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Hi Everyone, I have an application that has at least two forms and a Class. how do I access variable between two forms without initializing all varialbes each time I access the class.
this is how I access functions form the Class
In Form1 I do this:
ClassA myClass = new ClassA();
myClass.Function_A();
// do something with it.
IN Form2
ClassA myClass2 = new ClassA();
myClass2.Function_B();
// do something with it.
how do i prevent ClassA funtions from reinitializing all over again. I want to treat the ClassA's funtions and variables like Global variable.
Thanks
"Show me the way I will get there"
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This [^]one is a nice example
Manas Bhardwaj
Please remember to rate helpful or unhelpful answers, it lets us and people reading the forums know if our answers are any good.
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You could add a constructor to the form class that accepts a parameter that is another copy of the form. Then, write a clone method that copies the data from the speficied instance into the form you're creating. IMHO, this is a silly approach to pretty much anything, but it will do what you want.
If you're actually just interested in keeping just one instance of the form around and using it whenever you want, hide it when you're done with it, and show it again when you need it.
.45 ACP - because shooting twice is just silly
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"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
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"The staggering layers of obscenity in your statement make it a work of art on so many levels." - J. Jystad, 2001
modified on Wednesday, June 9, 2010 9:03 AM
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Similar to John Simmons's answer, but let each form's constructor take a ClassA. Now, create the ClassA before creating either form, and pass it to the form before showing it. The important fact is that neither form 'owns' (or instantiates) the shared instance of ClassA, rather, some larger scope owns it and makes it available to both forms that want to use it.
An alternative to passing the ClassA into the constructor is to make a ClassA property on each form, and assign the property before showing the form. This is a very common pattern when presenting dialogs whose purpose is to modify data that is used elsewhere. Here's a snippet:
public void DoFormStuff(ClassA ca)
{
using (MyForm frm = new MyForm())
{
frm.ClassA = ca;
frm.ShowDialog(this);
}
}
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HI LookSharp, I am not sure how to use it exactly, let me try first then I will ask you later.
Thanks for your help.
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Hi - I'm implementing a data access layer in LINQ to SQL.
I have a DataContext MyDataContext which extends DataContext.
DataContext implements IDisposable.
However when I try to put MyDataContext in a using statement I get a compiler error:
'MyDataContext':type used in a using statement must be implicitly convertible to 'System.IDisposable'.
So is IDisposable not implicitly usable for derived classes or am I doing something wrong? Here is some sample code:
using (MyDataContext context = new MyDataContext())
{
//do some work
}
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If your class inherits from DataContext, you get IDisposable for free. Could you post your class definition here so that we can take a look at it?
"WPF has many lovers. It's a veritable porn star!" - Josh Smith As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.
My blog | My articles | MoXAML PowerToys | Onyx
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I have a class in which I have a property that returns an array of enums (which are declared in a class that is used by this class through a using statement).
When I use this class, I access the property through the indexer.
The enum and accessor look like:
enum State
{
Flashing,
Played,
NotPlayed
}
class1.balls[i] = State.Played;
Now, what I want to do is take action when the property is set through the indexer like in the example above. I want to know the value of the indexer (i) and what it is being set to.
All the internet examples I see use a separate class for this, but that doesn't make sense to me. I can't see how to make the separate class access things within the original class I have the public property in.
Thanks!
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The C# spec has this to say about indexers:
Indexer declarations are similar to property declarations, with the main differences being that indexers are nameless (the “name” used in the declaration is this, since this is being indexed) and that indexers include indexing parameters. The indexing parameters are provided between square brackets.
edit: page 60/553 of ECMA-334 4th edition (June 2006)
Which means that you can not declare an indexer with a name, you can only use indexers to write expressions of the form instance[parameter list]
To give it a name, you have to cheat - for example by having a field (with the wanted name, of course) of a type that has an indexer. Usually, that would be a field of an other type, which you created solely to be indexed. That type should, of course, have enough information to be indexed, but you could pass in the entire "parent" instance (edit: at the ctor, when you initialize that field).
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Arrays are way to simple a structure for what you are looking for. If you want events fired when items are added to the list, try inheriting from Collection<T> and implementing the events. e.g.[^]
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Or he could use an indexer, as he suggested.. must simpler and faster that way
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You do need a separate class to do what you want to do, and it needs to expose an event that the class that uses it must handle in order to respond to changes in ball states. Here's an example (compiles under VS2008):
namespace BallStateExample
{
enum State {Flashing, Played, NotPlayed}
delegate void BallStateChanged(BallStateChangedEventArgs e);
class BallStateChangedEventArgs
{
public int BallIndex { get; set; }
public State NewState { get; set; }
}
class Balls
{
private readonly State[] _balls;
public Balls(int numBalls)
{
_balls = new State[numBalls];
}
public event BallStateChanged BallStateChanged;
private void OnBallStateChanged(int index, State newState)
{
if (BallStateChanged != null)
BallStateChanged(new BallStateChangedEventArgs { BallIndex = index, NewState = newState });
}
public State this[int index]
{
get { return _balls[index]; }
set
{
_balls[index] = value;
OnBallStateChanged(index, value);
}
}
}
class BallUser
{
private const int NUM_BALLS = 42;
public BallUser()
{
Balls = new Balls(NUM_BALLS);
Balls.BallStateChanged += Balls_StateChanged;
}
private void Balls_StateChanged(BallStateChangedEventArgs e)
{
}
public Balls Balls { get; private set; }
}
}
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Hi,
In my form based C# app, I use one (of many) option of logging/writing program steps to a text box on the form. It works ok for a while and then starts to slow down as more and more data is passed to it. Is there a way to make this more efficient ?
