.net 使用没有catch块的tryfinally块

You would use it to ensure some actions occur after the try content or on an exception, but when you don't wish to consume that exception.

Just to be clear, this doesn't hide exceptions. The finally block is run before the exception is propagated up the call stack.

You would also inadvertently use it when you use the using keyword, because this compiles into a try-finally (not an exact conversion, but for argument's sake it is close enough).

try
{
    TrySomeCodeThatMightException();
}
finally
{
    CleanupEvenOnFailure();
}

Code running in finally is not guaranteed to run, however the case where it isn't guaranteed is fairly edge - I can't even remember it. All I remember is, if you are in that case, chances are very good that not running the finally isn't your biggest problem :-) so basically don't sweat it.

Update from Tobias: finally will not run if the process is killed.

Update from Paddy: Conditions when finally does not execute in a .net try..finally block

The most prevalent example you may see is disposing of a database connection or external resource even if the code fails:

using (var conn = new SqlConnection("")) // Ignore the fact we likely use ORM ;-)
{
    // Do stuff.
}

Compiles into something like:

SqlConnection conn;

try
{
    conn = new SqlConnection("");
    // Do stuff.
}
finally
{
    if (conn != null)
        conn.Dispose();
}