问题描述
我有一个简单的问题(我认为):我正在尝试将 NSNumber 与 int 进行比较，看看它是 0 还是 1.代码如下:
I've a simple question (I think): I'm trying to compare a NSNumber with a int, to see if it is 0 or 1. Here is the code:
id i = [dictionary objectForKey:@"error"]; //class = NSCFNumber
NSLog(@"%@ == 0 -> %@", i, i == 0);
NSLog(@"%@ == 0 -> %@", i, [i compare:[NSNumber numberWithBool:NO]]);
我对方法进行了尝试，但结果为 null:
I tried this to methods but I get null as result:
2010-10-17 21:57:49.065 Api[15152:a0f] 0 == 0 -> (null)
2010-10-17 21:57:49.065 Api[15152:a0f] 0 == 0 -> (null)
你能帮帮我吗?
推荐答案
比较的结果是一个不是Objective-C对象的BOOL.因此，您应该不使用
%@打印它.改用%d(显示 0 或 1).
The result of comparison is a BOOL which is not an Objective-C object. Therefore you should not print it using
%@. Try%dinstead (shows 0 or 1).
[a compare:b] 如果 a < 则返回 -1b，如果 a == b 则为 0，如果 a > 则为 1b.所以你的第二个结果是预期的.
[a compare:b] returns -1 if a < b, 0 if a == b and 1 if a > b. So your 2nd result is expected.
您不能直接将 NSNumber 与整数进行比较.i == 0 实际上是一个 pointer 比较，它检查 i 是否为 NULL (0)，如果该数字存在，这当然是 FALSE.所以第一个结果也是预期的.
You cannot compare an NSNumber directly with an integer. That i == 0 is actually a pointer comparison which checks whether i is NULL (0), which of course is FALSE if that number exists. So the 1st result is also expected.
如果你想检查是否相等，使用[a isEqualToNumber:b].或者，您可以使用 [a intValue] 提取整数并直接与另一个整数进行比较.
If you want to check for equality, use [a isEqualToNumber:b]. Alternatively, you could extract the integer out with [a intValue] and compare with another integer directly.
所以以下应该可以工作:
So the followings should work:
NSLog(@"%@ == 0 -> %d", i, [i isEqualToNumber:[NSNumber numberWithInt:0]]);
NSLog(@"%@ == 0 -> %d", i, [i intValue] == 0);
如果数字"实际上是一个布尔值，最好使用 -boolValue.
If the "number" is in fact a boolean, it's better to take the -boolValue instead.
NSLog(@"%@ == 0 -> %d", i, ! [i boolValue]);
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