In an android application that I am developing Im using a thread, and to make sure I dont get the "java.lang.IllegalStateException: System services not available to Activities before onCreate()" I use a boolean called donecreate. Problem is that Android studio says I have a "java.lang.NullPointerException at picLoop.run(picLoop.java:24)"
Code main class:
import android.app.Activity;
import android.content.pm.ActivityInfo;
import android.media.AudioManager;
import android.os.Bundle;
import android.view.Display;
import android.view.Window;
import android.view.WindowManager;
import android.widget.Toast;
public class main extends Activity {
public Boolean donecreate;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(new eyeCanvas(this));
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
docreate();
}
public void docreate(){
donecreate = true;
}
public void checkHead(){
AudioManager am = (AudioManager)getSystemService(AUDIO_SERVICE);
if(am.isWiredHeadsetOn()){
Toast.makeText(getApplicationContext(), "HEADPHONES", Toast.LENGTH_LONG).show();
}
}
}
Code: pic loop
import android.graphics.Canvas;
//**Threading
public class picLoop extends Thread {
private eyeCanvas eye;
private main main = new main();
public picLoop(eyeCanvas eye) {
this.eye = eye;
}
#Override
public void run(){
Canvas c = null;
while(true) {
if(main.donecreate){ //<-- where error is
main.checkHead();
}
try {
// head.onCreate(Bundle savedInstanceState);
c = eye.getHolder().lockCanvas();
synchronized (eye.getHolder()) {
eye.onDraw(c);
}
} finally {
if (c != null) {
eye.getHolder().unlockCanvasAndPost(c);
}
}
try {
sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
Also if you guys could give me feedback on how I submitted, It would help :)
You can't create activities like you're trying to do. You can NEVER EVER do 'new Activity()', as the activity needs to be launched by the system to get set up properly and go through its lifecycle as intended.
So remove the line private main main = new main();.
To do what you're trying, make the boolean a static variable.
Change
public Boolean donecreate;
to
public static Boolean donecreate;
Then you can access it like you're trying to do, without creating an instance of main Activity.
There are a large number of things wrong with the assumptions you're making. Firstly, if your Thread requires your Activity to be created, don't start it until your Activity is created. Manage the lifecycle of this object within the Activity itself, i.e.:
#Override
public void onStart() {
super.onStart();
// Start your work here
}
#Override
public void onStop() {
super.onStop();
// Stop your work here
}
Secondly, please don't use the static access approach being recommended -- that makes the assumption that there is only one Activity instance (which is wrong immediately on a configuration change, and/or if you start another instance of that Activity in the task). And even if that assumption were true, you would need to set it back to false in onDestroy() (still, don't do that).
try setting donecreate to false initially
public class main extends Activity {
public Boolean donecreate = false;
#Override
protected void onCreate(Bundle savedInstanceState) {
....
You can request system service on application context, look at this answer.
So create a static variable in application class, initialize it like instance = this; in onCreate of Application class and then you'll be able to get app context whenever you want.
Related
I am trying to use a code from this link https://developer.android.com/training/connect-devices-wirelessly/nsd.html
"from Discover Services on the Network."
I copy and paste code as the following:
import android.net.nsd.NsdManager;
import android.net.nsd.NsdServiceInfo;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button aButton = (Button) findViewById(R.id.MyButton);
aButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// there is an error in the next line, ";" expected.
// but I do not know where to put ; exactly
public void initializeRegistrationListener() {
mRegistrationListener = new NsdManager.RegistrationListener() {
#Override
public void onServiceRegistered(NsdServiceInfo NsdServiceInfo) {
// Save the service name. Android may have changed it in order to
// resolve a conflict, so update the name you initially requested
// with the name Android actually used.
mServiceName = NsdServiceInfo.getServiceName();
}
#Override
public void onRegistrationFailed(NsdServiceInfo serviceInfo, int errorCode) {
// Registration failed! Put debugging code here to determine why.
}
#Override
public void onServiceUnregistered(NsdServiceInfo arg0) {
// Service has been unregistered. This only happens when you call
// NsdManager.unregisterService() and pass in this listener.
}
#Override
public void onUnregistrationFailed(NsdServiceInfo serviceInfo, int errorCode) {
// Unregistration failed. Put debugging code here to determine why.
