I am new to Xcode IDE and to swift and I'm trying to understand better how it works.
I'm aware that it's possible to make a delegation to an UI element, for example, a comboBox. This allows for working with methods that NSComboBoxDelegate supports. That's all fine. I understand how one comboBox can be linked to the method.
My question is: if there are two comboBox elements with delegation to a single .swift file, how do I define which one will "trigger" the method, for example, comboBoxSelectionDidChange? Do I have to have separate .swift files? Does the method work whenever each is changed? Is there a way to link each object to each method, as it's possible to do with outlets and actions?
I believe it's a simple question and probably one that programmers will answer with ease, but for beginners the abstraction and the simpler gapping holes slow comprehension too much.
Your Elements, for example UIPicker, can use the same delegate methods. You need to therefore differentiate between them by a tag. Or by actual reference. You need to give each one of your 'combo boxes' a tag first obviously, before you can use the tag option.
For Example:
func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int)
{
if(pickerView.tag == 0)
{
//do whatEver you want with the picker that has tag 0
}
else if(pickerView.tag == 1)
{
//do whatEver you want with the picker that has tag 1
}
}
Or by reference:
func pickerView(pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int)
{
if(pickerView == self.cityPicker)
{
//do whatEver you want with the city picker
}
else if(pickerView = self.countryPicker)
{
//do whatEver you want with the country picker
}
}
Related
I'm trying to implement Kingfisher prefetch feature inside an Rxswift project. The problem is with these 2 function
collectionView.rx.prefetchItems
collectionView.rx.cancelPrefetchingForItems
The instruction at Kingfisher github is quite short
override func viewDidLoad() {
super.viewDidLoad()
collectionView?.prefetchDataSource = self
}
extension ViewController: UICollectionViewDataSourcePrefetching {
func collectionView(_ collectionView: UICollectionView, prefetchItemsAt indexPaths: [IndexPath]) {
let urls = indexPaths.flatMap { URL(string: $0.urlString) }
ImagePrefetcher(urls: urls).start()
}
}
How can we implement with Rxswift? anyway to get the models and then the urls of models from array of indexpath. Thank.
I will walk you thru how I figured out the solution to help you figure out future solutions...
I'm assuming that the struct that holds the URL strings is called Item and that you have an Observable<[Item]> that you are currently using to load up the collection view. I'm also assuming that you only have one section in your collection.
First, we know that something needs to happen when the prefetchItemsAt sends an event so we start with that:
let foo = collectionView.rx.prefetchItems
Now inspect the type of foo to see that it is a ControlEvent<[IndexPath]>. A ControlEvent is a kind of observable. We just need the items part of the IndexPaths, so lets map that:
let foo = collectionView.rx.prefetchItems
.map { $0.map { $0.item } }
(The double map is an unfortunate consequence of Swift not supporting higher kinded types) Now inspect the type of foo. It is an Observable array of ints. Those ints are indexes into our items array. So we need access to the most recently emitted items:
(as above)
.withLatestFrom(items) { indexes, elements in
indexes.map { elements[$0] }
}
So withLatestFrom is like combineLatest except it only fires when the primary observable emits a value, not when the secondary observable does.
Now, inspecting the type of foo will find that it's an Observable array of Items. The exact items who's urls' we want to send to the ImagePrefetcher. So we need to extract the urlStrings into URLs.
(as above)
.map { $0.compactMap { URL(string: $0.urlString) } }
And with that, we have the array of URLs we want ImagePrefetcher to consume. Since it consumes data, it needs to be wrapped it in a subscribe block.
(as above)
.subscribe(onNext: {
ImagePrefetcher(urls: $0).start()
})
At this point, foo is a disposable so it just needs to be collected in our dispose bag... Here is the entire block of code.
collectionView.rx.prefetchItems
.map { $0.map { $0.item } }
.withLatestFrom(items) { indexes, elements in
indexes.map { elements[$0] }
}
.map { $0.compactMap { URL(string: $0.urlString) } }
.subscribe(onNext: {
ImagePrefetcher(urls: $0).start()
})
.disposed(by: bag)
One last bit to make everything clean... Everything between prefetchItems and the subscribe can be moved into the ViewModel if you have one.
