Sample StyleCop custom rules

Methods should not have more then 200 lines of code:

private void MethodShouldNotHaveMoreThanTwoHundredLines(CsElement element, CsElement parentElement)
        {
            if ((!element.Generated && (element.Declaration != null)) && (element.Declaration.Name != null))
            {
                switch (element.ElementType)
                {
                    case ElementType.Method:
                        //Checking 203 line as first line for method declaration and two lines for opening and closing parenthesis '{','}'
                        if (element.Location.LineSpan > 203)
                        {
                            base.AddViolation(element, "MethodShouldNotHaveMoreThanTwoHundredLines");
                        }
                        break;
                }
            }

        }

Prefix Private variables with underscore:

private void PrefixPrivateVariableNameWithUnderScore(CsElement element, CsElement parentElement)
        {
            // Flag a violation if the instance variables are not prefixed with an underscore.
            if (!element.Generated && element.ElementType == ElementType.Field && element.ActualAccess == AccessModifierType.Private &&
                 element.Declaration.Name.ToCharArray()[0] != '_')
            {
                //If field type is "const" than Pascal casing rule is applicable on it.
                if (((Field)element).Const) return;

                base.AddViolation(element, "PrefixPrivateVariableNameWithUnderScore");
            }
            else if (!element.Generated && element.ElementType == ElementType.Field && element.ActualAccess == AccessModifierType.Private
                && CheckCase(element.Declaration.Name.Substring(1), false))
            {
                base.AddViolation(element, "PrefixPrivateVariableNameWithUnderScore");
            }

        }

Avoid specifying type for Enum:

private void AvoidSpecifyingEnumType(CsElement element, CsElement parentElement)
        {
            if (element.ElementType == ElementType.Enum)
            {
                Microsoft.StyleCop.CSharp.Enum enm = (Microsoft.StyleCop.CSharp.Enum)element;
                if (enm.BaseType != null)
                {
                    base.AddViolation(element, "AvoidSpecifyingEnumType", new object[0]);
                }
            }
        }

Camel casing for local variable names and method arguments:

private void CamelCasingForMethodArgumentsAndLocalVariable(CsElement element, CsElement parentElement)
        {
            if (element.ElementType == ElementType.Method)
            {
                foreach (Variable tempVariable in element.Variables)
                {
                    //If argument type is 'EventArgs' allow non-Camel case variable name also.
                    if (!tempVariable.Type.Text.ToLower().EndsWith("EventArgs".ToLower()))
                    {
                        if (CheckFieldUnderscores(tempVariable.Name) || CheckCase(tempVariable.Name, false))
                        {
                            base.AddViolation(element, tempVariable.Location.LineNumber, "CamelCasingForMethodArgumentsAndLocalVariable");

                        }
                    }
                }
            }


        }

Avoid abbrivated character variable names, such as i, num, tmp:

private void AvoidAbbrivatedCharacterVariableNames(CsElement element, CsElement parentElement)
        {
            if (element.ElementType == ElementType.Field)
            {
                if (element.Declaration.Name.Length <= 3)
                    base.AddViolation(element, "AvoidAbbrivatedCharacterVariableNames", new object[0]);
            }
            if (element.ElementType == ElementType.Method)
            {
                foreach (Variable elem in element.Variables)
                {
                    if (!elem.Type.Text.ToLower().EndsWith("EventArgs".ToLower()))
                    {
                        if (elem.Name.Length <= 3)
                            base.AddViolation(element, elem.Location.LineNumber, "AvoidAbbrivatedCharacterVariableNames", new object[0]);
                    }
                }
            }   
        }

Using directive inside namespace:

private void UsingDirectiveOutSideOfNameSpace(CsElement element, CsElement parentElement)
        {
            if (!element.Generated && (element.ElementType == ElementType.UsingDirective))
            {
                // CsElement parentElement = element.ParentElement;
                if ((parentElement != null) && (parentElement.ElementType == ElementType.Namespace))
                {

                    AddViolation(element, "UsingDirectiveShouldOutSideOfNameSpace");

                }
            }
        }