I want to validate a TexFormField field to both check for a min value of 10 (done elsewhere) and also check that the value entered is a multiple of 10.
I've written a function that tries to handle both and it seems to work. However, it feels clunky. And it doesn't provide any feedback until the form is submitted. Here is what I've written:
final form = _formKey.currentState;
if ((form.validate()) && (_amount / 10 is int)) {
form.save();
return true;
}
return false;
}
Is there a cleaner way to check if an entered value is a multiple of 10 (or any integer)? For example, in the validator: property field itself?
validator: (String value) {
int n = int.parse(value);
int multipleOf = 10;
return n % multipleOf != 0 ? "not a multiple of $multipleOf" : null;
}
Related
is there a way to validate if a users input is a valid float?
I need to verify that the user is inputting valid project estimates $$
only costs up to the hundreds is allowed, example:
1.99
.99
no commas are allowed
no negative numbers
only one period is allowed
I am using a TextFormField, and I am using the following keyboard:
keyboardType: TextInputType.number,
I know I have to do some type of validation using the validator but I am stuck
validator: (str) {
if (str == '' || str == '.') {
return "Job estimate can't be empty";
}
if (str!.contains(',')) {
return 'No commas are allowed';
}
var strPlit = str.split('.');
print('strPlit: ${strPlit.length}');
if (strPlit.length != 1) {
if (strPlit.length > 2) {
return 'Only 1 period allowed';
}
if (strPlit[1].length > 2) {
return 'Estimate is only accurate to the hundreds';
}
}
return null;
},
I'm working on a friend suggestion algorithm for a flutter social media application. I'm still an amateur when it comes to Dart so I'm stuck on the following line of code:
class FriendSuggestionAlgorithm {
User friendSuggestion(User user) {
int max = -1;
User suggestion;
Map<User, int> map = new HashMap();
for (User friend in user.friends) {
for (User mutualFriend in friend.friends) {
if (mutualFriend.id != user.id && !user.friends.contains(mutualFriend)) {
map.putIfAbsent(mutualFriend, map.getOrDefault(mutual, 0) + 1);
}
}
}
for (MapEntry<User, int> mutualFriend in map.entries) {
if (mutualFriend.value > max) {
max = mutualFriend.value;
suggestion = mutualFriend.key;
}
}
return suggestion;
}
}
map.getOrDefault is underlined (I know the method doesn't exist in Dart). Do you know what the equivalent is in Dart? (PS, I'm just translating Java code into Dart.
Any help is appreciated!
Your code doesn't make sense. map.putIfAbsent will do work only if the key doesn't exist, so the hypothetical map.getOrDefault call with the same key would always return the default value anyway. That is, your logic would be the equivalent of map.putIfAbsent(mutual, () => 1), where nothing happens if the key already exists.
Map.putifAbsent takes a callback as its argument to avoid evaluating it unless it's actually necessary. I personally prefer using ??= when the Map values are non-nullable.
I presume that you actually want to increment the existing value, if one exists. If so, I'd replace the map.putIfAbsent(...) call with:
map[mutual] = (map[mutual] ?? 0) + 1;
Also see: Does Dart have something like defaultdict in Python?
You could do it like this:
map.putIfAbsent(mutual, (map.containsKey(mutual) ? map[mutual] : 0) + 1)
Maybe take a look at this for more info: https://dart.dev/guides/language/language-tour#conditional-expressions
Edit:
This code should work
class FriendSuggestionAlgorithm {
User? friendSuggestion(User user) {
int max = -1;
User? suggestion;
Map<User, int> map = {};
for (User friend in user.friends) {
for (User mutualFriend in friend.friends) {
if (mutualFriend.id != user.id && !user.friends.contains(mutualFriend)) {
map.putIfAbsent(mutualFriend, () => (map[mutualFriend] ?? 0) + 1);
}
}
}
for (MapEntry<User, int> mutualFriend in map.entries) {
if (mutualFriend.value > max) {
max = mutualFriend.value;
suggestion = mutualFriend.key;
}
}
return suggestion;
}
}
Note that suggestion nullable because it could happen that suggestion is never assigned. And therefore friendSuggestion(user) can return null;
To come back to your question
the correct code is
map.putIfAbsent(mutualFriend, () => (map[mutualFriend] ?? 0) + 1);
My mistake on my original answer, the ifAbsent part of this is a function. In the function the value of mutualFriend is retrieved. If that is null use 0.
