I'm trying to check when I save an object to my parse serve if something goes wrong. But I have two options and I have three options and I don't know the difference. I have these three options (if error == nil, or if object != nil, or if error == nil and object != nil). Which one should I use. Thanks
Option #1
let user = PFUser.current()!
user.saveInBackground (block: { (success:Bool, error:Error?) -> Void in
if error == nil{
}
)}
Option #2
let user = PFUser.current()!
user.saveInBackground (block: { (success:Bool, error:Error?) -> Void in
if object != nil{
}
)}
Option #3
let user = PFUser.current()!
user.saveInBackground (block: { (success:Bool, error:Error?) -> Void in
if error == nil && object != nil{
}
)}
I suggest and encourage you to use guard statement, which as made for such situations.
//Always safely unwrap optional value:
if let user = PFUser.current(){
user.saveInBackground (block: { (success:Bool, error:Error?) -> Void in
guard success, error == nil else {
//handle error somehow...(print or whatever...)
return
}
//Continue here as everything is fine...
)}
}
Better to use different handlers for success and for failure:
func saveInBackground(success: () -> Void, failure: (Error?) -> Void) {
/* do whatever you need */
if saved {
success()
} else {
failure(saveError)
}
}
saveInBackground(success: {
/* saving was succeed */
}, failure: { (error) in
/* saving was failed */
})
There should never be an error when the save operation succeeds, as a general rule of thumb, it depends on the next steps of your implementation. None of the approach is invalid, i would still recommend that you check the ‘happy value’, object, succeed dtc... before checking the error
Related
there're several elements inside configTypeBuilderList, if the value in ruleAttributes not same as the destinationField in ConfigTypeBuilder, it will log the error
ruleCriteriaList.forEach { configRuleCriteria ->
validateConfigTypeBuilder(configRuleCriteria.configTypeBuilderList, ruleAttributesNames)
}
private fun validateConfigTypeBuilder(configTypeBuilderList: List<ConfigTypeBuilder>, ruleAttributes: List<String>) {
val missAttributeList: MutableList<String> = mutableListOf()
configTypeBuilderList.forEach { configTypeBuilder ->
if(configTypeBuilder!= null) {
if (ruleAttributes.firstOrNull { ruleAttribute -> ruleAttribute == configTypeBuilder.destinationField } == null) {
if(!ruleAttributes.contains(configTypeBuilder.destinationField)) {
missAttributeList.add(configTypeBuilder.destinationField)
}
logger.error("{} is wrong", configTypeBuilder.destinationField)
}
}
}
The problem is each time there's only one element(configTypeBuilderList) go into validateConfigTypeBuilder, so the logger shows like this
logger.error("field1 is wrong")
logger.error("field2 is wrong")
...
What I need is, how can I modify my code in order to do this?
logger.error("field1, field2, field3 are wrong")
Edit
I tried the first solution, but I stuck here, I still get the same error result, the reason is because each time there's only one "destinationField", how can I make the list have all the error field, and then log the error, can I use continue or something?
Here are a couple of alternatives:
Add them to a list and log later.
fun foo()
val incorrectItems = mutableListOf<Any>()
// Do some stuff
// on error:
incorrectItems.add(someIncorrectItem)
// Do more stuff
// log the accumulated errors:
logger.error("${incorrectItems.joinToString("")} are wrong")
}
Partition your list into valid and invalid values. Log the invalid ones and process the good ones.
fun foo(someList: List<MyClass>) {
val (goodItems, badItems) = someList.partition { it.isValid() }
// ...where isValid() is whatever code you need to check is OK.
if (badItems.isNotEmpty()) {
logger.error("${badItems.joinToString("")} are wrong")
}
// Do stuff with goodItems
}
I want to implement a different error handling approach in a project without chaining exceptions.
To make it simple as possible, I am tend to write my own basic either-like model.
class Either<F, T> {
final F failure;
final T value;
const Either(this.failure, this.value);
Object check (){
if (failure != null) return failure;
return value;
}
}
I am concerning about returning the type Object, is there any problem or considerations with that in Dart or any other language?
Edit:
or returning dynamic type...
dynamic check(){
if (failure != null) return failure;
return value;
}
I think in your case, it's kind of a wired implementation. The question is, what do you want to do with the actual implementation ? Do you want to replace an if else that will appear over and over? In that case, what would you do if you have to handle the error (failure) ? I think a better approach is to use functions as parameters. Here's a short suggestion.
class Either<T, F> {
T value;
F fail;
Either(this.value, this.fail);
void check(success(T value), {failure(F fail)}) {
if (fail != null && failure != null) {
failure(fail);
} else if (value != null) {
success(value);
}
}
}
class SomeClass {
void checkTheImplementation() {
Either<String, Error> maybeString = Either("testing", null);
// if you don't want to handle the error.
