How to prevent if if if if if if...?

Question

4.50/5 (2 votes)

See more:

This one has been bothering me for a while. I need to check if somewhere around 8 values are not Nothing. I might not need to check them all at once, but a few at a time and then some nested If's. It makes code ugly and unreadable, but how to prevent so many If's or at least make it more readable and understandable?
A Select Case will not do, since ALL values need to be evaluated.

So how could I possibly make code like this better readable?

VB

If Not object1.Property1 Is Nothing AndAlso Not object2.Property1 Is Nothing AndAlso Not object2.Property1.Property1 Is Nothing Then

   Dim object3 = ' LINQ Query.

   If Not object3 Is Nothing Then

      If Not object4 Is Nothing AndAlso Not object3.Property1 Is Nothing Then
      '...
      ElseIf '...
      '...
      End If

   End If

End If

I could put some of it in a seperate Method, but that would only move the problem, not solve it. I am sure this is a problem that has existed for many many years, but I have never found a clear answer to it...

Posted 19-May-11 4:55am

Sander Rossel

Add a Solution

3 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Answer 1 · 2011-05-19T05:22:00

If cannot prevent it, you can design you code the way it uses much less "ifs". Did you here about totally data-driven development style where there are no a single "if" in application code? To me, this is overkill, but many would say it's not possible. It is possible.

To my taste, two levels of if is still quite acceptable, one more is questionable and more it totally unacceptable. You need to re-factor the code, but better have a good plan on how the whole thing should look like. Thinking on the programming-in-the-large level helps to avoid multilevel checks in first place, but in local place you can re-factor the code. In particular, using local predicates is a very convenient idea.

By the way, how about local predicate. There are methods, and there is no such thing as local method, or it is?
If you need some inspirational example, try to look at my small Tips/Tricks article: Hide Ad-hoc Methods Inside the Calling Method’s Body[^].

I do not insist you use this technique, not at all. I think just the ideas of thinking could be useful for you.

—SA

*dan!sh* · Answer 2 · 2011-05-19T06:57:00

I do not know VB so will try to explain using C# if it helps.

Three levels of if/else if fine but more than that is a no. This is something you could do to get rid nested of ifs.

Assume following class structure:

C#

class ParentClass
{
    public ChildClass ChildProperty { get; set; }
}
class ChildClass
{
    public int SomeProperty { get; set; }
}

Say, you need to do this kind of processing:

C#

ParentClass parentObj1 = new ParentClass();
ParentClass parentObj2 = new ParentClass();
ParentClass parentObj3 = new ParentClass();
if (parentObj1 != null && parentObj2.ChildProperty != null && parentObj2.ChildProperty.SomeProperty != null)
{
    ParentClass parentObj4 = new ParentClass();
    if (parentObj4 != null)
    {
        if (parentObj3 != null && parentObj4.ChildProperty != null)
        {
            if (parentObj4.ChildProperty.SomeProperty != null)
            {
            }
            else
            {
            }
        }
        else if (parentObj3 != null && parentObj3.ChildProperty != null && parentObj4.ChildProperty.SomeProperty != null)
        {
        }
        else
        {
        }
    }
}

This can be re-written as following:

C#

if (parentObj1 != null && parentObj2.ChildProperty != null && parentObj2.ChildProperty.SomeProperty != null)
{
    ParentClass ob3 = new ParentClass();
    switch (ValidateObjects(parentObj3, ob3))
    {
        case 0:
            // Do something
            break;
        case 1:
            // Do something
            break;
        case 2:
            // Do something
            break;
        case 3:
            // Do something
            break;
        default:
            //Do something
            break;
    }
}

ValidateObjects method could look like this:

C#

private static int ValidateObjects(ParentClass ob4, ParentClass ob3)
{
    int result =0;
    if (ob3 != null && ob4 != null && ob4.ChildProperty != null && ob3.ChildProperty.SomeProperty != null)
    {
        result = 0;
    }
    else if (ob3 != null && ob4 != null && ob3.ChildProperty != null && ob3.ChildProperty.SomeProperty != null)
    {
        result = 1;
    }
    else if (ob3 != null && ob4 != null && ob3.ChildProperty != null)
    {
        result = 2;
    }
    else if (ob3 != null)
    {
        result = 3;
    }
    return result;
}

You can opt for switch case in the method above too.

Still, you have a better understanding of the application so can think of better solutions. :)

#realJSOP · Answer 3 · 2011-05-19T05:16:00

Solution 1

Without knowing more about your code, I have to tell you that the way you're doing it is the only way. You *could* abstract out the comparisons into a few methods, but you'd have to design it carefully.

Posted 19-May-11 5:16am

#realJSOP

Comments

Sergey Alexandrovich Kryukov 19-May-11 11:23am

Well, this is not about concrete code, more about general approach.
Please see what I advise.
--SA

How to prevent if if if if if if...?

3 solutions

Solution 2

Solution 3

Solution 1

Add your solution here

Preview 0