}
};
} }
});
}
}
But there is an error in the this Line "public void initializeRegistrationListener()", ";" expected. but I do not know where to put ";" exactly or there is something else wrong that I cannot see it, can someone guide me, please?
PS: I am trying to make my phone discovers Mdns service that I created on my laptop using javascript, I have no experience in Java but I need to run the previous code to test the service that I have created already.
First of all you need an xml that contains an Button(this button will have android:id="#+id/mybutton", and that's the id you have to use on findViewById(R.id.mybutton).
In onCreate method of your activity you will write that code that you showed us, and you are good to go.
Another small step, if you wrote your own xml, make sure to have this line in onCreate
setContentView(R.layout.yourxml)
I am implementing a simple render view class for Android extending SurfaceView. My main activity class includes an infinite while loop for other operations.
However, the app shows a black screen when main activity is in the infinite loop. As far as I know, main activity and surface view classes have their own separate threads, so surface view class should keep rendering even when main activity class is busy. The app works just fine when I prevent infinite loop by setting 'running' boolean variable false in the code.
What might be the reason of that surface view class stops rendering when my main activity is in an infinite loop?
My main activity and surface view classes are as follows:
import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.view.WindowManager;
public class MainActivity extends Activity{
RenderSurfaceView renderView;
public boolean running = true;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate ( savedInstanceState );
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
renderView = new RenderSurfaceView(this);
setContentView(renderView);
loop();
}
public void loop(){
running = true;
while(running){
}
}
protected void onResume() {
super.onResume();
renderView.resume();
}
protected void onPause() {
super.onPause();
renderView.pause();
}
}
This my render class that extends SurfaceView:
import java.util.Random;
import android.content.Context;
import android.graphics.Canvas;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class RenderSurfaceView extends SurfaceView implements Runnable{
Thread renderThread = null;
SurfaceHolder holder;
volatile boolean running = false;
Random r = new Random();
public RenderSurfaceView(Context context) {
super(context);
holder = getHolder();
}
public void resume() {
running = true;
renderThread = new Thread(this);
renderThread.start();
}
public void run() {
while(running) {
if(!holder.getSurface().isValid())
continue;
render();
}
}
private void render(){
Canvas canvas = holder.lockCanvas();
canvas.drawRGB(r.nextInt(255), r.nextInt(255), r.nextInt(255));
holder.unlockCanvasAndPost(canvas);
}
public void pause() {
running = false;
while(true) {
try {
renderThread.join();
} catch (InterruptedException e) {
// retry
}
}
}
}
This
renderView = new RenderSurfaceView(this);
setContentView(renderView);
does not show the view immediately. Instead it has to go through a layout traversal first, which doesn't happen immediately but asynchronously to the Activity lifecycle methods, and it happens on the main thread. So running an infinite loop at the end of onCreate() prevents the layout traversal of the view hierarchy, which means your SurfaceView will never be shown.
In theory you could experiment with starting your infinite loop delayed using a Handler, for experimental purposes maybe. In general infinite loops on the main thread are a super bad idea and I can't see a reason why you would want to do this, apart from experiments maybe.
My self-answer to this question Modifying views in AsyncTask doInBackground() does not (always) throw exception has a bit more detail on what's going on behind the scenes. The question is not directly related to what you're asking here, but the background is the same I believe.
In a barebones Android application, I want to call a method in the MainActivity instance, from an asynchronous callback in the instance of another class. Why does Java force me to call a static method in the class, rather than a non-static method in the instance itself?
My app has a MainActivity class and a TextToSpeech (TTS) class. From the main activity, I instantiate the class, passing a pointer to the MainActivity instance. Instantiation of the TTS engine is an asynchronous operation. I cannot interact with the TTS instance until it has triggered an onInit() method.
Below is code that works. However, I had imagined that I would be able to call a non-static method in the MainActivity instance, and this appears not to be possible. The code below uses a static call to the MainActivity class itself, so no instance variables are available.
Here are the changes I made to a basic Hello World application in Android Studio.
