I have set a pan gesture to an imageView, though it's action method never being called in swift 3.
let panGesture = UIPanGestureRecognizer(target: self, action: #selector(self.panGestureHandler(panGesture:)))
panGesture.minimumNumberOfTouches = 1
imageview.addGestureRecognizer(panGesture)
the action method:
#objc func panGestureHandler(panGesture recognizer: UIPanGestureRecognizer) {
}
Am I missing anything?
Ok, seems dumb, but after debugging I've noticed that the imageView's userInteractionEnabled is set to false.
After adding this line imageview.isUserInteractionEnabled = true everything seems to be working properly.
You may try to use a function handler for you rUIPanGestureRecognizer like this.
func panGestureHandler(recognizer: UIPanGestureRecognizer) {
}
Related
I'm trying to setup a DocumentGroup in my app, but there's no examples out there yet ReferenceFileDocument is for. I know what a FileDocument is, but how are ReferenceFileDocuments different.
In the docs all it says is:
Conformance to ReferenceFileDocument is expected to be thread-safe,
and deserialization and serialization will be done on a background
thread.
There's a hint in the name: ReferenceFileDocument is a document that's a reference type (ie, a class). FileDocument is for a struct based document.
This has an effect on how documents are saved because SwiftUI can just make a copy of the reference type and save it without worrying about you coming along and modifying it during the save, since it's a value type or tree of value types.
With ReferenceFileDocument, there also doesn't seem to be a clear way for the SwiftUI to know when to save, so it depends on you telling it. There's no direct "doc is dirty, save it now" method, so the way you inform SwiftUI that you've done something that requires saving is through the undo manager.
You also need to provide a snapshot method to return a copy of the document that's safe for it to save.
final class QuizDocument: ReferenceFileDocument, ObservableObject {
#Published var quiz: QuizTemplate
init(quiz: QuizTemplate) {
self.quiz = quiz
}
static var readableContentTypes: [UTType] { [.exampleText] }
init(configuration: ReadConfiguration) throws {
guard let data = configuration.file.regularFileContents,
let quiz = try? JSONDecoder().decode(QuizTemplate.self, from: data)
else {
throw CocoaError(.fileReadCorruptFile)
}
self.quiz = quiz
}
// Produce a snapshot suitable for saving. Copy any nested references so they don't
// change while the save is in progress.
func snapshot(contentType: UTType) throws -> QuizTemplate {
return self.quiz
}
// Save the snapshot
func fileWrapper(snapshot: QuizTemplate, configuration: WriteConfiguration) throws -> FileWrapper {
let data = try JSONEncoder().encode(quiz)
return .init(regularFileWithContents: data)
}
}
ReferenceFileDocument is a document type that will auto-save in the background. It is notified of changes via the UndoManager, so in order to use it you must also make your document undo-able.
The only mention I see of it in the docs is here.
Here is a working example.
I am getting an error that I don't understand. I am not sure if it is a compiler error or if I am doing something wrong?
Inside a swiftUI View I have a list showing elements from core data (Figure 1). In the example below I replaced the t.name with "yo" for some undefined reason 😅.
Anyway, the tasks is a fetch request from Core Data:
#FetchRequest(entity: Task.entity(), sortDescriptors: []) var tasks: FetchedResults<Task>
FIGURE 1: Works fine to build and run the app.
FIGURE 2: Does not work to build and run the app.
Please help me understand what I am doing wrong or is this a compiler bug? Why can't I add the if block inside the ForEach? I can provide more information if needed. Thanks!
You can use if inside ForEach, but you should remember that ForEach is not language operator foreach but a struct type with ViewBuilder in constructor with generics in declaration, so it needs to determine type, which in your case it cannot determine.
The possible solution is to tell explicitly which type you return, as below (tested with Xcode 11.2 / iOS 13.2)
ForEach(tasks, id: \.id) { name -> Text in
if (true) {
return Text("name")
}
}
You have to return nil in case of a false condition. So you need to declare parameter as Optional and return nil in case of a false condition (XCode - 11.3.1).
ForEach(tasks, id: \.id) { t -> Text? in
return condition ? Text("text") : nil
}
}
For some reason, in the ForEach.init you're using, the view building closure isn't annotated with #ViewBuilder. This means that the if/else you're using is Swift's own if statement, not the SwiftUI construct which returns a _ConditionalContent.
I don't know if it's considered a bug by Apple, but I would definitely consider it to be one.
The easiest workaround is just to wrap the if/else in a Group - the Group.init is a #ViewBuilder, so will handle the if/else correctly.
What also worked for me was using a Group inside the ForEach like this:
ForEach(self.items, id: \.self { item in
Group {
if item.id == 0 {
Text(String(item.id))
}
}
}
Edit: Please note the question below discusses using delegation between
2 viewcontrollers that are also implemented in a UITabBarController.
I've done a fair bit of searching here and on YouTube, but haven't seen my issue replicated elsewhere. I'll keep it to the point.
