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Send exception to Caller method in c#

Hello guys i'm working on Database assignment in this i have one windows form and one class that i use to connect database and to execute queries and non-queries.
Question: I m using Post-Message label which inform only when "Product added successfully".but when i send wrong-data which can occur exception in executeNonQuery() in database class and after catching this exception and showing Error in message box.Control goes back to caller and it prints lblPostMsg in both cases which is "Product has been added successfully".
I want that when exception occur in database class i can stop executing rest of the code or if there is way that exception in calling method can be caught by caller method.
below is Code of windows Form button
private void btnInsert_Click(object sender, EventArgs e)
{
con = new DbConnection();
con.SqlQuery("INSERT INTO products VALUES(#products_ID,#products_Name)");
con.cmd.Parameters.AddWithValue("#products_ID", txtProID.Text);
con.cmd.Parameters.AddWithValue("#products_Name", txtProName.Text);
try
{
con.ExecuteNonQueryF();
this.categoriesTableAdapter1.Fill(this.purchasemasterDS.categories);
SystemSounds.Beep.Play();
lblPostMsg.Show();
lblPostMsg.Text = "Product has been added successfully";
}
catch (Exception ex)
{
throw;
}
finally
{
con.CloseCon();
}
}
This code is from dbclass
public void ExecuteNonQueryF()
{
try
{
_con.Open();
cmd.ExecuteNonQuery();
}
catch (System.Exception ex)
{
MessageBox.Show("Exception " + ex);
}

you are catching, handling, and suppressing the Exception in ExecuteNonQueryF:
catch (System.Exception ex)
{
MessageBox.Show("Exception " + ex);
}
Though this handles the Exception by showing the message, it causes the code to continue executing; the Exception won't be raised to the caller.
If you add throw after your MessageBox.Show is executed, the Exception will be raised to the caller and execution stops.
catch (System.Exception ex)
{
MessageBox.Show("Exception " + ex);
throw;
}
Another option is to completely remove that try-catch in ExecuteNonQueryF - letting the caller (your button onclick method) handle the Exception.

you need to throw an explicit exception in ExecuteNonQuery's catch block like
throw new Exception(ex)
and then in calle's catch block you need to write "return" to return from function. This will stop furter execution of function.

If you want the Exception will be raised to the caller and execution stops, then you must use throw at the last line of your catch block.
catch (System.Exception ex)
{
/*
write your desire code. then throw
*/
throw;
}

DirectoryNotFoundException was unhandled by user code

I'm quite new to the try catch and exception handling. I want my program to catch the exception when the directory or file is not found.
Whenever I run the program I get the error "DirectoryNotFoundException was unhandled by user code - An exception of type 'System.IO.DirectoryNotFoundException' occured in something.dll but was not handled in user code"
I can see that Visual Studio breaks at the DirectoryNotFoundDirection, any ideas?
try {
LiveDownloadOperation operation = await connectClient.CreateBackgroundDownloadAsync(filePath);
var result = await operation.StartAsync();
}
catch (FileNotFoundException filEx) {
Debug.WriteLine(filEx.Message);
throw filEx;
}
catch (DirectoryNotFoundException dirEx) {
Debug.WriteLine(dirEx.Message);
throw;
}
catch (IOException ioEx) {
Debug.WriteLine(ioEx.Message);
throw ioEx;
}
catch (Exception ex) {
Debug.WriteLine(ex.Message);
throw;
}
EDIT: to show code inside try

Because the directory does not exist (or has permissions problems, etc.), it throws an DirectoryNotFoundException.
Which you handle, then reraise -- because of the, the debugger rightly says that the exception is not handled.

Difference between try{..}catch{...} with finally and without it

What is the difference between code like this:
string path = #"c:\users\public\test.txt";
System.IO.StreamReader file = new System.IO.StreamReader(path);
char[] buffer = new char[10];
try
{
file.ReadBlock(buffer, index, buffer.Length);
}
catch (System.IO.IOException e)
{
Console.WriteLine("Error reading from {0}. Message = {1}", path, e.Message);
}
finally
{
if (file != null)
{
file.Close();
}
}
and this:
string path = #"c:\users\public\test.txt";
System.IO.StreamReader file = new System.IO.StreamReader(path);
char[] buffer = new char[10];
try
{
file.ReadBlock(buffer, index, buffer.Length);
}
catch (System.IO.IOException e)
{
Console.WriteLine("Error reading from {0}. Message = {1}", path, e.Message);
}
if (file != null)
{
file.Close();
}
Is really finally block necessary in this construction. Why Microsoft provided such construction? It seems to be redundant. Isn't it?

Imagine if some other exception occurred that you haven't handled, e.g. an ArgumentOutOfRangeException, or if you want to rethrow the exception or throw a wrapped exception from your catch block:
The first block would ensure that the file is closed regardless of whether or not an exception occurred.
The second block would only close the file if either no exception occurred or an IOException occurred. It does not handle any other cases.