//MainActivity.java
package com.example.callback;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
public class MainActivity extends ActionBarActivity {
private static TTS tts; // apparently this has to be static
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void onResume() {
super.onResume();
tts = new TTS();
Log.d("onResume", this.toString());
// D/Main﹕ com.example.callback.MainActivity#4a014e50
tts.init(this);
}
// Apparently this method has to be static
public static void ttsReady() {
tts.speakText("Hello world");
}
}
Custom class.
// TTS.java
package com.example.callback;
import android.app.Activity;
import android.content.Context;
import android.speech.tts.TextToSpeech;
import android.util.Log;
import java.util.HashMap;
import java.util.Locale;
public class TTS implements TextToSpeech.OnInitListener {
private TextToSpeech tts;
private Activity activity;
public void init(Activity currentActivity) {
activity = currentActivity;
Context context = activity.getApplicationContext();
tts = new android.speech.tts.TextToSpeech(context, this);
}
#Override
public void onInit(int status) {
if (status == TextToSpeech.SUCCESS) {
tts.setLanguage(Locale.UK);
Log.d("onInit", activity.toString());
// D/onInit﹕ com.example.callback.MainActivity#4a014e50
// activity.ttsReady();
// The line above does not compile. ttsReady() is not recognized as a
// method of activity, regardless of whether the tts variable and the
// ttsReady() method in the MainActivity class are made static or not,
// Making the activity variable static here has no effect either.
// The commented line below throws Error:(31, 35)
// error: non-static method toString() cannot be referenced from a static context
// So presumably MainActivity is a static variable.
// Log.d("onInit", MainActivity.toString())
// This works, if the tts variable and the ttsReady() method in the
// MainActivity class are made static. Is there a non-static alternative?
MainActivity.ttsReady();
}
}
// Deprecated signature for speak() used for compatibility with API 20
// and earlier
public void speakText(String toSpeak) {
int mode = android.speech.tts.TextToSpeech.QUEUE_FLUSH;
// Object hashMap = null; // Causes a "no suitable method error".
// How is HashMap null not the same as Object null? Using just plain null
// instead of hashMap also works with no problems.
HashMap hashMap = null;
tts.speak(toSpeak, mode, hashMap);
}
}
#Override
public void onInit(int status) {
if (status == TextToSpeech.SUCCESS) {
tts.setLanguage(Locale.UK);
Log.d("onInit", activity.toString());
((MainActivity)activity).ttsReady();
}
}
You are not referring to the instance of MainActivity when you say MainActivity.ttsReady(). That is why you can only access static methods. You need to make a call to the instance itself which you have stored in the activity variable.
Edit:
For a complete solution based on what you're trying to accomplish, I would probably set it up this way:
// TTSActivity.java
public abstract class TTSActivity extends Activity implements TextToSpeech.OnInitListener {
private TextToSpeech tts;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
tts = new TextToSpeech(this, this);
}
#Override
public void onInit(int status) {
if (status == TextToSpeech.SUCCESS) {
tts.setLanguage(Locale.UK);
ttsReady();
}
}
public void speakText(String toSpeak) {
int mode = android.speech.tts.TextToSpeech.QUEUE_FLUSH;
tts.speak(toSpeak, mode, null);
}
protected TextToSpeech getTts() {
return tts;
}
protected abstract void ttsReady();
}
then MainActivity becomes:
// MainActivity.java
public class MainActivity extends TTSActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
protected void ttsReady() {
speakText("Hello world");
}
}
Any Activity you want to use TTS in, all you have to do is extend TTSActivity and implements ttsReady().
As you can see, this is much more concise and easier to understand. However, your exact implementation will of course be dependent upon all the requirements you have in your particular application.
#zaventh's answer helped me to realize that a Java instance needs to be cast to the right class or interface for its methods to be found in the inheritance hierarchy. I have now rewritten my barebones project to include an interface that declares the ttsReady() method.
Here is the solution that allows me to access the methods of the MainActivity instance in a generic way.