Thanks in advance.
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It slows down because you've added a large amount of data to the String that it's showing you. Strings are immutable in .NET, so every time you add data to it, an entirely new string has to be created with the old data copied to it and the new data appended to the end.
The answer is simple. Don't use a TextBox. A common replacement for this particular use is a ListBox.
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Using a textbox should work, if done correctly. A new string need not be created each time text is appended to a textbox. As Luc said, you can use AppendText to add to a textbox. Textbox probably stores the text as an array of strings (elements are probably split on newline characters), and likely has special getters and setters for the Text property (e.g., if a line was added via AppendText, then add that to the string returned from Text when the getter is called).
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aspdotnetdev wrote: A new string need not be created each time text is appended to a textbox. As Luc said, you can use AppendText to add to a textbox
...which creates a new string... AppendText merely takes into account the current values of the Selection properties of the TextBox and replaces that text or appends text to that selection. In any case, the selected string is replaced or text is appended to the String, resulting in a new string being created and parsed when the control needs to render itself. The longer that string gets, the more time it takes to parse it and render what's visible.
aspdotnetdev wrote: Textbox probably stores the text as an array of strings
No, it doesn't. It uses a String field all the way back up it's inheritance chain.
aspdotnetdev wrote: and likely has special getters and setters for the Text property (e.g., if a line was added via AppendText, then add that to the string returned from Text when the getter is called).
Nope. If you open Reflector and lok for yourself, it's quite easy to see.
Here's the code for the Text property of the TextBox class:
Public Overrides Property [Text] As String
Get
Return MyBase.Text
End Get
Set(ByVal value As String)
MyBase.Text = value
Me.selectionSet = False
End Set
End Property
...and for AppendText (comes from TextBoxBase):
Public Sub AppendText(ByVal [text] As String)
If ([text].Length > 0) Then
Dim num As Integer
Dim num2 As Integer
Me.GetSelectionStartAndLength(num, num2)
Try
Dim endPosition As Integer = Me.GetEndPosition
Me.SelectInternal(endPosition, endPosition, endPosition)
Me.SelectedText = [text]
Finally
If ((MyBase.Width = 0) OrElse (MyBase.Height = 0)) Then
Me.Select(num, num2)
End If
End Try
End If
End Sub
There's nothing special in there.
As for WordWrap, that may or may not be a viable option depending on requirements. TextBox works with monolithic strings no matter what you do. ListBox works with an array of Objects and can handle much more of and more varied content than a TextBox can.
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Noooooo...... Argggghhhhhh; the horror. VB.NET in a C# forum..... Please Dave, change the reflector output target before you inadvertenly trigger the destruction of the universe.
"WPF has many lovers. It's a veritable porn star!" - Josh Smith As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.
My blog | My articles | MoXAML PowerToys | Onyx
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Sorry, that's the last setting I used... I'll be a little more careful with the "End of the World" next time. 
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Keep going down the chain. "MyBase.Text" is not a field... it's a property with its own logic. Also, I don't see any string concatenations in that AppendText function you posted.
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I haven't checked myself, I was told there is a native AppendText function, so one might expect that to be called. Now the real check would be to look at its instructions, i.e. how does it avoid concatenation and quadratic behavior?
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read formatted code with indentation, so please use PRE tags for code snippets.
I'm not participating in frackin' Q&A, so if you want my opinion, ask away in a real forum (or on my profile page).
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Luc Pattyn wrote: how does it avoid concatenation and quadratic behavior
Perhaps it maintains two data structures. An array where each element holds a line in the string, and a StringBuilder to hold the text that gets appended to Text (so, the only performance hit would be when the Text property is accessed and the StringBuilder has to be serialized to a string). The array of lines would be so the textbox can be painted quickly and the StringBuilder would be so concatenations wouldn't create a performance problem.
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In reality a StringBuilder too behaves quadratically, albeit at a lower frequency: its capacity grows by doubling its size and copying characters any time it is getting full, just like the internal arrays of Lists and other collections. So a number of strings get appended for free, then a new buffer twice the current capacity get allocated and all data copied, etc. Better than copying everything on every new line of text, but still quadratic.
While a ListBox is linear, except for the collection holding the references to the items, that too would double its capacity once in a while.
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read formatted code with indentation, so please use PRE tags for code snippets.
I'm not participating in frackin' Q&A, so if you want my opinion, ask away in a real forum (or on my profile page).
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I am well aware of the performance of StringBuilder. On average, there is only O(1) operation per string append. I would be willing to bet that ListBox has the same performance. I'm guessing it maintains a list internally to store the list of list box items. Lists have the same behavior as a StringBuilder (lists use an array that doubles when capacity is exceeded, just like StringBuilder does).
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StringBuilder.Append(string) [and TextBox.AppendText(string) as well] always copies the new characters, StringBuilder uses String.wstrcpy() to do so. OTOH ListBox.Items.Add(item) only copies a reference.
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read formatted code with indentation, so please use PRE tags for code snippets.
I'm not participating in frackin' Q&A, so if you want my opinion, ask away in a real forum (or on my profile page).
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It would still have to render that string, so it would still have to read it. It might have to perform less processing if the string was significantly longer than the viewable area, but that seems like a fringe case. Also, ListBox doesn't have the same features as a TextBox (e.g., the ability to copy all the text at once). I wouldn't base my decision on using TextBox/ListBox on performance... rather, I'd base it on the features of each.
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