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?

在任何情况下，最好的方法是检查给定字符串的长度。如果你的字符串是myString，那么代码是:

    int len = [myString length];
    if(len == 0){
       NSLog(@"String is empty");
    }
    else{
      NSLog(@"String is : %@", myString);
    }

- (BOOL)isEmpty:(NSString *)string{
    if ((NSNull *) string == [NSNull null]) {
        return YES;
    }
    if (string == nil) {
        return YES;
    }
    if ([string length] == 0) {
        return YES;
    }
    if ([[string stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceAndNewlineCharacterSet]] length] == 0) {
        return YES;
    }
    if([[string stringByStrippingWhitespace] isEqualToString:@""]){
        return YES;
    }
    return NO;
}

//Different validations:
 NSString * inputStr = @"Hey ";

//Check length
[inputStr length]

//Coming from server, check if its NSNull
[inputStr isEqual:[NSNull null]] ? nil : inputStr

//For validation in allowed character set
-(BOOL)validateString:(NSString*)inputStr
{
    BOOL isValid = NO;
    if(!([inputStr length]>0))
    {
        return isValid;

    }

    NSMutableCharacterSet *allowedSet = [NSMutableCharacterSet characterSetWithCharactersInString:@".-"];
    [allowedSet formUnionWithCharacterSet:[NSCharacterSet decimalDigitCharacterSet]];
    if ([inputStr rangeOfCharacterFromSet:[allowedSet invertedSet]].location == NSNotFound)
    {
        // contains only decimal set and '-' and '.'

    }
    else
    {
        // invalid
        isValid = NO;

    }
    return isValid;
}

试试下面的方法

NSString *stringToCheck = @"";

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

if (string.length == 0) stringIsEmpty;