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How to access all members and methods in the current activity through one instance method?

Hello Stack Overflow Community. I am currently working on an Android VoIP application, which uses WebRTC and therefore I have been trying to comprehend the source code which I found on GitHub. So far, I have been able to reproduce and understand a bit of the source code I found, but currently I stumbled across a problem with the implementation of the SignalingClient. To further understand my problem I think it is appropriate to be more detailed and ask the question more precisely: How to access all members in the current activity, without declaring an object of it from a class, through one instance method, which is defined in the same other class?I think pointing to it in the source code is also good to understand the question. I have shortened the code so it fits the question as close as possible.
SignalingClient.java
class SignallingClient {
private static SignallingClient instance;
private String roomName = null;
private Socket socket;
boolean isChannelReady = false;
boolean isInitiator = false;
boolean isStarted = false;
private SignalingInterface callback;
...
public static SignallingClient getInstance() {
if (instance == null) {
instance = new SignallingClient();
}
if (instance.roomName == null) {
//set the room name here
instance.roomName = "vivek17";
}
return instance;
}
public void init(SignalingInterface signalingInterface) {
...
}
...
}
MainActivity.java
public class MainActivity extends AppCompatActivity implements View.OnClickListener, SignallingClient.SignalingInterface {
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED
|| ContextCompat.checkSelfPermission(this, Manifest.permission.RECORD_AUDIO) != PackageManager.PERMISSION_GRANTED) {
ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.CAMERA, Manifest.permission.RECORD_AUDIO}, ALL_PERMISSIONS_CODE);
} else {
// all permissions already granted
start();
}
}
...
public void start() {
// keep screen on
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
initViews();
initVideos();
getIceServers();
SignallingClient.getInstance().init(this); //Here is my lack of understanding/reproducing/comprehending,
//because at this point I have access to all members(variables)
//in the SignalingClient.java class : boolean isChannelReady,
//boolean isInitiator, boolean isStarted
//and also other methods which are public...
//Shouldnt it be like this?
/*
SignalingClient obj = new SignalingClient();
obj.getInstance();
obj.init(this);
*/
...
}
...
}
After experimenting around and looking up on the web [1][2][3][4] and many other related stackoverflow questions I noticed that this behaviour has something to do with the static modifier according to these sources [5][6][7] but also the fact that
class SignallingClient{... //SignallingClient
private static SignallingClient instance;... //SignallingClient
public static SignallingClient getInstance() {... //SignallingClient
the class, the instance member and also the getInstance method all have/share the same "name" as we can see on the line comments above. Getting back to my question, I would really like to know how this works, or if this is a trick to access all possible members and methods (and other things I don't know yet) without declaring an object. I would really appreciate any answer followed by a good explanation to this topic as well as dropping some good sources/tutorials/university scripts etc. where I can read up on this.
Thank you very much.

Accessing COM Interface with JNA

I'm trying to access the IDesktopWallpaper interface with JNA, but I've hit a wall.
I went through ShOljIdl_core.idl (from Windows 10 SDK) and discovered the GUID of the interface as follows
// IDesktopWallpaper
[
uuid(B92B56A9-8B55-4E14-9A89-0199BBB6F93B),
object
]
and the GUID of the concrete class that implements the interface
// CLSID_DesktopWallpaper
[uuid(C2CF3110-460E-4fc1-B9D0-8A1C0C9CC4BD)] coclass DesktopWallpaper { interface IDesktopWallpaper; }
So I followed the official example in the JDA github and wrote the following
#ComObject(clsId="{C2CF3110-460E-4fc1-B9D0-8A1C0C9CC4BD}")
public interface DesktopWallpaper extends IUnknown{
}
and in Main
Ole32.INSTANCE.CoInitializeEx(Pointer.NULL, Ole32.COINIT_MULTITHREADED);
try {
Factory factory = new Factory();
try {
DesktopWallpaper dw = factory.createObject(DesktopWallpaper.class);
} finally {
factory.disposeAll();
factory.getComThread().terminate(1 * 1000);
}
} finally {
Ole32.INSTANCE.CoUninitialize();
}
But the factory.createObject(DesktopWallpaper.class) throws No such interface supported(HRESULT: 80004002) (puArgErr=)and I don't know how to get around this or why it is happening.
Can any experts enlighten me on what's happening? (I am a complete noob) I will provide any further info that's necessary. Can JNA achieve what I want or do I have to use something else like Com4j?

