I am trying to create an internal file in an android application. I have generated the code that works fine with java, but in order to create the internal file I believe I must have the context to do so.
Example: File file = new File(Context.getFilesDir(), "somefile.txt");
The problem I am running into is that the file creation and checks if it is made are maintained in a singleton class that I have created. When using the following
Example: File file = new File("somefile.txt");
everything seems to compile and work, but after closing the application it seems the file wasn't created. This leads me to believe that I need the application directory using the 1st example given. The problem is how do I get the applications context within a single class?
The problem is how do I get the applications context within a single class?
From Android Docs:
There is normally no need to subclass Application. In most situation, static singletons can provide the same functionality in a more modular way. If your singleton needs a global context (for example to register broadcast receivers), the function to retrieve it can be given a Context which internally uses Context.getApplicationContext() when first constructing the singleton.
Create your singleton like this:
// ...
private Context mAppContext = null;
private static MySingleton mSingleton = null;
// ...
private MySingleton(Context context) {
mAppContext = context;
// ... other initialization
}
public static MySingleton get(Context context) {
if (mSingleton == null) {
/*
* Get the global application context since this is an
* application-wide singleton
*/
mSingleton = new MySingleton(
context.getApplicationContext());
}
return mSingleton;
}
The each time you obtain your singleton from any activity, you have access to the global application context.
You can use it for your creation of files within your singleton like:
public void createFile(String filename) {
File file = new File(mAppContext.getFilesDir(), filename);
}
Or you can use the other ways mentioned here
Or you could extend Application class thats already a Singleton. It can be rather usefull :)
package com.example.myapp;
import android.app.Application;
import android.content.Context;
public class MyApp extends Application {
private static Context context;
private static MyApp my_instance;
#Override
public void onCreate() {
// TODO Auto-generated method stub
super.onCreate();
my_instance = this;
context = this;
}
public static synchronized MyApp getInstance() {
return my_instance;
}
public static synchronized Context getContext() {
return context;
}
}
The mehod:
new File("filename")
does not create a file on disk.
You need to open the file and write to it for the file to be created, or use
File.createNewFile
Related
I guess this question is more about understanding context and how to use it properly.
After having googled and "stackoverflowed" a lot I could not find the answer.
Problem:
when using DateUtils.formatDateTime I cannot use "this" as a context. The error message is as described in the title.
Application Info:
This is a simple weather app retrieving weather information via JSON and displaying it on the screen.
Activities:
- MainActivity.java
- FetchData.java
MainActivity: displaying the info
FetchData: getting JSON info from the API, formatting it and sending it back to MainActivity
I am using DateUtils.formatDateTime in the FetchData.java activity and using "this" as a context does not work.
As from my understanding Context provided the "environment" (?) of where the method is being called.
Why is the "environment" of FetchData not valid?
What content should be provided instead?
Help is much appreciated.
Thank you :)
Code:
private ArrayList<String> getWeatherDataFromJson(String forecastJsontStr) throws JSONException {
ArrayList<String> dailyWeatherInfo = new ArrayList<>();
int dataCount;
DateUtils tempDate = new DateUtils();
JSONObject weatherData = new JSONObject(forecastJsontStr);
JSONArray threeHourWeatherData = weatherData.getJSONArray(JSON_LIST);
dataCount = weatherData.getInt("cnt");
JSONObject tempJSONWeatherData;
for (int i = 0; i < dataCount; i++) {
tempJSONWeatherData = threeHourWeatherData.getJSONObject(i);
tempDate.formatDateTime(this,tempJSONWeatherData.getLong("dt"),
DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_SHOW_WEEKDAY |
DateUtils.FORMAT_ABBREV_ALL);
[more code here]
return dailyWeatherInfo;
}
Edit: I just realized I left out an important detail, namely this activity extends AsyncTask. After some further research apparently you provide the context bei adding WeakReference and then adding context in the constructor.
I added the following code:
private WeakReference<Context> contextWeakReference;
public FetchData (Content context) {
contextWeakReference = new WeakReference<>();
}
tempDate.formatDateTime(contextWeakReference.get(),tempJSONWeatherData.getLong("dt"),
DateUtils.FORMAT_SHOW_DATE | DateUtils.FORMAT_SHOW_WEEKDAY |
DateUtils.FORMAT_ABBREV_ALL);
This made the error disappear but I still don't understand why "this" doesn't work.
I am using DateUtils.formatDateTime in the FetchData.java activity and
using "this" as a context does not work. As from my understanding
Context provided the "environment" (?) of where the method is being
called.
