Setobject: forkey: and setValue: forkey:

Time：2022-2-9
1： Differences and relations between setobject: forkey: and setValue: forkey:

1. Setobject: forkey: unique to nsmutabledictionary;
SetValue: forkey: is the main method of KVC;

2. Setobject: forkey:Object cannot be nil, otherwise an error will be reported ；As long as the parameter of key is an object, it is not limited to nsstring ；

The value in setValue: forkey: can be nil, and the removeobject: forkey: method will be called automatically at this time;The parameter of key can only be nsstring type ；

3. Nil is different from null, [nsnull null] indicates that it is an empty object, not nil;

4. SetValue: forkey: it is created in the nsobject object, that is, all objects have this method, which can be used in any class; (when the method caller is an object)

2： Objectforkey: and valueforkey:

There are two methods for nsdictionary value, objectforkey: and valueforkey:
(it is recommended to use objectforkey:)

1.If the key does not start with @ match, they are the same ；

2.If key starts with @For example: @ “@ hhisiskey”, valueforkey: will remove @, and then execute [super valueforkey] with the rest;

3. Example: person * person = [person alloc] init];
person.name = @“Chen”;
Pass: [person valueforkey: @ “name”]; Take out: Chen. This is KVC’s method.

4. Valueforkey: the value is to find a property accessor with the same name as the specified key. If it is not found, execute valueforundefined key:, while valueforundefined key: by default, throw a crash exception;

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