Check if an NSString is just made out of spaces

问题

I want to check if a particular string is just made up of spaces. It could be any number of spaces, including zero. What is the best way to determine that?

回答1:

NSString *str = @"         ";
NSCharacterSet *set = [NSCharacterSet whitespaceCharacterSet];
if ([[str stringByTrimmingCharactersInSet: set] length] == 0)
{
    // String contains only whitespace.
}

回答2:

Try stripping it of spaces and comparing it to @"":

NSString *probablyEmpty = [myString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
BOOL wereOnlySpaces = [probablyEmpty isEqualToString:@""];

回答3:

It's significantly faster to check for the range of non-whitespace characters instead of trimming the entire string.

NSCharacterSet *inverted = [[NSCharacterSet whitespaceAndNewlineCharacterSet] invertedSet];
NSRange range = [string rangeOfCharacterFromSet:inverted];
BOOL empty = (range.location == NSNotFound);

Note that "filled" is probably the most common case with a mix of spaces and text.

testSpeedOfSearchFilled - 0.012 sec
testSpeedOfTrimFilled - 0.475 sec
testSpeedOfSearchEmpty - 1.794 sec
testSpeedOfTrimEmpty - 3.032 sec

Tests run on my iPhone 6+. Code here. Paste into any XCTestCase subclass.

回答4:

Try this:

[mystring stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

[mystring stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

回答5:

I'm really surprised that I am the first who suggests Regular Expression

NSString *string = @"         ";
NSString *pattern = @"^\\s*$";
NSRegularExpression *expression = [[NSRegularExpression alloc] initWithPattern:pattern options:0 error:nil];
NSArray *matches = [expression matchesInString:string options:0 range:NSMakeRange(0, string.length)];
BOOL isOnlyWhitespace = matches.count;

Or in Swift:

let string = "         "
let pattern = "^\\s*$"
let expression = try! NSRegularExpression(pattern:pattern)
let matches = expression.matches(in: string, range: NSRange(string.startIndex..., in: string))
let isOnlyWhitespace = !matches.isEmpty

Alternatively

let string = "         "
let isOnlyWhitespace = string.range(of: "^\\s*$", options: .regularExpression) != nil

回答6:

Have to use this code for Swift 3:

func isEmptyOrContainsOnlySpaces() -> Bool {

    return self.trimmingCharacters(in: .whitespaces).characters.count == 0
}

回答7:

Trim space and check for number of characters remaining. Take a look at this post here

回答8:

Here is an easily reusable category on NSString based on @Alexander Akers' answer, but that also returns YES if the string contains "new lines"...

@interface NSString (WhiteSpaceDetect)
@property (readonly) BOOL isOnlyWhitespace;
@end
@implementation NSString (WhiteSpaceDetect)
- (BOOL) isOnlyWhitespace { 
  return ![self stringByTrimmingCharactersInSet:
          [NSCharacterSet whitespaceAndNewlineCharacterSet]].length;
}
@end

and for those of you untrusting souls out there..

#define WHITE_TEST(x) for (id z in x) printf("\"%s\" : %s\n",[z UTF8String], [z isOnlyWhitespace] ? "YES" :"NO")

WHITE_TEST(({ @[

    @"Applebottom",
    @"jeans\n",
    @"\n",
    @""
    "",
    @"   \
    \
    ",
    @"   "
];}));

➜

"Applebottom" : NO
"jeans
" : NO
"
" : YES
"" : YES
"   " : YES
"   " : YES

回答9:

Here's the Swift version code for the same,

var str = "Hello World" 
if count(str.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())) == 0 {
     // String is empty or contains only white spaces
}
else {
    // String is not empty and contains other characters
}

Or you can write a simple String extension like below and use the same code with better readability at multiple places.

extension String {
    func isEmptyOrContainsOnlySpaces() -> Bool {
        return count(self.stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())) == 0
    }
}

and just call it using any string like this,

var str1 = "   "
if str.isEmptyOrContainsOnlySpaces() {
    // custom code e.g Show an alert
}

回答10:

Here is a simple Swift solution:

//Check if string contains only empty spaces and new line characters
static func isStringEmpty(#text: String) -> Bool {
    let characterSet = NSCharacterSet.whitespaceAndNewlineCharacterSet()
    let newText = text.stringByTrimmingCharactersInSet(characterSet)
    return newText.isEmpty
}

来源：https://stackoverflow.com/questions/7275380/check-if-an-nsstring-is-just-made-out-of-spaces

标签

objective-c

string

cocoa-touch

cocoa

nsstring