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Hi Trak4Net,
When running the new thread, I got the bellow error:
"{Text = '((System.Windows.Forms.TextBox)(txtLopDiaChi)).Text' threw an exception of type 'Microsoft.VisualStudio.Debugger.Runtime.CrossThreadMessagingException'} System.Windows.Forms.TextBox
"
Do you know how to fix it ?
Thanks and regards,
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You should read up about making thread-safe calls to controls here is one link http://msdn.microsoft.com/en-us/library/ms171728.aspx[^]
Anytime you access a control from a thread other than the thread the control was created on you will need to use Invoke or BeginInvoke to modify. Usually if there are several common controls I create a method that accepts a control as a parameter as well as the text to set and inside that method it checks if invoke is required.
Here is an example of something you could do. You don't show enough code to know exactly what you are trying but this can be modified to work with different controls etc.
Hope this is helpful.
private delegate void ChangeTextDel(System.Windows.Forms.TextBox obj, string newtext);
private void ChangeText(System.Windows.Forms.TextBox obj, string newtext)
{
if (obj.InvokeRequired)
{
obj.Invoke(new ChangeTextDel(ChangeText), new object[] { obj, newtext });
}
else
{
obj.Text = newtext;
}
}
ChangeText(txtLopDiaChi, "my new text value");
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Thank you.
I resolved this error earlier.
Kind regards,
Tai
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Hi,
I am searching for MDI child using this code and activating it when exists.
I want to know how can I set label text before the search_form.Activate() line? I tried search_form.lblFindWhat.Text = "something" but it was not recognized although i set the lblFindWhat Modifier to Public.
here is the code:
foreach (Form search_form in this.MdiChildren)
{
if ((string)search_form.Tag == "BROWSE_PATIENTS")
{
search_form.lblFindWhat.Text = "something";
search_form.Activate();
is_form_exists = true;
break;
}
}
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What do you mean by "but it was not recognized"? Did the code compile?
/ravi
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I mean getting this error:
Error 9
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The compiler is correct. A Form doesn't define a lblFindWhat member. You need to cast search_form to the specialized type of the form you're using before accessing its lblFindWhat member.
/ravi
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Please, don't set controls to public - it fixes the design of the form, because you can't change the label out without it affecting (and possibly breaking) outside objects.
Instead, create a public property which allows access, and set the label text yourself within the property. That way, you can replace the label with a more suitable control at some future date, and nothing gets changed outside.
In your search form:
public string Prompt
{
get { return myLabel.Text; }
set { myLable.Text = value; }
}
In your external class:
search_form.Prompt = "something";
The next problem is that a Form does not contain your controls. You have to cast it to an instance of your search form before the compiler can know what it contains:
foreach (Form form in this.MdiChildren)
{
MySearchForm search_form = form as MySearchForm;
if (search_form != null && (string)search_form.Tag == "BROWSE_PATIENTS")
{
search_form.Prompt = "something";
search_form.Activate();
is_form_exists = true;
break;
}
}
Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water
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Ugh. I should've just pointed the OP to your post. 
/ravi
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 I do it all the time...
Ideological Purity is no substitute for being able to stick your thumb down a pipe to stop the water
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I'm still new, so I don't know if this is the best way to do what I am needing, and would like some feedback/advice.
I have a class that contains a double value. This double could represent a dollar value or it could represent a percentage value. Only one or the other, it will never have both. At runtime, I will need to be able to tell what type of value this is. Here is what I came up with, which appears to work, but if there is a better way, I would prefer that.
public class Rate
{
public double Value;
}
public class RateDollar : Rate {}
public class RatePercentage : Rate {}
public class TransactionLine
{
public Rate Amount;
}
myTransactionLine.Amount = new RateDollar();
if(myTransactionLine.Amount.GetType() == typeof(RateDollar))
if(myTransactionLine.Amount.GetType() == typeof(RatePercent))
For some reason, this seems like it is a clunky workaround. It also seems like it's possible for someone to create the value that is neither a RateDollar or RatePercent, and just as a plain Rate. Is there some way to prevent this, or is there a better way to accomplish what I am trying to do?
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It doesn't make much sense to have a Rate class if all it does is contain a double. Is there more to it then that? Is the Rate used elsewhere? I'm gonna go out on a limb and say that TransactionLine should just have a double Rate property and a RateType enum property that says whether its a % or $ amount.
