feldman@umd5.umd.edu (Mark Feldman) (02/02/89)
Objective C (obj-C), the Interface Builder (IB), and runtime binding (RB), without a doubt, make writing applications and incorporating previously created objects relatively easy. Non-programmers or, at least, ``light weight programmers'' can connect objects and create interfaces without having to know the underlying obj-C. If you have an object and know its actions and outlets (input and output messages), NeXT provides a wondeful erector set-like environment. The problem that I have run into is what happens when there are obj-C RB problems. What happens when certain connections are not made or actions contain typos or use the wrong parameters? You have to become a programmer to find the problem -- that's what. When writing one application, I accidentally put a space in the name of an action for an object that I was creating. The space wasn't very noticable in IB because of the font being used. Proportional fonts are great things... for some applications. I couldn't figure out why the input to the interface wasn't getting to my object. I would like to see a way of trapping messages sent off to space without being forced to use the the GNU debugger (gdb). I'm not putting down gdb, I just don't think that gdb is an appropriate tool for people doing little or no progamming, just connecting objects. If you write and distribute product-quality objects that will be integrated into other applications -- one of the goals of NeXT, obj-C, and object oriented programming in general -- your objects should be robust and be able to operate around a poorly formed environment, failing gracefully when other needed objects do not exist or do not make use of the actions and parameters that you think that they should. An example is in order... I write and distribute an object called foobar (don't you just love realistic examples?). A foobar undestands the method foo and it talks to an outlet called bar. The message that a foobar sends to its bar outlet is setStringValue. If someone uses (buys?) my foobar and either forgets to connect its bar outlet or connects it to something that doesn't understand setStringValue, they will be at a loss if things stay as they are. I would like to trap the fact that [bar setStringValue:myString] went off into space or was not understood and have the chance to take corrective action. Perhaps my corrective action would be nothing more than to put up a small window explaining what had gone wrong in English. Ideas? Comments? Large sums of money? Mark
gore@eecs.nwu.edu (Jacob Gore) (02/02/89)
/ comp.sys.next / feldman@umd5.umd.edu (Mark Feldman) / Feb 1, 1989 / >I would >like to trap the fact that [bar setStringValue:myString] went off into space >or was not understood and have the chance to take corrective action. >Perhaps my corrective action would be nothing more than to put up a small >window explaining what had gone wrong in English. > >Ideas? I'm afraid I'm in no position to test this at the moment, and my Objective-C manual and knowledge are a couple of years old. But you did ask for ideas, so: Here's what that old manual says in the listing of methods for class Object (which every other class inherits from, directly or transitively): -doesNotRecognize:(STR)aMessage The message routine reports that the receiver did not recognize aMessage by sending 'doesNotRecognize:aMessage' to the receiver instead. It is defined as: return [self error:"%s does not recognize %s", NAMEOF(self), aMessage] In plain English, this means that what happens in your example is that '[bar doesNotRecognize:"setStringValue"]' is done, and 'bar' probably deals with it according to the "doesNotRecognize:" method it inherited from class Object (unless some class in between bar's class and class Object redeclared that method, in which case bar's class, of course, would inherit it from there). So, all you have to do is provide your own "doesNotRecognize:(STR)aMessage" method to 'bar', either in the definition of its class, or in the definition of one of its superclasses. If the current implementation of Objective-C supports multiple inheritance, the best way to handle this is to create a class, say, NotRecognizedPanel, which defines "doesNotRecognize:" to pop up one of those error panels with OK/Cancel/etc. choices. Then bar's class can just add NotRecognizedPanel to the list of its superclasses. Inheritance is fun. Jacob Gore Gore@EECS.NWU.Edu Northwestern Univ., EECS Dept. {oddjob,gargoyle,att}!nucsrl!gore