I am new into Kotlin and trying to learn, how to fetch Data with retrofit and store this data into a Room DB. But as soon as i start the Activity where this process takes place i get a NullPointerException.
EDIT: As far as i could find out now, my "database" in the RoomViewmodel class is still NULL when i want to access it, even though i have an override oncreate function, where it is created
Here is also a link to the GitHub repository from the mini-project I'm working on: https://github.com/Engin92/Dog_Breeds/tree/RoomDatabase
here is my complete errorlist:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.dogbreeds, PID: 14803
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.dogbreeds/com.example.Breedlist.activity.DetailedViewActivity}: kotlin.KotlinNullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3782)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3961)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2386)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:213)
at android.app.ActivityThread.main(ActivityThread.java:8178)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101)
Caused by: kotlin.KotlinNullPointerException
at com.example.Breedlist.activity.DetailedViewActivityRepository.getBreeds(DetailedViewActivityRepository.kt:23)
at com.example.Breedlist.activity.DetailedViewActivityViewModel.getAllBreedList(DetailedViewActivityViewModel.kt:23)
at com.example.Breedlist.activity.DetailedViewActivity.onCreate(DetailedViewActivity.kt:42)
at android.app.Activity.performCreate(Activity.java:8086)
at android.app.Activity.performCreate(Activity.java:8074)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1313)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3755)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3961)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:91)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:149)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:103)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2386)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:213)
at android.app.ActivityThread.main(ActivityThread.java:8178)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:513)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1101)
The important part of DetailedViewActivity
class DetailedViewActivity : AppCompatActivity() {
lateinit var breedRecyclerView: RecyclerView
lateinit var detailedViewActivityViewModel: DetailedViewActivityViewModel
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_detailed_view)
breedRecyclerView = findViewById(R.id.breedRecyclerView)
detailedViewActivityViewModel = ViewModelProviders.of(this).get(
DetailedViewActivityViewModel::class.java)
if(isOnline(this))
{
detailedViewActivityViewModel.getBreedsFromAPIAndStore()
}
else
{
Toast.makeText(this,"No internet connection. Showing cached list!",Toast.LENGTH_LONG).show()
}
detailedViewActivityViewModel.getAllBreedList().observe(this, Observer<List<CurrentBreedResponseItem>> { breedList ->
Log.e(MainActivity::class.java.simpleName,breedList.toString())
setUpBreedRecyclerView(breedList!!)
})
} ....
the class RoomViewModel, where i build the DB (where i Think the error is, the var database is still NULL, after trying to access (write/read) it)
class RoomViewModel : Application() {
companion object {
var database: BreedDatabase? = null
}
override fun onCreate() {
super.onCreate()
database = Room.databaseBuilder(applicationContext, BreedDatabase::class.java, "breed_db").fallbackToDestructiveMigration().build()
}
}
getBreeds function in DetailedViewActivityRepository:
fun getBreeds() : LiveData<List<CurrentBreedResponseItem>>
{
return RoomViewModel.database!!.currentBreedDao().getAllBreeds()
}
getAllBreedList function in DetailedViewActivityViewModel
fun getAllBreedList(): LiveData<List<CurrentBreedResponseItem>>
{
return detailedViewActivityRepository.getBreeds()
}
There are two problem in your code. The first one is very clear you are trying to access a null object and you are getting NullPointerException. So be careful when you use !! operator.
The reason you are getting it is, inside your RoomViewModel your database instance is null.
class RoomViewModel : Application() {
companion object {
var database: BreedDatabase? = null
}
override fun onCreate() {
super.onCreate()
database = Room.databaseBuilder(applicationContext, BreedDatabase::class.java, "breed_db")
.fallbackToDestructiveMigration().build()
}
}
You may think you are initializing the database instance in onCreate() but the onCreate() is not getting called. The reason is to make the application class work you need to add it to your AndroidManifest.xml file.
Solution:
Add this RoomViewModel class to your AndroidManifest.xml file like this.
<application
android:name=".view.RoomViewModel"
android:allowBackup="true"
We do it as application tag's name attribute as you can see above.
This will fix your null pointer exception. But your program will again crash, because you are using Kotlin and do make room work with kotlin this thing needs to be added in your app level build.gradle file.
kapt "android.arch.persistence.room:compiler:1.1.1"
After adding it to your app level build.gradle inside dependencies block. Sync your project and run it should work.
If you want to learn more about Room Database in Android, you can check this Room Database Tutorial.
Hope this will help you.
Related
I am trying to integrate Hystrix javanica into my existing java EJB web application and facing 2 issues with running it.
When I try to invoke following service it always returns response from fallback method and I see that the Throwable object in fallback method has "com.netflix.hystrix.exception.HystrixTimeoutException" exception.
Each time this service is triggered, HystrixCommad and fallback methods are called multiple times around 50 times.
Can anyone suggest me with any inputs? Am I missing any configuration?
