Visual Basic

Re: What would you think if a property has value inside a class but inside a form?

15-Feb-09 4:56

Hi,

I am experiencing a strange proplem which is a property doesn't return a value when I try to use the class explicitly as shown below. I have checked to make sure if property has a value inside a class and the anawer was yes. However when try to use MetaData class inside the form Artist name returns nothing. Where do I make mistake?

Any Idea?

<br />
'FORM<br />
<br />
MetaDataFactory.GetMetaData ("FileNameGoesHere")<br />
<br />
Dim XData as New MetaData<br />
<br />
Artist = XData.Artist 'Doesn't return the value.<br />
<br />
'----------------------------------------------------------<br />
'SUB CLASS USES AN INTERFACE<br />
<Serializable()> _<br />
Public Class MetaData<br />
    Implements IMetaData<br />
<br />
Private _Artist as String = Nothing<br />
<br />
    Public Property Artist() As String Implements IMetaData.Artist<br />
        Get<br />
            Return _Artist<br />
        End Get<br />
        Set(ByVal value As String)<br />
            _Artist = value<br />
        End Set<br />
    End Property<br />
<br />
Public Interface IMetaData<br />
    Property Artist() As String<br />
End interface<br />
<br />
'-----------------------------------------------------------------------------<br />
'METADATAFACTORY CLASS<br />
Public Class MetaDataFactory<br />
    Public Shared Function GetMetaData(ByVal filename As String) As MetaData<br />
    Dim XX as new MetaData<br />
        xx.Artist = "BOB MARLEY"<br />
End Function   <br />
End Class<br />
<br />
<br />
<br />

What a curious mind needs to discover knowledge is noting else than a pin-hole.

modified on Sunday, February 15, 2009 11:30 AM

riced15-Feb-09 5:26

Re: What would you think if a property has value inside a class but inside a form?

15-Feb-09 5:26

Why would it have a value when the GetMetaData() function is not called by this code:

Dim XData as New MetaData

Artist = XData.Artist 'Doesn't return the value.

Another thing is that GetMetaData needs to return xx i.e. a MetaData object.

Regards
David R

JUNEYT15-Feb-09 5:31

Re: What would you think if a property has value inside a class but inside a form?

15-Feb-09 5:31

Sorry I forgot to type it. Just assume that it is there. It is still not functioning.

What a curious mind needs to discover knowledge is noting else than a pin-hole.

riced15-Feb-09 5:43

Re: What would you think if a property has value inside a class but inside a form?

15-Feb-09 5:43

Try this where the changes are in bold:

Dim XData as New MetaData
XData = MetaDataFactory.GetMetaData ("FileNameGoesHere")
Artist = XData.Artist 'Doesn't return the value.

....

Public Class MetaDataFactory
   Public Shared Function GetMetaData(ByVal filename As String) As MetaData
      Dim XX as new MetaData
      xx.Artist = "BOB MARLEY"
      GetMetaData = xx
   End Function
End Class

Regards
David R

Guffa15-Feb-09 12:34

Guffa

15-Feb-09 12:34

JUNEYT wrote:
Sorry I forgot to type it. Just assume that it is there. It is still not functioning.

Paste the actual code that you are using. It's very hard to find the error in the code that you are using by looking at some other code that you are not using...

Despite everything, the person most likely to be fooling you next is yourself.

Re: What would you think if a property has value inside a class but inside a form?

Guffa15-Feb-09 12:25

Guffa

15-Feb-09 12:25

In the GetMetaData method you create an instance of the MetaData class, put some data in it and throw away the instance.

Then you create a new instance of the MetaData class, and you expect it to contain the data that was in the instance that you threw away.

Do you see the problem?

Despite everything, the person most likely to be fooling you next is yourself.

How could a function read any type of variable's value and return it as a string?

JUNEYT15-Feb-09 2:02

Re: How could a function read any type of variable's value and return it as a string?

15-Feb-09 2:02

Hi,

I have passed several types of variables as (Byte,String,int32 and etc.) into a function. The my aim is to get the value of passed variable and check to see if it is null or not. If it is null, The function should return "Undefined" as a string. If it is not, it should assign the variable's original value to function.

I have no idea how to run the function for several types of variable and get their value and assign it to the function. The vb.net is no longer supporting variants.

Thanks.

What a curious mind needs to discover knowledge is noting else than a pin-hole.

riced15-Feb-09 3:09

Re: How could a function read any type of variable's value and return it as a string?

15-Feb-09 3:09

I'm assuming that there is only one function with one parameter.
Make the function's parameter an object. Then in the function use a series of if statements with typeof...is operator.
The function would have to return an object since you don't know whether it is a string or other type.
It's not pure OO but would do the job. Some sample of your code would help to get a better answer.

