Re: Properties, read only and bindings

[Bill Bumgarner]

On Aug 6, 2008, at 9:51 PM, Steven W Riggins wrote:

I'm winding my way through KVO, readonly properties and bindings.







Changing the readonly property to a normal ivar works fine.

I have an object which has a bool state. I have a method that toggles that state. I have a button that calls the method that toggles the state. The button has a title, which I've bound to a readonly property, which has a getter that returns a localized label based on the state. So when I change the state, obviously the readonly property doesn't change, and thus the button label does not change. Is there a way to use a synthesized property in this manner, or is it even proper?

You can solve this in the following two ways (amongst others):



I.e.

.h:
@interface Foo : NSObject
{
        BOOL f;
}

@property(readonly, nonatomic) BOOL f;
@end

.m
@interface Foo()
@property(readwrite, nonatomic) BOOL f;
@end

@implementation Foo
@synthesize f;
// ... use the setter and getter as needed
@end

(2) Call willChange/didChange before/after you change the value:

- (void) toggle: sender
{
        .... logic ...
        [self willChangeValueForKey: @"f"];
        f = ... new state ...;
        [self didChangeValueForKey: @"f"];
}

b.bum

(1) Redeclare the property as readwrite in a class extension in your .m file and then use dot syntax or the synthesized setter/getter to set the value.

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