TL;DR
After a lot of googling, I finally got it to work. The problem (at least to my current understanding) is that the current JNA helpers only work with interfaces that inherit from IDispatch. So if the interface in question such as IDesktopWallpaper does not inherit from IDispatch, then one should use vtable for function calls. I got this information from this amazing Google forum post in which the poster also provided a code sample that got me started.
Here is some working code for the SetWallpaper() function:
public class DesktopWallpaperHandler extends Unknown{
private static final GUID CLSID_DesktopWallpaper = new GUID("{C2CF3110-460E-4fc1-B9D0-8A1C0C9CC4BD}");
private static final GUID IID_IDesktopWallpaper = new GUID("{B92B56A9-8B55-4E14-9A89-0199BBB6F93B}");
private DesktopWallpaperHandler(Pointer pvInstance) {
super(pvInstance);
}
public static DesktopWallpaperHandler create(){
PointerByReference p = new PointerByReference();
WinNT.HRESULT hr = Ole32.INSTANCE.CoCreateInstance(CLSID_DesktopWallpaper, null, WTypes.CLSCTX_SERVER, IID_IDesktopWallpaper, p);
COMUtils.checkRC(hr);
DesktopWallpaperHandler handler = new DesktopWallpaperHandler(p.getValue());
return handler;
}
public void SetWallpaper(WTypes.LPWSTR monitor, WTypes.LPWSTR wallpaper){
int result = this._invokeNativeInt(3, new Object[]{this.getPointer(), monitor, wallpaper});
COMUtils.checkRC(new HRESULT(result));
}
}
And then in Main:
Ole32.INSTANCE.CoInitializeEx(Pointer.NULL, Ole32.COINIT_MULTITHREADED);
try {
WTypes.LPWSTR path = new LPWSTR("C:\\Users\\Harry\\Desktop\\1.jpg");
DesktopWallpaperHandler handler = DesktopWallpaperHandler.create();
handler.SetWallpaper(null, path);
} finally {
Ole32.INSTANCE.CoUninitialize();
}
The original motive to use IDesktopWallpaper was to access the fade in transition effect, and now that can be done by adding the following:
User32.INSTANCE.SendMessageTimeout(User32.INSTANCE.FindWindow("Progman", null), 0x52c, 0, 0, 0, 500, null);

possible alternative to static inner classes to prevent memory leaks in android/java?

lately i have been researching about memory leaks in java/android and pretty much everywhere it says that instead of anonymous classes i should use static inner classes with weak references.
so, in my android app i started doing that but very quickly got tired of it because it's a lot of boilerplate code... i think have an alternative solution which i would prefer to use, but i'm juts not sure that it is a valid alternative to static inner classes in terms of preventing memory leaks. as i said before, i haven't seen this solution suggested anywhere else (all say to use static inner classes) so thats why im not sure my alternative will work.
ill use a simple example from my app:
i have a class called WebClient which handles asynchronous web requests and it accepts an interface called iCallback which returns the response from the server to the caller, and in my activity once i get this callback i need to dismiss a dialog, and maybe perform some activity related things (like trigger onBackPressed() and setResult()).
so here is my static inner class i have created:
private static class CallBack implements WebClient.ICallback
{
private WeakReference<ProgressDialog> mProgDiag;
private WeakReference<BaseActivity> mActivity;
public CallBack(BaseActivity activity, ProgressDialog progDiag)
{
this.mProgDiag = new WeakReference<>(progDiag);
this.mActivity = new WeakReference<>(activity);
}
#Override
public void onCallback(String data)
{
String responseAsString = Utils.extractStringFromResponse(...);
final BaseActivity parentActivity = mActivity.get();
ProgressDialog dialog = mProgDiag.get();
if(dialog != null)
{
dialog.dismiss();
}
if (responseAsString == null)
{
if(parentActivity != null)
{
Utils.makeServerErrorDialog(parentActivity,
new iDialogButtonClickedListener()
{
#Override
public void onDialogButtonClicked()
{
parentActivity.onBackPressed();
}
});
}
return;
}
//everything is ok
if (responseAsString.equals("1"))
{
if(parentActivity != null)
{
Intent result = new Intent();
result.putExtra(...);
parentActivity.setResult(Activity.RESULT_OK, result);
}
}
else
{
Utils.reportErrorToServer(...);
if(parentActivity != null)
{
parentActivity.setResult(Activity.RESULT_CANCELED);
}
}
if(parentActivity != null)
{
parentActivity.onBackPressed();
}
}
}
so for every variable i need in this static inner class i have to create a new weak reference, then retrieve the object itself, and then every time i want to access it i need to check whether it's null... that seems like a lot of code to me.
and here is my suggested alternative:
public abstract class BaseActivity extends AppCompatActivity
implements WebClient.ICallback
{
private static final String TAG = "BaseActivity";
WebClient.ICallback mCallBack;
ProgressDialog mProgDiag;
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(...);
mCallBack = this;
//some code to invoke a server request on button click
//and passing mCallBack to the request
}
#Override
public void onCallback(String data)
{
String responseAsString = Utils.extractStringFromResponse(...);
mProgDiag.dismiss();
if (responseAsString == null)
{
Utils.makeServerErrorDialog(this,
new iDialogButtonClickedListener()
{
#Override
public void onDialogButtonClicked()
{
onBackPressed();
}
});
return;
}
//everything is ok
if (responseAsString.equals("1"))
{
Intent result = new Intent();
result.putExtra(...);
setResult(Activity.RESULT_OK, result);
}
else
{
Utils.reportErrorToServer(...);
setResult(Activity.RESULT_CANCELED);
}
onBackPressed();
}
#Override
protected void onPause()
{
mCallBack = null;
super.onPause();
}
#Override
protected void onResume()
{
super.onResume();
mCallBack = this;
}
}
to me this seems much cleaner: no creating and retrieving instances of weak references for every variable i need access to, i can directly invoke activity methods (e.g. onBackPressed()), and no checking for null everywhere.
the only place i would now have to check for null is inside WebClient class before invoking the callBack method.
so my question is, does this approach achieve the same result in terms of preventing memory leaks? is it a "worthy" alternative to static inner classes?

