I want to do a core api service integration in my Android project.
My core service class is as follows:
public class TestApplication extends MultiDexApplication {
private static final String LOG_TAG_NETWORK = "GNetwork";
public static JacksonConverterFactory factory;
private static TestApplication instance;
private OkHttpClient.Builder okHttpBuilder;
private TestService testtService;
private Location lastKnownLocation;
public static TestApplication getInstance() {
return instance;
}
#Override
public void onCreate() {
super.onCreate();
instance = this;
Pref.init(this);
okHttpBuilder = new OkHttpClient.Builder();
okHttpBuilder.connectTimeout(UrlConstants.CONNECT_TIMEOUT_IN_SECONDS, TimeUnit.SECONDS)
.readTimeout(UrlConstants.READ_TIMEOUT_IN_SECONDS, TimeUnit.SECONDS)
.writeTimeout(UrlConstants.WRITE_TIMEOUT_IN_SECONDS, TimeUnit.SECONDS);
if (BuildConfig.LOG_ENABLED) {
HttpLoggingInterceptor httpLoggingInterceptor =
new HttpLoggingInterceptor(message -> Log.d(LOG_TAG_NETWORK, message));
httpLoggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
okHttpBuilder.addInterceptor(httpLoggingInterceptor);
}
factory = getJacksonConverterFactory();
}
#NonNull
private JacksonConverterFactory getJacksonConverterFactory() {
ObjectMapper objectMapper = new ObjectMapper();
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
return JacksonConverterFactory.create(objectMapper);
}
public void setupRetrofit() {
String BASE_URL = "http://xxxxx";
Retrofit retrofit = new Retrofit.Builder().baseUrl(BASE_URL).client(okHttpBuilder.build())
.addConverterFactory(factory).build();
testService = retrofit.create(TestService.class);
}
public TestService getTestService() {
return testService;
}
}
Then I create an instance from this core class. But here my constant getIntance value returns null.
TestApplication.getInstance().setupRetrofit();
I can't understand that. GetInstance method always return null;
In my app build.gradle file is multiDexEnabled true.
How to solve this situation?
never use instance of application like this. for get application instance you need activity and in your activity you can use
static TestApplication getInstance(Activity activity) {
if (instance == null)
instance = ((TestApplication) activity.getApplication());
return instance;
}
this will solve your issues but the way you implement retrofit and using it is not best practices. You can find better way that doesn't need activity.
change getInstance()
from this
public static TestApplication getInstance() {
return instance;
}
to this
public static TestApplication getInstance() {
instance=new TestApplication();
return instance;
}
and also remove this line from oncreate
instance = this;
After Enabling Multidex
Replace With:-
public class Application extends MultiDexApplication {
public static final String TAG = Application.class.getSimpleName();
#Override
public void onCreate() {
super.onCreate();
ApplicationHelper.initDatabaseHelper(this);
PostInteractor.getInstance(this).subscribeToNewPosts();
}
}
Related
I am implementing a command pattern in android.
This is what I have right now. For some reason this does not run. It is like the AddUserRequest is getting garbage collected for some reason.
RequestManager.java:
public class RequestManager extends BroadcastReceiver {
private static final RequestManager instance = new RequestManager();
private boolean isConnected = false;
private static ArrayList<Request> requestQueue = new ArrayList<Request>();
private RequestManager() {
}
/* singleton class */
public static RequestManager getInstance() {
return instance;
}
public void invokeRequest(Request request) {
request.execute(); // only to test this, this will change
return;
}
}
AddUserRequest.java
public class AddUserRequest extends InsertionRequest {
User user;
public AddUserRequest(User user) {
this.user = user;
}
public void execute() {
System.out.println("TEST!!!");
}
}
Request.java:
public abstract class Request {
public abstract void execute();
}
}
InsertionRequest.java
public abstract class InsertionRequest extends Request {
}
RequestManagerTest.java
public class RequestManagerTest extends ActivityInstrumentationTestCase2 {
public RequestManagerTest(){
super(MainActivity.class);
}
public void testAddUserRequest() {
User user = new User();
user.setName("Tester12345");
AddUserRequest request = new AddUserRequest(user);
RequestManager.getInstance().invokeRequest(request);
}
}
For some reason this does not print "TEST!!!" and for the life of me I cannot figure out why. I looked in the debug log and everytime request.execute() in RequestManager.java gets called there is a "GC Explicit..." which I suspect has to do with garbage collection. What is the proper way to do what I am trying to do?