The key takeaway here is that you can use the types to guide you, and you need to know what operators are available to manipulate Observables which you can find at http://reactivex.io/documentation/operators.html
I want to create before save and after save method hooks for my Go structs how can I achieve this?
type Person struct {
FirstName string
LastName string
}
func (p *Person) Save() {
// call beforeSave()
// Save person data
// call afterSave()
}
func (p *Person) Update() {
// call beforeUpdate()
// Update person data
// call afterUpdate()
}
type Order struct {
Number bson.ObjectId
Items []Item
}
func (o *Order) Save() {
// call beforeSave()
// Save order data
// call afterSave()
}
func (o *Order) Update() {
// call beforeUpdate()
// Update order data
// call afterUpdate()
}
For any struct I create as a model I want it to have a beforeSave() and afterSave() hook called automatically and be able to further override if necessary.
Packages like gorm use callback hooks heavily. But if you are writing your own engine (for some specific logic) using interfaces can help greatly (sample).
https://medium.com/#matryer/the-http-handler-wrapper-technique-in-golang-updated-bc7fbcffa702
I would only add to that article above, which I think well answers your question, that you can go further using pipelines (methods that return the associated variable they are bound to). It's particularly interesting as in the above article, as relates to being able to interpose anything between two processes, and you can use this to create tees and journalling/logging systems, and it can go a long way towards compensating for the kinda primitive error handling in Go.
I designed a number of related byte slice processing libraries that were able to be easily chained without needing to break a a line, although obviously more than about 3-4 in a line can get confusing and you can find yourself wanting to pass things in a DAG style pattern, at which point I think channels would make sense.
Here is my problem:
Aurelia app:
a few custom elements (already sharing a view via #UseView) doing almost the same thing (specific func shoud be defined by every element itself), how to manage shared code (inkl #bindable)?
How to refactor this:
https://gist.run/?id=897298ab1dad92fadca77f64653cf32c
The "shared" code you refer to in your question is lifecycle-related stuff in your custom elements, which isn't really suited for sharing. You would need to do inheritance, and with custom elements that's setting yourself up for a lot of headaches.
Rather than sharing code, why not focus on the things which are variable and try to make them configurable? By looking at your gist, that seems by far the most straightforward solution here.
Say you have a custom element that calls a function when a property changes. This function needs to be different for some instances of the element. You could accomplish that with a bindable function, and use the .call behavior, like so:
some-element.js
import { bindable } from 'aurelia-framework';
export class SomeElement {
#bindable value;
#bindable processValue;
valueChanged(newValue, oldValue) {
if (this.processValue) {
this.processValue({ val: newValue });
}
}
}
consumer.html
<some-element value.bind="myValue" process-value.call="myFunc(val)"></some-element>
<some-element value.bind="anotherValue" process-value.call="anotherFunc(val)"></some-element>
consumer.js
myFunc(val) {
console.log("val: " + val);
}
anotherFunc(val) {
console.log("val: " + val);
}
I am writing an iOS App (using xcode 7.3 and swift 2.2) using JavascriptCode framework. Calling javascript methods from swift works perfect, but when I call the swift method from javascript, xcode simply shows a "loading" type of symbol and nothing happens. I need to "force quit" xcode to get out of this state.
I have followed https://www.raywenderlich.com/124075/javascriptcore-tutorial and http://nshipster.com/javascriptcore/ and I am trying pretty simple calls.
Has anyone faced this kind of issue?
