Representing dictionaries as strings, Storing dictionaries – Apple WebObjects 3.5 User Manual

Page 205

Commonly Used Dictionary Methods

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– removeObjectForKey:

Removes the entry for a speciﬁed key.

– removeObjectsForKeys:

Removes the entries for each key in a speciﬁed array.

– setDictionary:

Removes all the entries in the receiver, then adds the entries from
a speciﬁed dictionary.

Representing Dictionaries as Strings

– description

Returns a string that represents the contents of the receiver. For
example, the following code excerpt produces the string
“{“seatAssignment” = “Window”; “section” = “Non-smoking”;
“aircraft” = “747”}”:

id preferences = [NSMutableDictionary

dictionaryWithObjects:@("window", "non-smoking", "747")
forKeys:@("seatAssignment", "section", "aircraft")];

id description = [preferences description];

Storing Dictionaries

– writeToFile:atomically:

Writes the dictionary’s string representation to a speciﬁed ﬁle
using the

description

method. Returns YES on success and NO on

failure. If YES is speciﬁed for

atomically:

, this method attempts to

write the ﬁle safely so that an existing ﬁle with the speciﬁed path
is not overwritten. It does not create a new ﬁle at the speciﬁed
path unless the write is successful. The resulting ﬁle is suitable
for use with

dictionaryWithContentsOfFile:

. For example, the following

excerpt creates an NSMutableDictionary from the contents of the
ﬁle speciﬁed by

path

, updates the object for the key @“Language”,

and saves the updated dictionary back to the same ﬁle:

id defaults = [NSMutableDictionary

dictionaryWithContentsOfFile:path];

[defaults setObject:newLanguagePreference forKey:@"Language"];
[defaults writeToFile:path atomically:YES];