

What should i put for the type parameter?

2) Using class Bitmap's FromResource(...) method as show below

public static Bitmap FromResource(
   IntPtr hinstance,
   string bitmapName
);

How do i get the instance of my application?

Weiye, Chen
When pursuing your dreams, don't forget to enjoy your life...

Re: About loading an image from resource...

Rocky Moore11-Jun-03 23:52

Rocky Moore

11-Jun-03 23:52

I have simply used:

new Bitmap(this.GetType().Assembly.GetManifestResourceStream("MyNameSpace.MyBitmap"));

Rocky Moore <><

'System.ObjectDisposedException'

dratti11-Jun-03 19:13

dratti

11-Jun-03 19:13

Sorry for another question, but Im stumped on this: Im getting the following exception when I close my application:

An unhandled exception of type 'System.ObjectDisposedException' occurred in system.windows.forms.dll

Additional information: Cannot access a disposed object named "MainForm".

MainForm is the name of...my main form. It sounds like my main form is getting disposed for it actually should, but Im not explicitliy disposing it anywhere, and really dont have any idea where to look. Any ideas, or at least where to start?

Thanks

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