这对我来说是一种魅力

如果NSString是s

if ([s isKindOfClass:[NSNull class]] || s == nil || [s isEqualToString:@""]) {

    NSLog(@"s is empty");

} else {

    NSLog(@"s containing %@", s);

}

我见过的最好的解决方案之一(比Matt G的更好)是这个改进的内联函数，我从一些Git Hub repo (Wil Shipley的一个，但我找不到链接):

// Check if the "thing" passed is empty
static inline BOOL isEmpty(id thing) {
    return thing == nil
    || [thing isKindOfClass:[NSNull class]]
    || ([thing respondsToSelector:@selector(length)]
        && [(NSData *)thing length] == 0)
    || ([thing respondsToSelector:@selector(count)]
        && [(NSArray *)thing count] == 0);
}

只需将字符串传递给以下方法:

+(BOOL)isEmpty:(NSString *)str
{
    if(str.length==0 || [str isKindOfClass:[NSNull class]] || [str isEqualToString:@""]||[str  isEqualToString:NULL]||[str isEqualToString:@"(null)"]||str==nil || [str isEqualToString:@"<null>"]){
        return YES;
    }
    return NO;
}

斯威夫特版本

即使这是一个Objective C问题，我需要在Swift中使用NSString，所以我也会在这里包括一个答案。

let myNSString: NSString = ""

if myNSString.length == 0 {
    print("String is empty.")
}

或者NSString是可选的:

var myOptionalNSString: NSString? = nil

if myOptionalNSString == nil || myOptionalNSString!.length == 0 {
    print("String is empty.")
}

// or alternatively...
if let myString = myOptionalNSString {
    if myString.length != 0 {
        print("String is not empty.")
    }
}

正常的Swift String版本是

let myString: String = ""

if myString.isEmpty {
    print("String is empty.")
}

请参见:检查Swift中的空字符串?

我检查了一个空字符串使用以下代码:

//Check if we have any search terms in the search dictionary.
if( (strMyString.text==(id) [NSNull null] || [strMyString.text length]==0 
       || strMyString.text isEqual:@"")) {

   [AlertView showAlert:@"Please enter a valid string"];  
}

试试下面的方法

NSString *stringToCheck = @"";

if ([stringToCheck isEqualToString:@""])
{
   NSLog(@"String Empty");
}
else
{
   NSLog(@"String Not Empty");
}