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Thanks for the response! The enum seems like it would be a simpler way to handle this. Since the Rate may be used in multiple different classes, I think I should go with an enum in the Rate class.
public enum ENRateType { Dollar, Percent }
public class Rate
{
public ENRateType RateType;
public double Rate;
}
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Thanks for responding!
I haven't really gotten to learning a lot about interfaces (or abstract classes), but I am thinking that will be the next topic I tackle.
The reason for this setup is because I am interacting with another software, and that software has one value that represents either a dollar value or a percentage. For example, this is how it would show a transaction:
Widget $12.00
Shipping $3.95
Subtotal $15.95
Tax 8.875%
Total $30.11
When I get this information from the program, they have a rate class that contains three members, an enum for the price type (dollar or percent), a double for the Dollar value, and a double for the Percent value. Because the line can only be a dollar or value and not both, one of the doubles will always be null.
I get the feeling (but I may be wrong) that they way they did their setup isn't the best. I will probably implement a Rate class that contains an enum and a double, which should work, but if there is a 'better' way to do this, I would prefer to learn about that type of implementation.
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To me this information indicates you are "free" to change the Rate class in the program you get the information from: is that correct ?
The use of the phrases "They have," and "they did," and, "I am interacting with another software," is what gives me the idea you may not have freedom to change the Rate class.
thanks, Bill
"Everything we call real is made of things that cannot be regarded as real." Niels Bohr
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Definitely would not use an interface here. Whats the point? Not everything needs to be an interface. Having 3 classes (or interfaces or whatever) just to hold a double is over engineering at its finest  .
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Collin Jasnoch wrote: Because he has not stated his reason for layers but is trying to use it. That is
the point.
He did. He wanted to be able to tell the difference between a % and a $ amount. In which case an enum (or even a bool would suffice).
Collin Jasnoch wrote: I have seen cases where an empty interface is even used. It is not over
engineering. It is creating a base API.
By what the OP was an
interface is exactly what should be used.
OP wanted to have a single double that held 2 different types of values and wanted to know a way to tell the difference between them. Using his GetType() solution required having 3 classes. The enum solution requires an enum & a single class.
I'm not against interfaces, I use them all the time. I don't do stuff just cuz I can, I do stuff when its appropriate. I could also wear a tuxedo to go to Burger King, but I don't cuz that's slightly overkill .
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A quick and dirty solution;
public class Rate
{
public double Value;
public override string ToString ()
{
string typeName = GetType().Name;
if (typeName.StartsWith(typeof(Rate).Name))
typeName = typeName.Substring(typeof(Rate).Name.Length);
return typeName;
}
}
It'd be cleaner to introduce a new property than to abuse the ToString-method. Putting an enum in there that returns "Dollar" or "%" would require the base-class to have knowledge thereof.
..unless you introduce an abstract property that returns an object. Yes, that introduces an extra cast in the calling code, but that could easily be wrapped in a utility-method.
Bastard Programmer from Hell 
if you can't read my code, try converting it here[^]
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Thanks for the code! That would work as a temporary solution, I think!
It's sounding like I should really start looking into abstract classes/properties for this type of need! I haven't gotten that far yet in my learning, but it's going to be my next topic for sure!
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hpjchobbes wrote: Thanks for the code! That would work as a temporary solution, I think!
You're welcome. PIEBald has an even neater solution btw 
Bastard Programmer from Hell
if you can't read my code, try converting it here[^]
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I'd make Rate abstract and maybe make it a struct or replace the field with a read-only property.
hpjchobbes wrote: if(myTransactionLine.Amount.GetType() == typeof(RateDollar))
if(myTransactionLine.Amount is RateDollar
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Lots of the responses here seem to be WAY over thinking things. 3 classes to hold a double value? Really? It doesn't seem like there is going to be any code in any of those 3 classes, so it should just be a single class with an enum indicating what it is. You aren't going to get around type checking all over the place. If you give us more info on what you are actually doing with the rates, we could provide more help. If its just for formatting, well, you would still have a single class and just override the ToString() that switches on the enum and formats with a % or $. And actually, the $ version should use the system formatter which formats currency according to the local settings.
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SledgeHammer01 wrote: so it should just be a single class with an enum
A boolean would be sufficient.
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