I am new to Dart programming language and anyone help me find the best string concatenation methods available in Dart.
I only found the plus (+) operator to concatenate strings like other programming languages.
There are 3 ways to concatenate strings
String a = 'a';
String b = 'b';
var c1 = a + b; // + operator
var c2 = '$a$b'; // string interpolation
var c3 = 'a' 'b'; // string literals separated only by whitespace are concatenated automatically
var c4 = 'abcdefgh abcdefgh abcdefgh abcdefgh'
'abcdefgh abcdefgh abcdefgh abcdefgh';
Usually string interpolation is preferred over the + operator.
There is also StringBuffer for more complex and performant string building.
If you need looping for concatenation, I have this :
var list = ['satu','dua','tiga'];
var kontan = StringBuffer();
list.forEach((item){
kontan.writeln(item);
});
konten = kontan.toString();
Suppose you have a Person class like.
class Person {
String name;
int age;
Person({String name, int age}) {
this.name = name;
this.age = age;
}
}
And you want to print the description of person.
var person = Person(name: 'Yogendra', age: 29);
Here you can concatenate string like this
var personInfoString = '${person.name} is ${person.age} years old.';
print(personInfoString);
Easiest way
String get fullname {
var list = [firstName, lastName];
list.removeWhere((v) => v == null);
return list.join(" ");
}
The answer by Günter covers the majority of the cases of how you would concatenate two strings in Dart.
If you have an Iterable of Strings it will be easier to use writeAll as this gives you the option to specify an optional separator
final list = <String>['first','second','third'];
final sb = StringBuffer();
sb.writeAll(list, ', ');
print(sb.toString());
This will return
'first, second, third'
Let's think we have two strings
String a = 'Hello';
String b = 'World';
String output;
Now we want to concat this two strings
output = a + b;
print(output);
Hello World
Input: String str="Fund testing testing";
Output: str="Fund";
After fund whatever the text is there need to remove that text.
Please suggest some solution.
The easiest way to solve this is a .Substring() method, as you can provide it the start index of your original string and length of the string you need:
var length = "Fund".Length;
var str = "Fund testing testing";
Console.WriteLine(str.Substring(0, length)); //returns "Fund"
var str1 = "testFund testing testing";
Console.WriteLine(str1.Substring(4, length)); //returns "Fund"
var str2 = "testFund testing testing";
Console.WriteLine(str2.Substring(str2.IndexOf("Fund"), length)); //returns "Fund"
You can also use regular expression like this:
string strRegex = #".*?(Fund).*";
Regex myRegex = new Regex(strRegex, RegexOptions.Singleline);
string strTargetString = #"Fund testing testing";
string strReplace = #"$1";
return myRegex.Replace(strTargetString, strReplace);
As mentioned in comments below, replace can lack performance and is kind of overkill, so regex Match can be better. Here is how it looks like:
string strRegex = #".*?(Fund).*";
Regex myRegex = new Regex(strRegex, RegexOptions.None);
string strTargetString = "\n\n" + #" Fund testing testing";
foreach (Match myMatch in myRegex.Matches(strTargetString))
{
if (myMatch.Success)
{
var fund = myMatch.Groups[1].Value;
Console.WriteLine(fund);
}
}
Note that Groups first element is your entire match
How can I remove last character from String variable using Swift? Can't find it in documentation.
Here is full example:
var expression = "45+22"
expression = expression.substringToIndex(countElements(expression) - 1)
Swift 4.0 (also Swift 5.0)
var str = "Hello, World" // "Hello, World"
str.dropLast() // "Hello, Worl" (non-modifying)
str // "Hello, World"
String(str.dropLast()) // "Hello, Worl"
str.remove(at: str.index(before: str.endIndex)) // "d"
str // "Hello, Worl" (modifying)
Swift 3.0
The APIs have gotten a bit more swifty, and as a result the Foundation extension has changed a bit:
var name: String = "Dolphin"
var truncated = name.substring(to: name.index(before: name.endIndex))
print(name) // "Dolphin"
print(truncated) // "Dolphi"
Or the in-place version:
var name: String = "Dolphin"
name.remove(at: name.index(before: name.endIndex))
print(name) // "Dolphi"
Thanks Zmey, Rob Allen!