Unfortunately, your approach does not work. By implementing the WebClient.ICallback in your activity, rather than an inner class, you don't get rid of the leak. The leak happens not because the references to activity and dialog are implicit in an anonymous class, or in lambda, or in a non-static inner class instance; the happens when the WebClient keeps this reference while the activity is gone (it is not destroyed, because there is a strong reference to it).
The special mCallBack that you set to null when the activity is paused, gains nothing. Just as well, you can simply pass your activity instance to the WebClient. Now there is a strong reference to your activity, which is managed by someone (async handlers of the WebClient), who is not under your control. If you are unlucky, the async handler will get stuck somewhere and will never release this reference.
Please read this detailed explanation.
Note that WebView itself can cause a memory leak, if special measures are not undertaken!

Call a class with AsyncTaks from a static class

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.

Instantiating TextToSpeech inside GCMIntentService

So I have a bit of a problem. I am trying to make my app do things based on the message it receives through GCM. In this case it's supposed to make a sound by using the TextToSpeech class. It kind of works, but not the first time I send the message. I realise this is probably because TextToSpeech hasn't been instantiated, but I'm not sure how go to about and do that? I tried onInit(), but that didn't work at all.
Also, what is the best way to shut down TTS in my example?
Disclaimer: I come from a PHP background, and know very little Java. I try to learn by doing, so please forgive me if this is a silly question. Thanks in advance!
public class GCMIntentService extends GCMBaseIntentService {
private static final String TAG = "GCMIntentService";
public static TextToSpeech mtts;
public GCMIntentService() {
super(SENDER_ID);
}
#Override
protected void onMessage(Context context, Intent intent) {
Log.i(TAG, "Received message");
String message = intent.getExtras().getString("message");
mtts = new TextToSpeech(context, null);
if (message.startsWith("makeSound")) {
mtts = new TextToSpeech(context, null);
mtts.setLanguage(Locale.US);
mtts.speak(message, TextToSpeech.QUEUE_FLUSH, null);
}
}
}

It doesn't work the first time because the initialization of TextToSpeech is asynchronous. You can not simple instantiate it and use it as you are doing. You should provide a callback to be called once the TextToSpeech has been initialized if you want to use it right away.
mTextToSpeech = new TextToSpeech( this, new TextToSpeech.OnInitListener()
{
#Override
public void onInit( int status )
{
// Check for status might not be initialized due to errors
// Configure language/speed
}
} );
It does work the rest of the times, because mtts is static. This means that is a class variable and is not destroyed/initialized when creating new instances of the service. By the second time you use this service, this variable was already initialized in the first service execution.