I am including following libraries in my project.
project libraries
I have setup my aspect file as follows:
<aspectj>
<weaver options="-verbose -showWeaveInfo"></weaver>
<aspects>
<aspect name="com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect"/>
</aspects>
</aspectj>
Here is my config.properties file in META-INF/config.properties
hystrix.command.default.execution.timeout.enabled=false
Here is my rest service file
#Path("/hystrix")
public class HystrixService {
#GET
#Path("clusterName")
#Produces({ MediaType.APPLICATION_JSON })
public Response getClusterName(#QueryParam("id") int id) {
ClusterCmdBean clusterCmdBean = new ClusterCmdBean();
String result = clusterCmdBean.getClusterNameForId(id);
return Response.ok(result).build();
}
}
Here is my bean class
public class ClusterCmdBean {
#HystrixCommand(groupKey = "ClusterCmdBeanGroup", commandKey = "getClusterNameForId", fallbackMethod = "defaultClusterName")
public String getClusterNameForId(int id) {
if (id > 0) {
return "cluster"+id;
} else {
throw new RuntimeException("command failed");
}
}
public String defaultClusterName(int id, Throwable e) {
return "No cluster - returned from fallback:" + e.getMessage();
}
}
Thanks for the help.
If you want to ensure you are setting the property, you can do that explicitly in the circuit annotation itself:
#HystrixCommand(commandProperties = {
#HystrixProperty(name = "execution.timeout.enabled", value = "false")
})
I would only recommend this for debugging purposes though.
Something that jumps out to me is that Javanica uses AspectJ AOP, which I have never seen work with new MyBean() before. I've always have to use #Autowired with Spring or similar to allow proxying. This could well just be something that is new to me though.
If you set a breakpoint inside the getClusterNameForId can you see in the stack trace that its being called via reflection (which it should be AFAIK)?
Note you can remove commandKey as this will default to the method name. Personally I would also remove groupKey and let it default to the class name.
I am using Enterprise Library 5.0 in my win-form Application.
1. Regarding creating instances of Enterprise Library objects
What is the best way to Resolve the reference for Logging / exception objects? In our application, we have different applications in solution. So Solutions have below project:
CommonLib (Class Lib)
CustomerApp (winform app)
CustWinService (win service proj)
ClassLib2 (class Lib)
I have implemented logging / exceptions as below in CommonLib project. Created a class AppLog as below:
public class AppLog
{
public static LogWriter defaultWriter = EnterpriseLibraryContainer.Current.GetInstance<LogWriter>();
public static ExceptionManager exManager = EnterpriseLibraryContainer.Current.GetInstance<ExceptionManager>();
public AppLog()
{
}
public static void WriteLog(string LogMessage, string LogCategories)
{
// Create a LogEntry and populate the individual properties.
if (defaultWriter.IsLoggingEnabled())
{
string[] Logcat = LogCategories.Split(",".ToCharArray());
LogEntry entry2 = new LogEntry();
entry2.Categories = Logcat;
entry2.EventId = 9007;
entry2.Message = LogMessage;
entry2.Priority = 9;
entry2.Title = "Logging Block Examples";
defaultWriter.Write(entry2);
}
}
}
And then I used Applog class as below for logging and exception in different projects:
try
{
AppLog.WriteLog("This is Production Log Entry.", "ExceCategory");
string strtest = string.Empty;
strtest = strtest.Substring(1);
}
catch (Exception ex)
{
bool rethrow = AppLog.exManager.HandleException(ex, "ExcePolicy");
}
So its the correct way to use Logging and Exception? or any other way i can improve it?
2. Logging File Name dynamic
In logging block, we have fileName which need to be set in app.config file. Is there a way I can assign fileName value dynamically through coding? Since I don't want to hard code it in config file and paths are different for production and development environment.
Thanks
TShah
To keep your application loosely coupled and easier to test, I would recommend defining separate logging and exception handling interfaces, then having your AppLog class implement both. Your application can then perform logging and exception handling via those interfaces, with AppLog providing the implementation.
You can have a different file name set per environment using config transforms, which I believe you can use in a winforms application by using Slow Cheetah.
I found that I was unable to return collections from my JAX-WS Web Service.
I appreciate that the Java Collections API may not be supported by all clients, so I switched to return an array, but I can't seem to do this either.
I've set up my web service as follows:
#WebService
public class MyClass {
public ReturnClass[] getArrayOfStuff() {
// extremely complex business logic... or not
return new ReturnClass[] {new ReturnClass(), new ReturnClass()};
}
}
And the ReturnClass is just a POJO. I created another method that returns a single instance, and that works. It just seems to be a problem when I use collections/arrays.
When I deploy the service, I get the following exception when I use it:
javax.xml.bind.MarshalException - with linked exception:
[javax.xml.bind.JAXBException: [LReturnClass; is not known to this context]
Do I need to annotate the ReturnClass class somehow to make JAX-WS aware of it?
Or have I done something else wrong?
I am unsure of wheter this is the correct way to do it, but in one case where I wanted to return a collection I wrapped the collection inside another class:
#WebService
public class MyClass {
public CollectionOfStuff getArrayOfStuff() {
return new CollectionOfStuff(new ReturnClass(), new ReturnClass());
}
}
And then:
public class CollectionOfStuff {
// Stuff here
private List<ReturnClass> = new ArrayList<ReturnClass>();
public CollectionOfStuff(ReturnClass... args) {
// ...