I am trying to solve a puzzle, and it has been suggested that I use backtracking - I did not know the term so did some investigation, and found the following in Wikipedia:
In order to apply backtracking to a specific class of problems, one must provide the data P for the particular instance of the problem that is to be solved, and six procedural parameters, root, reject, accept, first, next, and output. These procedures should take the instance data P as a parameter and should do the following:
root(P): return the partial candidate at the root of the search tree.
reject(P,c): return true only if the partial candidate c is not worth completing.
accept(P,c): return true if c is a solution of P, and false otherwise.
first(P,c): generate the first extension of candidate c.
next(P,s): generate the next alternative extension of a candidate, after the extension s.
output(P,c): use the solution c of P, as appropriate to the application.
The backtracking algorithm reduces the problem to the call backtrack(root(P)), where backtrack is the following recursive procedure:
procedure backtrack(c) is
if reject(P, c) then return
if accept(P, c) then output(P, c)
s ← first(P, c)
while s ≠ NULL do
backtrack(s)
s ← next(P, s)
I have attempted to use this method for my solution, but after the method finds a rejected candidate it just starts again and finds the same route, rather than the next possible one.
I now don't think I have used the next(P,s) correctly, because I don't really understand the wording 'after the extension s'.
I've tried 2 methods:
(a) in the first() function, generating all possible extensions, storing them in a list, then using the first. The next() function then uses the other extensions from the list in turn. But this maybe can't work because of the calls to backtrack() in between the calls to next().
(b) adding a counter to the data (i.e. the class that includes all the grid info) and incrementing this for each call of next(). But can't work out where to reset this counter to zero.
Here's the relevant bit of code for method (a):
private PotentialSolution tryFirstTrack(PotentialSolution ps)
{
possibleTracks = new List<PotentialSolution>();
for (Track trytrack = Track.Empty + 1; trytrack < Track.MaxVal; trytrack++)
{
if (validMove(ps.nextSide, trytrack))
{
ps.SetCell(trytrack);
possibleTracks.Add(ps);
}
}
return tryNextTrack(ps);
}
private PotentialSolution tryNextTrack(PotentialSolution ps)
{
if (possibleTracks.Count == 0)
{
ps.SetCell(Track.Empty);
return null;
}
ps = possibleTracks.First();
// don't use same one again
possibleTracks.Remove(ps);
return ps;
}
private bool backtrackTracks(PotentialSolution ps)
{
if (canExit)
{
return true;
}
if (checkOccupiedCells(ps))
{
ps = tryFirstTrack(ps);
while (ps != null)
{
// 'testCells' is a copy of the grid for use with graphics - no need to include graphics in the backtrack stack
testCells[ps.h, ps.w].DrawTrack(g, ps.GetCell());
if (ps.TestForExit(endColumn, ref canExit) != Track.MaxVal)
{
drawRowColTotals(ps);
return true;
}
ps.nextSide = findNextSide(ps.nextSide, ps.GetCell(), ref ps.h, ref ps.w);
if (ps.h >= 0 && ps.h < cellsPerSide && ps.w >= 0 && ps.w < cellsPerSide)
{
backtrackTracks(ps);
ps = tryNextTrack(ps);
}
else
return false;
}
return false;
}
return false;
}
and here's some code using random choices. This works fine, so I conclude that the methods checkOccupiedCells() and findNextSide() are working correctly.
private bool backtrackTracks(PotentialSolution ps)
{
if (canExit)
{
return true;
}
if (checkOccupiedCells(ps))
{
Track track = createRandomTrack(ps);
if (canExit)
return true;
if (track == Track.MaxVal)
return false;
ps.SetCell(track);
ps.nextSide = findNextSide(ps.nextSide, track, ref ps.h, ref ps.w);
if (ps.h >= 0 && ps.h < cellsPerSide && ps.w >= 0 && ps.w < cellsPerSide)
backtrackTracks(ps);
else
return false;
}
}
If it helps, there's more background info in the puzzle itself here
I'm writing a function where I iterate thru a map and look test for valid values on an function. My question is there is a better way to correctly break from a foreach loop when an error is found?
