Re: Ambiguous constructor signatures? - C# Discussion Boards

DaveyM6922-Oct-09 4:58

DaveyM69

22-Oct-09 4:58

This is expected behavior. MyClass(G) when G is a string becomes MyClass(string). As a constructor with those parameter types already exists a new one is not generated by the compiler as the parameter list must be different to successfully overload.

Dave

Generic BackgroundWorker - My latest article!
BTW, in software, hope and pray is not a viable strategy. (Luc Pattyn)
Why are you using VB6? Do you hate yourself? (Christian Graus)

Keith Barrow22-Oct-09 5:09

Keith Barrow

22-Oct-09 5:09

I'd go further and say this is the desired behaviour for the generic overload (i.e. I think the .Net framework makes the correct choice). MyClass(string foo) is explicitly stating "I deal with strings" and is therefore concrete, whereas MyClass(G foo) is stating "I deal with 'G's" which is less concrete.

The design in the OP needs refactoring IMO, the concrete MyClass(string foo) ctor needs to be removed unless there is a specific reason for dealing with strings specifically. The validation performed on the strings is likely to be, but not necessarily, valid for other types.

CCC solved so far: 2 (including a Hard One!)

Clive D. Pottinger22-Oct-09 7:34

Clive D. Pottinger

22-Oct-09 7:34

Thanks guys.

That explains why it acts like it does.

keefb wrote:
The design in the OP needs refactoring [...] unless there is a specific reason for dealing with strings specifically.

In the actual code MyClass is a class that represents some kind of value. The first ctor (MyClass(string initStr)) is used when the initStr holds a formula that needs to be parsed and evaluated to get the value. The second ctor (MyClass(G initVal, bool dummy)) is used when the value is already known, and does not need to be parsed or evaluated. The confusion arose, of course, when the value is a known string.

I will take your recommendation to remove the first ctor into consideration, but at this point, I don't see a way for it work (is MyClass("foo()") a request for the string returned by foo or for the string "foo()"?). In the meantime, I will take it that my "workaround" is not wrong/dangerous/problematic/laughable.

Thanks again.

Clive Pottinger
Victoria, BC

Keith Barrow22-Oct-09 11:46

Keith Barrow

22-Oct-09 11:46

Clive D. Pottinger wrote:
The first ctor (MyClass(string initStr)) is used when the initStr holds a formula that needs to be parsed and evaluated to get the value

This is a worry*, and the source of your problem. If possible, you should defer the instantiation of this class until you have the value you want to use. If I understand you correctly, by passing the formula as a string will require the current class to be responsible for performing the parsing as well as whatever this class is meant to do with the result, this is probably bad object encapsulation.

A better way to handle this is to create an object which is responsible for the storage and parsing of the formula, and pass the results of the formula into the current class ,explained in your original post. This will separate the concerns more clearly.

* This is a worry because, unless you are parsing text entries from a user or some other source (e.g. text input from a UI or file), writing formulas in strings and then evaluating them is bad design (and a real pain. If this is the case, then it's unavoidable. If you are just using this to pass formulae around within the application, you should look at c# delegates(which allow you to pass methods around as parameters) and possibly the strategy pattern.

Hope this helps!

CCC solved so far: 2 (including a Hard One!)

Reading grayscale values into Bitmap

Clive D. Pottinger23-Oct-09 6:31

Clive D. Pottinger

23-Oct-09 6:31

Thanks for the clarification, keefb.

keefb wrote:
If I understand you correctly, by passing the formula as a string will require the current class to be responsible for performing the parsing as well as whatever this class is meant to do with the result, this is probably bad object encapsulation.

Agreed. But the class is not actually responsible for the parsing or evaluation (it passes those tasks off to another class), nor is it responsible for acting on the value. The class just holds on to expression tree created by parsing the formula and uses it to provide a value when requested. Perhaps my original example was over-simplified.

keefb wrote:
...unless you are parsing text entries from a user or some other source (e.g. text input from a UI or file), writing formulas in strings and then evaluating them is bad design...