My swift code is as follows:
#objc protocol WindowJSExports : JSExport {
var name: String { get set }
func getName() -> String
static func createWindowWithName(name: String) -> WindowJS
}
#objc class WindowJS : NSObject, WindowJSExports {
dynamic var name: String
init(name: String) {
self.name = name
}
class func createWindowWithName(name: String) -> WindowJS {
return WindowJS(name: name)
}
func getName() -> String {
NSLog("getName called from JS context")
return "\(name)"
}
}
I am initializing the context as follows:
runContext = JSContext()
runContext.name = "test_Context"
windowToJs = WindowJS(name: "test")
runContext.setObject(windowToJs.self, forKeyedSubscript: "WindowJS")
If I replace the last two lines in above code with below code without instantiating it, the code simply fails to load.
runContext.setObject(WindowJS.self, forKeyedSubscript: "WindowJS")
And the javascript code is as simple as
function check() {
return WindowJS.getName()
}
I do see the breakpoint being hit in the JS function check and when the WindowJS.getName gets called, xcode simply becomes unresponsive.
The setTimeout could be solved by adding following piece of code to my swift function.
let setTimeout: #convention(block) (JSValue, Int) -> () =
{ callback, timeout in
let timeVal = Int64(timeout)
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, timeVal), dispatch_get_main_queue(), { callback.callWithArguments(nil)})
}
To expose this native code to the JS context, I also added following.
runContext.setObject(unsafeBitCast(setTimeout, AnyObject.self), forKeyedSubscript: "setTimeout")
Things then worked fine.
You're creating a deadlock since you are calling from Swift to JavaScript back to Swift. I'm not sure exactly why it is a deadlock but I had a similar issue with WKWebView on Mac recently.
You need to decouple this and make the communication asynchronous. This obviously means you cannot simply return a value from your JS function in this case.
To decouple, you can break the deadlock by deferring the work the JavaScript function needs to do out of the current runloop iteration using setTimeout:
function myFunction() {
setTimeout(function() {
// The actual work is done here.
// Call the Swift part here.
}, 0);
}
The whole native ↔︎ JavaScript communication is very, very tricky. Avoid it if you can. There's a project called XWebView that may be able to help you as it tries to ease bridging between the two worlds.
I've tried to follow this guide:
Quick Start for Collection Views
using an NSImageView in the Collection View Item.
Nothing shows up, neither if i set the image with a Image Well neither if i set the array via code.
So i tried to do it programmatically, using
func representedObject(representedObject: AnyObject)
{
super.representedObject = representedObject
photoImageView.image = (representedObject as! NSImage)
println("\(representedObject)")
}
in the Collection View Item (subclassed).
If I don't subclass Collection View Item Xcode tells me that there is no prototype set, if i subclass it it tells that "could not load the nibName"... (it's in the storyboard with correct identity set)
I can't have this Collection View to work :-(
Anyway, i like the bindings... so i'd like to achieve the correct result with bindings..
I checked and rechecked every passage in the document at the link and everything seems fine. the main difference is that the document uses the app delegate, i'm using a view controller.
i translated KVC methods in swift, i think they are correct since i know them have been called. Here them are:
func insertObject(p: ClientPhoto, inClientPhotoArrayAtIndex index: Int) {
images.insertObject(p, atIndex: index)
}
func removeObjectFromClientPhotoArrayAtIndex(index: Int) {
images.removeObjectAtIndex(index)
}
func setClientPhotoArray(a: NSMutableArray) {
images = a
}
func clientPhotoArray() -> NSArray {
return images
}
Their are basically 2 ways to work with NSCollectionView. 1 is to set the itemPrototype property and the other is to override newItemForRepresentedObject. The override method is more flexible and has the advantage that you using the technique below you can create the nscollectionviewitem in storyboard and all the outlets will be set correctly. Here is an example of how I use it:
class TagsCollectionView: NSCollectionView {
// ...
override func newItemForRepresentedObject(object: AnyObject!) -> NSCollectionViewItem! {
let viewItem = MainStoryboard.instantiateControllerWithIdentifier("tagCollectionViewItem") as! TagCollectionViewItem
viewItem.representedObject = object
return viewItem
}