I don't know if this is still a bug inherent in Swift, or if I'm getting something wrong, but here goes.
I have a class for creating menus (like a main menu and an options menu) in an iOS app, coded in Swift.
public class GameMenuScreen {
private var _labels: Dictionary<String, SKLabelNode>
// Getter/Setter indirection
internal var labels: Dictionary<String, SKLabelNode> {
get {
return self._labels
}
}
...
}
class MainMenu: GameMenuScreen {
...
}
My issue is that labels is inherited by MainMenu, but when I attempt to access MainMenu.labels in a method, it throws EXC_BAD_ACCESS.
My thinking is that because the call to MainMenu.labels is sent to GameMenuScreen, the return value is GameMenuScreen._labels, not MainMenu._labels, and because there is no instance of GameMenuScreen, accessing GameMenuScreen._labels accesses unallocated memory.
I'd like to know how I structure this such that any call to labels refers to self._labels and not super._labels.
Running Xcode 6.0.1
I think you would access an instance of it as MainMenu().whatever. You need the (). Not sure if that is your problem without seeing the full code. Can you post more?
Related
In the Apple developer docs chapter "There and Back Again" the watch app's App is written like this:
#main
struct MyWatchApp: App {
#WKExtensionDelegateAdaptor(ExtensionDelegate.self) var extensionDelegate
#SceneBuilder var body: some Scene {
WindowGroup {
NavigationView {
ContentView()
}
}
}
}
Unfortunately I get a purple runtime warning on my var declaration that says
#WKExtensionDelegateAdaptor should only be used within an extension based process
There must be something in Xcode that explicitly defines the App structure as "extension-based" but I can't find it!
Edit: More clarification... I am trying to handle the special method that gets called after you run the HealthKit method startWatchApp(with:completion:)
The special method for watch extensions is func handle(_ workoutConfiguration: HKWorkoutConfiguration)
I cannot seem to find a way to link this function on the new App structure for watch apps.
Ok, I found it. The solution is to simply replace WKExtensionDelegate with the new WKApplicationDelegate!
You can try this solution, it is simple and universal.
import WatchKit
class ExtensionDelegate: NSObject, WKExtensionDelegate {
static var current: ExtensionDelegate? {
return (WKExtension.shared().delegate as? ExtensionDelegate)
}
...
}
Then access this current instance like below, because it is Singleton, you can access it in the entire project scope.
ExtensionDelegate.current?.dosomething()
I want an embedded view to be able to call a function from the parent view, so I'm trying to have the child reference its parent by injection. This seems to work fine as long as the embedded view is created onDock:
class TestView : View() {
override val root = vbox {
label("Parent Label")
}
init {
println("Parent is instantiating.")
}
override fun onDock() {
val child = find(TestView2::class)
root.add(child)
}
fun doThing() {
println("Parent is doing a thing.")
}
}
class TestView2 : View() {
val parentClass: TestView by inject()
override val root = hbox {
label("Sub-view label 1")
label("Sub-view label 2")
}
init {
println("Sub-view is instantiating.")
parentClass.doThing()
}
}
I'd like it to be cleaner though. I'd prefer it if I was able to use the find function while creating the parent root. That's a problem, as calling the child view within any part of the init process creates a circular instantiation loop. Any way to avoid this or will I just have to settle for onDock and deal with it?
EDIT:
Just to note, I tried the onDock method again in a real, more complicated application and I got a cycle detection error. So even that method is not guaranteed to work.
You can create cyclic dependencies, but you can't call functions in both component's init block, as that would be impossible to resolve. The main takeaway here is that you're probably doing something you shouldn't. Views should not communicate with each other directly. This creates a tight coupling and prevents reuse. Instead you should communicate with one of the following:
State from a ViewModel
Controller function calls
Events using the EventBus
Since your code example is made up, it's not known what exactly you're trying to achieve in your actual app, but you will find the correct approach in the list above.
I see the urge to call functions in views and setting data directly into ui components instead of using bindings a lot, and in absolutely every case there is a much better way to solve the problem :)
I'm coding in IntelliJ IDEA. When debugging my application, I can't use some default method implementations in Watches.
