How can I pass data to a view and use it directly in the "header"? All tutorials I made are accessing the data in the view body - which works fine - but I want to call a graphlql method from the UpdateAccountView and than render a view based on the result.
My class for passing data:
class Account {
var tel: Int
init(tel: Int) {
self.tel = tel
}
}
My main view where the class is initialised (simplified - normally the "tel" will come from an input)
struct ContentView: View {
var account: Account = Account(tel: 123)
var body: some View {
NavigationView {
NavigationLink(
destination: UpdateAccountView(account: account),
label: {
Text("Navigate")
})
}
}
}
The view I call to do the request and call the next view based on the result
UpdateAccount is taking tel:Int as a parameter.
And here is the problem. I cannot access account.tel from the passed data.
struct UpdateAccountView: View {
var account: Account
#ObservedObject private var updateAccount: UpdateAccount = UpdateAccount(tel: account.tel)
#ViewBuilder
var body: some View {
if updateAccount.success {
AccountVerifyView()
} else {
ContentView()
}
}
}
The error:
Cannot use instance member 'account' within property initializer; property initializers run before 'self' is available
Update method (GraphQL):
class UpdateAccount: ObservableObject {
#Published var success: Bool
init(tel: Int){
self.success = false
update(tel: tel)
}
func update(tel: Int){
Network.shared.apollo.perform(mutation: UpdateAccountMutation(tel: tel)) { result in
switch result {
case .success(let graphQLResult):
self.success = graphQLResult.data!.updateAccount.success
case .failure(let error):
print("Failure! Error: \(error)")
self.success = false
}
}
}
I saw that there is an EnvironmentObject but than the variable become available globally as far as I understood, which is not necessary here.
Thank you for your help.
You can make it in explicit init, like
struct UpdateAccountView: View {
var account: Account
#ObservedObject private var updateAccount: UpdateAccount // << declare
init(account: Account) {
self.account = account
self.updateAccount = UpdateAccount(tel: account.tel) // << here !!
}
// ... other code
}
I am trying to create a GUI with a series of text entry fields:
package main
import ("github.com/andlabs/ui")
func main() {
ui.Main(makeMainWin)
}
func makeMainWin(){
var entlist = []ui.NewEntry //Error here. How to declare an array of ui.NewEntry?
var box = ui.NewVerticalBox()
for i,_ := range [5]int{} {
println(i)
box.Append(ui.NewEntry(), false)
}
var mainWindow = ui.NewWindow("Hello", 200, 100, false)
mainWindow.SetChild(box)
mainWindow.OnClosing( func (*ui.Window) bool {
ui.Quit(); return true } )
mainWindow.Show()
}
However, there is error on var entlist = []NewEntry
I am not able to create an array of NewEntry components. I have tried []ui.NewEntry, []*ui.NewEntry, []ui.NewEntry() and []*ui.NewEntry()
Where is the problem and how can it be solved? Thanks for your help.
ui.NewEntry returns *Entry, therefore your slice should be declared as:
var entlist []*ui.Entry
I have a class which will perform a search. Once complete I want the search class to pass back the results to which ever instance (of another class) started the search. My thinking was to pass a reference to the class which instantiates the search class and use that reference to call a function. Here's a basic example of what I'm trying to do. How can I get this to work, or is there another/better way?
Search Class (I've tried AnyObject and UITableViewContoller):
class SearchClass : NSObject, NSURLConnectionDelegate, NSURLConnectionDataDelegate {
var callingClass : AnyObject? = nil //To store reference to the "other" class
var searchResults : [[String : AnyObject]]? = nil
init(callingClass: AnyObject) { //I don't know the name of the ViewController class which will instantiates this as it will be called by several different classes
self.callingClass = callingClass
}
func startSearch(searchString: String) {
//NSURLConnection etc
}
func connectionDidFinishLoading(connection: NSURLConnection) {
//more code
searchResults = ...
callingClass!.searchCompleted(searchResults) //Pass the search results back to the class instance which started the search
}
}
Other Classes:
class RandomViewController : UITableViewController {
//The casting on the next line fails
let Searcher = SearchClass(callingClass: self as! UITableViewController) //OR AnyObject
func randomFunction() {
searcher.startSearch("search query")
}
func searchComplete(searchResults: [[String : AnyObject]]) {
self.searchResults = searchResults
tableView.reloadData()
}
}
You can add a closure parameter to your startSearch function in your search class:
typealias SearchResultHandler = (result: [String : AnyObject]) -> ()
func startSearch(query: String, resultHandler: SearchResultHandler) {
// send the search request and in the completion handler of the request call your result handler:
resultHandler(result: searchResult)
}
Which you would then call from any class:
let searcher = SearchClass()
searcher.startSearch("query") { (result) -> () in
self.searchResults = results
tableView.reloadData()
}
You can use generics when you don't know what the class is going to be:
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Generics.html
However....
