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I have the following event declaration in a base class window form with a button btnNew
public void btnNew_Click(object sender, System.EventArgs e)
{
btnDelete.Text = "Deleteddy";
// btndelete is another button on the form
And the following event declaration derived class that inherits from the above base class window
new public void btnNew_Click(object sender, System.EventArgs e)
{
MessageBox.Show("Derived");
}
I am using the new modifier in the derived class to "hide" the behaviour in the base class. But when I click the btnNew, both events get fired.
Can anyone explain why ?
Thanks
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First, that's not an event. That's a handler, and these generally should not be public. Second, when you handle the event you use a delegate which is a managed function pointer to the method you passed. Using new would not solve this problem - it is a different method and has a different address. Instead, consider declaring the first method with virtual and using override in the second case. This uses the IL instruction callvirt, which is a polymorphic instruction.
Microsoft MVP, Visual C#
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Thank you very much.
I was under the impression that a virtual function can have no code in it. I modified the first method with virtual and used override in the second case. Now it does not execute the code in the base class but does the code in the derived handler twice.
Regards
Ganesh
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You might be thinking of abstract.
If your event handler is firing twice (presumably before you had one to the base and derived methods), it means you have both methods hooked up. If you attempt to add a handler to a method that is already attached to the event, it shouldn't add another one. However, when you add a handler to a virtual method the compiler actually follows the virtual chain to the last method, which would be your derived method. This would make it possible to add the same handler (in essence) twice. Make sure in your code you only add a handler for one (like your base class, if you're going for a good polymorphic design where derived class's event handlers are fired in lieu of the base class's.
Also, when you override a method or property, you can use the base keyword to refer to the base class's implementation, much like you use this to refer to your own implementation (even though using this with a virtual function will still use the IL callvirtu instruction to call overriding methods in derived classes.
Microsoft MVP, Visual C#
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Yes, thank you very much.
The windows designer had automatically added the
click event handler in the derived class. Once I commented that out, it is working like you described, that is the derived class handlers are fired in lieu of the base class's instead of cascading the two.
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I have 2 simple controls. How can I do so that one becomes a child control of another.
Before:
Control1
Control2
After:
Control1
--Control2
I tried just to change the parent property, but after doing that, the control (who's parent property I just changed) disappeared. I tried calling Show() method but resulted nothing. So what's the trick ?
Regards, Desmond
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On the would-be parent:
parent.Controls.Add(child); This sets the Parent property of the child, but there's more involved than simply that. Since Windows controls are backing these, the Windows handle must be recreated with the new parent Window handle.
Microsoft MVP, Visual C#
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Hi,
I just have a simple question about auto checking of input value on NumericUpDown control.
Normally, if we press enter key after entered value on UpDown Control, it will automatically check whether it is between its max & min Value, and it will also limit the value. But if we just enter a value, didn't press enter key, it won't auto check the value.
I know we can use Validating to solve this problem, but inside Validating method, we also will need to compare the value by ourselves, I just feel quite inconvenient if we have 10 or more updown control in a Form...
Is there any build-in method of updown control that we can use to check the value ??
Thanks
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Actually, both the Enter key behavior and validation work the same way - the control has to lose the focus (for validation) or the change has to be committed (by hitting the Enter key, which calls the set accessor of the Text property). See the documentation for the UpDownBase.UserEdit property in the .NET Framework SDK for a discussion of this behavior.
A good way to solve this would be to extend the NumericUpDown control and override either IsInputChar or IsInputKey, which are called with each key-down. Validate the entire number, though - not just the char or Keys that was passed to the method. Then change your code to instantiate this new control instead of the NumericUpDown. It's still a NumericUpDown control, though - you only extended it.
One other way is handle each NumericUpDown.KeyDown event (inherited from Control) with the same handler, in which case you could do something like this:
numericUpDown1.KeyDown += new KeyEventHandler(ValidateNumber);
numericUpDown2.KeyDown += new KeyEventHandler(ValidateNumber);
private void ValidateNumber(object sender, KeyEventArgs e)
{
NumericUpDown nud = sender as NumericUpDown;
if (nud != null)
{
int value = int.Parse(nud.Text);
if (value < nud.Minimum || value > nud.Maximum)
e.Handled = true;
}
}As the comment said, you should also take things into account like the NumericUpDown.ThousandsSeparator and the like. You can use Int32.Parse (or Int64.Parse) using the overload that uses the NumberFormatStyles as the second parameter. Do a bit-wise OR to construct the enum that you'll pass using the properties of the NumericUpDown control.
Microsoft MVP, Visual C#
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hm.... Thank you so much for your reply, Heath.
I just got an idea from your reply; instead of extenting the control, I would prefer using same handler for my UpdownControls. As I have 10 updowncontrols, so I assigned the same Validating handler for each of them.
private void UpDownValidating(object sender, System.ComponentModel.CancelEventArgs e)
{
NumericUpDown nud = sender as NumericUpDown;
if(nud != null)
{
if(nud.Value < nud.Minimum)
nud.Value = nud.Minimum;
if(nud.Value > nud.Maximum)
nud.Value = nud.Maximum;
}
}
but I don't know will it cause any hidden effect? I think this method is better and simpler for me..