TTSUser Interface
package com.example.callback;
interface TTSUser {
void ttsReady();
}
MainActivity
package com.example.callback;
import android.app.Activity;
import android.os.Bundle;
// TTUser Interface ensures the existence of the ttsReady() method in every instance
public class MainActivity extends Activity implements TTSUser {
private TTS tts; // non-static
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void onResume() {
super.onResume();
tts = new TTS();
tts.init(this);
}
public void ttsReady() { // non-static
tts.speakText("Hello world");
}
}
TTS Class
package com.example.callback;
import android.app.Activity;
import android.content.Context;
import android.speech.tts.TextToSpeech;
import java.util.Locale;
public class TTS implements TextToSpeech.OnInitListener {
private TextToSpeech tts;
private TTSUser activity;
// Use the TTSUser interface in the signature
public void init(TTSUser activity) {
this.activity = activity;
// Cast to generic Activity, to access .getApplicationContext()
Context context = ((Activity) activity).getApplicationContext();
tts = new android.speech.tts.TextToSpeech(context, this);
}
#Override
public void onInit(int status) {
if (status == TextToSpeech.SUCCESS) {
tts.setLanguage(Locale.UK);
activity.ttsReady(); // accessible through the TTSUser interfaceg
}
}
// Deprecated signature for speak() used for compatibility with API 20
// and earlier
public void speakText(String toSpeak) {
int mode = android.speech.tts.TextToSpeech.QUEUE_FLUSH;
tts.speak(toSpeak, mode, null);
}
}
(Background: all I want is a unique and persistent Google Play identifier for the user. (even after uninstalls, or on different devices) This is the only reason I am doing this.)
I am using Cordova. This is my main activity.
Problem: the onConnected function never runs. I am able to sign in fine, however. (I can see the sign in window, the sign in circle, and everything else) but it just never runs.
NOTE: onConnectionFailed runs once, with a SIGN_IN_REQUIRED statusCode.
package com.myapp;
import android.content.Intent;
import android.content.IntentSender.SendIntentException;
import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.api.GoogleApiClient;
import com.google.android.gms.common.api.GoogleApiClient.ConnectionCallbacks;
import com.google.android.gms.common.api.GoogleApiClient.OnConnectionFailedListener;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.games.Players;
import com.google.android.gms.games.Games;
import android.os.Bundle;
import org.apache.cordova.*;
import android.util.Log;
public class MyApp extends CordovaActivity implements GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener {
private static final String LOGTAG = "GooglePlayServices";
// Client used to interact with Google APIs.
private GoogleApiClient mGoogleApiClient;
private CordovaActivity activity;
boolean mResolvingError;
#Override public void onCreate (Bundle savedInstanceState) {
activity = this;
super.onCreate (savedInstanceState);
super.init ();
mGoogleApiClient = new GoogleApiClient.Builder (this)
.addConnectionCallbacks (this)
.addOnConnectionFailedListener (this)
.addApi (Games.API)
.addScope(Games.SCOPE_GAMES)
.build ();
mGoogleApiClient.connect ();
super.loadUrl(Config.getStartUrl());
}
#Override public void onConnectionFailed (ConnectionResult result) {
if (mResolvingError) return;
if (!result.hasResolution()) {mResolvingError = true; return;}
Log.d (LOGTAG, result.toString());
try {
mResolvingError = true;
result.startResolutionForResult (this, result.getErrorCode());
} catch (SendIntentException e) {
// There was an error with the resolution intent. Try again.
mGoogleApiClient.connect ();
}
}
#Override public void onConnected (Bundle connectionHint) {
// This never runs... this is the most critical part. I need the player ID!
String playerId = Games.Players.getCurrentPlayerId (mGoogleApiClient);
Log.w (LOGTAG, playerId);
}
// I saw this one with an #Override in others' code, but it won't compile if I add that.
public void onDisconnected () {}
protected void onStart () {super.onStart (); mGoogleApiClient.connect ();}
protected void onStop () {
super.onStop ();
if (mGoogleApiClient.isConnected()) mGoogleApiClient.disconnect ();
}
protected void onActivityResult (int requestCode, int responseCode, Intent intent) {
if (!mGoogleApiClient.isConnecting()) mGoogleApiClient.connect ();
}
public void onConnectionSuspended (int cause) {mGoogleApiClient.connect ();}
}
"Your Oauth2 client CAN NOT be created from Google APIs Console, it MUST be created from the Google Play UI."
