==oc== Dictionary Collection = =

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=========== Dictionary Collection ========== Dictionary Collection ========= Dictionary collection ============//

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/*

Dictionaries are used to hold collections with mapping relationships (Key-value pairs) of data

A key-value is considered an entry, and the dictionary is a container for storing key-value pairs.

Unlike arrays, arrays access data by subscript, and array subscripts are unique

Dictionary accesses elements by key, key cannot be duplicated, value must be object

Key-value pairs are stored in the dictionary as unordered

Dictionaries are divided into: immutable dictionaries (nsdictionary) can be read only cannot be changed and mutable dictionary (nsmutabledictionary)

*/

Immutable dictionary, initialization dictionary, general key value is a string object, null value is represented by the Nsnull object

Nsdictionary *dic1 = [nsdictionary dictionarywithobject:@ "value1" forkey:@ "Key1"];

Nsdictionary *dic2 = [nsdictionary dictionarywithobjectsandkeys:@ "value2", @ "Key2", @ "Value3", @ "Key3", nil];

Nsdictionary *dic3 = [Nsdictionary dictionarywithdictionary:dic2];

Nsdictionary *dic4 = @{@ "Key1": @ "value1" @ "Key2": @ "value2"};//syntax sugar, between key-value pairs with "," separated by ":" Between the key and value values

Get the number of dictionaries

Nsinteger int1 = [Dic1 count];

NSLog (@ "%lu", int1);

Get value values by key value

NSString *result = [Dic2 objectforkey:@ "Key2"];//takes the value out of the key value to remove the Key2 corresponding value

NSLog (@ "%@", result);

The key value is taken out according to value, and all key values can be removed

Nsarray *RESULT2 = [Dic2 allkeysforobject:@ "value2"];//remove the key value based on value (all key values can be taken)

NSLog (@ "%@", RESULT2);

Takes all key values to return an array, which is received with the array Nsaarry

Nsarray *keyarray = [dic3 AllKeys];

NSLog (@ "%@", Keyarray);

Remove all value values

Nsarray *valuearray = [dic3 allvalues];

NSLog (@ "%@", ValueArray);

Converts the key value of a dictionary into an enumeration object for traversing

Nsenumerator *enumerator = [Dic2 keyenumerator];

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Variable dictionary/////////

Initialize, similar to immutable dictionaries

Nsmutabledictionary *DIC4 = [Nsmutabledictionary dictionary];

Nsmutabledictionary *dic5 = [nsmutabledictionary dictionarywithobjectsandkeys:@ "value1", @ "Key1", @ "value2", @ "Key2", NIL];

Add a dictionary to another

[Dic4 Addentriesfromdictionary:dic1];

Add elements to a dictionary

[Dic5 setobject:@ "Value3" forkey:@ "Key3"];

Set the content of DIC5 to the same content as Dic1

[Dic5 Setdictionary:dic1];

Removes all elements. Depending on the key value, you can also set the key value to array to pass in the array.

[Dic5 removeallobjects];

[Dic5 removeobjectforkey:@ "Key1"];

[Dic5 Removeobjectsforkeys:valuearray];

Fast Traversal method

For (ID key in dic5) {

ID obj = [dic5 Objectforkey:key];

NSLog (@ "%@", obj);

}

Common traversal methods

Nsarray *akey = [Dic5 AllKeys];

Nsinteger length = [Akey count];

for (int i = 0; i<length; i++) {

ID keynew = [akey objectatindex:i];

ID obj = [dic5 objectforkey:keynew];

NSLog (@ "%@", obj);

}

Using enumerator traversal

Nsenumerator *EMU1 = [Dic5 keyenumerator];

ID key = [emu1 nextobject];

while (key) {

ID obj = [dic5 Objectforkey:key];

NSLog (@ "%@", obj);

key = [EMU1 nextobject];

}

==oc== Dictionary Collection = =