Check if an NSString is just made out of spaces - objective-c

Question

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?

Answer 1

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

Answer 2

Try stripping it of spaces and comparing it to #"":
NSString *probablyEmpty = [myString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
BOOL wereOnlySpaces = [probablyEmpty isEqualToString:#""];

Answer 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.

Answer 4

Try this:
[mystring stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
or
[mystring stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

Answer 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

Answer 6

Have to use this code for Swift 3:
func isEmptyOrContainsOnlySpaces() -> Bool {
return self.trimmingCharacters(in: .whitespaces).characters.count == 0
}

Answer 7

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

Answer 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

Answer 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
}

Answer 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
}