我如何捕获异常块内引发的异常

Question

I am working on a .net console application, and i have the following code:-

try {
    SPFile destFile = projectid.RootFolder.Files.Add(destUrl, fileBytes, false);
} catch (System.IO.DirectoryNotFoundException e) {
    SPFile destFile = projectid.RootFolder.Files.Add(destUrl, fileBytes, false);
} catch {}

now if an exception is raised inside the try block, the 2 other catch blocks will catch it, depending on the exception type!!. but if an exception is raised inside the catch (System.IO.DirectoryNotFoundException e) block then the console will end. now i thought if an exception is raised inside the catch (System.IO.DirectoryNotFoundException e) block, then the last catch block will be reached but seems this is not the case.. so can anyone advice how i can catch an exception raised inside an Exception block??

Answer 1

You should notice that try-catch should never be part of your code logic which means you should never use try-catch to control your branch. This is the reason why you'll find it hard to let the exceptions flow through your each catch block.

If you'd like to catch the second block, you can write like this (but not recommended ):

try
{
    SPFile destFile = projectid.RootFolder.Files.Add(destUrl, fileBytes, false);
}
catch (System.IO.DirectoryNotFoundException e)
{
    try
    {
        SPFile destFile = projectid.RootFolder.Files.Add(destUrl2, fileBytes, false);
    }
    catch
    {
        // Do what you want to do.
    }
}
catch
{
}

You'd better not to write like this above. Instead, it's recommended to detect the folder exists ahead like this:

try
{
    YourMainMethod();
}
catch (Exception ex)
{
    // Handle common exceptions that you don't know when you write these codes.
}

void YourMainMethod()
{
    var directory = Path.GetDirectoryName(destUrl);
    var directory2 = Path.GetDirectoryName(destUrl2);

    if (Directory.Exists(directory))
    {
        SPFile destFile = projectid.RootFolder.Files.Add(destUrl, fileBytes, false);
    }
    else if (Directory.Exists(directory2))
    {
        SPFile destFile = projectid.RootFolder.Files.Add(destUrl2, fileBytes, false);
    }
    else
    {
        // Handle the expected situations.
    }
}

Answer 2

要解决此问题，您必须在正在处理DirectoryNotFoundException的catch块中编写另一个try .. catch块try .. catch

Answer 3

It might make more sense to use File.Exists to see if the path already exists, and then attempt to write the file:

string path = null;

if(!File.Exists(destUrl))
{
    path = destUrl;
}
else
{
    if(!File.Exists(destUrl2))
    {
        path = destUrl2;
    }
}

if(!string.IsNullOrWhiteSpace(path))
{
    try
    {
        SPFile destFile = projectid.RootFolder.Files.Add(path, fileBytes, false);
    }
    catch
    {
        // Something prevented file from being written -> handle this as your workflow dictates
    }
}

Then, the only exception you would expect to happen is a failure to write the file, which you would need to handle as your application dictates (permission issues should be treated differently than invalid binary data, corrupted streams, etc.)

You might find this worth a read, if you haven't done so: Best practices for exceptions

Answer 4

Depending on your needs, you could be try-catching in huge nested statements.

If you have a list of destinations you want to try, then you could do something like this

var destinations = new List<string>() {dest1,dest2,dest3, ...};

SPFile destFile = null;

foreach(var destination in destinations)
{
    try
    {
        destFile = projectid.RootFolder.Files.Add(destination, fileBytes, false);
        // we are working
        Console.WriteLine($"Destination Success!!: {destination}");
        break;
    }
    catch(DirectoryNotFoundException ex)
    {
         Console.WriteLine($"Destination failed : {destination} - {ex.Message}");
    }
} 

if(destFile != null)
   // do something with your destFile 
else
   // oh noez!!!