如何测试NSString是否为零？

Question

我可以简单地使用

if(myString == nil)

由于某种原因,我知道的字符串为null,这个语句失败了.

Answer 1

您的字符串可能实际上nil不是,而只是一个空字符串？您可以尝试测试是否[myString length] == 0.

Answer 2

您可以在此处找到有关目标C字符串的更多信

+ (BOOL ) stringIsEmpty:(NSString *) aString {

    if ((NSNull *) aString == [NSNull null]) {
        return YES;
    }

    if (aString == nil) {
        return YES;
    } else if ([aString length] == 0) {
        return YES;
    } else {
        aString = [aString stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceAndNewlineCharacterSet]];
        if ([aString length] == 0) {
            return YES;
        }
    }

    return NO;  
}

+ (BOOL ) stringIsEmpty:(NSString *) aString shouldCleanWhiteSpace:(BOOL)cleanWhileSpace {

    if ((NSNull *) aString == [NSNull null]) {
        return YES;
    }

    if (aString == nil) {
        return YES;
    } else if ([aString length] == 0) {
        return YES;
    } 

    if (cleanWhileSpace) {
        aString = [aString stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceAndNewlineCharacterSet]];
        if ([aString length] == 0) {
            return YES;
        }
    }

    return NO;  
}

Answer 3

你可以用这个检查你的字符串

   if(myString==(id) [NSNull null] || [myString length]==0 || [myString isEqualToString:@""])
    {
     //String is null or bad response
    }