Here is a condensed example:
public class Friendship {
interface Friend {
default void sayHiTo(Friend friend) {
System.out.println("Hi, " + friend.hashCode());
}
default int amountOfHands() {
return 2;
}
}
public static class BasicFriend implements Friend {
int numberOfFaces() {
return 1;
}
}
public static void main(String[] args) {
System.out.println("Put a breakpoint here");
}
}
In main() method I put a breakpoint and set up three watches:
// Default interface method with dependency
new BasicFriend().sayHiTo(new BasicFriend())
// Default interface method without dependency
new BasicFriend().amountOfHands()
// Class method
new BasicFriend().numberOfFaces()
The first watch throws NoSuchMethodException complaining that method Friendship$BasicFriend.sayHiTo() doesn't exist.
The second watch runs successfully, but strangely it reports a boxed object
{java.lang.Integer#537} "2" instead of just a primitive 2.
The third watch reports a primitive 1, just as expected.
Why is the first watch not working? Is this a bug? Is this actually IDE related? Is it because of some conceptual flaw of default methods? Should it be working as I want it to in the first place? Is the strange result of the second watch somehow related to the issue in the first watch?
Prior to JDK 8u40, default and static interface methods were not supported by JDI (Java Debugger Interface), JDWP (Java Debugger Wire Protocol) and JDB (the standard Java debugger). This is bug JDK-8042123, which is recorded as fixed in 8u40 and a corresponding blurb appears in the 8u40 release notes.
Update to 8u40 or later to fix this issue, at least on the JDK side.
From the bug description, it looks like debugger-side changes are also required, to avoid casting com.sun.jdi.InterfaceType objects to com.sun.jdi.ClassType, but instead call InterfaceType.invokeMethod() directly.
In the specific case of IntelliJ, Suseika confirmed in a comment that 14.1.2 has mostly fixed the issue (except the unexpected boxing), though Mike Kobit still experiences this problem on that version with a ClassCastException suggestive of the incorrect cast above.
I get this error when opening one specific form. The rest is working fine and I have no clue why this one isn't.
Error: An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported.
I get the error at _oDBConnection when I try to save. When I watch _oDBConnection while running through the code, it does not exist. Even when I open the main-window it does not exist. So this form is where the DataContext is built for the very first time.
Every class inherits from clsBase where the DataContext is built.
My collegue is the professional one who built it all. I am just expanding and using it (learned it by doing it). But now I'm stuck and he is on holiday. So keep it simple :-)
What can it be?
clsPermanency
namespace Reservation
{
class clsPermanency : clsBase
{
private tblPermanency _oPermanency;
public tblPermanency PermanencyData
{
get { return _oPermanency; }
set { _oPermanency = value; }
}
public clsPermanency()
: base()
{
_oPermanency = new tblPermanency();
}
public clsPermanency(int iID)
: this()
{
_oPermanency = (from oPermanencyData in _oDBConnection.tblPermanencies
where oPermanencyData.ID == iID
select oPermanencyData).First();
if (_oPermanency == null)
throw new Exception("Permanentie niet gevonden");
}
public void save()
{
if (_oPermanency.ID == 0)
{
_oDBConnection.tblPermanencies.InsertOnSubmit(_oPermanency);
}
_oDBConnection.SubmitChanges();
}
}
}
clsBase
public class clsBase
{
protected DBReservationDataContext _oDBConnection;
protected int _iID;
public int ID
{
get { return _iID; }
}
public DBReservationDataContext DBConnection
{
get { return _oDBConnection; }
}
public clsBase()
{
_oDBConnection = new DBReservationDataContext();
}
}
Not a direct answer, but this is really bad design, sorry.
Issues:
One context instance per class instance. Pretty incredible. How are you going to manage units of work and transactions? And what about memory consumption and performance?
Indirection: every entity instance (prefixed o) is wrapped in a cls class. What a hassle to make classes cooperate, if necessary, or to access their properties.
DRY: far from it. Does each clsBase derivative have the same methods as clsPermanency?
Constructors: you always have to call the base constructor. The constructor with int iID always causes a redundant new object to be created, which will certainly be a noticeable performance hit when dealing with larger numbers. A minor change in constructor logic may cause the sequence of constructor invocations to change. (Nested and inherited constructors are always tricky).
Exception handling: you need a try-catch everywhere where classes are created. (BTW: First() will throw its own exception if the record is not there).
Finally, not a real issue, but class and variable name prefixes are sooo 19xx.
What to do?
