如何在简单方法中正确使用try-catch？

Question

I would like to make sure my classes are robust - even if they are simple and seem dumb to an experienced programmer.

Let's say I have a method as written below that accepts a string[] and returns it as an int[].

public static int[] GetIntArrayFromStringArray(string[] stringArray)
    {
        int i = 0;
        int[] ints = new int[stringArray.Length];
        foreach (var str in stringArray)
        {
            ints[i++] = (str != "" ? int.Parse(str) : 0);
        }
        return ints;
    }

Is the best option to use try-catch and throw an exception? When I try to use try-catch, it seems to have issues with my variables not being in scope but I need them to be in a try-catch to catch any errors with the stringArray being null!

Perhaps I should use this?

    if (stringArray == null) //do something ...

but not sure what to do in the event of an error ... do I return a null int[] or throw exception?

(I also have to check that the int.Parse(str) doesn't fail - I'm getting to that one but hoped it could be in the try-catch block!)

As I said, these are simple tasks that I want to try and get correct now before I develop too many bad habits. Thanks.

Answer 1

You can use int.TryParse() instead.

http://msdn.microsoft.com/en-us/library/f02979c7.aspx

Answer 2

1. If stringArray is null, immediately throw a NullArgumentException .

2. Try something simpler for the conversion:

   return stringArray.Select(s => IntParseOrDefault(s, 0)).ToArray();

Where IntParseOrDefault is just like this:

int IntParseOrDefault(string s, int defaultVal)
{
    int i;
    if (!int.TryParse(s, out i)) i = defaultVal;
    return i;
}

If you want the method to fail if any of the strings is not a valid integer, then instead of using a default value, throw an InvalidArgumentException when TryParse fails.

Answer 3

Here an example

        foreach (string str in stringArray)
        {
            int nr = 0;
            int.TryParse(str, out nr);

            if (nr > 0)
                ints[i++] = nr;
        }

here is the full code

public static int[] GetIntArrayFromStringArray(string[] stringArray)
{
    if (stringArray == null || stringArray.Length == 0)
        throw new ArgumentNullException("string array is null or empty");

    int i = 0;
    int[] ints = new int[stringArray.Length];
    foreach (var str in stringArray)
    {
        int nr = 0;
        int.TryParse(str, out nr);
        if (nr > 0)
            ints[i] = nr;
        i++;
    }
    return ints;
}

Answer 4

Here is how you can use try - catch:

public static int[] GetIntArrayFromStringArray(string[] stringArray)
{
    int i = 0;
    int[] ints = null;
    try {
        ints = new int[stringArray.Length];
        foreach (var str in stringArray)
        {
            ints[i++] = (str != "" ? int.Parse(str) : 0);
        }
    }
    catch {
         // Throw custom exception
    }
return ints;
}

Answer 5

I would throw a custom-exception in the catch-block. So the user of your class can catch for this exception.

Answer 6

public static int[] GetIntArrayFromStringArray(string[] stringArray)
    {
        int i = 0;
        int[] ints;
        int num;
        if (stringArray == null && stringArray.Length > 0)
        {
        ints = new int[stringArray.Length]
        foreach (var str in stringArray)
        {
            if (string.IsNullOrEmpty(str) && int.TryParse(str, num))
            {
            ints[i++] = num;
            }  
        }
        }
        return ints;
    }

Answer 7

    public static int[] GetIntArrayFromStringArray(string[] stringArray)
    {
        if (stringArray == null)
        {
            throw new ArgumentNullException("stringArray");
        }

        int count = stringArray.Length;
        int[] ints = new int[count];
        for (int i = 0; i < count; i++)
        {
            int intValue;
            ints[i] = int.TryParse(stringArray[i], out intValue) ? intValue : 0;
        }
        return ints;
    }

Answer 8

Many methods in the .NET Framework that throw exceptions on invalid input have non-throwing counterparts, usually prefixed with Try , that return a boolean value instead. For instance, in the case of int.Parse , you'll have an easier time calling int.TryParse , eg:

public static int[] GetIntArrayFromStringArray(string[] stringArray)
{
    int i = 0;
    int[] ints = new int[stringArray.Length];
    foreach (var str in stringArray)
    {
        int a = 0
        int.TryParse(str, out a)
        ints[i++] = a;
    }
    return ints;
}