Regards
David R

Eddy Vluggen15-Feb-09 3:37

Eddy Vluggen

15-Feb-09 3:37

Public Function ToStringStuff(ByVal someNumber As Nullable(Of Integer))
    If (someNumber.HasValue) Then
        Return someNumber.ToString()
    Else
        Return "Undefined"
    End If
End Function

Public Function ToStringStuff(ByVal someBool As Nullable(Of Boolean))
    If (someBool.HasValue) Then
        Return someBool.ToString()
    Else
        Return "Undefined"
    End If
End Function

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Dim a As Nullable(Of Integer) = Nothing
    TextBox1.Text = ToStringStuff(a)
End Sub

Something like this?

I are troll Smile | :)

Re: How could a function read any type of variable's value and return it as a string?

riced15-Feb-09 4:37

Re: How could a function read any type of variable's value and return it as a string?

15-Feb-09 4:37

Better answer than my off-the-top-of-the-head reply.

Regards
David R

JUNEYT15-Feb-09 7:22

Re: How could a function read any type of variable's value and return it as a string?

15-Feb-09 7:22

Thank you so much! Fantastic sample. Smile | :)

What a curious mind needs to discover knowledge is noting else than a pin-hole.

Eddy Vluggen15-Feb-09 7:49

Eddy Vluggen

15-Feb-09 7:49

You're welcome Smile | :)

I are troll Smile | :)

KeyDown Event keeps firing

Zaegra14-Feb-09 23:25

Zaegra

14-Feb-09 23:25

Hey,

I have some problems with the KeyDown event. When a user keeps a key pressed, the KeyDown event keeps being fired. I don't want this to happen, I just want to trap it once so I know that the key is pressed. I use the KeyUp event to check if the key is released.

Can somebody help me out on this one? Wink | ;)

Zaegra

Motivation is the key to software development.

Wendelius15-Feb-09 0:57

Wendelius

15-Feb-09 0:57

Could you add a boolean flag and set it to true in key down and to false in key up. If the flag is true, ignore the event. Something like this in keydown:

if (keydown = false) then
   keydown = true
   ... your other code ...
end if

and in keyup

keydown = false

The need to optimize rises from a bad design.My articles[^]

riced15-Feb-09 0:59

15-Feb-09 0:59

You can't stop the event being fired.
What you could do is declare a boolean variable, e.g. keyIsDown, and set it to true in the KeyDown handler and false in the KeyUp handler. The variable would then be used to control whatever you're doing in the handlers.

Without knowing exactly what you are rying to do I can't suggest anything else.

Regards
David R

Zaegra15-Feb-09 2:23

Zaegra

15-Feb-09 2:23

Well, I'd like to trap Key Combinations like Alt+F4 etcetera but I can't find a way to do this, because the event keeps being fired, so I get 20x Shift and 1x F4 D'Oh! | :doh:

Any suggestions on how to trap Key Combinations? OMG | :OMG:

Motivation is the key to software development.

riced15-Feb-09 2:48

15-Feb-09 2:48

I'm a bit hazy on this since I've not used Key events for some years.
But here's my suggestion.
When KeyDown fires store the key code in a variable (as well as setting keyIsDown flag).
When the event fires again, if the current key code is same as previous just ignore it. When the code changes do whatever you have to.

One thing that stopped me using key events is that generally I wouldn't want to change the behavior of standard key combinations like Alt=F4.

Regards
David R

Eddy Vluggen15-Feb-09 3:27

Eddy Vluggen

15-Feb-09 3:27

Are you checking them both at the same time, or one after another? The event gets fired alot, but firing an event doesn't eat away too much CPU-time. If you only need the combination of the keys, then try this;

VB.NET

Private Sub TextBox1_KeyDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox1.KeyDown
    If (e.KeyCode = Keys.F4 And e.Shift) Then
        MessageBox.Show("Hit it, Sam!")
    End If
End Sub

I are troll Smile | :)

Luc Pattyn15-Feb-09 9:56

Luc Pattyn

15-Feb-09 9:56

Hi,

don't try anything that adds state variables (such as a KeyIsDown variable) since that is bound to fail under special circumstances (e.g. when the app looses focus in between a key going down and up again, the state variable will be incorrect on the next KeyDown, which then won't get processed since KeyIsDown is still true...)

You don't need to track the modifier keys (ALT, CTRL, SHIFT) at all, the system does that for you: you can get their immediate value at all times; in particular there is Control.ModifierKeys which always reflects the current situation; but there is even better: each KeyDown event has a KeyEventArgs which holds properties Alt, Control, Shift.

So simply check the key is F4 and Alt is true.

Smile | :)

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