Thank you all so much! I just started in Kotlin which probably should be called the K language (like C and F), and have found so many solutions here on this site...it's awesome!
I have an independent class file called AppTime.kt and it's declared in the AndroidManifest.xml file:
<application
android:name=".AppTime"
class AppTime : Application() {
fun burntToast(sMsg: String) {
Toast.makeText(this.applicationContext, "!", Toast.LENGTH_LONG).show()
}
}
It doesn't run when called anywhere from a Fragment class:
class FirstFragment : Fragment() {...
AppTime().burntToast()
I've tried every approach using parameters for the Toast following makeText(...
and then to call it from a Fragment with or without context or string parameters.
Is it the type of class I have?
Functions defined inside a class can only be called on an instance of that class, as you already found.
But you cannot simply instantiate an arbitrary Application and expect it to work. Android does a lot of behind-the-scenes setup of framework classes before they are usable. Any Application or Activity that you instantiate yourself is useless. You have to use the instances that are provided to you through the lifecycle of the Activities that get launched in your application.
If you want to call this function from your Fragment, you will have to get an instance of your application, which you can get from its associated Activity. Since the Activity class doesn't know about your specific subclass of Application, you must also cast the application to your specific subclass to be able to call its unique functions. You can get the Activity by using requireActivity().
(requireActivity().application as AppTime).burntToast()
Related
My code use apache.ml.clustering.GaussianMixture, but its init method private def initRandom(...) does not work well, so I want to customize a new init method.
At first I want to "extends" class GuassianMixture, but initRandom is a private method.
Then I tried another way, it is to set initial GMM, but sadly source code says that TODO: SPARK-15785 Support users supplied initial GMM.
I've also tried to copy the code of class GuassianMixture for my custom class, but there are too many things attached to it. GaussianMixture.scala comes with sort of classes and traits, some of which are only accessible within ML packages.
I solved it by myself. Here is my solution.
I created class CustomGaussianMixture which extends GaussianMixture from official package org.apache.spark.ml.clustering.
And within my project, I created a new package, also named as org.apache.spark.ml.clustering(to prevent deal with scope of sort of complexity classes/traits/objects in org.apache.spark.ml.clustering). And place my custom class in it.
The next thing is to override the method(fit) call initRandom, a non-private method, so I can override it. Specifically, Just write my new init method in class CustomGaussianMixture, and copy method fit from official source code in GaussianMixture.scala to class CustomGaussianMixture, remember to modify code in CustomGaussianMixture.fit() to call my custom init method.
At last, just use CustomGaussianMixture instead of GaussianMixture when needed.
If the Application has a Custom Application object. It is needed to annotate this with #HiltAndroidApp
ex:
#HiltAndroidApp
class AppCore: Application
Appcore has some initialization logic which is needed for the app to run
Now in the Instrumentation tests We also need to Extend the custom Application object.
#CustomTestApplication(AppCore::class)
interface HiltTestApplication
This gives an error #CustomTestApplication value cannot be annotated with #HiltAndroidApp
Is there any other way of using HILT in instrumentation tests with custom Application objects
public abstract interface HiltTestApplication {
^
#CustomTestApplication value cannot be annotated with #HiltAndroidApp. Found: AppCore
As suggested in the issue tracker. Can you abstract your initialization logic into a base class, say BaseAppCore : Application then in your prod application extend it #HiltAndroidApp AppCore : BaseAppCore and then for tests make Hilt generate a test app based on your abstract one, #CustomTestApplication(BaseAppCore::class) interface AppCoreTestApplication. It might be best to file this issue in https://github.com/google/dagger/issues
You will need to create a new class with the #HiltAndroidApp annotation, which would be different from the one you will use in your tests.
open class AppCore: Application
{
// Existing code.
}
#HiltAndroidApp
class ProdAppCore : AppCore
{}
#CustomTestApplication(AppCore::class)
interface HiltTestApplication
If you are using Robolectric, you can set:
application = $packageName.HiltTestApplication_Application
And in your AndroidManifest.xml, set:
<application
android:name="$packageName.ProdAppCore"
where $packageName is the package where ProdAppCore and HiltTestApplication class have been defined.
This is also discussed here: https://github.com/google/dagger/issues/2033
Edit: So far it looks like the answer to my question is, "You can't do that in Swift." I currently have a solution whereby the subclass names are listed in an array and I loop around and instantiate them to trigger the process I'm describing below. If this is the best that can be done, I'll switch it to a plist so that least it's externally defined. Another option would be to scan a directory and load all files found, then I would just need to make sure the compiler output for certain classes is put into that directory...
