Re: Exception Handling in Windows application. - C# Discussion Boards

18-Dec-07 9:27

Hi All,

I can't find any good examples of throwing exceptions. I have the following code. I want to include all the possible exceptions i can. Help me out on this. I am just moving away from console object and moving towards exception object.

public int DeleteFilesOlderThan(int Days, int Hrs, int Mins, string filter)
{
DateTime dt = GetRelativeDateTime(Days, Hrs, Mins);
ArrayList oldFilePaths = FilesOlderThan(dt, filter);
int count = 0;
string message = null;
foreach (string filePath in oldFilePaths)
{
try
{
File.Delete(filePath);
count++;
}
//* System.Exception is too general..I want something more like FileNotFoundException...any exception that can be related to my code
catch (Exception e)
{
message = "Unable to delete " + filePath + "\r\n";
message += String.Format("Reason: {0}", e.Message);
MessageBox.Show(message);
}
}
return count;
}

// Using GetRelativeDateTime as a private method instead of public however as it is only to be used internally
private static DateTime GetRelativeDateTime(int days, int hours, int minutes)
{
return DateTime.Now.AddDays(-days).AddHours(-hours).AddMinutes(-minutes);
}

public ArrayList FilesOlderThan(DateTime dt, string filter)
{
//m_FolderPath = @"C:\CsharpTempFolder";
// Using the supplied path
//DirectoryInfo directory = new DirectoryInfo(Directory.GetCurrentDirectory())
DirectoryInfo directory = new DirectoryInfo(m_FolderPath);
// Filter is applied to the directory.GetFiles method to get files of given extension
// get FileInfos for the files in the current directory matching the filter expression
FileInfo[] files = directory.GetFiles(filter);
//list to hold the result
ArrayList older = new ArrayList();
foreach (FileInfo file in files)
{
//if smaller (older) than the relative time
if (file.CreationTime < dt)
older.Add(file.FullName); //add it to the list
}
return older;
}

pmarfleet18-Dec-07 10:23

18-Dec-07 10:23

A try block can have multiple catch blocks. These should be arranged t-b in decdending order of specificity. You could have a block to specifically catch the FileNotFoundException exception, followed by a general block to catch any exceptions that derive from System.Exception. If an exception is raised, execution will branch into the first relevent catch block.

Paul Marfleet

"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush

Shani Aulakh18-Dec-07 10:34

18-Dec-07 10:34

So, is that it then?
catch (FileNotFoundException e)
{
message = "Unable to delete " + filePath + "\r\n";
message += String.Format("Reason: {0}", e.Message);
MessageBox.Show(message);
}
catch (DirectoryNotFoundException e)
{
message = "Unable to delete " + filePath + "\r\n";
message += String.Format("Reason: {0}", e.Message);
MessageBox.Show(message);
}
catch (Exception e)
{
message = "Unable to delete " + filePath + "\r\n";
message += String.Format("Reason: {0}", e.Message);
MessageBox.Show(message);
}

pmarfleet18-Dec-07 10:46

18-Dec-07 10:46

Yes, that looks OK. Try it out and judge for yourself.

Paul Marfleet

"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush

Shani Aulakh18-Dec-07 10:56

18-Dec-07 10:56

How can i fail my program so this works?

pmarfleet18-Dec-07 11:01

18-Dec-07 11:01

Shani Aulakh wrote:
How can i fail my program so this works?

What do you mean? Why would you want cause your program to deliberately fail?

Paul Marfleet

"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush

Shani Aulakh18-Dec-07 11:13

18-Dec-07 11:13

Sorry for the confusing question. I meant to say, what should i do to see if it actually handle all exceptions

pmarfleet18-Dec-07 11:20

18-Dec-07 11:20

If you want to produce a FileNoFoundException or DirectoryNotFoundException, just try doing something that involves a file/directory that doesn't exist.

Paul Marfleet

"No, his mind is not for rent
To any God or government"
Tom Sawyer - Rush

Kalvin @ Work18-Dec-07 11:16

Kalvin @ Work

18-Dec-07 11:16

If you just want to test that your catch blocks work the way you intend you can always throw an exception from code during testing. Just make sure to remove exception once you are convinced you're exception handling works the way you want. Depending on the application you could also use a driver for this.

throw new System.ApplicationException("Your message here");

You can replace ApplicationException with the exception types you actually want to test.

Shani Aulakh18-Dec-07 11:21