Question

Here is my code:

.h

@interface AppDelegate : NSObject <NSApplicationDelegate>{
    NSString *lastValue;
}

.m

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
    lastValue = nil; 
}

- (void) fullDMXReceived:(NSString*)finalData {

    if (finalData != lastValue) {
        lastValue = finalData;

        // doing something
     }
}

For some reason, ‘doing something’ is only called once, and it stops.

Some background info: ‘fullDMXReceived’ is called every 100 miliseconds or so with new information. Sometimes (many times actually) the data is the same, and thus, I do not want ‘doing something’ to run. If it’s different, I DO want ‘doing something’ to happen.

I’m not sure why it’s only running ‘doing something’ once even when the finalData changes.

Any ideas?

Answer 1

If buffer in fullDMXReceived: is a NSMutableString instance that is reused you will need to copy the actual string instead of just assign the instance, try something like this:

- (void) fullDMXReceived:(NSString*)finalData {
    if (finalData != nil &&
        ![finalData isEqualToString:lastValue]) {
        [lastValue release]; // only needed if you don't use ARC
        lastValue = [finalData copy];
        // doing something
     }
}