I'm looking for a way to do something that I've done in C++ a few times. Essentially, I want to build a series of concrete classes that implement a particular protocol, and I want to those classes to automatically register themselves such that I can obtain a list of all such classes. It's a classic Prototype pattern (see GoF book) with a twist.
Here's my approach in C++; perhaps you can give me some ideas for how to do this in Swift 4? (This code is grossly simplified, but it should demonstrate the technique.)
class Base {
private:
static set<Base*> allClasses;
Base(Base &); // never defined
protected:
Base() {
allClasses.put(this);
}
public:
static set<Base*> getAllClasses();
virtual Base* clone() = 0;
};
As you can see, every time a subclass is instantiated, a pointer to the object will be added to the static Base::allClasses by the base class constructor.
This means every class inherited from Base can follow a simple pattern and it will be registered in Base::allClasses. My application can then retrieve the list of registered objects and manipulate them as required (clone new ones, call getter/setter methods, etc).
class Derived: public Base {
private:
static Derived global; // force default constructor call
Derived() {
// initialize the properties...
}
Derived(Derived &d) {
// whatever is needed for cloning...
}
public:
virtual Derived* clone() {
return new Derived(this);
}
};
My main application can retrieve the list of objects and use it to create new objects of classes that it knows nothing about. The base class could have a getName() method that the application uses to populate a menu; now the menu automatically updates when new subclasses are created with no code changes anywhere else in the application. This is a very powerful pattern in terms of producing extensible, loosely coupled code...
I want to do something similar in Swift. However, it looks like Swift is similar to Java, in that it has some kind of runtime loader and the subclasses in this scheme (such as Derived) are not loaded because they're never referenced. And if they're not loaded, then the global variable never triggers the constructor call and the object isn't registered with the base class. Breakpoints in the subclass constructor shows that it's not being invoked.
Is there a way to do the above? My goal is to be able to add a new subclass and have the application automatically pick up the fact that the class exists without me having to edit a plist file or doing anything other than writing the code and building the app.
Thanks for reading this far — I'm sure this is a bit of a tricky question to comprehend (I've had difficulty in the past explaining it!).
I'm answering my own question; maybe it'll help someone else.
My goal is to auto initialize subclasses such that they can register with a central authority and allow the application to retrieve a list of all such classes. As I put in my edited question, above, there doesn't appear to be a way to do this in Swift. I have confirmed this now.
I've tried a bunch of different techniques and nothing seems to work. My goal was to be able to add a .swift file with a class in it and rebuild, and have everything automagically know about the new class. I will be doing this a little differently, though.
I now plan to put all subclasses that need to be initialized this way into a particular directory in my application bundle, then my AppDelegate (or similar class) will be responsible for invoking a method that scans the directory using the filenames as the class names, and instantiating each one, thus building the list of "registered" subclasses.
When I have this working, I'll come back and post the code here (or in a GitHub project and link to it).
Same boat. So far the solution I've found is to list classes manually, but not as an array of strings (which is error-prone). An a array of classes such as this does the job:
class AClass {
class var subclasses: [AClass.Type] {
return [BClass.self, CClass.self, DClass.self]
}
}
As a bonus, this approach allows me to handle trees of classes, simply by overriding subclasses in each subclass.
I want to use BroadcastReceiver inside SystemSensorManager class (android.hardware). I managed to define an object of type BroadcastReceiver but when I tried to register this receiver using :
registerReceiver(BroadcastReceiver receiver, IntentFilter filter)
This method cannot be found and the source code doesnt compile.
I tried the to do similar thing in the Activity class and it succeeded. whats wrong with the SystemSensorManager class ?
registerReceiver is defined on Context and its descendants. SystemSensorManager receives context in constructor, but does not remember it. You should find a relevant Context for your change.
