Nsdictionary usage and common methods (start, add elements, delete elements, modify element values, etc.)

Dictionary dictionary is a kind of collection class.
Collections: Array, dictionary dictionary, set; arrays are sequential, and elements can be repeated; dictionaries are not sequential, keys are unique, values are repeatable, set is unordered, and cannot be duplicated.
A dictionary is a set of data that exists in the form of a key-value pair;
The key to the dictionary is unique;
The value of the dictionary is repeatable;
The key value of the dictionary is one by one corresponding, that is, how many keys, there are many values;
The key value pairs in the dictionary are not in order;
For example: ID card & name, ID card is the key, name is value.

Dictionaries are divided into variable dictionaries and variable dictionaries.
Attention:
Key values are object types and cannot be base values;

In particular, the keys are generally string object settings;

Immutable dictionary
//initialization
nsdictionary *dict001 = [[Nsdictionary alloc] initwithobjectsandkeys:@ "Zhang Shaofeng", @ "name", @ "male", @ " Sex ", nil];
NSLog (@ "\ n dict001 =%@ \ n", dict001);

Attribute
//1 count
nsinteger count = dict001.count;
NSLog (@ "\ n count =%ld \ n", count);

2 All keys
nsarray *keyarray = Dict001.allkeys;
NSLog (@ "\ n");
For (NSString *string in Keyarray)
{
	NSLog (@ "string =%@", string);
}

3 All values
nsarray *valuearray = dict001.allvalues;
NSLog (@ "\ n");
For (NSString *string in ValueArray)
{
	NSLog (@ "string =%@", string);
}

Dictionary operation
//Get key corresponding value
nsstring *value = [dict001 objectforkey:@ "name"];
NSLog (@ "\ n");
NSLog (@ "name =%@", value);

Variable dictionary
nsmutabledictionary *dict002 = [Nsmutabledictionary dictionarywithdictionary:dict001];
NSLog (@ "\ n dict002 =%@ \ n", dict002);

When adding objects
//1 SetObject, the value must be a Non-empty object type, and if the value is a non object type, the error
[dict002 setobject:@ "University than Industry" forkey:@ "education"];
[dict002 setobject:nil forkey:@ "Education"]; Compile an error
NSLog (@ "\ dict002 =%@ \ n", dict002);

2 SetValue, regardless of the value is not the object type, will not be an error, but the object will not be added to the dictionary
[dict002 setvalue:@ "Senior electrician" forkey:@ "job"];
[dict002 setvalue:nil forkey:@ "job"]; Can be compiled normally, but the object is not added to the dictionary
NSLog (@ \ dict002 =%@ \ n, dict002);

Replaces the value of the specified key
[dict002 setvalue:@ "IOS Dve" forkey:@ "job"];
NSLog (@ "\ n dict002 =%@ \ n", dict002);

Deletes the value corresponding to the specified key
//1 deletes the value corresponding to the specified key
[dict002 removeobjectforkey:@ "Job"];
NSLog (@ "\ n dict002 =%@ \ n", dict002);

2 Delete the specified key array corresponding to the value
nsarray *keys = @[@ "Education", @ "sex"];
[dict002 Removeobjectsforkeys:keys];
NSLog (@ "+\n dict002 =%@ \ n", dict002);

3 Delete all key values
[dict002 removeallobjects];
NSLog (@ "-\n dict002 =%@ \ n", dict002);

Reinitialize value
[dict002 setdictionary:dict001];
NSLog (@ "\ n dict002 =%@ \ n", dict002);