This seems like something that you should use protocol / delegates for.
// NOTE: weak references must be class type
protocol SearchClassDelegate: class {
func searchComplete(results: [[String: AnyObject]?])
}
// This is where you define T as the generic class
class SearchClass {
weak var delegate: SearchClassDelegate? // This is your "callingClass"
// NOTE: make sure it's weak
// ...
func connectionDidFinishLoading() {
// ...
self.delegate?.searchComplete(results)
}
}
// Set to the delegate
class ViewController: UIViewController, SearchClassDelegate {
// ...
// Make sure you set the delegate
// Here is where you implement this function
func searchComplete(results: [[String : AnyObject]?]) {
// Do whatever
// ...reloadData() etc.
}
}
I'm trying to have variables in swift that are critical app-wide user settings so they must be persisted to disk after every change. There is a small amount of these variables and I'm content with the first read happening from disk after the app starts.
I have code that looks similar to this:
var _myEnumMember:MyEnum?
var myEnumMember:MyEnum {
get {
if let value = _myEnumMember { // in memory
return value
}
var c:Cache = Cache()
var storedValue:MyEnum? = c.get("SomeStorageKey");
if let value = storedValue { // exists on disk
self.myEnumMember = value // call setter to persist
return self.myEnumMember // call getter again with value set
}
self.myEnumMember = .DefaultValue // assign via setter
return self.rankingDuration // call getter after `set`
}
set (newValue){
self._myEnumMember = newValue // assign to memory
var c:Cache = Cache()
c.put("SomeStorageKey", data: ser) // store in disk
}
I have about 5-6 properties that need to do this - I don't want to repeat myself over and over - is there any way to DRY this code up so I won't have to repeat this logic in several places?
(Note: Asking here and not CR.SE because I'd like answers to explain how to DRY getters/setters in these situations rather than receive critique on a particular piece of code)
I was working on something similar recently - this may be your best bet. I used this as a nested struct, but it doesn't strictly need to be nested.
First, define a LocalCache type that will handle the persistence of your properties:
struct LocalCache {
// set up keys as constants
// these could live in your class instead
static let EnumKey = "EnumKey"
static let IntKey = "IntKey"
static let StringKey = "StringKey"
// use a single cache variable, hopefully?
var cache = Cache()
// in-memory values go in a Dictionary
var localValues: [String: Any] = [:]
// fetch from local storage or from disk
// note that the default value also sets the return type
mutating func fetch<T>(key: String, defaultValue: T) -> T {
if localValues[key] == nil {
localValues[key] = cache.get(key) ?? defaultValue
}
return localValues[key]! as T
}
// save in both local storage and to disk
mutating func store(key: String, _ value: Any) {
localValues[key] = value
cache.put(key, data: value)
}
}
Then add a LocalCache instance to your class, and you can have much simpler getter/setters.
class Test {
// instance of the local cache
var localCache = LocalCache()
var enumPropery: MyEnum {
get { return localCache.fetch(LocalCache.EnumKey, defaultValue: MyEnum.DefaultValue) }
set { localCache.store(LocalCache.EnumKey, newValue) }
}
var intProperty: Int {
get { return localCache.fetch(LocalCache.IntKey, defaultValue: 0) }
set { localCache.store(LocalCache.IntKey, newValue) }
}
var stringProperty: String {
get { return localCache.fetch(LocalCache.StringKey, defaultValue: "---") }
set { localCache.store(LocalCache.StringKey, newValue) }
}
}
If you're using swift in an iOS or OS X context then NSUserDefaults are ABSOLUTELY the right way to do this.
https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSUserDefaults_Class/index.html
http://www.codingexplorer.com/nsuserdefaults-a-swift-introduction/
I begin my project with a split view controller as initial view controller and start it automatically from storyboard.
Generally, an app with this UI have one and only one split view controller as root, so I create a static variable in the subclass and set it when initialisation was done.
So I want try this behaviour with swift.
I read the Swift programming language guide book on iBook about Type properties (with static and class keyword) and trying a piece of code to the job:
import UIKit
class SplitViewController: UISplitViewController {
class func sharedInstance() -> SplitViewController {
return SplitViewController.instance
}
class let instance: SplitViewController = nil
init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) {
super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
self.initialization()
}
init(coder aDecoder: NSCoder!) {
super.init(coder: aDecoder);
self.initialization()
}
func initialization() {
SplitViewController.instance = self;
}
}
but I figured out when Xcode say the class keyword for type properties wasn't supported yet.
