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Re: why would this crash?

To: REALbasic Network Users Group <realbasic-nug at lists dot realsoftware dot com>
Subject: Re: why would this crash?
From: Chris Halford <chris at icctools dot com>
Date: Thu, 3 Jul 2003 12:45:24 -0600

On Thursday, July 3, 2003, at 12:19  PM, Thomas Reed wrote:

If you want to get a pixel color, you need to access that color from the original Picture you drew into the canvas.

Actually, that's what I was doing, and moved it to the backdrop when the crashing started.

Well, though you didn't comment on it, I hope you read the rest of my message, since it'll give you at least some of the details you need to solve these problems.
I did.

BTW, you need to be more specific in the future when you say "bomb" or "crash".

Application stops running. No exception handling can prevent it. I get a message from the os telling me that the app has encountered a problem and needs to close. Microsoft is kind enough to add "We are sorry for the inconvenience"

Technically, I don't think you're seeing a crash. If your app is quitting and telling you there was a NilObjectException, that's not really a crash.
Nope. that's not what is happening. I have an exception handler that never gets touched.

It's a graceful exit on an error condition. Your code could handle the exception and keep going without crashing.
Nope, it can't in this case. That would be my preference, and how I normally code to handle exceptions.

Further, it tells you exactly what the problem is -- in this case, you're trying to access a property or method of an object that is nonexistent (nil).
I have a picture that I'm trying to get a colour from. I've set it as the backdrop of a canvas. The canvas' backdrop graphics cannot be accessed, and the only reason I tried to do that is because the original picture object's graphics cannot be accessed either. I now have excessive checking for nil ( i'm checking everything ) Checking for p.grahics = nil bombs me. Bomb meaning that no exception handler is touched - the application stops and no further code is executed. And, no, if I was simply trying to access something that is nil, then I wouldn't be emailing the list. I have enough experience to know how to check for a nil object. When I check for it being nil, I bomb ( bomb as explained above )


So, please tell what you mean by "crash" in the future.
Noted above.

  If it's an exception, say so and give the exception type.
It isn't.

If it's a hard crash of some kind (freeze, crash with the Finder reporting the application unexpectedly quit, etc), describe it.
Above.




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