The dictionary NSDictionary in OC and the dictionary nsdictionary in oc

The dictionary NSDictionary in OC and the dictionary nsdictionary in oc

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Dictionary

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NSDictionary * dict = [[NSDictionary alloc] initWithObjectsAndKeys: @ "One", @ "1", @ "Two", @ "2", @ "Three ", @ "3", @ "One", @ "4", nil];

// The data in the dictionary is stored as a key-value pair.

// @ "One" and @ "1" form a key-Value Pair

// @ "1" is called a key)

// @ "One" is called a value)

// The value is the data to be stored, and the key is the index of the data to be searched.

// The function of the dictionary is to quickly find the value through the key.

// The value can be repeated and the key is unique.

// The key-value pairs in the dictionary are not ordered. There is no so-called first key-value pair, and the second key-Value Pair

// Keys and values are all arbitrary objects, and the address of the objects stored in the dictionary. However, keys often use strings.

NSDictionary * dict2 =@ {@ "4": @ "Four", @ "1": @ "One", @ "2": @ "Two ", @ "3": @ "Three "};

NSLog (@ "% @", dict );

NSLog (@ "% @", dict2 );

// The address of the returned value through the Input key

NSString * value = [dict objectForKey: @ "3"];

Value = dict [@ "3"];

// After Xcode 4.6

// If no corresponding key exists, nil is returned.

NSLog (@ "% @", value );

// Total number of return key-value pairs

NSUInteger count = [dict count];

NSLog (@ "% lu", count );

// Return all keys

NSArray * keys = [dict allKeys];

// Return all values

NSArray * values = [dict allValues];

// Traverse the dictionary

For (NSString * key in dict ){

// Each cycle key points to a key

// Uses the traversal key to indirectly traverse the value

NSLog (@ "% @", dict [key]);

}

NSMutableDictionary * mutableDict = [[NSMutableDictionary alloc] init];

// Reset the dictionary

[MutableDict setDictionary: @ {@ "1": @ "One", @ "2": @ "Two", @ "3": @ "Three"}];

// Add

[MutableDict setObject: @ "Four" forKey: @ "4"];

// Delete

// Delete a value using the key

[MutableDict removeObjectForKey: @ "3"];

// Delete multiple values using multiple keys

[MutableDict removeObjectsForKeys: @ [@ "1", @ "2", @ "3"];

// Delete all key-value pairs

[MutableDict removeAllObjects];

△Oc is a very beautiful language. Its names are basically a combination of words. You can learn about this method or the role of this variable through the name;