So i was trying to use clear function of kotlin while building an app in android studio though clear is kotlin built in function it is giving an unresolved reference error my code is:
Var peerListListener= WifiP2pManager.PeerListListner(){
val refreshedPeers= peerList.deviceList
If(!refreshedPeers.equals(peers)){
Peers.clear()
}
}
Please help me to resolve this issue and this code is done outside the oncreate function
peers is defined as:
var peers:List<WifiP2pDevice>=mutableListof<WifiP2pDevice>()
I have tried declaring this both globally and locally
First you got typo, you're defining the variable as peer but trying to use clear on Peer.
Second you're exposing peer as an immutable list by saying List<WifiP2pDevice> and List interface does not have clear as it is immutable. Expose peer as mutable list by defining it as MutableList<WifiP2pDevice> and you will be able to use clear().
Related
I've been playing recently with KSP and have managed to develop interesting capabilities (such as automatic recyclerview and view holder generators based on their layout id), and so far all is well.
However, I am now trying to do something different than creating files based on the annotations I design. Instead of creating files, I would only want to populate a list with the classes/objects annotated by me.
Example:
ClassA.kt
#MyAnnotation
class ClassA(context: Context): SomeBaseClass(context) {
override fun baseClassFunction() {
// custom code goes here
}
}
ClassB.kt
#MyAnnotation
class ClassB(context: Context): SomeBaseClass(context) {
override fun baseClassFunction() {
// custom code goes here
}
}
MyListAgregator.kt
object MyListAgregator {
const val classList: List<SomeBaseClass> = mutableListOf()
}
Where my custom KSP would do the following
Collect all classes/objects (the usual) that are annotated by my
#MyAnnotation
Create an instance of them with the appropriate
parameters (in this case just a context)
Add each one to the classList in the MyListAgregator
I can always get to the point of the class collection (step 1) but the rest is a complete mystery to me, and feels like KSP always expects to create code, not execute it? Perhaps I am incorrect on the later one, but I could not find anything related to that explained in the available documentation.
Another alternative I considered, but would rather avoid out of concern for any negative hit (performance, for example) is to actually modify that MyListAgregator file directly to include all the instances in the list, as if I had written them myself. However, I would still prefer to go with the previous option instead if it is at all possible.
First, you need to establish a ruleset that will be applied to the classes annotated with your annotation (symbol in KSP glossary). For example, they must contain one argument, that argument must be a member property and of type Context and must be subclass of SomeBaseClass. I suggest first look up for correct inheritance then look up for argument count and type.
You are still within reading and exploring all files with this symbol. Filtering based on this ruleset you will land with a set of classes at point 2.
Here, KSP can provide you with the interface to generate your code. However, KSP will not let you edit the source file, but generate new one based on your conditions. Here you have to write your implementation for the overriden function, by visiting it
You can preserve the output (newly generated classes at step 2) and generate your MyListAggregator object.
I am using realm in our iOS and Android app. For some reason i want to rename one of my realm object.
Initially we name the object Demo and now I want to change it to RealmDemo
In android we achieved it by using #RealmClass annotation
#RealmClass(name = "Demo")
open class RealmDemo : RealmObject() {
}
On iOS side i am not sure how exactly i can do similar as i did in android.
class RealmDemo: Object {
override static func className() -> String {
"Demo"
}
}
I tried above ^ but getting following error "Terminating app due to uncaught exception 'RLMException', reason: 'Object type 'Demo' not managed by the Realm'"
Two things.
First, You can name an object anything you want and change its name at any time.
HOWEVER, that's a destructive change, and Realm doesn't have any way to know the the newly named object 'is the same object' as the prior object.
How that's handled depends on what the use case is:
If this is a development situation, delete your local Realm files and run the app and the object with the new name will be created automatically.
If this is production then a migration block is needed (as on any platform) to migrate the data from the old object to the new one.
Secondly, The other important thing is the name of the object is now RealmDemo, whereas the prior object is Demo
class RealmDemo: Object {
so technically those are two separate objects. To Realm, you've abandoned the Demo object totally and that's a destructive change. Demo is still hanging around but is not referenced in your code so an error is thrown
On a possibly unrelated note, the className function references Demo
override static func className() -> String {
"Demo"
}
But the object name is RealmDemo.
It's not clear why the className function exists but it's not required or really needed. See the documentation for objects to get a feel for their structure - they may need a Primary Key
Seems like realm does not support className overriding for cocoa/ios.
https://github.com/realm/realm-cocoa/issues/2194
https://github.com/realm/realm-cocoa/issues/6624
I am currently using objectbox via koin dependency injection within my android app. It works fine however i need to re-initialise my DI and so i need to destroy the boxStore before. This is because i initialise the box via DI and if i do not destroy the current BoxStore I cannot create a new one.
I've found a similar post How to close Objectbox Store and delete data files however it hasn't solved my issue.
I have tried calling deleteAllFiles however i am getting an error.
