I'm getting an error in this code:
void main() {
List<String> wave(String str) {
List<String> results = [];
String newStr;
int i = 0;
for (String ltr in str.split('')) {
newStr = str;
if (ltr != ' ') {
newStr[i] = ltr.toUpperCase();
results.add(newStr);
}
i++;
}
return results;
}
print(wave(' gap '));
}
the error is at the line:
newStr[i] = ltr.toUpperCase;
Despite when I try print(newStr[i]); I don't get an error and the code is executed correctly!
In Dart String operation, operator[] returns a string. Which means, array[index] is used for getting the string in the index position. That is why you're getting that error, because you can't set at specific index using this operator[] in dart. See the documentation for details.
To replace at the specific index in dart, you can use replaceFirst(Pattern from, String to, [int startIndex = 0]) as the other answer mentioned. Or, you can use substring(int start, [int? end]) as follows:
if (ltr != ' ' && i < newStr.length) {
newStr = newStr.substring(0, i) + ltr.toUpperCase() + newStr.substring(i+1);
results.add(newStr);
}
To make the code bug free, I've added the checking of the value of i in it. You should add the checking to avoid out of bound access.
try to replace
newStr[i] = ltr.toUpperCase();
to
newStr = newStr.replaceFirst(ltr,ltr.toUpperCase(),i);
So the result will be [ Gap , gAp , gaP ]
Honestly, I don't know how char is defined in Dart, but I think accessing index of String is kind of getter, thus cannot be set to a new value.
Related
Been doing this code in "Include" file. But I am encountering the error "not all control paths return a value. What should I do?
double CalculateTakeProfit (double entryPrice, int takeProfitPips, double GetPipValue)
{
if (bIsBuyPosition == True)
{
double result = 0;
entryPrice = Ask;
result = (entryPrice + takeProfitPips * GetPipValue());
return result;
}
else if (bIsBuyPosition == False)
{
double result = 0;
entryPrice = Bid;
result = (entryPrice - takeProfitPips * GetPipValue());
return result;
}
}
Your if... else is wrong and you are also not using the variables passed to the function. You are instead referencing another function or overwriting them. Mixing variable types in a calculation can also lead to undesirable results (takeProfitPips should be of type double). You can also cut a few lines of your code down as follows
double CalculateTakeProfit(double entryPrice, double takeProfitPips, double GetPipValue)
{
if(bIsBuyPosition) return(entryPrice+takeProfitPips*GetPipValue);
else return(entryPrice-takeProfitPips*GetPipValue);
}
var items = [];
var index = 0;
var value = items[index]; // returns invalid value error, understood!
I should rather use following to prevent the error
if (index < items.length) {
value = items[index];
}
Since there are ? operators in Dart, I wanted to know is there any way I can do something like:
var value = items?.[0] ?? -1;
var value = items?[0] ?? -1;
No. ? is used to for null-aware operators (or for the ternary operator). Accessing an invalid element of a List throws an exception instead of returning null, so null-aware operators won't help you.
If you like, you could add a helper function and make it more convenient as an extension:
extension ListGet<E> on List<E> {
E? get(int index, [E? defaultValue]) =>
(0 <= index && index < this.length) ? this[index] : defaultValue;
}
and now you should be able to do
var value = items.get(0, -1);
Is there a way to split a string by some symbol but only at first occurrence?
Example: date: '2019:04:01' should be split into date and '2019:04:01'
It could also look like this date:'2019:04:01' or this date : '2019:04:01' and should still be split into date and '2019:04:01'
string.split(':');
I tried using the split() method. But it doesn't have a limit attribute or something like that.
You were never going to be able to do all of that, including trimming whitespace, with the split command. You will have to do it yourself. Here's one way:
String s = "date : '2019:04:01'";
int idx = s.indexOf(":");
List parts = [s.substring(0,idx).trim(), s.substring(idx+1).trim()];
You can split the string, skip the first item of the list created and re-join them to a string.
In your case it would be something like:
var str = "date: '2019:04:01'";
var parts = str.split(':');
var prefix = parts[0].trim(); // prefix: "date"
var date = parts.sublist(1).join(':').trim(); // date: "'2019:04:01'"
The trim methods remove any unneccessary whitespaces around the first colon.
Just use the split method on the string. It accepts a delimiter/separator/pattern to split the text by. It returns a list of values separated by the provided delimiter/separator/pattern.
