Cocoa KVC：“类不符合关键值编码”

Question

I'm trying to update some properties with KVC. The properties have been synthesized.

This line works:

myObject.value = intValue;

This doesn't work:

[self setValue:[NSNumber numberWithInt:intValue] forKey:@"myObject.value"];

And blows up with: Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<MyViewController 0xd1cec0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key myObject.value.'

Yet further up the method (awakeFromNib) other instances of the same class respond fine to setValue:forKey: calls. The only difference is this particular instance was created and wired up in IB.

Answer 1

You cannot pass a key path as the second argument to -[NSObject setValue:forKey:] . You want to use setValue:forKeyPath: instead:

[self setValue:[NSNumber numberWithInt:intValue] forKeyPath:@"myObject.value"];

My understanding is that setValue:forKey: is provided as a performance optimization. Since it cannot take a key path, it doesn't have to parse the key string.

Answer 2

它告诉你这不是该对象的有效键，实际上它不是：“myObject.value”是一个键路径，而不是一个键。

Answer 3

I agree with Chuck.

I think you need to do this instead:

[self setValue:[NSNumber numberWithInt:intValue] forKeyPath:@"myObject.value"];

or via each part of the key path like:

id myObject = [self objectForKey:@"myObject"];
[myObject setValue:[NSNumber numberWithInt:intValue] forKey:@"value"];