I have a little problem... I have made an Android application which extends the webview. The webview Html page with a map on like this: Map example, it was also here I got my inspiration. My onCreate method looks like this:
super.onCreate(savedInstanceState);
//Removes the title bar in the application
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main);
//Creation of the Webview found in the XML Layout file
browserView = (WebView)findViewById(R.id.webkit);
//Removes both vertical and horizontal scroll bars
browserView.setVerticalScrollBarEnabled(false);
browserView.setHorizontalScrollBarEnabled(false);
myLocationManager=(LocationManager)getSystemService(Context.LOCATION_SERVICE);
//Enable Javascripts
url = "http://www.my-homepage.dk/map_example.html";
browserView.getSettings().setJavaScriptEnabled(true);
//The website which is wrapped to the webview
browserView.loadUrl(url);
So when My application gets a GPS location, it invokes this method:
LocationListener onLocationChange=new LocationListener() {
public void onLocationChanged(Location location) {
StringBuilder buf=new StringBuilder(url);
buf.append("?");
buf.append("lon=");
buf.append(String.valueOf(location.getLongitude()));
buf.append("&");
buf.append("lat=");
buf.append(String.valueOf(location.getLatitude()));
browserView.loadUrl(buf.toString());
}
So it basically just loads another URL.... But, my problem is, 1. it keeps the orignal website "map image", i imagined it would "unload" the page, and 2. When the second url is loaded, it takes quite a long time before it is finished, and when i am testing on my HTC Desire, it sometimes doesnt show the second loaded page (the map with location) before it turns the screen off and lock, or if i go out and in the application, that sometimes helps too...
Hope you can help :)
A suggestion - in onLocationChanged, make locationFound(); the first statement instead of the last.
It would be good to stop the listener immediately, as the loadUrl statement could take some time to complete, while the provider could be sending more updates.
Here is the solution... The GPS listener apparently broadcast more than once ;) so, when the GPS finds a location it loads the url and then stops broadcasting.
So the problem before was, that it sent loads of URL's to the html page, and therefore never just loaded 1 single url. And i just simplified the onLocationChanged a bit.
public void locationFound(){
myLocationManager.removeUpdates(this);
}
#Override
public void onLocationChanged(Location location) {
String lon = "lon="+String.valueOf(location.getLongitude());
String lat = "lat="+String.valueOf(location.getLatitude());
browserView.loadUrl(url+"?"+lon+"&"+lat);
locationFound();
}
Here is the SourceCode for the application:
package com.webview;
import android.app.Activity;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.util.Log;
import android.view.Window;
import android.webkit.WebChromeClient;
import android.webkit.WebView;
import android.webkit.WebViewClient;
public class WebViewTest extends Activity implements LocationListener{
private WebView browserView;
private static String PROVIDER="gps";
private LocationManager myLocationManager=null;
private String url;
private boolean LocFound = false;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//Removes the title bar in the application
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.main);
//Creation of the Webview found in the XML Layout file
browserView = (WebView)findViewById(R.id.webkit);
//Removes both vertical and horizontal scroll bars
browserView.setVerticalScrollBarEnabled(false);
browserView.setHorizontalScrollBarEnabled(false);
myLocationManager=(LocationManager)getSystemService(Context.LOCATION_SERVICE);
//Enable Javascripts
url = "http://www.test.dk/test.html";
browserView.getSettings().setJavaScriptEnabled(true);
//The website which is wrapped to the webview
browserView.loadUrl(url);
}
#Override
public void onResume() {
super.onResume();
myLocationManager.requestLocationUpdates(PROVIDER, 0,
0,
this);
}
#Override
public void onPause() {
super.onPause();
myLocationManager.removeUpdates(this);
}
public void locationFound(){
myLocationManager.removeUpdates(this);
}
#Override
public void onLocationChanged(Location location) {
String lon = "lon="+String.valueOf(location.getLongitude());
String lat = "lat="+String.valueOf(location.getLatitude());
browserView.loadUrl(url+"?"+lon+"&"+lat);
locationFound();
}
#Override
public void onProviderDisabled(String provider) {
// TODO Auto-generated method stub
}
#Override
public void onProviderEnabled(String provider) {
// TODO Auto-generated method stub
}
#Override
public void onStatusChanged(String provider, int status, Bundle extras) {
// TODO Auto-generated method stub
}
}