One more question,
Do you know any article that teaching us to make own control library. The idea is I want to make my own controls in my home, so that sometimes they can be used in my project by just import the control library.
Thanks a lot~~
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Why would there be any "hidden side effect"? This is a perfectly reasonable solution, although I'd prefer encapsulation because it makes for a better OO design and doesn't force you to handle your events each time (which one could forget).
Developing a control library is trivial. In VS.NET, start a new Windows Control Library. Really, all this is is a DLL project, it just starts you off with a single control (with a bad name - so don't use it). Develop your controls and components deriving from the appropriate control and component classes. Don't forget to add decent designer support. There's a good, extensive section in MSDN that describes various base classes, attributes, and other design-time features that you should take into account for a good component library. See Developing Components[^].
Microsoft MVP, Visual C#
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Hi
I sent a solution for this problem to Ronboy in the message boards. Have a look there. hopefully it helps you.
bye
HuseyinAltindag
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Hi,
Anyone have any ideas about generating/displaying reports in VC#.Net without using Crystal Reports? For example, is there a way to use MS Access reports?
Or is there a way to use a stand-alone Crystal Reports file. I'm using Visual Studio Standard, and there is nothing for Crystal Reports included with it.
Any ideas are appreciated.
Matt
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Hi !
(calling an ActiveX thing from Delphi 7)
Any clues as to why I am getting the following error msg ?
error msg; Undeclared identifier: 'Layer2'
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
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This is the C# forum, no Delphi. Most likely, though, you can't declare a variable with a global scope inside a procedure. Not sure, though, since I don't know Delphi. That's why it's better to ask in a Delphi forum, which CodeProject doesn't have.
Microsoft MVP, Visual C#
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Thanks Heath,
I'll try a forum that has a Delphi section.
Cliff
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I have a an application tha creates several usercontrols during runtime. The usercontrol is called "Clock", and for this matter, it contains a combobox called simply "comboBox1"
<br />
clocks=new Clock[4];<br />
for (int i=0; i<4; i++) <br />
{<br />
this.clocks[i]=new Times.Clock();<br />
this.clocks[i].Location = new System.Drawing.Point((i%2)*width, 136+(i/2)*112);<br />
this.clocks[i].Name = "clocks"+i;<br />
this.clocks[i].Size = new System.Drawing.Size(width, 112);<br />
this.clocks[i].TabIndex = 8+i;<br />
this.clocks[i].setSource(dsCities);<br />
this.Controls.Add(clocks[i]);<br />
}<br />
the dsCities is a DataSet that has one table.
now the problem is with the setSource function:
<br />
public void setSource(DataSet data)<br />
{<br />
this.comboBox1.DisplayMember="City";<br />
this.comboBox1.DataSource = data.Tables[0];<br />
this.comboBox1.SelectedIndex=0;<br />
}<br />
The function works fine for controls that where created on design-time, but doesn't seem to perform the data-binding itself when called from a run-time control.
Did anyone ever encounter this behavior?
Any help would be welcome.
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At what point are you calling the DataBind method? At the Page_Load()?
Smitha
Every person, all the events of your life, are there because you have drawn them there. What you choose to do with them is up to you.
-- Richard Bach
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This is a WinForm application, not a web-based one.
The data-binding is made after the call to the InitializeComponent() function, in the form's constructor.
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Why not set a break-point at setSource and see if you have data or not.
- Nick Parker
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Of course I set a breakpoint there. That's in the Debugging101 course.
The problem is that when I put a breakpoint in the setSource function, all I see is that the DataMemeber is set okay, but when the DataSource is assigned, its value doesn't change, and the value of DataMember if set to "".
I actually managed to solve this specific problem, by calling the setSource function only after the control was added to the form.
However, I did encounter the same problem somewhere else in the application, when I tried to add more clocks.
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I have a problem that loads a dataset full of data and serves text to telnet clients. Everything in the program has worked well so far until now, whenever I go into this one function i just made, as soon as the first line hits, MOST of the class members dissapear!
I'm not really sure what kinds of information to provide except the watch result of one of the elements that goes BOOM:
BEFORE:
Name: dbGalaxy.Players Vaue: {GalaxyDatabase.glxDataset.PlayersDataTable}
AFTER:
Name: dbGalaxy.Players Value: error: cannot obtain value
Both the functions are within the main class (the server) and the dbGalaxy is also in this class. Why all of a sudden uppon entering a function, that an entire object and about 50 other members just simply dissapear...
Any ideas?
Philippe Durand
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Euphorix wrote:
I'm not really sure what kinds of information to provide except the watch result of one of the elements that goes BOOM
How about some code snippets? Printing the watch state doesn't help solve anything.
Microsoft MVP, Visual C#
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I have a windows form that has four input text boxes. The input for each of these must be integers. Is there a way (e.g. property) that I can set which will only allow the user to enter intergers??? Thanks for any help.
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