Swift 2.0+ Way
There are a few ways to accomplish this:
Via the Foundation extension, despite not being part of the Swift library:
var name: String = "Dolphin"
var truncated = name.substringToIndex(name.endIndex.predecessor())
print(name) // "Dolphin"
print(truncated) // "Dolphi"
Using the removeRange() method (which alters the name):
var name: String = "Dolphin"
name.removeAtIndex(name.endIndex.predecessor())
print(name) // "Dolphi"
Using the dropLast() function:
var name: String = "Dolphin"
var truncated = String(name.characters.dropLast())
print(name) // "Dolphin"
print(truncated) // "Dolphi"
Old String.Index (Xcode 6 Beta 4 +) Way
Since String types in Swift aim to provide excellent UTF-8 support, you can no longer access character indexes/ranges/substrings using Int types. Instead, you use String.Index:
let name: String = "Dolphin"
let stringLength = count(name) // Since swift1.2 `countElements` became `count`
let substringIndex = stringLength - 1
name.substringToIndex(advance(name.startIndex, substringIndex)) // "Dolphi"
Alternatively (for a more practical, but less educational example) you can use endIndex:
let name: String = "Dolphin"
name.substringToIndex(name.endIndex.predecessor()) // "Dolphi"
Note: I found this to be a great starting point for understanding String.Index
Old (pre-Beta 4) Way
You can simply use the substringToIndex() function, providing it one less than the length of the String:
let name: String = "Dolphin"
name.substringToIndex(countElements(name) - 1) // "Dolphi"
The global dropLast() function works on sequences and therefore on Strings:
var expression = "45+22"
expression = dropLast(expression) // "45+2"
// in Swift 2.0 (according to cromanelli's comment below)
expression = String(expression.characters.dropLast())
Swift 4:
let choppedString = String(theString.dropLast())
In Swift 2, do this:
let choppedString = String(theString.characters.dropLast())
I recommend this link to get an understanding of Swift strings.
Swift 4/5
var str = "bla"
str.removeLast() // returns "a"; str is now "bl"
This is a String Extension Form:
extension String {
func removeCharsFromEnd(count_:Int) -> String {
let stringLength = count(self)
let substringIndex = (stringLength < count_) ? 0 : stringLength - count_
return self.substringToIndex(advance(self.startIndex, substringIndex))
}
}
for versions of Swift earlier than 1.2:
...
let stringLength = countElements(self)
...
Usage:
var str_1 = "Maxim"
println("output: \(str_1.removeCharsFromEnd(1))") // "Maxi"
println("output: \(str_1.removeCharsFromEnd(3))") // "Ma"
println("output: \(str_1.removeCharsFromEnd(8))") // ""
Reference:
Extensions add new functionality to an existing class, structure, or enumeration type. This includes the ability to extend types for which you do not have access to the original source code (known as retroactive modeling). Extensions are similar to categories in Objective-C. (Unlike Objective-C categories, Swift extensions do not have names.)
See DOCS
Use the function removeAtIndex(i: String.Index) -> Character:
var s = "abc"
s.removeAtIndex(s.endIndex.predecessor()) // "ab"
Swift 4
var welcome = "Hello World!"
welcome = String(welcome[..<welcome.index(before:welcome.endIndex)])
or
welcome.remove(at: welcome.index(before: welcome.endIndex))
or
welcome = String(welcome.dropLast())
The easiest way to trim the last character of the string is:
title = title[title.startIndex ..< title.endIndex.advancedBy(-1)]
import UIKit
var str1 = "Hello, playground"
str1.removeLast()
print(str1)
var str2 = "Hello, playground"
str2.removeLast(3)
print(str2)
var str3 = "Hello, playground"
str3.removeFirst(2)
print(str3)
Output:-
Hello, playgroun
Hello, playgro
llo, playground
let str = "abc"
let substr = str.substringToIndex(str.endIndex.predecessor()) // "ab"
var str = "Hello, playground"
extension String {
var stringByDeletingLastCharacter: String {
return dropLast(self)
}
}
println(str.stringByDeletingLastCharacter) // "Hello, playgroun"
Short answer (valid as of 2015-04-16): removeAtIndex(myString.endIndex.predecessor())
Example:
var howToBeHappy = "Practice compassion, attention and gratitude. And smile!!"
howToBeHappy.removeAtIndex(howToBeHappy.endIndex.predecessor())
println(howToBeHappy)
// "Practice compassion, attention and gratitude. And smile!"
Meta:
The language continues its rapid evolution, making the half-life for many formerly-good S.O. answers dangerously brief. It's always best to learn the language and refer to real documentation.
With the new Substring type usage:
Swift 4:
var before: String = "Hello world!"
var lastCharIndex: Int = before.endIndex
var after:String = String(before[..<lastCharIndex])
print(after) // Hello world
Shorter way:
var before: String = "Hello world!"
after = String(before[..<before.endIndex])
print(after) // Hello world
Use the function advance(startIndex, endIndex):
var str = "45+22"
str = str.substringToIndex(advance(str.startIndex, countElements(str) - 1))
A swift category that's mutating:
extension String {
mutating func removeCharsFromEnd(removeCount:Int)
{
let stringLength = count(self)
let substringIndex = max(0, stringLength - removeCount)
self = self.substringToIndex(advance(self.startIndex, substringIndex))
}
}
Use:
var myString = "abcd"
myString.removeCharsFromEnd(2)
println(myString) // "ab"
Another way If you want to remove one or more than one character from the end.
var myStr = "Hello World!"
myStr = (myStr as NSString).substringToIndex((myStr as NSString).length-XX)
Where XX is the number of characters you want to remove.