For instance I want to take this
public class SomeClass {
public static final String GREET_STRING = "Hello!";
//...
and change it to something like:
public class SomeClass {
public static final String GREET_STRING = getString(R.string.greet_string);
//...
Can this be done or do I need some kind of Context instantiation to get the resources for the string loading?
To use getString() you will need a context. A Resource string cannot be static final because it is possible for String resources to change as you change Locales (if you have multiple String files such as strings.xml (us) and strings.xml (uk))
Try this:
public abstract class SomeClass extends AppCompatActivity {
public static String GREET_STRING(Context context) {
if (context == null) {
return null;
}
return context.getResources().getString(R.string.greet_string);
}
}
Res/Value/String:
<resources>
<string name="greet_string">Hello!</string>
</resources>
Call SomeClass from MainClass
public class MainClass extends SomeClass {
private final static String TAG = MainClass.class.getName();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// call SomeClass from MainClass
Log.i(TAG, SomeClass.GREET_STRING(this));
}
}
There are two ways access the string inside the class which is not extending Activity or Fragment.
Pass Context or Activity to class constructor
public class SomeClass {
private Context context;
public SomeClass(Context context) {
this.context = context;
}
public static final String GREET_STRING = context.getString(R.string.greet_string);
}
The second way is if you don`t want to pass context to class. You need to create an instance of the Application and static function get instance.
public class App extends Application {
private static App instance = null;
#Override
public void onCreate() {
super.onCreate();
instance = this;
}
public static App getInstance() {
// Return the instance
return instance;
}
}
public class SomeClass {
public static final String GREET_STRING = App.getInstance().getString(R.string.greet_string);
}
if i need use a global class what is the best option and why?
public class Global {
public static JSONObject GetJsonResquest(String url){
....
};
}
and then call Global.GetJsonResquest(url) in my activity
OR
public class Singleton {
private static Singleton ourInstance = new Singleton();
public static Singleton getInstance() {
return ourInstance;
}
private Singleton() {
}
public JSONObject GetJsonResquest(String url){
.....
}
}
and then use via Singleton.getInstance().GetJsonResquest("Asd");
When I need a global static variable, I like to group them into a class like
public class MyConstants {
public static final int TIMEOUT = 10000;
}
To use it, i can call it like
long tick = System.currentThreadMillis();
while((System.currentThreadMillis() - tick) < MyConstants.TIMEOUT){
Thread.sleep(1000);
}
So that when I change the TIMEOUT value, I don't have to change other classes that calls it
For global static method, I use them like
public class Utility{
public static boolean isStringValidJson(String jsonString){
return false;
}
}
Same reason as above. When I change isStringValidJson, other classes that calls it don't change
I do use the singleton pattern but only when I override the Application class. However, I set the instance value in OnCreate instead. This means that if OnCreate was not called, getInstance will return null
public class MyApplication extends Application {
private static MyApplication instance;
#Override
public void onCreate() {
super.onCreate();
instance = this;
}
public static synchronized MyApplication getInstance(){
return instance;
}
}
How can I have access to a file in my res/raw folder from a Singleton (not an activity) on Android?
I've tried:
InputStream is = MainActivity.getResources().openRawResource("data.json");
which doesn't work since "non-static method getResouces() cannot be referenced from static content".
I've also tried:
URL fileURL = getClass().getClassLoader().getResource(R.raw.data);
String filePath = fileURL.getPath();
which throws a Null-pointer exception.
My Singleton:
public class CoursesDataManager {
private static CoursesDataManager instance;
private final List<Course> courses;
public static CoursesDataManager getInstance() {
if (instance == null)
instance = new CoursesDataManager();
return instance;
}
private CoursesDataManager() {
courses = parseCourses(**filePath/inputStream**);
}
The reason I want to get the file is that I want my Singleton to parse the data in that file once, store this data, and have this data never change and be accessible throughout the lifetime of my application.
