Date: 27 Aug 2009 Comments: 11 so far

1.Using String variables:

if (someString.Length > 0)
{
// …
}

… but someString could be a null:

if  (!String.IsNullOrEmpty(someString))
{
// much better now !?
}

2.String concatenation

string s = “dev”;
s += “-”;
s += “the”;
s += “-”;
s += “web”;
s += “.”;
s += “com”;

This is not very effective and the program will work slower instead of using StringBuilder class and it’s Append method:

StringBuilder sb = new StringBuilder();
sb.Append(“dev”);
sb.Append(“-”);
sb.Append(“the”);
sb.Append(“-”);
sb.Append(“web”);
sb.Append(“.”);
sb.Append(“com”);
3.Using Console

Console.WriteLine(“A= ” + 1 + ” B=” + 2 + ” C= ” + someValue);

same as 2. it’s not very effective. What about this:

Console.WriteLine(“A: {0}nB: {1}nC: {2}”, 1, 2, someValue);

4.Parse Integer value from string variable

int i = int.Parse(Request.QueryString["id"]);

but if we’ve a url like this yourpage.aspx?id=A6 the above method will throw an exception. What about TryParse method?

int i;
if (!int.TryParse(Request.QueryString["id"] , out i))
{
//…
}

5. Calling IDbConnection’s Close method

IDbConnection dbConn = null;

try
{
dbConn = new SqlConnection(“some Connection String”);
dbConn.Open();
}
finally
{
dbConn.Close();
}

Calling SqlConnection’ constructor may throw an Exception, should we call Close method then !?

IDbConnection dbConn = null;

try
{
dbConn = new SqlConnection(“Some Connection String”);
dbConn.Open();
}
finally
{
if (dbConn != null)
{
dbConn.Close();
}
}

6.Using List class

public void SomeMethod(List<SomeItem> items)
{
foreach(var item in items)
{
// do something with the item…
}
}

If we just loop through the List of items. In this case, requiring a list is an over specification, so it could done in this way:

public void SomeMethod(IEnumerable<SomeItem> items)
{
foreach(var item in items)
{
// do something with the item…
}
}

7.Use numbers in more that simple numbers way

if(mode == 1) { … }
else if(mode == 2) { … }
else if(mode == 3) { … }

Why don’t we use Enumerations in this case:

public enum SomeEnumerator
{
DefaultMode = 1,
SafeMode = 2,
NormalMode = 3
}

if(mode == SomeEnumerator.DefaultMode) { … }
else if(mode == SomeEnumerator.SafeMode) { … }
else if(mode == SomeEnumerator.NormalMode) { … }

8.String Replace

string s = “www.DevTheWeb.NET is a cool site”;
s.Replace(“cool”, “awful”);

Nothing changed in s’ value, it’s still “www.DevTheWeb.NET is a cool site”

s = s.Replace(“cool”, “awful”);

Now s’ value is realy changed.

I hope you’ll like the list of common C# mistakes

P.S. If you know some cool C# mistake, please, post a comment about it