I have a broadcast receiver which is listening to the WifiManager.SCAN_RESULTS_AVAILABLE_ACTION.
In that receiver I filter all the available networks and return a list of networks with a specific SSID. I nned to pass that list back to the MainActivity of my application.
I know I can create an inner class for my Broadcast receiver but I prefer to create a separate class for better organization.
I am thinking in creating a static variable in my mainActivity class and then set that value.
Is this a good practice?
A good way of sharing and access information a cross of Activites and other classes is by using the application object. You can access the application object from all your classes as long as you have the application context.
See this tutorial about application object: How to use application object
Usage from activities:
MyApplicationObject app = (MyApplicationOjbject)getApplicationContext();
app.setMyVariable(variable);
From other classes outside activity:
MyApplicationObject app = (MyApplicationOjbject)context.getApplicationContext();
app.setMyVariable(variable);
Stefan is right, this static link is not pretty. You can sometimes have multiple instance of the same activity (when recreated, until Garbage collector collect it). Or multiple broadcast happening, overwriting your static variable value.
If you don't want to use an anonymous inner class, you can override the constructor and pass a reference to your current activity that you will be able to use to send the results when processing onReceive(). Just clean up this reference when you are done to avoid leaking your activity.
I've used the same technique with success. The one time this bit me was when I did not consider that the user could tilt the screen and the activity would be recreated. I failed to check if the static variable was already set and replaced it repeatedly. Watch out for that.
One more technique I can think of is to share a callback between the activity and the broadcast receiver. The receiver makes a call to the callback which stores a reference to the right activity and calls runOnUiThread(action) to make UI updates. References should be updated onStart() and onStop(). I've never really used this pattern. Thought about it in the shower :)
I recommend to not use a static variable to deliver the information. If your main activity is the only object receiving the information from the receiver make the BroadcastReceiver local to the main activity. Doing so groups those elements which share a responsibility.
This is how I get data from broadcasts, little bit of more code but its way simpler to read
for future, in case of complex stuff get going.
Intent intent = new Intent(context, BroadcastReciever.class);
SimpleResultReciever resultReciever = new SimpleResultReciever(new Handler())
.setCallback(new OnLocationCallback() {
#Override
public void onRecieverLocation(Location location) {
if(location != null) {
MainActivity.this.location = location;
}
}
});
intent.putExtra(SimpleResultReciever.KEY_RESULT_RECIEVER, resultReciever);
//call intent or create pending intent you will use broadcast stuff.
public class SimpleResultReciever extends ResultReceiver {
public final static String KEY_RESULT_RECIEVER = "bundle.broadcast.reciever.callback";
private OnLocationCallback callback;
public LocationResultReciever setCallback(OnLocationCallback callback) {
this.callback = callback;
return this;
}
/**
* Create a new ResultReceive to receive results. Your
* {#link #onReceiveResult} method will be called from the thread running
* <var>handler</var> if given, or from an arbitrary thread if null.
*
* #param handler
*/
public LocationResultReciever(Handler handler) {
super(handler);
}
#Override
protected void onReceiveResult(int resultCode, Bundle resultData) {
super.onReceiveResult(resultCode, resultData);
Location location = resultData.getParcelable(LocationManager.KEY_LOCATION_CHANGED);
if(callback != null) {
callback.onRecieverLocation(location);
}
}
}
public class LocationBroadcastReciever extends BroadcastReceiver {
public LocationBroadcastReciever() {
super();
}
#Override
public void onReceive(Context context, Intent intent) {
Bundle extra = intent.getExtras();
Location location = extra.getParcelable(LocationManager.KEY_LOCATION_CHANGED);
ResultReceiver res = extra.getParcelable(LocationResultReciever.KEY_RESULT_RECIEVER);
if(res != null) {
Bundle data = new Bundle();
data.putParcelable(LocationManager.KEY_LOCATION_CHANGED, location);
res.send(Activity.RESULT_OK, data);
}
}
}
if u r launching an Main activity form the receiver and then u can pass the list in by using putextra(), and then you can get that in the main activity.
some thing like this.
Intent intent = new Intent(ctx.getApplicationContext(), targetActivity);
intent.putCharSequenceArrayListExtra(name, value);
Related
Inside my activity I have a broadcast receiver that I initialize as such:
private BroadcastReceiver mReceiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
updateViews();
}
};
updateViews() is a function inside the activity that is only used within the broadcast receiver. How can I create this receiver as a separate class that can play with the views (rotate, delete etc.) of my activity?
In addition, I have a compass within the activity. It works, however I would also like to make the compass a separate class that can send data to the activity. It will not change the views of the activity but only update certain double/float values.
#Override
public void onSensorChanged(SensorEvent event) { }
#Override
public void onAccuracyChanged(Sensor sensor, int accuracy) { }
How can I create this receiver as a separate class...?