maybeString.check((value) => print(value));
// if you want to handle the error
maybeString.check((value) => print(value), failure: (err) {
print(err.toString());
});
}
}
I have looked over and decided to go with baihu92's either_type way. It's much more clear and comprehensible than either in the dartz package. Here is my implementation:
and the usage is like:
I am trying to convert this Objective-C block into Swift:
[self.client downloadEntity:#"Students" withParams: nil success:^(id response) {
// execute code
}
failure:^(NSError *error) {
// Execute code
}];
This is my code in Swift, but the syntax seems to be a bit off:
client.downloadEntity("Students", withParams: nil, success: {(students: [AnyObject]!) -> Void in
print("here")
}, failure: { (error: NSError!) -> Void! in
print ("here")
}
This is giving me a few compilation errors:
Value of 'AnyObject' has no member 'downloadEntity'
It is complaining about the lack of commas (,) right after the failure part of the code
Try this:
client.downloadEntity("Student", withParams: nil,
success: { (responseObj) -> Void in
print("success: \(responseObj)")
},
failure: { (errorObj) -> Void in
print("treat here (in this block) the error! error:\(errorObj)")
})
You need to switch to the new Swift error syntax, and you can also using trailing closures. I had to use a bool for the example to show how you would call your success closure, or you would throw an error.
var wasSuccessful = true // This is just here so this compiles and runs
// This is a custom error type. If you are using something that throws an
// NSError, you don't need this.
enum Error:ErrorType {
case DownloadFailed
}
// Hopefully you have control over this method and you can update
// the signature and body to something similar to this:
func downloadEntity(entityName: String, success: ([AnyObject]) -> Void) throws {
let students = [AnyObject]()
// download your entity
if wasSuccessful {
// Call your success completion handler
success(students)
}
else {
throw Error.DownloadFailed
}
}
When you have a function that can throw an error, you need to call it with try inside a do/catch block.
// Calling a function that can throw
do {
try downloadEntity("Students") { students in
print("Download Succeded")
}
}
catch Error.DownloadFailed {
print("Download Failed")
}
// If you are handling NSError use this block instead of the one above
// catch let error as NSError {
// print(error.description)
// }
Consider the following code:
enum MyErrorType:ErrorType {
case BadTimes
}
var mightHaveAValue: String?
do {
if let value = mightHaveAValue {
// do stuff with value
} else {
throw MyErrorType.BadTimes
}
// do stuff with NSFileManager using mightHaveAValue which might throw
} catch {
// handle error
}
...in which I have a large do/try/catch block. In this instance the error handling will be the same, whether mightHaveAValue is empty or something bad happens with NSFileManager later on. So it makes sense to re-use the error handling code.
Is this the cleanest approach going in Swift2, or is there some way I can automatically throw/catch on unwrapping an optional with no value?
It looks ok, but it's even better with guard let instead of if let because it lets you use the unwrapped value in the main do block instead of having to work inside an if let branch. You can also use several catch branches to handle different error types.
do {
guard let value = mightHaveAValue else {
throw MyErrorType.BadTimes
}
// do stuff with value
} catch let error as MyErrorType {
// handle custom error
} catch let error as NSError {
// handle generic NSError
}
There is no automatic way to handle unwrapping optionals, you have to use one of the many known ways: if let, guard let, nil coalescing, etc.
Maybe just use an extension like this 🤔
extension Optional {
func throwing() throws -> Wrapped {
if let wrapped = self {
return wrapped
} else {
throw NSError("Trying to access non existing value")
}
}
}
I know this is probably a simple queston, I would like to return the value of currentLocGeoPoint and return the array of Objects which is of type PFObject.
Tried to save it as a global variable, but it doesn't work because it is asynchronous and doesn't take a value yet. Returns empty.
Tried to return currentLocGeoPoint and changed Void in to PFGeoPoint in. Gives error: PFGeoPoint is not convertible to 'Void'
So I'm not sure how I can fetch the variable currentLocGeoPoint.
func locationManager(manager: CLLocationManager!, didUpdateLocations locations: [AnyObject]!) {
CLGeocoder().reverseGeocodeLocation(manager.location, completionHandler: { (placemarks, error) -> Void in
if (error != nil) {
println("Error:" + error.localizedDescription)
//return
}
if placemarks.count > 0 {
let pm = placemarks[0] as CLPlacemark
self.displayLocationInfo(pm)
currentLoc = manager.location
currentLocGeoPoint = PFGeoPoint(location:currentLoc)
var query = PFQuery(className:"Bar")
query.whereKey("BarLocation", nearGeoPoint:currentLocGeoPoint, withinMiles:10)
query.limit = 500
query.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]!, error: NSError!) -> Void in
if objects != nil {
} else {
println("error: \(error)")
}
}
} else {
println("error: \(error)")
}
})
}
I don't understand the notion of "I want to return currentLocGeoPoint". Return it to what? You're in a CLLocationManagerDelegate method, so there's no one to return it to.
What you could do, though, is, when the request is done (i.e. within this closure), call some other function that needed the currentLocGeoPoint. Or you could update the UI to reflect the updated information (make sure to dispatch that update to the main thread, though). Or, if you have other view controllers or model objects that need to know about the new data, you might post a notification, letting them know that there is an updated currentLocGeoPoint. But within this method, there's no one to whom you would "return" the data.
You could assign it to a stored property of your class. Just use
self.<property> = currentLocGeoPoint