Question

如何判断NSMutableDictionary是否有某个key

Answer 1

如下判断
keyEnumerator
Returns an enumerator object that lets you access each key in the receiver.

- (NSEnumerator *)keyEnumerator

Return Value
An enumerator object that lets you access each key in the receiver.

Discussion
The following code fragment illustrates how you might use this method.

NSEnumerator *enumerator = [myDictionary keyEnumerator];
id key;

while ((key = [enumerator nextObject])) {
/* code that uses the returned key */
}

If you use this method with instances of mutable subclasses of NSDictionary, your code should not modify the entries during enumeration. If you intend to modify the entries, use the allKeys method to create a “snapshot” of the dictionary’s keys. Then use this snapshot to traverse the entries, modifying them along the way.

Note that the objectEnumerator method provides a convenient way to access each value in the dictionary.

Availability
Available in iPhone OS 2.0 and later.
See Also
– allKeys
– allKeysForObject:
– getObjects:andKeys:
– objectEnumerator
– nextObject (NSEnumerator)
Declared In
NSDictionary.h