The first block will close the file even if there is an uncaught exception.
The second block will close the file only if there are no exceptions, or any thrown exceptions are caught.
The first will also ensure that the file is closed if the try has a break, goto, return, continue, or any other jump construct that would cause the execution to move outside of the try block. The second doesn't, and as such it could result in the resource not being closed.

In your example, if your code throws an exception other than System.IO.IOException, your cleanup code is not guaranteed to run. With the finally block, the code within it will run no matter what type of exception is thrown.

In that case it's redundant.
It's usefull if you for example will rethrow an exception and still want some code to run after the block:
try {
// do something dangerous
} catch(...) {
// log the error or something
throw; // let the exception bubble up to the caller
} finally {
// this always runs
}
// this only runs if there was no exception
Another example is if the catch may throw an exception for a different reason:
try {
// do something dangerous
} catch(...) {
// handle the error
// log the error, which may cause a different exception
} finally {
// this runs even if the catch crashed
}
// this only runs if there was no exception, or the code in the catch worked
Simply, as code might crash for plenty of reasons you might not even know about, it's useful to put the cleanup in a finally block just to be sure that it runs whatever happens.

Imagine there was an exception inside catch{}, code inside finally would still run but if (file != null){} block will not.

Try inside catch to ensure finally executes

I have to process items off a queue.
Deleting items off the queue is a manual call to Queue.DeleteMessage. This needs to occurs regardless of whether or not the processing succeeds.
var queueMessage = Queue.GetMessage();
try
{
pipeline.Process(queueMessage);
}
catch (Exception ex)
{
try
{
Logger.LogException(ex);
}
catch { }
}
finally
{
Queue.DeleteMessage(queueMessage);
}
Problem:
On failure, I log the error to some data store. If this logging fails (perhaps the data store is not available), I still need the message to be deleted from the queue.
I have wrapped the LogException call in another try catch. Is this the correct way or performing thing?

Following code is enough. finally blocks execute even when exception is thrown in catch block.
var queueMessage = Queue.GetMessage();
try
{
pipeline.Process(queueMessage);
}
catch (Exception ex)
{
Logger.LogException(ex);
}
finally
{
Queue.DeleteMessage(queueMessage);//Will be executed for sure*
}

The finally block always executes, even if it throws an unhandled error (unless it end the app). So yes.

Handling Error "WebDev.WebServer.Exe has stopped working"

Is there a way to handle the error "WebDev.WebServer.Exe has stopped working" in ASP.NET and keep the page running or even the just the WebServer running? Or is this an impossible task and is essentially like asking how to save someone's life after they've died?
I have the error-causing code inside a try/catch block, but that doesn't make a difference. I've also tried registering a new UnhandledExceptionEventHandler, but that didn't work either. My code is below in case I'm doing something wrong.
Also to be clear, I'm not asking for help on how to prevent the error; I want to know if and when the error happens if there's anything I can do to handle it.
UPDATE 1: TestOcx is a VB6 OCX that passes a reference of a string to a DLL written in Clarion.
UPDATE 2: As per #JDennis's answer, I should clarify that the catch(Exception ex) block is not being entered either. If I removed the call to the OCX from the try\catch block it still won't reach the UnhandledException method. There are essentially two areas that don't ever get executed.
UPDATE 3: From #AndrewLewis, I tried to also add a regular catch block to catch any non-CLS compliant exceptions, and this did not work either. However, I later found that since .NET 2.0 on, all non-CLS exceptions are wrapped inside RuntimeWrappedException so a catch (Exception) will catch non-CLS compliant exceptions too. Check out this other question here for more info.
public bool TestMethod()
{
AppDomain.CurrentDomain.UnhandledException +=
new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);
string input = "test";
string result = "";
try
{
TestOcx myCom = new TestOcx();
result = myCom.PassString(ref input); // <== MAJOR ERROR!
// do stuff with result...
return true;
}
catch (Exception ex)
{
log.Add("Exception: " + ex.Message); // THIS NEVER GETS CALLED
return false;
}
}
private static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
// THIS NEVER GETS CALLED
try
{
Exception ex = (Exception)e.ExceptionObject;
log.Add("Exception: " + ex.Message);
}
catch (Exception exc)
{
log.Add("Fatal Non-UI Error: " + exc.Message);
}
}

You should try catching non-CLS compliant exceptions to make sure nothing is being thrown (keep in mind you don't want to do this in production, always be specific!):
try
{
TestOcx myCom = new TestOcx();
result = myCom.PassString(ref input); // <== MAJOR ERROR!
// do stuff with result...
return true;
}
catch (Exception ex)
{
log.Add("Exception: " + ex.Message); // THIS NEVER GETS CALLED
return false;
}
catch
{
//do something here
}

Your code reads //THIS NEVER GETS CALLED.
If you catch the exception it is no longer un-handled. this is why it doesn't fire an unhandledexception event.