On 6 Oct 2011, at 15:23, Stephan Michels wrote:
>
> Am 06.10.2011 um 15:54 schrieb Torsten Curdt:
>
>> Well, if the model is more complex and you bind the view to the model
>> you can of course trigger the re-display on the observed changes. But
>> what about a simple title property of e.g. a NSButton?
>>
>> ...and I guess triggering a re-display is not the only use case for
>> this "setter extension" - or whatever you want to call it.
>
> I never implement setters/getters for myself. I find it error-prone and it
> feels wrong to me.
>
> To give you another example. I use KVO to generate background images
> in UIButton
>
> [self addObserver:self forKeyPath:@"color"
> options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld |
> NSKeyValueObservingOptionInitial context:NULL];
> [self addObserver:self forKeyPath:@"size"
> options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld |
> NSKeyValueObservingOptionInitial context:NULL];
> [self addObserver:self forKeyPath:@"showShadow"
> options:NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld |
> NSKeyValueObservingOptionInitial context:NULL];
>
> - (void)observeValueForKeyPath:(NSString *)keyPath
> ofObject:(id)object
> change:(NSDictionary *)change
> context:(void *)context {
> if (![change keyValueChanged]) {
> return;
> }
>
> if([keyPath isEqualToString:@"color"] ||
> [keyPath isEqualToString:@"size"] ||
> [keyPath isEqualToString:@"showShadow"]) {
> [self setBackgroundImage:[HDEButton
> backgroundImageForButtonWithColor:self.color size:self.size]
> forState:UIControlStateNormal];
> [self setBackgroundImage:[HDEButton
> backgroundImageForButtonWithColor:HDEGrayBackgroundColor size:self.size]
> forState:UIControlStateDisabled];
> [...]
>
> Self observing works great for me.
Note that you should really pass in a context pointer and test that in the
-observe… method, rather than testing the key paths. Call super for all other
key paths.
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