You're incorrect, Context is Android context which is (from documentation):
Interface to global information about an application environment. This
is an abstract class whose implementation is provided by the Android
system. It allows access to application-specific resources and
classes, as well as up-calls for application-level operations such as
launching activities, broadcasting and receiving intents, etc.
DateUtils.formatDateTime() needs Context as one of its parameter. So, you need to pass a context.
Android Activity is sub class of Context, so you can use this (which refer to itself) as the context like the following:
public class MyActivity extends Activity {
...
protected void doSomething() {
// this refer to the MyActivity instance which is a Context.
DateUtils.formatDateTime(this, ...);
}
...
}
You need to pass the Context for every class that is not a Context subclass.
You can't use this in AsyncTask because it's not a Context subclass. So, you need to pass the Context using WeakReference to avoid Context leaking, like the following:
private class AsyncTaskRunner extends AsyncTask<String, String, String> {
private WeakReference<Context> contextWeakReference;
public FetchData (Content context) {
contextWeakReference = new WeakReference<>();
}
private void doSomething() {
// We have the context from the WeakReference
Context context = contextWeakReference.get();
DateUtils.formatDateTime(context, ...);
}
}
Last, you don't need to create a DateUtils object when calling DateUtils.formatDateTime(), so this isn't necessary:
DateUtils tempDate = new DateUtils();
tempDate.formatDateTime(...);
You can directly call it because it's a static method:
DateUtils.formatDateTime(...);
tempDate.formatDateTime(this,tempJSONWeatherData.getLong("dt"), instead of this you can pass context of application, this refers on class FetchData
My installer is storing some information in a singleton class during the installation process. Now, I have noticed that in elevated action, the singleton class does not have the same instance. So far, I have not found any workaround/solution so that they share the same instance. So, I have decided to make sure that if anyone wants to get an instance of the singleton, they must call from an unelevated environment. Let's say the singleton looks like the following:
public class InvestigatorReport {
private final List<Report> reports = new ArrayList<>();
private final static InvestigatorReport INSTANCE = new InvestigatorReport();
private InvestigatorReport() {
MyLogger.logInfo(getClass(), "initiating...");
}
public static InvestigatorReport getInstance(Context context) {
if (context.hasBeenElevated()) {
throw new IllegalAccessError(
"this method must be called unelevated!");
}
return INSTANCE;
}
private boolean addReport(Report report) {
return reports.add(report);
}
}
But the problem is, There are some cases when I have to call this add report from an action class that is elevated. So I have tried the following in my elevated action class:
if (context.hasBeenElevated()) {
return (Boolean) context.runUnelevated(new RemoteCallable() {
#Override
public Serializable execute() {
return getInstance(context).addReport(report);
}
});
}
But, as you can see if I am passing the same context object from the elevated action class to the RemoteCallable class so, even though I am running the class unelevated, the context.hasBeenElevated() still returns true.
Is there any other way that I can check the elevation level other than the context? If you have any other better idea on preventing anyone from calling the singleton getInstance() method, I am all ears.
I would use a different pattern. Make all methods of your singleton static and wrap the data access with runUnelevated calls:
public static boolean addReport(Report report, Context context) {
context.runUnelevated(new RemoteCallable() {
#Override
public Serializable execute() {
InvestigatorReport.reports.add(report);
return null;
}
});
}
In that way, you can call the methods from both elevated and unelevated code without having to check anything at the call site.
I found in one of github project class:
public class AppContext {
private static Context sContext;
private static Application sApplication;
public static Application getApplication() {
if (sApplication == null) {
throw new IllegalStateException("AppContext.setApplication was not called in Application.onCreate() method. " +
"Please inherit your application from the com.blandware.android.atleap.BaseApplication class.");
}
return sApplication;
}
public static void setApplication(Application application) {
sApplication = application;
}
public static Context getContext() {
if (sContext == null) {
throw new IllegalStateException("AppContext.setContext was not called in Application.onCreate() method. " +
"Please inherit your application from the com.blandware.android.atleap.BaseApplication class.");
}
return sContext;
}
public static void setContext(Context context) {
sContext = context;
}
}
It seams create, don't need more pass context to static function etc. But I'm worried about memory leaks. Can AppContext make it? When i shoud use Aplication context when activity context or view?
The Application object can not leak. There is always exactly one Application object for every app. It looks like the author is just using this class to make it easy to access in places where another Context is not available to be used to call getApplicationContext() to get the Application object.
Context, on the other hand, could be an Activity or a Service, and those really should not be stored beyond their lifetime. You will have to look at exactly which Context objects are being stored here to find out if there is a leak.