This is exactly what I am doing. The formulas are read from user-created XML files and used to control the program's behaviour. This is fun... every criticism you offer just seems to confirm that I'm doing it correctly Laugh | :laugh:

. Keep going, keefb... one more critique should cement that I'm the bona fide genuis that I always knew myself to be Cool | :cool:

(no matter what those jerks at Mensa had to say Mad | :mad:

)

Clive Pottinger
Victoria, BC

proxy server

Zeyad Jalil22-Oct-09 3:28

Zeyad Jalil

22-Oct-09 3:28

hi all,

I have a client-server project and i want to connect to the server from the client by socket via proxy..
any one can help me ??

thanks all

econner22-Oct-09 2:33

econner

22-Oct-09 2:33

I have a third party dll that is written in C++ that saves a bitmap image as the actual grayscale values and not a Bitmap format. I am looking for a way to read in the grayscale values and convert them to use C#/.NET 's Bitmap class.

Thanks

Re: Reading grayscale values into Bitmap

stancrm22-Oct-09 2:52

stancrm

22-Oct-09 2:52

You must read your custom grayscale format and save it in byte[] for example.
Then create a new bitmap and use method SetPixel to put your byte[] in
Bitmap.

http://msdn.microsoft.com/en-us/library/system.drawing.bitmap.setpixel.aspx[^]

Filter Gridview that are bound to an XML file

Ronni Marker22-Oct-09 2:19

22-Oct-09 2:19

Hi everyone.

I am currently playing around with XML files and gridview, and wondered if there were any easy way to filter data, so only rows with specific content are shown.

I have the following.

DataTable dt = new DataTable("Subscribers");
dt.Columns.Add("ID");
dt.Columns.Add("Email");
dt.Columns.Add("signup");
dt.Columns.Add("recent");
dt.Columns.Add("Amount");
dt.Columns.Add("Status");
dt.ReadXml(Application.StartupPath + @"\subscribers.xml");
dataGridView1.DataSource = dt;
dataGridView1.Refresh();

and would like to filter it so rows who fx. only have the value 0 in the columns "Status" would be shown.

Initially hoped that I could use dt.Select("Status == 0") but that didnt work.

so any supercoders out there? yes, yes i did try to google my issue, but didnt find any solution to my small challenge here...

other alternative that I will go back to my good old SQL Server, skip XML files and just use what I am used to - but that would be too easy...

stancrm22-Oct-09 2:30

stancrm

22-Oct-09 2:30

Try it with dt.Select("Status = 0")

Ronni Marker22-Oct-09 2:33

22-Oct-09 2:33

no, that didnt work either. (too bad though)

stancrm22-Oct-09 2:39

stancrm

22-Oct-09 2:39

See this example (it works):

DataTable dataTable = new DataTable("MyTable");
dataTable.Columns.Add("Column1");

DataRow dataRow = dataTable.NewRow();
dataRow["Column1"] = "0";
dataTable.Rows.Add(dataRow);

DataRow[] foundRows = dataTable.Select("Column1 = 0");
Trace.Write(foundRows); // <- Count = 1

Have you checked your dataTable ?
Are there rows with content 0 in Status ?

Ronni Marker22-Oct-09 2:58

22-Oct-09 2:58

Yes, well came to the conclusion that the error for me is that I thought it would be enough to add a line into the code and that would be that. But can see that I need to do more than that.

Basically tried to add

dt.Select("Status =1");

after reading the XML file and also tried to filter it like this

dataGridView1.DataSource = dtSelect("Status =1");

<- this actually gave an interesting output.

But seems that I wouldnt be able to get away with only a line of code thist time here.

So what would be the best way to do this? (just imagine that I have an XML file with more than 2000 Rows)

Henry Minute22-Oct-09 5:59

Henry Minute

22-Oct-09 5:59

No guarantees that this will work but you could try adding a BindingSouce component to your form and then the bindings become

datagrid.DataSource = bindingSource1;
bindingsource1.DataSource = dt;

BindingSource has a Filter property that you can use.

In fact, if you search MSDN for BindingSource.Filter, the example uses XML which should make getting your stuff to work a bit easier. Smile | :)

Henry Minute

Do not read medical books! You could die of a misprint. - Mark Twain
Girl: (staring) "Why do you need an icy cucumber?"
“I want to report a fraud. The government is lying to us all.”

Ronni Marker22-Oct-09 6:15