setting properties in a contructor 3

[intrex]

I am getting an error message that is throwing me for a loop. Basiclly I am setting the value of a bool property in the constructor of a class (the same class that the property is in). As soon as I try to set the value I get
Exception of type System.StackOverflowException was thrown.

The constructor is overloaded. Below are the overloads.

#region overloaded constructors

public GetLabelParams(string StoredProcedure, string connections)
{
spname = StoredProcedure;

HasError = false;

//set the datatable to null because no parameters are passed with this
//constructor
dtParamTypes = new DataTable();

//set connnection name to enum sent from calling code
connectionname = connections;

//connect to the database and stored procedure specified.
try
{
connection = ConfigurationSettings.AppSettings[connections.ToString()];
}
catch(Exception ex)
{
error = error + "The " + connectionname + " information was not found in the web.config file <br> Server error <br>" +
ex.Message;
HasError = true;
}

}

//overloaded constructor for receiving a Datatable of parameters
//and types for each parameter. The Datatable has 4 columns.
//parameter names, parameter values, parameter type, and value
public GetLabelParams(string StoredProcedure, string connections, DataTable ParamsAndTypes)
{
spname = StoredProcedure;

connectionname = connections;

//set the has errors property to false on class instantiation
HasError = false;

//connect to the database and stored procedure specified.
try
{
connection = ConfigurationSettings.AppSettings[connections.ToString()];
}
catch(Exception ex)
{
error = error + "The " + connectionname + " information was not found in the web.config file <br> Server error <br>" +
ex.Message;
HasError = true;
}

dtParamTypes = new DataTable();
dtParamTypes = ParamsAndTypes;

}

#endregion

As soon as I set the HasError property to false the error is thrown. Here are my properties.

#region error properties

/// <summary>
/// This is the error property called by the main code.
/// </summary>

public bool HasError
{
get
{
return HasError;
}
set
{
HasError = value;
}
}

public string errors
{
get
{
return error;
}

}

#endregion

This seems so straight forward I am not sure what the problem is. I have tried to delete the dlls and recompile. I have tried renaming the property. I have tried refrencing the property by this.HasError. Any suggestions would be great.

 

[tgreer]

Public get/set accessor methods are used to set private variables.

You have public bool HasError getting and setting itself, which is a problem, I think.

You need to declare a private variable, call it _HasError or hasError, or whatever naming convention you use to distinguish private from public. The public method would set the private variable:

private bool hasError;
public bool HasError
{
   get
   {
     return hasError;
   }
   set 
   {
      hasError = value;
   }
}

Thomas D. Greer

http://www.tgreer.com

Providing PostScript & PDF
Training, Development & Consulting

 

[obislavu]

The solution is already posted but I would like to add some explanations.

private bool HasError;
public bool HasError // Compile error because HasError is already defined
{
	get{return HasError;}
	set{HasError=value;}
}

The above code does not compile.

public bool HasError 
{
	get{return HasError;}
	set{HasError=value;}
}


HasError = true; // line somewhere in code

The above code will produce a StackOverflow because of the infinite recursion.
When 'line somewhere' get executed,then the statement

set{HasError=value;}

get executed. Evaluating {HasError = value;} calls again {HasError=value} in order assign value to HasError and so on.
This happend because the only way to change HasError is by executing {HasError=value;}.
Calling the function inside of the same function is a recursion. That is not an error but there are techniques to accomplish that but not this set/get method.
The next example is interesting one.

using System;
using System.Data;
public class Form1 : System.Windows.Forms.Form
{
	
	private DataSet DataSet(string sConnection)
		{
	
			DataSet ds = new DataSet();
			ds.Tables.Add(new DataTable("abcd"));
			return ds;
		}
	private void button1_Click(object sender, System.EventArgs e)
		{
		     
			DataSet ds1 = DataSet("abcd");
		}
}

All above code is working well.
The first method's name is DataSet (!!!) , takes a string parameter and returns a DataSet object.
Nothing is wrong but it is not recommended.
There is no recursion here because DataSet ds = new DataSet(); is in fact:
System.Data.DataSet ds = new System.Data.DataSet();
But, in the button1_Click the DataSet() method is called (the object here is 'this' e.g. Form1 object) :

DataSet ds1 = DataSet("abcd"); // e.g. DataSet ds1 = this.DataSet("abcd");

-obislavu-

 

[chiph]

To add to obislavu's and tgreer's excellent posts:

When creating private member variables, there's no official standard for naming them, but there are a couple of conventions:

   // Use leading underscores
   private bool _HasError;

   // Use leading leading "m_"
   private bool m_HasError;

   // Use camel-casing for private member and
   // pascal-casing for property
   private bool hasError;
   public bool HasError
   {
      get { return hasError; }
      set { hasError = value; }
   }

Which one do I like? I like the leading underscore style, but the "m_" is pretty good too. I don't like separating them by only the case of the leading letter -- too easy to have your finger slip off the shift key and get recursion.

Chip H.


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[intrex]

Thanks for all of the feedback. I will be trying all of this in my code monday morning. I have seen lots of the leading underscore commenting and never really understood what the convention was. The recursion issues makes complete sense.