I am trying to initialize a class that calls another class that uses AsyncTask. I am using GetDataFromDB gDataFromDB = new GetDataFromDB() but that does not initialize the class, it just gives me access to any static methods in the class. So what do I do to get the onCreate method to run? I have tried using intent but keep getting an error because this is a static class
public class FacadeDataFromDB extends Activity {
static ArrayList<HashMap<String, String>> visitorsList;
private static FacadeDataFromDB dataFromDB;
static boolean accessDB = false;
private FacadeDataFromDB() {
}
public static void initInstance() {
}
public static FacadeDataFromDB getInstance() {
if (dataFromDB == null) {
// Create the instance
dataFromDB = new FacadeDataFromDB();
}
return dataFromDB;
}
public static void setData() {
if (!accessDB) {
GetDataFromDB gDataFromDB = new GetDataFromDB();
accessDB = true;
}
// visitorsList = gDataFromDB.returnInfoFromDB();
}
public static ArrayList<HashMap<String, String>> getVisitorForDay() {
// TODO Auto-generated method stub
setData();
return visitorsList;
}
}
GetDataFromDB is the other class that I am calling. The current class is a static class and uses a singleton because I only want one initialization of the class the gets data from the db. If you have more questions or want me to post code let me know. Thanks
It seems to me that your two classes FacadeDataFromDB GetDataFromDB should not inherit Activity
Activities are made for GUI and user-interaction (I don't see any in your example) and their life-cycle is managed by the framework : you never create them manually with new.
See the android tutorial : https://developer.android.com/guide/components/activities.html and Activity javadoc : https://developer.android.com/reference/android/app/Activity.html.
I'm not sure that you completely understand the Android runtime. You should start Activities using Intent objects, not by creating them with the new keyword as you are. To ensure that your onCreate() method is called within your Activity, you could launch an explicit Intent from some other Activity/Context: Intent intent = new Intent(currentContext, FacadeDataFromDB.class);.
Also, when it comes to Activities, you shouldn't use private constructors. See this post for reasons why.
I am trying to test using AndroidTestCase. I am trying to test only one particular class in my application, however this class does not extend Activity, Service or anything else. It is basically a plain Java class apart from the fact that it requires a Context. It is a pojo and some of its variables are objects that require android api calls in their creation, e.g. a call to the SensorManager.
I tried to use:
Context context = getContext();
When running my tests this gives me the exception "System services not available to activites before onCreate()". Does that method have to be overridden?
final Context context = new IsolatedContext(null, getContext()) gives the same thing.
The reason I am using the Android testing framework and not something like Robolectric is because the class I'm testing gathers hardware information about a device and so I want to run the tests on an actual device. I have looked at the developer docs for AndroidTestCase but can't see what I'm looking for in the examples. I'm not sure the other test case classes will achieve what I want. Any ideas?
My test class:
public class DeviceTest extends AndroidTestCase {
ClassToTest mClassToTest;
#Override
protected void setUp() throws Exception {
final Context context = new IsolatedContext(null, getContext()) {
#Override
public Object getSystemService(final String pName) {
return getContext().getSystemService(pName);
}
};
mClassToTest = new ClassToTest(context);
super.setUp();
}
public void testClassMethod() {
Object mObject;
mObject = mClassToTest.getObject();
assertNotNull(mObject);
}
#Override
protected void tearDown() throws Exception {
mClassToTest = null;
super.tearDown();
}
}
Thanks in advance.
UPDATE: After changing my setup to the following:
#Override
protected void setUp() throws Exception {
super.setUp();
context = this.getContext();
mClassToTest = new ClassToTest(context);
}
I am getting an error that context is null. In what scenarios would AndroidTestCase.getContext() return null? My setup seems to be ok....
From AndroidTestCase you can access directly mContext, or call getContext().
From the context returned by those, you could also call Context.getApplicationContext() if you wanted that one.
You can use mContext from super class (AndroidTestCase). I used it for the testing of the database where context is required.
AndroidTestCase.class
public class AndroidTestCase extends TestCase {
protected Context mContext;
...
}
You would be able to use Context in the inherited class of AndroidTestCase.
TestDb.java
public class TestDb extends AndroidTestCase {
void deleteTheDatabase() {mContext.deleteDatabase(DB_NAME)};
}
There are a few ways around this, you could use a mockcontext as one solution or if you really do not care what the context is just that is valid you can use an InstrumentationTestCase and get the context of the test apk via getInstrumentation().getContext().
I think the reason your context is null is that actually no android context exists at this point, you can get one by creating an application or an activity.