I have an if statement that checks to see if an array element matches a local variable.
if pinArray.contains(where: {$0.title == restaurantName})
How would I create a variable of this element?
I attempted
let thePin = pinArray.contains(where: {$0.title == restaurantName})
but this comes with "could not cast boolean to MKAnnotation".
I also tried variations of
let pins = [pinArray.indexPath.row]
let pinn = pins(where: pin.title == restaurantName) (or close to it)
mapp.selectAnnotation(thePin as! MKAnnotation, animated: true)
to no avail. What basic step am I missing?
contains(where:) returns a Bool indicating whether a match was found or not. It does not return the matched value.
So thePin is a Bool which you then attempt to force-cast to a MKAnnotation which of course crashes.
If you want the matching value, change your code to:
if let thePin = pinArray.first(where: { $0.title == restaurantName }) {
do {
mapp.selectionAnnotation(thePin, animated: true)
} catch {
}
} else {
// no match in the array
}
No need for contains at all. No need to cast (assuming pinArray is an array of MKAnnotation).
Related
i have trouble during making the letter checker, my code is like this: if !containLetters(“1234h”){print(“pass”)}
my function is
func containsOnlyNum(input: String) -> Bool {
var ok = false
for chr in input {
for check in "1234567890.-"{
if chr == check{
ok = true
}
}
if ok != true{
return false
}
}
return true
}
If I check for “h” then didn’t pass, but if i check for ”1h” then it still pass! Please help me to fix this problem. I will give a big thank for anyone who helped me
The simplest way to fix the algorithm is this way:
func containsOnlyNum(input: String) -> Bool {
// check every character
for chr in input {
var isNum = false
for check in "1234567890.-"{
if chr == check {
isNum = true
// if we have found a valid one, we can break the iteration
break
}
}
if !isNum {
return false
}
}
return true
}
print(containsOnlyNum(input: "1234")) // true
print(containsOnlyNum(input: "1234h")) // false
However, then you can directly simplify it to:
func containsOnlyNum(input: String) -> Bool {
return input.allSatisfy { chr in
"1234567890.-".contains(chr)
}
}
which does exatly the same but uses allSatisfy and contains functions, which represent the logical operators ALL and EXISTS.
However, programmers normally use regular expressions for similar tasks:
func containsOnlyNum(input: String) -> Bool {
return input.range(of: "^[0-9.\\-]+$", options: .regularExpression) != nil
}
You can check that a string contains only the characters you're interested in like this:
extension String {
var containsOnlyNum: Bool {
let wanted = CharacterSet.decimalDigits
.union(CharacterSet(charactersIn: "-."))
return unicodeScalars
.allSatisfy(wanted.contains)
}
}
"-12.34".containsOnlyNum // true
"A1234".containsOnlyNum // false
But if you are interested in numbers, then this is a problem:
"-12.-34.".containsOnlyNum // true
Instead, you can just try casting the string to a double and see if it is a number or not
Double("1234") != nil // true, a number
Double("-1.234") != nil // true, a number
Double("A1234") != nil // false, not a number
Double("-12.-34.") != nil // false, not a number
Which is almost right unless you don't want this case:
Double("1234e2") != nil // true, a number
But you can use both checks if you don't want to allow that, or else if you are able to parse a Double from the input you can just do the cast.
I have to update a struct, but this struct needs a long expression to be found from my viewController :
let theMessage:Message? = self.messageSections.first(where: { $0.date == DateDMY(fromNSDate:msg.date) })?
.msgs.first(where: { $0 == msg })
I want to mutate one property of this struct, but not a copy of it, I want to update it "where it is", that is in messageSections[].msgs[]
The problem here is that if I try this code after the one above :
theMessage.status = .NOT_SENT
Only the local copy will be updated, and not the real one in messageSections[].msgs[]. So when I reload my collectionView, nothing changes.
I could do
self.messageSections.first(where: { $0.date == DateDMY(fromNSDate:msg.date) })?
.msgs.first(where: { $0 == msg }).status = .NOT_SENT
But if I have to manipulate this property several times in my function, I dont want to re-write the whole expression each time. So what I'm looking for is something like in C :
let theMessage:Message?* = &self.messageSections.first(where: { $0.date == DateDMY(fromNSDate:msg.date) })?
.msgs.first(where: { $0 == msg })
if(theMessage != NULL)
theMessage->status = .NOT_SENT
I saw in other questions that I could use & before argument and inout before parameter name, but its only for functions calling. I'm looking for a way to create an alias for a big expression when affecting a variable, just to avoid re-writting it each time.
You can use firstIndex to get the index of the element in the array, then access the element directly using the retrieved index.
if let messageSectionIndex = self.messageSections.first(where: { $0.date == DateDMY(fromNSDate:msg.date) }), let messageIndex = self.messageSections[messageSectionIndex].msgs.firstIndex(where: { $0 == msg }) {
self.messageSections[messageSectionIndex].msgs[messageIndex].status = .NOT_SENT
}
With this code I enable a button if any form value is not nil:
myButton.isEnabled = !myForm.values.contains(where: { $0 == nil })
Is there any way to add multiple checks? I want to enable my button:
if the value of any field is nil (done, as you can see above);
if the value of any field is > 0;
if the value of any field is < 2;
(that is, the value should NOT be nil and should NOT be outside the range 0.0 - 2.0)
Can I still use contains(where:) to do it?