BoxStore.deleteAllFiles(context, (BoxStoreBuilder.DEFAULT_NAME))
BoxStore.deleteAllFiles(context, null)
I am getting the error message:
java.lang.IllegalStateException: Cannot delete files: store is still open
this is on the line of code mentioned above. Any suggestions would be very helpful
solution:
i had to access each of my boxes individually and delete them one at a time.
fun clearAll(){
firstBox.box.removeAll()
secondBox.box.removeAll()
.......
}
fun closeAll(){
firstBox.box.close()
secondBox.box.close()
.......
}
You can just close the boxStore and then delete all files:
boxStore.close();
boxStore.deleteAllFiles();
There's also a static method for deleting all the files ( if you want to delete all files before you open boxStore )
It's the most efficient way.
Ref: https://github.com/objectbox/objectbox-java/issues/317
I can suggest a solution. You can get all entity classes and get each box and clear them.
boxStore.getAllEntityClasses().forEach( entityClass ->
boxStore.boxFor(entityClass
).removeAll());
This is simple question. In Java you can create String variable or couple of variables without adding any value to it. This is used at start of the class before onCreate() is called in Activity. I've used lateinit property in Kotlin to achieve that, but now I have a problem with changing visibility of RecyclerView. It will throw exception "lateinit property recyclerView has not been initialized".
Is there any way how to know if property is initialized? This is called at start of the parent activity in Fragment (hide recyclerView and show ProgressBar till data are binded to recyclerView).
In Java you can create String variable or couple of variables without adding any value to it
Actually in that case it is implicitly declared null. Kotlin does not do that, because of its nullability mechanism. You must explicitly declare a variable nullable to allow null:
var str: String // does not work
var str: String? // does not work
var str: String? = null // works
Also see this answer.
Your other option indeed is to mark it lateinit:
lateinit var str: String // works
If you need to make a check to see if it is initialized before using it, you use
if (::str.isInitialized)
But really you should avoid this check and just make sure it is initialized before using it.
If you need to get your UI element in Kotlin, you do not need to create variable and initialise it by using findViewById anymore (though you can). Use kotlin view binding, which works pretty well.
https://kotlinlang.org/docs/tutorials/android-plugin.html#view-binding
In the last year I've become a mobile developer and a functional programming admirer.
In each of the mobile arenas there are components with lifecycle methods that make up the meat of the app. The following will use Android and Kotlin as examples, but the same applies to iOS and Swift.
In Android, there are Activity's with lifecycle methods like onCreate(). You might also define a function, onButtonClicked(), which will do exactly what the name describes.
For the purposes of the question, let's say there's a variable defined in onCreate() that is used in a button click handler onButtonClickedPrintMessageLength() (This is usually the case - onCreate() is essentially Activity's setup method).
The example class would look like this:
class ExampleActivity: Activity() {
var savedStateMessage: String? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
savedStateMessage = "Hello World!"
}
fun onButtonClickedPrintMessageLength() {
System.out.println(savedStateMessage?.length)
}
}
Notice the declaration of savedStateMessage as a String? (nullable string) and the use of ?. (null safe call). These are required because the compiler cant guarantee that onCreate() will be called before onButtonClickedPrintMessageLength(). As developers though, we know that onCreate will always be called first* **.
My question is how can I tell the compiler about the guaranteed order of these methods and eliminate the null checking behavior?
* I suppose it's possible to new up our ExampleActivity and call onButtonClickedPrintMessageLength() directly, thus sidestepping the Android framework and lifecycle methods, but the compiler/JVM would likely run into an error before anything interesting happened.
** The guarantee that onCreate is called first is provided by the Android framework, which is an external source of truth and might break/function differently in the future. Seeing that all Android apps are based on this source of truth though, I believe it's safe to trust.
Although this won't answer your actual question, in Kotlin you can use lateinit to tell the compiler that you'll initialize a var at a later point in time:
lateinit var savedStateMessage: String
You'll get a very specific UninitializedPropertyAccessException if you try to use this variable before initializing it. This feature is useful in use cases like JUnit, where you'd usually initialize variables in #Before-annotated method, and Android Activitys, where you don't have access to the constructor and initialize stuff in onCreate().
As mentioned in another answer, lateinit is available as an option to defer initialization to a later point in a guaranteed lifecycle. An alternative is to use a delegate:
var savedStateMessage: String by Delegates.notNull()
Which is equivalent, in that it will report an error if you access the variable before initializing it.
In Swift this is where you would use an implicitly-unwrapped Optional:
class Example: CustomStringConvertible {
var savedStateMessage: String! // implicitly-unwrapped Optional<String>
var description: String { return savedStateMessage }
init() {
savedStateMessage = "Hello World!"
}
}
print(Example()) // => "Hello World!\n"
By using the operator ! at the end of String in the second line of the example you are promising that the variable will be set before it can be used. This is accomplished in the init method of the example. It's still an Optional but code can treat it as a String since it will be automatically unwrapped before each use. You must take care that the variable is never set to nil when it might be accessed or a runtime exception may be generated.