I don't think you can change your colleague's design in his absence. But I'd really talk to him about it in due time. Just study some linq-to-sql examples out there to pick up some regular patterns.
The exception indicates that somewhere between fetching the _oPermanency instance (in the Id-d constructor) and saving it a new _oDBConnection is created. The code as shown does not reveal how this could happen, but I assume there is more code than this. When you debug and check GetHashCode() of _oDBConnection instances you should be able to find where it happens.
Im working on a MVVM Windows phone app that displays weather info.
When the app loads up it opens MainPage.xaml. It makes a call the the service to get weather info and binds that data to the UI. Both Fahrenheit and Celcius info are returned but only one is displayed.
On the setting page, the user can select to view the temp in either Fahrenheit or Celcius.
The user can change this setting at any time and its stored in IsolatedStorageSettings.
The issue Im having is this:
when the user navigates to the Settings page and changes their preference for either Fahrenheit or Celcius, this change is not reflected on the main page.
This issue started me thinking about this in a broader context. I can see this being an issue in ANY MVVM app where the display depends on some setting in IsolatedStorage. Any time any setting in the IsoStore is updated, how does the ViewModels know this? When I navigate back in the NavigationStack from the settings page back to MainPage how can I force a rebind of the page?
The data in my model hasnt changed, only the data that I want to display has changed.
Am I missing something simple here?
Thanks in advance.
Alex
Probably you have code like this:
public double DisplayTemperature
{
get { return (IsCelsium) ? Celsium : Fahrenheit; }
}
And IsCelsium is:
public double IsCelsium
{
get { return (bool)settings["IsCelsium"]; }
set { settings["IsCelsium"] = value; }
}
So you need to add NotifyPropertyChanged event to notify UI to get new values from DisplayTemperature property:
public double IsCelsium
{
get { return (bool)settings["IsCelsium"]; }
set
{
settings["IsCelsium"] = value;
NotifyPropertyChanged("DisplayTemperature");
}
}
Take a look at Caliburn Micro. You could implement something similar or use CM itself. When using CM I don't even think about this stuff, CM makes it so simple.
When your ViewModel inherits from Screen there are life-cycle events that fire that you can override. For example, OnInitialize fires the very first time the ViewModel is Activated and OnActivate fires every time the VM is activated. There's also OnViewAttached and OnViewLoaded.
These methods are the perfect place to put logic to populate or re-populate data.
CM also has some special built in features for allowing one to easily tombstone a single property or an entire object graph into Iso or phone state.
ok, so Ive come up with a solution. Before I get to it, let me provide some background. The app that Im working on uses both MVVM Light and WP7Contrib. That being the case, I am using Funq for DI and the MVVMLight Toolkit. After I posted my initial question, I gave the question a bit more thought. I remembered a video that I watched a while back from MIX2011 called Deep Dive MVVM with Laurent Bugnion
http://channel9.msdn.com/Events/MIX/MIX11/OPN03
In it, he talks about just this problem (view models not living at the same time) on Windows Phone. The part in question starts around the 19 minute mark.
Anyway, after I remembered that and realized that the ViewModel locator is exposed in App.xaml, this became a trivial problem to solve. When the user changes the Fahrenheit/Celcius option on the setting page, I simply get a reference to the MainViewModel via the ViewModelLocator and reset the collection that is bound to the UI thus causing the bindings to update.
public bool AddOrUpdateValue(string Key, Object value)
{
bool valueChanged = false;
// If the key exists
if (settings.Contains(Key))
{
// If the value has changed
if (settings[Key] != value)
{
// Store the new value
settings[Key] = value;
valueChanged = true;
}
}
// Otherwise create the key.
else
{
settings.Add(Key, value);
valueChanged = true;
}
return valueChanged;
}
public bool ImperialSetting
{
get
{
return GetValueOrDefault<bool>(ImperialSettingKeyName, ImperialSettingDefault);
}
set
{
if (AddOrUpdateValue(ImperialSettingKeyName, value))
{
Save();
RaisePropertyChanged("ImperialSettingText");
var vml = new ViewModelLocator();
vml.MainViewModel.Cities = (App.Current as App).Cities;
}
}
}
It was a mistake on my part not to realize that I could get access to the viewModel via the ViewModelLocator. Hopefully this post saves someone else the time I burned on this issue.