Usage:
const str = 'date: 2019:04:01';
final values = string.split(': '); // Notice the whitespace after colon
Output:
Inspired by python, I've wrote this utility function to support string split with an optionally maximum number of splits. Usage:
split("a=b=c", "="); // ["a", "b", "c"]
split("a=b=c", "=", max: 1); // ["a", "b=c"]
split("",""); // [""] (edge case where separator is empty)
split("a=", "="); // ["a", ""]
split("=", "="); // ["", ""]
split("date: '2019:04:01'", ":", max: 1) // ["date", " '2019:04:01'"] (as asked in question)
Define this function in your code:
List<String> split(String string, String separator, {int max = 0}) {
var result = List<String>();
if (separator.isEmpty) {
result.add(string);
return result;
}
while (true) {
var index = string.indexOf(separator, 0);
if (index == -1 || (max > 0 && result.length >= max)) {
result.add(string);
break;
}
result.add(string.substring(0, index));
string = string.substring(index + separator.length);
}
return result;
}
Online demo: https://dartpad.dev/e9a5a8a5ff803092c76a26d6721bfaf4
I found that very simple by removing the first item and "join" the rest of the List
String date = "date:'2019:04:01'";
List<String> dateParts = date.split(":");
List<String> wantedParts = [dateParts.removeAt(0),dateParts.join(":")];
Use RegExp
string.split(RegExp(r":\s*(?=')"));
Note the use of a raw string (a string prefixed with r)
\s* matches zero or more whitespace character
(?=') matches ' without including itself
You can use extensions and use this one for separating text for the RichText/TextSpan use cases:
extension StringExtension on String {
List<String> controlledSplit(
String separator, {
int max = 1,
bool includeSeparator = false,
}) {
String string = this;
List<String> result = [];
if (separator.isEmpty) {
result.add(string);
return result;
}
while (true) {
var index = string.indexOf(separator, 0);
print(index);
if (index == -1 || (max > 0 && result.length >= max)) {
result.add(string);
break;
}
result.add(string.substring(0, index));
if (includeSeparator) {
result.add(separator);
}
string = string.substring(index + separator.length);
}
return result;
}
}
Then you can just reference this as a method for any string through that extension:
void main() {
String mainString = 'Here was john and john was here';
print(mainString.controlledSplit('john', max:1, includeSeparator:true));
}
Just convert list to string and search
productModel.tagsList.toString().contains(filterText.toLowerCase())
In Dart the trim(), trimLeft() and trimRight() string methods do not take a parameter to specify unwanted non-whitespace characters.
What is the best way to trim a specific character from the ends of a string in Dart?
I am using this for now, but it feels hard to remember and not very generic:
final trailing = RegExp(r"/+$");
final trimmed = "test///".replaceAll(trailing, "");
assert(trimmed == "test");
There is no specific functionality to trim non-whitespace from the end of a string.
Your RegExp based approach is reasonable, but can be dangerous when the character you want to remove is meaningful in a RegExp.
I'd just make my own function:
String removeTrailing(String pattern, String from) {
if (pattern.isEmpty) return from;
var i = from.length;
while (from.startsWith(pattern, i - pattern.length)) i -= pattern.length;
return from.substring(0, i);
}
Then you can use it as:
final trimmed = removeTrailing("/", "test///")
assert(trimmed == "test");
The corresponding trimLeading function would be:
String trimLeading(String pattern, String from) {
if (pattern.isEmpty) return from;
var i = 0;
while (from.startsWith(pattern, i)) i += pattern.length;
return from.substring(i);
}
Since the existing answer by lrn has a lot of problems - including infinite loop scenarios - I thought I'd post my version.
String trimLeft(String from, String pattern){
if( (from??'').isEmpty || (pattern??'').isEmpty || pattern.length>from.length ) return from;
while( from.startsWith(pattern) ){
from = from.substring(pattern.length);
}
return from;
}
String trimRight(String from, String pattern){
if( (from??'').isEmpty || (pattern??'').isEmpty || pattern.length>from.length ) return from;
while( from.endsWith(pattern) ){
from = from.substring(0, from.length-pattern.length);
}
return from;
}
String trim(String from, String pattern){
return trimLeft(trimRight(from, pattern), pattern);
}
To trim all trailing/right characters by specified characters, use the method:
class StringUtil {
static String trimLastCharacters(String srcStr, String pattern) {
if (srcStr.length > 0) {
if (srcStr.endsWith(pattern)) {
final v = srcStr.substring(0, srcStr.length - 1 - pattern.length);
return trimLastCharacters(v, pattern);
}
return srcStr;
}
return srcStr;
}
}
For example, you want to remove all 0 behind the decimals
$23.67890000
then, invoke the method
StringUtil.trimLastCharacters("$23.67890000", "0")
finally, got the output:
$23.6789
I'd like to know if there's any Dart function like PHP's strrev(). If not, could you please show my any source code how to make it on my own?
Thank you.
Lists can be reversed, so you can use this to reverse a String as well:
new String.fromCharCodes("input".charCodes.reversed.toList());
I haven't found one in the API, as a brand new Dart user (as of this afternoon). However, reversing a string is pretty easy to do in any language. Here's the typical O(n) solution in Dart form:
String reverse(String s) {
var chars = s.splitChars();
var len = s.length - 1;
var i = 0;
while (i < len) {
var tmp = chars[i];
chars[i] = chars[len];
chars[len] = tmp;
i++;
len--;
}
return Strings.concatAll(chars);
}
void main() {
var s = "dog";
print(s);
print(reverse(s));
}
May be a standardized reverse() method will be implemented in future in List (dart issue 2804), the following is about 8 to 10 times faster than the previous typical solution:
String reverse(String s) {
// null or empty
if (s == null|| s.length == 0)
return s;
List<int> charCodes = new List<int>();
for (int i = s.length-1; i>= 0; i-- )
charCodes.addLast(s.charCodeAt(i)) ;
return new String.fromCharCodes(charCodes);
}
try this instead of others.
String try(str) {
return str.split('').reversed.join('');
}
String theString = "reverse the string";
List<String> reslt = theString.split("");
List<String> reversedString = List.from(reslt.reversed);
String joinString = reversedString.join("");
print(joinString);
Ouput: gnirts eht esrever