将NSNumber与int进行比较

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:

我有一个简单的问题(我想):我试图比较NSNumber和int，看看它是0还是1。这是代码:

id i = [dictionary objectForKey:@"error"]; //class = NSCFNumber

NSLog(@"%@ == 0 -> %@", i, i == 0);
NSLog(@"%@ == 0 -> %@", i, [i compare:[NSNumber numberWithBool:NO]]);

I tried this to methods but I get null as result:

我尝试了这个方法，但结果是空的:

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)

Can you help me?

你能帮我吗?

5 个解决方案

#1

The result of comparison is a BOOL which is not an Objective-C object. Therefore you should not print it using %@. Try %d instead (shows 0 or 1).

比较的结果是一个BOOL，它不是Objective-C对象。因此，不应该使用%@打印它。尝试%d(显示0或1)。
[a compare:b] returns -1 if a < b, 0 if a == b and 1 if a > b. So your 2nd result is expected.

[a compare:b]如果a < b，返回-1;如果a = b，返回0;如果a = b，返回1。
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.

不能直接将NSNumber与整数进行比较。i == 0实际上是一个指针比较，它检查i是否为NULL(0)，如果这个数字存在，它当然是假的。所以第一个结果也是预期的。
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.

如果你想检查平等，使用[a isEqualToNumber:b]。或者，您可以使用[一个intValue]提取整数，并直接与另一个整数进行比较。

So the followings should work:

因此，下面的工作应该是:

NSLog(@"%@ == 0 -> %d", i, [i isEqualToNumber:[NSNumber numberWithInt:0]]);
NSLog(@"%@ == 0 -> %d", i, [i intValue] == 0);

If the "number" is in fact a boolean, it's better to take the -boolValue instead.

如果“数字”实际上是一个布尔值，最好使用-boolValue代替。

NSLog(@"%@ == 0 -> %d", i, ! [i boolValue]);

#2

Here you're comparing the pointer of the object i with 0, which I'm afraid is not what you want.

这里你比较的是对象i和0的指针，恐怕不是你想要的。

You most probably want to compare the value of i:

你可能想要比较i的值:

if ([i intValue]==0) {
  ...
}

#3

You can easily write:

你可以写:

NSNumber *number = [NSNumber numberWithInt:123];
int integer = 1234;

NSLog(@"%@ == %i : %i", number, integer, [number intValue] == integer);

Output should be

输出应该

123 == 1234 : 0

I hope i can help you!

我希望我能帮助你!

#4

You have two problems:

你有两个问题:

You are confusing the NSNumber object with the value it represents.
您将NSNumber对象与它表示的值混淆。
Your NSLog format string does not match the types of the arguments that you provide.
您的NSLog格式字符串不匹配您提供的参数的类型。

Regarding the first problem: i is an address, perhaps something like 0x1f84b. When you test whether i == 0, you are testing whether i == NULL. In this case, that means you are testing whether the key "error" was present in the dictionary or not, since looking up a non-existent key garners a NULL.

关于第一个问题:i是一个地址，比如0x1f84b。当您测试i是否= 0时，您是在测试i是否== NULL。在本例中，这意味着您正在测试是否在字典中出现了关键的“错误”，因为查找不存在的密钥garners为NULL。

[i intValue], on the other hand, is an integer. If the NSNumber contains a value representable as an integer, this will be the value of the NSNumber. That is what you see when you print the NSNumber's description using the %@ format specifier.

另一方面，[i intValue]是一个整数。如果NSNumber包含一个可表示为整数的值，那么这个值就是NSNumber的值。当您使用%@格式说明符打印NSNumber的描述时，您将看到这一点。

Regarding the second problem: Comparisons in C and Objective-C return an integer, either 0 (meaning false) or 1 (meaning true). In order to directly print the result of a comparison, you thus need to use the integer format specifier. There are actually two such specifiers, %i and %d. You could wrap the result of the comparison in an NSNumber and use %@ to print that, but that's more work than it's worth.

关于第二个问题:C和Objective-C中的比较返回一个整数，0(表示false)或1(表示true)。为了直接打印比较的结果，因此需要使用整数格式说明符。实际上有两个这样的说明符，%i和%d。您可以将比较的结果封装在一个NSNumber中，并使用%@来打印它，但这比它的价值要大得多。

So, here's what you should be doing:

所以，这是你应该做的:

NSNumber *i = [dictionary objectForKey:@"error"];
BOOL haveValue = (i != NULL);
if (haveValue) {
    int iValue = [i intValue];
    NSLog(@"%d == 0 -> %d", iValue, iValue == 0);
    NSLog(@"%@ compared to 0 -> %d", i, [i compare:[NSNumber numberWithInt:0]]);
} else {
    NSLog(@"*** Dictionary has no value for key \"error\"!");
}

#5

This worked

这个工作

if (thevariable.intValue==0) {
  ...
}

#1

The result of comparison is a BOOL which is not an Objective-C object. Therefore you should not print it using %@. Try %d instead (shows 0 or 1).

比较的结果是一个BOOL，它不是Objective-C对象。因此，不应该使用%@打印它。尝试%d(显示0或1)。
[a compare:b] returns -1 if a < b, 0 if a == b and 1 if a > b. So your 2nd result is expected.

[a compare:b]如果a < b，返回-1;如果a = b，返回0;如果a = b，返回1。
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.

不能直接将NSNumber与整数进行比较。i == 0实际上是一个指针比较，它检查i是否为NULL(0)，如果这个数字存在，它当然是假的。所以第一个结果也是预期的。
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.

如果你想检查平等，使用[a isEqualToNumber:b]。或者，您可以使用[一个intValue]提取整数，并直接与另一个整数进行比较。