I have 2 view controllers that I coded myself -not generated by XCode-; TabOneController, and TabTwoController
below are the coding for both...
import UIKit
class TabOneController: UIViewController{
private let instanceOfTabOneView = TabOneView()
var vc1Delegate: fromOneToTwo!
override func loadView() {
super.loadView()
view.addSubview(instanceOfTabOneView.buildTheVu())
view.backgroundColor = UIColor.white
runThisOnce()
}
func runThisOnce(){
vc1Delegate.passTheValue(heroNameIs: "pass this to TabTwoController")
}
}
protocol fromOneToTwo{
func passTheValue(heroNameIs: String)
}
as for tab 2...
import UIKit
class TabTwoController: UIViewController, fromOneToTwo{
private let instanceOfTabTwoView = TabTwoView()
override func loadView() {
super.loadView()
view.addSubview(instanceOfTabTwoView.buildTheVu())
assignDelegateToSelf()
}
func assignDelegateToSelf(){
let instanceTabOne = TabOneController()
instanceTabOne.vc1Delegate = self
}
func passTheValue(heroNameIs:String){
instanceOfTabTwoView.txtFld.text = heroNameIs
}
}
I'm getting the following error at runtime -the app builds successfully-...
fatal error: unexpectedly found nil while unwrapping an Optional value
on the following line...
vc1Delegate.passTheValue(heroNameIs: "pass this to TabTwoController")
When I comment out the above line, the app builds and runs successfully, but of course the app doesn't execute the delegation.
I kinda understand what the compiler is trying to tell me, that the
vc1Delegate
hasn't been instantiated -I guess-. But I searched under every rock, and can't seem to find how to get around this.
I'd appreciate any help or guidance. Sorry if my code seems immature, I'm new to Swift and programming in general. Thank you.
In a UITabBarController, the first tab is instantiating by default. The view controller initialization executes the loadView and finds a nil because the second tab did not initialize yet; this is normal behavior. My suggestion is making the delegate weak optional with the ? suffix and run the delegate code elsewhere. Also, always capitalize the first letter in class and protocol names.
weak var vc1Delegate: FromOneToTwo?
If this structure is mandatory, try with a custom notification observer instead.
First thing first, your error happens in line var vc1Delegate: fromOneToTwo! while you declared this delegate variable as not null but then calling passTheValue on it. A correct practice will be
var vc1Delegate: fromOneToTwo?
func runThisOnce(){
if let delegate = vc1Delegate {
vc1Delegate.passTheValue(heroNameIs: "pass this to TabTwoController")
}
}
Secondly, you are not using delegate correctly. In the assignDelegateToSelf() function, you are creating a new instance of TabOneController
and then assign delegate. Instead, you need to find out the existing TabOneController instance and assign delegate.
I try this and worked add delegate = self in table cellforRowAt
like this
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell
{
let cell = tableView.dequeueReusableCell(withIdentifier: "ChapterPracticeTableViewCell") as! ChapterPracticeTableViewCell
cell.deligate = self
return cell
}
I have a fair amount of code that looks something like this...
let wantsIgnored = UserDefaults.standard.bool(forKey: "ViewShowIgnoredElements") ?? true
The idea was that if the defaults didn't include that key, it would still get a reasonable default value. This worked fine in Swift 2, but in Swift 3 it warns...
Left side of nil coalescing operator '??' has non-optional type 'Double', so the right side is never used
So it seems that UserDefaults.standard.bool will always return a value, which I guess makes sense if it's a Bool. Ok fine, but what is the best way to solve this problem? I could check every key with objectForKey, but that makes the code much messier. Or I could not do this check at all, and make sure that every key is in the initial set of defaults, by hand I guess.
I'm sure I'm not the only one to have faced this, any canonical solutions?
I'm afraid you would think this as messy, but you can write something like this:
let wantsIgnored = UserDefaults.standard.object(forKey: "ViewShowIgnoredElements") as? Bool ?? true
Please try.
Shouldn't it be:
let wantsIgnored = UserDefaults.standard.set(true, forKey: "ViewShowIgnoredElements")
Then to change it:
UserDefaults.standard.set(false, forKey: "ViewShowIgnoredElements")
And to call it:
let xxxx = UserDefaults.standard.bool(forKey: "ViewShowIgnoredElements")
or:
func boolTest (_myBool: Bool){
if _myBool{
//do something
}
}
//and call that function
boolTest(_myBool: UserDefault.standard.bool(forKey: "ViewShowIgnoredElements"))
Here's a link to a jsfiddle: http://jsfiddle.net/Qt972/
When you run the fiddle you'll see a name and a button to make the "person" say hello. This works fine, however the "event" is undefined.
An even simpeler case also fails:
http://jsfiddle.net/CCg2K/1/
Does anyone know how I can fix this issue?
When you do a console.log(arguments) inside your action callback you can see that there are actually 3 parameters passed. The first one is the view, the second is the event and the third is the context.
You can rewrite your edit action like this:
edit: function(view, event, context) {
var target = event.target;
...
}
UPDATE: since commit 657a2664 - available in release 0.9.6 I guess - only a single event parameter is passed which has the view and context as properties. So if you want to access those you have to do the following:
edit: function(event) {
var view = event.view;
var context = event.context;
...
}