Swift 3 (according to the docs) 20th Nov 2016
let range = expression.index(expression.endIndex, offsetBy: -numberOfCharactersToRemove)..<expression.endIndex
expression.removeSubrange(range)
The dropLast() function removes the last element of the string.
var expression = "45+22"
expression = expression.dropLast()
Swift 4.2
I also delete my last character from String (i.e. UILabel text) in IOS app
#IBOutlet weak var labelText: UILabel! // Do Connection with UILabel
#IBAction func whenXButtonPress(_ sender: UIButton) { // Do Connection With X Button
labelText.text = String((labelText.text?.dropLast())!) // Delete the last caracter and assign it
}
I'd recommend using NSString for strings that you want to manipulate. Actually come to think of it as a developer I've never run into a problem with NSString that Swift String would solve... I understand the subtleties. But I've yet to have an actual need for them.
var foo = someSwiftString as NSString
or
var foo = "Foo" as NSString
or
var foo: NSString = "blah"
And then the whole world of simple NSString string operations is open to you.
As answer to the question
// check bounds before you do this, e.g. foo.length > 0
// Note shortFoo is of type NSString
var shortFoo = foo.substringToIndex(foo.length-1)
Swift 3: When you want to remove trailing string:
func replaceSuffix(_ suffix: String, replacement: String) -> String {
if hasSuffix(suffix) {
let sufsize = suffix.count < count ? -suffix.count : 0
let toIndex = index(endIndex, offsetBy: sufsize)
return substring(to: toIndex) + replacement
}
else
{
return self
}
}
complimentary to the above code I wanted to remove the beginning of the string and could not find a reference anywhere. Here is how I did it:
var mac = peripheral.identifier.description
let range = mac.startIndex..<mac.endIndex.advancedBy(-50)
mac.removeRange(range) // trim 17 characters from the beginning
let txPower = peripheral.advertisements.txPower?.description
This trims 17 characters from the beginning of the string (he total string length is 67 we advance -50 from the end and there you have it.
I prefer the below implementation because I don't have to worry even if the string is empty
let str = "abc"
str.popLast()
// Prints ab
str = ""
str.popLast() // It returns the Character? which is an optional
// Print <emptystring>
I need a string splitted into groups of characters in ActionScript like this:
var txt:String = "Hello World";
var arr:Array = txt.split(3);
// Now arr should contain a value like: ["Hel", "lo ", "Wor", "ld"]
This is possible in PHP like this:
$arr = str_split(txt, 3);
But I need a ActionScript equivalent of this PHP code.
You can use a regex:
var txt:String = "Hello World";
var arr:Array = txt.match(/.{3}|.+/g);
trace(arr);
// Hel,lo ,Wor,ld
I'm building a short quiz where the user needs to input the meaning of an acronym.
This means I need to compare a long string (usually a sentence) typed in by the user with an acronym.
I have a feeling I'm not doing it right. For my testing I'm copy-pasting the correct answer to make sure the spelling is correct however I keep getting the feedback that the answer is incorrect.
My question is, am I comparing correctly?
Here's my code:
var arrQuestions:Array = [["LOL","Laughing Out Loud"], ["OMG", "Oh My God"], ["BTW", "By The Way"]];
var i:Number=0;
function setup():void {
quiztext_txt.text = arrQuestions[i][0];
trace(quiztext_txt.text);
trace(arrQuestions[i][1]);
check_btn.addEventListener(MouseEvent.CLICK, clickHandler);
}//End of Setup()
setup();
function clickHandler(event:MouseEvent):void {
var givenString:String;
var inputString:String;
inputString = userinput_txt.text;
givenString = arrQuestions[i][1];
if (inputString == givenString) {
feedback_txt.text = "Correct!";
} else {
feedback_txt.text = "Wrong!";
}
}
Is there any whitespace before/after the user input? Is the value of i changing in between?
else
{
//what does it trace?
trace("given answer: " + inputString + "\ncorrect answer: " + givenString);
feedback_txt.text = "Wrong!";
}
try clearing the text field in your setup function like so:
function setup():void
{
userinput_txt.text = "";
quiztext_txt.text = arrQuestions[i][0];
trace(quiztext_txt.text);
trace(arrQuestions[i][1]);
check_btn.addEventListener(MouseEvent.CLICK, clickHandler);
}//End of Setup()
For any kind of string matching I would strongly recommend looking into regular expressions (RegExp). In the regular expression written below I am matching each word, then I say [ ]+ which means "at least one or more spaces", then at the end of the expression I use /gi to say that the expression is case insensitive. In the code above if I type the phrase in lowercase its not going to match, a quick fix for this would be to use this if(inputString.toLowerCase() == givenString.toLowerCase()) which would catch this. Heres the regexp example:
// testString could easily equal myTextField.text
var testString:String = "lauGHing OuT loUD";
// you could store each one in an array, as you were before
var regEx:RegExp = /laughing[ ]+out[ ]+loud/gi
trace( regEx.test( testString ) ); //returns true,test() returns a Boolean
Hope this helps.