}
}
Disclaimer: I don't have the actual code in front of me, so I guess my example lacks some annotations or the like, but that's the gist of it.
I am getting started with Logging in a WPF desktop app, using Log4Net as the logging component. Here is my question: In a simple desktop app, is there any reason not to instantiate my logger as a property ov the App class (App.xaml.cs), like this?
public partial class App : Application
{
private static readonly ILog p_Logger = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
public ILog Logger
{
get { return p_Logger; }
}
#endregion
}
}
That would allow me to invoke the logger
One reason springs to mind: since the App class's static constructor is the first bit of your code that will run, you will be instantiating the ILog instance before you've configured log4net. Therefore, you ILog instance won't be usable. Generally, you would instead do something like this:
public partial class App : Application
{
private static ILog log;
static App()
{
XmlConfigurator.Configure();
log = LogManager.GetLogger(typeof(App));
}
}
BTW, that MethodBase business really makes me cringe. Why not just use typeof(App)? You shouldn't be copy/pasting code without verifying it, anyway...and typeof(App) will work just fine with refactoring tools...
A couple of cases against using one global instance. By using one logger per class you get:
the benefit of logger hierarchies automatically following your class structure.
lesser coupling (your classes no longer have a dependency on the App class).
I did find a reason not to use a global logger in the App object. It works fine, but there is an advantage to getting a logger from within each class that will use it--It makes my log messages shorter and easier to write.
So I call GetLogger() in each class that will log, and I specify the name to be used for the logger. For example, in my OpenFile method, I can get a logger like this:
// Get logger
var logger = LogManager.GetLogger("OpenFile");
That relieves me of entering the class name in every error message I write. I still configure log4net in the App() constructor, since that only needs to be done once. That gives me a log message that looks like this:
2010-03-29 15:51:41,951 OpenFile [DEBUG]- Data file opened.
Kent's answer is still the accepted answer, but I figured I'd pass along what I had learned.
I am writing my first Android database backend and I'm struggling to unit test the creation of my database.
Currently the problem I am encountering is obtaining a valid Context object to pass to my implementation of SQLiteOpenHelper. Is there a way to get a Context object in a class extending TestCase? The solution I have thought of is to instantiate an Activity in the setup method of my TestCase and then assigning the Context of that Activity to a field variable which my test methods can access...but it seems like there should be an easier way.
You can use InstrumentationRegistry methods to get a Context:
InstrumentationRegistry.getTargetContext() - provides the application Context of the target application.
InstrumentationRegistry.getContext() - provides the Context of this Instrumentation’s package.
For AndroidX use InstrumentationRegistry.getInstrumentation().getTargetContext() or InstrumentationRegistry.getInstrumentation().getContext().
New API for AndroidX:
ApplicationProvider.getApplicationContext()
You might try switching to AndroidTestCase. From looking at the docs, it seems like it should be able to provide you with a valid Context to pass to SQLiteOpenHelper.
Edit:
Keep in mind that you probably have to have your tests setup in an "Android Test Project" in Eclipse, since the tests will try to execute on the emulator (or real device).
Your test is not a Unit test!!!
When you need
Context
Read or Write on storage
Access Network
Or change any config to test your function
You are not writing a unit test.
You need to write your test in androidTest package
Using the AndroidTestCase:getContext() method only gives a stub Context in my experience. For my tests, I'm using an empty activity in my main app and getting the Context via that. Am also extending the test suite class with the ActivityInstrumentationTestCase2 class. Seems to work for me.
public class DatabaseTest extends ActivityInstrumentationTestCase2<EmptyActivity>
EmptyActivity activity;
Context mContext = null;
...
#Before
public void setUp() {
activity = getActivity();
mContext = activity;
}
... //tests to follow
}
What does everyone else do?
You can derive from MockContext and return for example a MockResources on getResources(), a valid ContentResolver on getContentResolver(), etc. That allows, with some pain, some unit tests.
The alternative is to run for example Robolectric which simulates a whole Android OS. Those would be for system tests: It's a lot slower to run.
You should use ApplicationTestCase or ServiceTestCase.
Extending AndroidTestCase and calling AndroidTestCase:getContext() has worked fine for me to get Context for and use it with an SQLiteDatabase.
The only niggle is that the database it creates and/or uses will be the same as the one used by the production application so you will probably want to use a different filename for both
eg.
public static final String NOTES_DB = "notestore.db";
public static final String DEBUG_NOTES_DB = "DEBUG_notestore.db";
First Create Test Class under (androidTest).
Now use following code:
public class YourDBTest extends InstrumentationTestCase {
private DBContracts.DatabaseHelper db;
private RenamingDelegatingContext context;
#Override
public void setUp() throws Exception {
super.setUp();
context = new RenamingDelegatingContext(getInstrumentation().getTargetContext(), "test_");
db = new DBContracts.DatabaseHelper(context);
}
#Override
public void tearDown() throws Exception {
db.close();
super.tearDown();
}
#Test
public void test1() throws Exception {
// here is your context
context = context;
}}
Initialize context like this in your Test File
private val context = mock(Context::class.java)