MyForm is a dictionary like this one:
["oct": nil,
"jan": Optional(3666.0),
"nov": nil,
"apr": nil,
"sep": nil,
"feb": nil,
"jul": nil,
"mar": nil,
"dec": nil,
"may": nil,
"jun": nil,
"aug": nil]
(strange enough, due to the behavior of a 3rd party library, it accepts nil values)
Yes, you can. If you want to enable the button if there is at least one Double value in range 0.0..<2.0 you don't need to call values. You can call contains on the dictionary directly. The where keyword is syntactic sugar and can be omitted when using trailing closure syntax.
The code uses the pattern matching operator to check the range.
myButton.isEnabled = myForm.contains { (_, value) in
guard let value = value as? Double else { return false }
return 0.0..<2.0 ~= value
}
If you want to enable the button if all values are Double in the given range you have to check inverted
myButton.isEnabled = !myForm.contains { (_, value) in
guard let value = value as? Double else { return true }
return !(0.0..<2.0 ~= value)
}
You can do it just by filtering all values like this:
myButton.isEnabled = !myForm.values.filter {
if let value = $0 { return value.field > 0.0 && value.field < 2.0 }
return false
}.count > 0
contains function is not appropriate solution in your case, because it should be used when you need to check if array contain some specific element. But in your case you need to check if values is in specific range.
It is possible to use contains function but it is not correct way
I want to use the sorted method on an array.
public func sorted(by areInIncreasingOrder: (Self.Iterator.Element, Self.Iterator.Element) -> Bool) -> [Self.Iterator.Element]
And I can see that it takes a function (which takes 2 Elements and returns a Bool), and then returns an an array of the Element (sorted)
Where I am getting stuck, is by trying to pass an anonymous function (closure), using $0 and $1 as arguments
I want to add a special case, for a specific key ("module")
And then I want to access a property on $0 and $1
But this means, ostensibly, that I have to cast those arguments, so that I can then access the properties on those arguments
And to make things worse, because the arguments could either be String or Node, I currently have repeated code (the switch statement)
So anyways, do any of you Swift veterans see things that I could do to make this better?
return self.sorted(by: {
for descriptor in sortDescriptors {
if descriptor.key == "module" {
if let firstNode = $0 as? Node {
if let secondNode = $1 as? Node {
let firstModule = firstNode.module?.name ?? ""
let secondModule = secondNode.module?.name ?? ""
let newDescriptor = NSSortDescriptor(key: nil, ascending: descriptor.ascending, selector: descriptor.selector)
switch newDescriptor.compare(firstModule, to: secondModule) {
case .orderedAscending:
return true
case .orderedDescending:
return false
case .orderedSame:
continue
}
}
}
}
switch descriptor.compare($0, to: $1) {
case .orderedAscending:
return true
case .orderedDescending:
return false
case .orderedSame:
continue
}
}
return false
})
}
My problem is that I have some text fields that the user enters in numbers, the entered numbers then get saved to the corresponding variable.
However if the user doesn't enter a number and leaves it blank, the text field has a value of 'nil' and so would crash if unwrapped.
So I used an if statement to only unwrap if the contents of the test field are NOT nil, however this doesn't work. My program still unwraps it and crashes because the value is nil...
I don't understand how my if statement is not catching this.
On another note, how do I change my if statement to only allow Int values to be unwrapped and stored, strings or anything else would be ignored.
#IBAction func UpdateSettings() {
if CriticalRaindays.text != nil {
crit_raindays = CriticalRaindays.text.toInt()!
}
if EvapLess.text != nil {
et_raindays_lessthan_11 = EvapLess.text.toInt()!
}
if EvapMore.text != nil {
et_raindays_morethan_11 = EvapMore.text.toInt()!
}
if MaxWaterStorage.text != nil {
max_h2Ostore = MaxWaterStorage.text.toInt()!
}
if CarryForward.text != nil {
carry_forward = CarryForward.text.toInt()!
}
}
Your issue is that while the text exists, it doesn't mean toInt() will return a value.
Say the text was abc, CriticalRaindays.text != nil would be true but CriticalRaindays.text.toInt()! can still be nil, because abc cannot be converted to an Int.
The exact cause of your crash is likely that .text is equal to "", the empty string. It's not nil, but definitely not an Int either.
The better solution is to use optional binding to check the integer conversion and see if that passes, instead of merely the string existing:
if let rainDays = CriticalRaindays.text.toInt() {
crit_raindays = rainDays
}
If that doesn't compile, you possibly need to do Optional chaining:
if let rainDays = CriticalRaindays.text?.toInt()
Not on a Mac atm so can't test it for you but hope this makes sense!
Why not use an if let to unwrap on if the the text field's text is non-nil?
if let textString = self.textField.text as String! {
// do something with textString, we know it contains a value
}
In your ViewDidLoad, set CarryForward.text = "" This way it will never be nil
Edit:
To check if a textfield is empty, you can use this:
if (CarryForward.text.isEmpty) {
value = 10
}
else {
value = CarryForward.text
}