('break' does not work on foreach())
Since I am not able to use the break function here so i had to place a bool marker :/
Any help in making this code nice looking would be appreciated :)
Future<bool> saveToKeychainFunc(Map data) {
bool saved = false;
bool error = false;
data?.keys?.forEach((item) async {
if (data[item] != null) {
await _storage.write(key: item.toString(), value: data[item].toString());
} else {
//TODO
// data error, we got null for a value!
error = true;
}
saved = true;
});
return (error == true) ? false : saved;
}
I've experienced this. My work around is using for loop instead.
ex:
for (int i = 0; i < jsonTransactions.length; i++) {
Transaction transaction = Transaction.fromJson(jsonTransactions[i]);
transactions.add(transaction);
}
You can just add conditions, and add your break inside the loop if conditions are met. Since you're using a map, my code should not be very different since Map also has .length
I am new to RxJava2.
I am trying to get a list of Transaction object both from cache and from server.
I want to compare the server value to cache value and if the server value is the same, then ignore it.
I was able to do it easily using .scan() because we can return null and when null is returned from the .scan() the value got ignored(filtered).
RxJava 1
private Observable<List<Transaction>> getTransactionsFromCacheAndServer() {
return Observable.concat(
getTransactionsFromCache(),
getTransactionsFromServer()
)
.scan((p1, p2) -> {
if (p1 == null && p2 != null) {
return p2;
} else if (p1 != null && !isListSame(p1, p2)) {
return p2;
} else {
return null;
}
});
}
With RxJava 2, since I cannot return null anymore, things are not easy.
RxJava 2
private Observable<List<Transaction>> getTransactionsFromCacheAndServer() {
return Observable.concat(
getTransactionsFromCache(),
getTransactionsFromServer()
)
.map(FilterObject::new)
.scan((filterObject1, filterObject2) -> {
List<Transaction> p1 = (List<Transaction>)filterObject1.value;
List<Transaction> p2 = (List<Transaction>)filterObject2.value;
if (p1.size() == 0 && p2.size() > 0) {
return filterObject2;
} else if (!isListSame(p1, p2)) {
return filterObject2;
} else {
filterObject2.filter = true;
return filterObject2;
}
})
.filter(filterObject -> !filterObject.filter)
.map(filterObject -> (List<Transaction>)filterObject.value);
}
Where FilterObject is:
public class FilterObject {
public Object value;
public boolean filter;
public FilterObject(Object value) {
this.value = value;
}
}
Even though I can achieve the same thing using above method, it seems very ugly. Also I had to include two maps which might not be so performance friendly.
Is there a simple/clean way to achieve what I want?
I don't think there is a generic solution to this problem, since an empty list and a list that needs to be filtered (which happens to be empty in all cases) are two different things (the output of the scan) and needs to be handled differently.
However, in your particular case you never emit an empty list, except maybe for the first output.
(I am using String instead Transaction, shouldn't matter)
private Observable<List<String>> getTransactionsFromCacheAndServer() {
return Observable.concat(
getTransactionsFromCache(),
getTransactionsFromServer()
)
.filter(list -> !list.isEmpty())
// If you prefer a consistent empty list over the first
// empty list emission getting filtered
.startWith((List<String>) Collections.EMPTY_LIST)
// Newly emitted value cannot be empty, it only depends only on the comparison
.distinctUntilChanged(this::isListSame);
}
That's the closest I could get with as few operators as possible. Hope it solves your problem.
Based on andras' answer, I modified little bit to achieve what I want.
private Observable<List<String>> getTransactionsFromCacheAndServer() {
return Observable.concat(
getTransactionsFromCache(),
getTransactionsFromServer()
)
.filter(list -> !list.isEmpty())
.distinctUntilChanged(this::isListSame)
.switchIfEmpty(Observable.just(new ArrayList<>()));
}
Andreas' answer will always receive an empty list and then a real data.
My solution above will receive:
1. Data from cache (and then data from server if different)
2. Empty list if both cache and server returns Empty list.