Hi I am trying to learn JAVA deeply and so I am digging into the JDK source code in the following lines:
URL url = new URL("http://www.google.com");
URLConnection tmpConn = url.openConnection();
I attached the source code and set the breakpoint at the second line and stepped into the code. I can see the code flow is: URL.openConnection() -> sun.net.www.protocol.http.Handler.openConnection()
I have two questions about this
First In URL.openConnection() the code is:
public URLConnection openConnection() throws java.io.IOException {
return handler.openConnection(this);
}
handler is an object of URLStreamHandler, define as blow
transient URLStreamHandler handler;
But URLStreamHandler is a abstract class and method openConnection() is not implement in it so when handler calls this method, it should go to find a subclass who implement this method, right? But there are a lot classes who implement this methods in sun.net.www.protocol (like http.Hanlder, ftp.Handler ) How should the code know which "openConnection" method it should call? In this example, this handler.openConnection() will go into http.Handler and it is correct. (if I set the url as ftp://www.google.com, it will go into ftp.Handler) I cannot understand the mechanism.
second. I have attached the source code so I can step into the JDK and see the variables but for many classes like sun.net.www.protocol.http.Handler, there are not source code in src.zip. I googled this class and there is source code online I can get but why they did not put it (and many other classes) in the src.zip? Where can I find a comprehensive version of source code?
Thanks!
First the easy part:
... I googled this class and there is source code online I can get but why they did not put it (and many other classes) in the src.zip?
Two reasons:
In the old days when the Java code base was proprietary, this was treated as secret-ish ... and not included in the src.zip. When they relicensed Java 6 under the GPL, they didn't bother to change this. (Don't know why. Ask Oracle.)
Because any code in the sun.* tree is officially "an implementation detail subject to change without notice". If they provided the code directly, it helps customers to ignore that advice. That could lead to more friction / bad press when customer code breaks as a result on an unannounced change to sun.* code.
Where can I find a comprehensive version of source code?
You can find it in the OpenJDK 6 / 7 / 8 repositories and associated download bundles:
http://hg.openjdk.java.net/jdk6/jdk6 - http://download.java.net/openjdk/jdk6/
http://hg.openjdk.java.net/jdk7/jdk7 - http://download.java.net/openjdk/jdk7/
http://hg.openjdk.java.net/jdk8/jdk8
Now for the part about "learning Java deeply".
First, I think you are probably going about this learning in a "suboptimal" fashion. Rather than reading the Java class library, I think you should be reading books on java and design patterns and writing code for yourself.
To the specifics:
But URLStreamHandler is a abstract class and method openConnection() is not implement in it so when handler calls this method, it should go to find a subclass who implement this method, right?
At the point that the handler calls than method, it is calling it on an instance of the subclass. So finding the right method is handled by the JVM ... just like any other polymorphic dispatch.
The tricky part is how you got the instance of the sun.net.www.protocol.* handler class. And that happens something like this:
When a URL object is created, it calls getURLStreamHandler(protocol) to obtain a handler instance.
The code for this method looks to see if the handler instance for the protocol already exists and returns that if it does.
Otherwise, it sees if a protocol handler factory exists, and if it does it uses that to create the handler instance. (The protocol handler factory object can be set by an application.)
Otherwise, searches a configurable list of Java packages to find a class whose FQN is package + "." + protocol + "." + "Handler", loads it, and uses reflection to create an instance. (Configuration is via a System property.)
The reference to handler is stored in the URL's handler field, and the URL construction continues.
So, later on, when you call openConnection() on the URL object, the method uses the Handler instance that is specific to the protocol of the URL to create the connection object.
The purpose of this complicated process is to support URL connections for an open-ended set of protocols, to allow applications to provide handlers for new protocols, and to substitute their own handlers for existing protocols, both statically and dynamically. (And the code is more complicated than I've described above because it has to cope with multiple threads.)
This is making use of a number of design patterns (Caches, Adapters, Factory Objects, and so on) together with Java specific stuff such as the system properties and reflection. But if you haven't read about and understood those design patterns, etcetera, you are unlikely to recognize them, and as a result you are likely to find the code totally bamboozling. Hence my advice above: learn the basics first!!
Take a look at URL.java. openConnection uses the URLStreamHandler that was previously set in the URL object itself.
The constructor calls getURLStreamHandler, which generates a class name dynamically and loads, and the instantiates, the appropriate class with the class loader.
But URLStreamHandler is a abstract class and method openConnection()
is not implement in it so when handler calls this method, it should go
to find a subclass who implement this method, right?
It has to be declared or abstract or implemented in URLStreamHandler. If you then give an instance of a class that extends URLStreamHandler with type URLStreamHandler and call the openConnection() method, it will call the one you have overriden in the instance of the class that extends URLStreamHandler if any, if none it will try to call the one in URLStreamHandler if implemented and else it will probably throw an exception or something.