Did you have a solution to do this ?
Embedding a struct can work just fine as a workaround:
class SomeClass
{
// class var classVariable: Int = 0
// "Class variables not yet supported." Weird.
// Workaround:
private struct SubStruct { static var staticVariable: Int = 0 }
class var workaroundClassVariable: Int
{
get { return SubStruct.staticVariable }
set { SubStruct.staticVariable = newValue }
}
}
The SomeClass.workaroundClassVariable computed type property can then be used as if it were a stored type property.
Swift now has support for static variables in classes. This is not exactly the same as a class variable (because they aren't inherited by subclasses), but it gets you pretty close:
class X {
static let y: Int = 4
static var x: Int = 4
}
println(X.x)
println(X.y)
X.x = 5
println(X.x)
It seems to be possible to declare variables with static storage duration in file scope (as in C):
var sharedInstance: SplitViewController? = nil
class SplitViewController: UISplitViewController {
....
func initialization() {
sharedInstance = self
}
}
My preferred method is to just use a private file scope var outside of the class and then implement class/static getters and setters:
private var _classVar: Int = 0;
class SomeClass
{
public class var classVar: Int
{
get { return _classVar }
set { _classVar = newValue }
}
}
As of Swift 1.2 (available with Xcode 6.3b1 and onwards), static class properties and methods are supported.
class SomeClass
{
static var someVariable: Int = 0
}
Using a dispatch_once singleton model in Swift
Seems to be the best answer so far, avoiding the use of a global variable.
A solution enough similar than var in file scope but more customisable and near singleton is to use a struct which support static var as property of class
struct PersonSharedData {
static var backstore = ""
var data: String {
get { return PersonSharedData.backstore }
set { PersonSharedData.backstore = newValue }
}
}
class Person {
var shared=PersonSharedData() //<< pseudo class var
var family: String {
get { return shared.data }
set { shared.data=newValue }
}
var firstname = ""
var lastname = ""
var sexe: Sexe = .Unknown
}
Ok, with the solution of Nikolai that do the work. I post my changes in this thread for information
var instance: SplitViewController? = nil
class SplitViewController: UISplitViewController {
class func sharedInstance() -> SplitViewController? {
return instance;
}
init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: NSBundle?) {
super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
self.initialization()
}
init(coder aDecoder: NSCoder!) {
super.init(coder: aDecoder);
self.initialization()
}
func initialization() {
instance = self
}
}
and for example, in my appDelegate, I can access this static method like this
SplitViewController.sharedInstance()!.presentsWithGesture = false
The wording in the error heavily implies this will be a language feature in the future.
You may want to resort temporarily to declaring a property variable in the Application Delegate and retrieve it from there. Not ideal, definitely an anti-pattern, but would give you a central place to retrieve the UISplitViewController when needed.
You have to wrap the class variables inside an inner struct variable
class Store{
var name:String
var address:String
var lat:Int
var long:Int
init(name:String, address:String, lat:Int, long:Int){
self.name = name
self.address = address
self.lat = lat
self.long=long
}
private struct FACTORY_INITIALIZED_FLAG { static var initialized: Bool = false
static var myStoreList:[Store]?
static func getMyStoreList()->[Store]{
if !initialized{
println("INITIALIZING")
myStoreList = [
Store(name: "Walmart", address: "abcd", lat: 10, long: 20),
Store(name: "JCPenny", address: "kjfnv", lat: 23, long: 34)
]
initialized = true
}
return myStoreList!
}
}
}
var a = Store.FACTORY_INITIALIZED_FLAG.getMyStoreList()
var b = Store.FACTORY_INITIALIZED_FLAG.getMyStoreList()
// only prints INITIALIZING once
Try this:
class var instance: SplitViewController {
return nil
}
It is called Type Property in Swift.
You define type properties with the static keyword. For computed type properties for class types, you can use the class keyword instead to allow subclasses to override the superclass’s implementation. The example below shows the syntax for stored and computed type properties:
struct SomeStructure {
static var storedTypeProperty = "Some value."
static var computedTypeProperty: Int {
return 1
}
}
enum SomeEnumeration {
static var storedTypeProperty = "Some value."
static var computedTypeProperty: Int {
return 6
}
}
class SomeClass {
static var storedTypeProperty = "Some value."
static var computedTypeProperty: Int {
return 27
}
class var overrideableComputedTypeProperty: Int {
return 107
}
}
Read more at link below,
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Properties.html#//apple_ref/doc/uid/TP40014097-CH14-ID254