在NSDictionary中设置值时，@“ 1.5”和@（1.5）有什么区别？

Question

In iPhone project,

It was while I was while setting Value in dictionary,

NSMutableDictionary*dictionary=[[NSMutableDictionary alloc] init];
        [dictionary setValue:@(2.8) forKey:@"Why"];

AND,

NSMutableDictionary*dictionary=[[NSMutableDictionary alloc] init];
        [dictionary setValue:@"2.8" forKey:@"Why"];

My question is Why not @"2.5" and @(2.5) ?

Answer 1

You have two questions, it would be better to have a single question.

But as to the difference, @"2.5" is an NSString where @(2.5) is an NSNumber . There is a big difference between textual and numeric data.

As for why you need an NSNumber and not NSString is obvious: the kerning is a numeric value.

Answer 2

using the @() syntax you can box arbitrary C expressions. This makes it trivial to turn basic arithmetic calculations into NSNumber objects see below:

double x = 24.0;
NSNumber *result = @(x * .15);
NSLog(@"%.2f", [result doubleValue]);

You can also refer NSNumber object as @"" string but cant make calculations like above example. In your case both are acceptable but here calculation makes difference.

Answer 3

When you use

@"2.5" it's behave like a string

NSMutableDictionary*dictionary=[[NSMutableDictionary alloc] init];
  [dictionary setValue:@"2.8" forKey:@"Why"];;
  NSString *a =   [dictionary ValueforKey:@"Why"];

but when you use @(2.8) then it's behave like a NSNumber

NSMutableDictionary*dictionary=[[NSMutableDictionary alloc] init];
  [dictionary setValue:@(2.8) forKey:@"Why"];;
  NSNumber *a =   [dictionary ValueforKey:@"Why"];

Answer 4

@(2.8) is a type of NSNumber.

@"2.8" is a type of NSString.

Both the type and value were different between there two.