Thanks a lot.
public class CoursesDataManager {
private static CoursesDataManager instance;
private final List<String> courses;
public static CoursesDataManager getInstance(Context context) {
if (instance == null)
instance = new CoursesDataManager(context);
return instance;
}
private CoursesDataManager(Context context) {
courses =context.getResources().openRawResource(R.raw.filename);
}
}
call it from Activity
CoursesDataManager.getInstance(getApplicationContext());
You need context to access resources. You could use Application context for this purpose. Subclass your Application, save the context in a static variable. Use the context inside singleton.
Create a Application class:
public class MyApplication extends Application {
public static MyApplication context = null;
public void onCreate() {
super.onCreate();
context = this;
}
}
In your manifest, specify the name of the Application class:
<application
android:name=".MyApplication"
...
>
</application>
Now, use this context in singleton:
InputStream is = MyApplication.context.getResources().openRawResource("data.json");
Note: You can use this method, even when you are creating the singleton instance from outside the Activity, where you dont have Activity context.
Add the context to your class and change it to something like that:
public class CoursesDataManager {
private static CoursesDataManager instance;
private Context context;
private final List<Course> courses;
public static CoursesDataManager getInstance(Context context) {
if (instance == null)
instance = new CoursesDataManager(context.getApplicationContext());
return instance;
}
private CoursesDataManager(Context context) {
this.context = context;
courses = parseCourses(**filePath/inputStream**);
}
public class CoursesDataManager {
private static CoursesDataManager instance;
private static Context mContext;
private final List<Course> courses;
public static CoursesDataManager getInstance(Context context) {
if (instance == null)
{
instance = new CoursesDataManager();
}
mContext = context;
return instance;
}
private CoursesDataManager() {
courses = parseCourses(**filePath/inputStream**);
}
You can use resource from here like
mContext.getResources().openRawResource(resourceId);
I've write a Singleton, but this singleton need a Context as a param to initialize itself. As the Context is used only once in its constructor, I would not like to add it in getInstance(Context). After thinking more, I came out the following answer:
public class Singleton {
private static Context sContext;
public static void init(Context context) {
sContext = context;
}
public static Singleton getInstance() {
return SingletonHolder.INSTANCE;
}
private static class SingletonHolder {
private static Singleton INSTANCE = new Singleton();
}
private Singleton() {
if (sContext == null) {
throw new IllegalArgumentException("#init should be called in Application#onCreate");
}
// Initialize the Singleton.
// .....
// After the constructed, remove the sContext.
sContext = null;
}
}
It's well, with a class method init called in Android/Applicaiton#onCreate method.
It's not instance the SingletonHolder.INSTANCE, as it's not loaded.
Could some give someone advice on my solution。Thanks！
With the help of # WarrenFaith I changed my code.
public class Singleton {
public static Singleton getInstance() {
return SingletonHolder.INSTANCE;
}
private static class SingletonHolder {
private static Singleton INSTANCE = new Singleton();
}
private Singleton() {
final Context context = BaseApplication.getApplication();
// Initialize the Singleton.
// .....
}
}
public class BaseApplication extends Application {
private static Application sApplication;
public static Application getApplication() {
return sApplication;
}
#Override
public void onCreate() {
super.onCreate();
sApplication = this;
}
}
Why not using a way easier solution:
public class Singleton {
private final static Singleton mInstance = new Singleton();
private final static Context sContext;
private Singleton() {
sContext = MyApplication.getInstance();
// do more
}
public static Singleton getInstance() {
return mInstance;
}
}
That is a pretty bullet proof singleton pattern.
Of course you need to implement your application class to be a singleton but by definition it already is.
public class MyApplication extends Application {
private static MyApplication mInstance;
#Override
protected void onCreate() {
super.onCreate();
mInstance = this;
// create your Singleton!
Singleton.getInstance();
}
public static MyApplication getInstance() {
return mInstance;
}
}