when to use “willChangeValueForKey” and “didChangeValueForKey”?

Question

I saw these lines in a demo project, but I couldn\'t understand why it did that.

[self willChangeValueForKey:@\"names\"];
[self didChangeValueForKey:@\"names\"];         


        

Answer 1

Agree with Barry. I just meet the same problem. Here is a case of using those two methods. I declared a readonly property. So I can't use the property's accessor to change the value.

@property (nonatomic, readonly) BOOL var;

When I want to change the "var", I need to call these two methods manually. Otherwise, observers won't get notified.

self willChangeValueForKey:@"var"];
var = YES;
[self didChangeValueForKey:@"var"];