Rx : Issue with Exception handling stream - system.reactive

Question

I am trying to create a small rx Exception handling chunk of code, where I am expecting to get the same exception shown under a particular situation.
The actual use case is that I have a button that attempts to get data from the Clipboard, that the user may or may not have access to, which should result in a SecurityException being raised.
There is also the possibility that some other Exception may occur, which I would also like to handle (albeit showing a different error message to user).
There is also the possibility that something goes wrong with the stream itself, which I want to deal with in the subscribers OnError method.
Here is what I have so far (note I am using a TextBox to simulate the text that would be on the clipboard, and a checkbox to simulate whether a SecurityException should be raised or not)
private Subject<bool> simulatedPasteCommandSubject = new Subject<bool>();
private readonly CompositeDisposable disposables = new CompositeDisposable();
public Form1()
{
InitializeComponent();
WireUpSimulatedPasteCommandSubject();
}
private Func<IObservable<string>> ObserverableFactory
{
get
{
return () =>
{
return Observable.Defer(() =>
{
return simulatedPasteCommandSubject
.Select(_ => this.GetText())
.Where(x => !string.IsNullOrWhiteSpace(x))
.TrySelect<string, string>(this.TrySelectClipboardData);
});
};
}
}
private void WireUpSimulatedPasteCommandSubject()
{
var clipboardStream = ObserverableFactory();
this.disposables.Add(clipboardStream
.Catch((SecurityException ex) =>
{
this.ShowError("SecurityException");
return ObserverableFactory();
})
.Catch((Exception ex) =>
{
this.ShowError("Exception");
return ObserverableFactory();
})
.Do(data => LogData(data))
.Subscribe(
data => this.ImportTheClipboardData(data),
ex => this.ShowError("Something very bad happened")));
}
private void ImportTheClipboardData(string data)
{
MessageBox.Show(string.Format("Importing Clipboard data\r\n {0}", data));
}
private string GetText()
{
if (chkShouldThrow.Checked)
throw new SecurityException("SecurityException");
// simulate text coming from Clipboard
return textBox1.Text;
}
private void button1_Click(object sender, EventArgs e)
{
simulatedPasteCommandSubject.OnNext(true);
}
private bool TrySelectClipboardData(string dataIn, out string dataOut)
{
dataOut = string.Join("", dataIn.Reverse());
return true;
}
private void LogData(string data)
{
string dataLog = string.Format("Data : {0}", data);
Debug.WriteLine(dataLog);
}
private void ShowError(string ex)
{
string error = string.Format("Error : {0}", ex);
MessageBox.Show(error);
}
Sorry for the largish listing. Thing is if I type some text into the TextBox (to simulate the ClipBoard) and then click the button (which is simulating what the user would do, which makes the clipboard stream yield (OnNext)), I get what I expect. In this case a simple reversed string.
If however I click my CheckBox that should simulate a SecurityException being raised,and then click the button (which is simulating what the user would do, which makes the clipboard stream yield (OnNext)), I do indeed Catch the SecurityException, and see that logged. All good so far
Problem comes when I try and click the button again with the CheckBox that should simulate a SecurityException being raised still checked. I then get the following
"Exception"
Then when I try and click the button again with the CheckBox that should simulate a SecurityException being raised still checked. I then get the following
"Something very bad happened"
When what I am expecting to see is "SecurityException" being caught EVERY TIME, as it was the 1st time.
I have a feeling this is to do with the same stream being returned which was previously in the catch of the "SecurityException"

Answer 1

If I understand your code properly, You want all SecurityExcetions to be swallowed and the sequence to reconnect transparently to the user. ie If the user tries to access the clipboard multiple times they get the error message multiple times.
If this is the case, your problem lies with your lack of a loop. You get the sequence initially from the factory. If this sequence errors, then you get a second sequence. However if the 2nd sequence errors, you have no catch on that.
I think what you want to do is to catch the expected exceptions, show the message box, and then continue the sequence with the error. This will then allow you to log the error and also leverage the Retry() operator.
Maybe something like this will help
clipboardStream
.Catch((SecurityException ex) =>
{
this.ShowError("SecurityException");
return Observable.Throw<string>(ex);
})
.Catch((Exception ex) =>
{
this.ShowError("Exception");
return Observable.Throw<string>(ex);
})
.Do(data => LogData(data))
.Retry()
.Subscribe(
data => this.ImportTheClipboardData(data),
ex => this.ShowError("Wont get here (I dont think!)"));
Attempt 2
clipboardStream
.Do(data => LogData(data))
.Catch((SecurityException ex) =>
{
this.ShowError("SecurityException");
return Observable.Throw<string>(ex);
})
.Retry()
.Catch((Exception ex) =>
{
this.ShowError("Exception");
return Observable.Throw<string>(ex);
})
.Retry()
.Subscribe(
data => this.ImportTheClipboardData(data),
ex => this.ShowError("Wont get here (I dont think!)"));

Answer 2

Ok, So Lee Campbell Attempt 2 works a treat and gives me what I wanted. Here is full reworked solution (Thanks Lee)
public partial class Form1 : Form
{
private Subject<bool> simulatedPasteCommandSubject = new Subject<bool>();
private readonly CompositeDisposable disposables = new CompositeDisposable();
public Form1()
{
InitializeComponent();
WireUpSimulatedPasteCommandSubject();
}
private Func<IObservable<string>> ObserverableFactory
{
get
{
return () =>
{
return Observable.Defer(() =>
{
return simulatedPasteCommandSubject
.Select(_ => this.GetText())
.Where(x => !string.IsNullOrWhiteSpace(x))
.TrySelect<string, string>(this.TrySelectClipboardData);
});
};
}
}
private void WireUpSimulatedPasteCommandSubject()
{
var clipboardStream = ObserverableFactory();
this.disposables.Add(clipboardStream
.Do(data => LogData(data))
.Catch((SecurityException ex) =>
{
this.ShowError("SecurityException");
return Observable.Throw<string>(ex);
})
.Retry()
.Catch((Exception ex) =>
{
this.ShowError("Exception");
return Observable.Throw<string>(ex);
})
.Retry()
.Subscribe(
data => this.ImportTheClipboardData(data),
ex => this.ShowError("Wont get here (I dont think!)")));
}
private void ImportTheClipboardData(string data)
{
MessageBox.Show(string.Format("Importing Clipboard data\r\n {0}", data));
}
private string GetText()
{
if (chkShouldThrow.Checked)
throw new SecurityException("SecurityException");
// simulate text coming from Clipboard
return textBox1.Text;
}
private void button1_Click(object sender, EventArgs e)
{
simulatedPasteCommandSubject.OnNext(true);
}
private bool TrySelectClipboardData(string dataIn, out string dataOut)
{
dataOut = string.Join("", dataIn.Reverse());
return true;
}
private void LogData(string data)
{
string dataLog = string.Format("Data : {0}", data);
Debug.WriteLine(dataLog);
}
private void ShowError(string ex)
{
string error = string.Format("Error : {0}", ex);
MessageBox.Show(error);
}
}