This answer assumes that "separate class" means you want a BroadcastReceiver that is defined in its own source file and is not an inner class of an activity. Before offering a solution, I'll ask, what do you expect to gain by this? Do you have multiple activities that will use the receiver? If not, it's best to leave it as an inner class of the single activity that uses it. If you don't like using the anonymous inner class in the code you posted, you can declare is as an inner class:
private class MyBroadcastReceiver extends BroadcastReceiver {
#Override
public void onReceive(Context context, Intent intent) {
// As an inner class of the activity, this receiver has
// access to all activity members.
updateViews();
}
}
If you really want it as a standalone receiver, the example code below is a starting point. Be sure to register/unregister the receiver in your activity's onResume/onPause callbacks. The example includes code for a less safe approach, using a plain activity reference, and a safer approach using a weak reference. Only one is needed.
public class MyBroadcastReceiver extends BroadcastReceiver {
// For less safe use
private MyClientActivity mActivity;
// For more safe use
private WeakReference<MyClientActivity> mActivityRef;
public MyBroadcastReceiver(MyClientActivity activity) {
mActivity = activity;
mActivityRef = new WeakReference<MyClientActivity>(activity);
}
#Override
public void onReceive(Context context, Intent intent) {
// Less safe
mActivity.findViewById(R.id.action_bar);
mActivity.someActivityMemberMethod();
// etc
// More safe. Guards against failure to unregister
// this receiver when activity is paused.
MyClientActivity act = mActivityRef.get();
if (act != null && !act.isDestroyed()) {
mActivity.findViewById(R.id.action_bar);
mActivity.someActivityMemberMethod();
// etc
} else {
// Error: Activity failed to unregister this receiver
}
}
}
I would also like to make the compass a separate class that can send
data to the activity
Same assumption and question as above: Will the compass be used by multiple activities? If not, it's probably best to make it an inner class of the single activity. If there are multiple client activities, consider using a started-service. It could notify activities of sensor events using a local broadcast or an event bus such as greenrobot.
I am learning Android. I have made a simple Activity then in the Activity start the Service that do some high network operation now I want when high network load call complete then I want to update to my Activity.
Is it possible to update the Activity from the Service ?
Thanks in advance.
This is code taken and modified from a now depreciated library called DataDroid but it is relevant to what you are attempting to do.
private final class RequestReceiver extends ResultReceiver {
RequestReceiver() {
super(new Handler(Looper.getMainLooper()));
}
#Override
public void onReceiveResult(int resultCode, Bundle resultData) {
/*
* Depending on how you implement this either update activity from here
* or instantiate it with an interface that your activity implements and
* call that here.
*/
}
}
Create service with somethinglike this:
RequestReceiver requestReceiver = new RequestReceiver();
Intent i = new Intent(mContext, Service);
i.putExtra(RequestService.INTENT_EXTRA_RECEIVER, requestReceiver);
mContext.startService(i);
You could also just use the previously mentioned library and modify it to fit your current use case or use one of the many other similar libraries available.
I have implemented a bus for my app for communication between fragments and activities. I add a subscriber by adding an instance of either a Fragment or an Activity to a list. and I iterate through that list invoking a method to notify each of the subscribers of what is going on. Now I need to keep the list clean, I don't want to add multiple instances of of the same class in the list. I can use equals() for an Activity but I cant for a Fragment because its final so I cant override it.
WHAT I HAVE TRIED
I have tried to keep a Class object of each subscriber in the list which works fine until I go to invoke the method. You cant invoke a method without an instance to invoke it from. So that doesnt work.
I could also keep a separate list, one to hold Class objects and one to hold the actual instance. But I want to avoid adding another dependency if at all possible.
I could also manually do a instanceof check for each Fragment, but I dont want to do that because I already have 5 fragments, and if I add or remove any then I have to come back here and update this method.
So my question is, other than adding another List to hold the Class objects or manual instanceof checks, are there any other ways I can make sure I dont add multiple instances to the subscribers List?
Here is the relevant code if you need it:
public void subscribe(Object object) {
if (!mSubscribers.contains(object)) {
mSubscribers.add(object);
}
}
public void notifySubscribers(BusEvent event) throws InvocationTargetException, IllegalAccessException {
for (Object o : mSubscribers) {
Method methodToCall = getMethodToCall(o);
if (methodToCall != null) {
methodToCall.invoke(o, event);
}
}
}
Ok I have found a suitable answer to my problem. I want to share it here in hopes that it will help someone else out. Android has a class called LocalBroadcastManager. It is available in the v4 support library. In your activity you call 'LocalBroadcastManager.getInstance().registerReceiver()'. You pass into that method a class that extends BroadcastReceiver and an 'IntentFilter' to tell the receiver what to listen for. Then in any class including Fragments you call LocalBroadcastManager.getInstance().sendBroadcast() and pass in an Intent that matches the IntentFilter you used when registering. Here is the code I used to get it to work:
private void registerLocalBroadcastReceiver() {
// call this method in your activity (or any class you want to listen for broadcasts)
LocalBroadcastManager manager = LocalBroadcastManager.getInstance(this);
manager.registerReceiver(new OpenMenuBroadcastReceiver(), new IntentFilter("open-html"));
}
private void sendMessageToActivity(int position) {
// use this in a fragment (or any other class) to send a message
LocalBroadcastManager broadcast = LocalBroadcastManager.getInstance(getActivity());
Intent message = new Intent("open-html");
String name = (String) getListAdapter().getItem(position);
message.putExtra("name", name);
broadcast.sendBroadcast(message);
}
class OpenMenuBroadcastReceiver extends BroadcastReceiver {
// this is an inner class to my activity, when you send the message this method
// will be called to handle the message
#Override
public void onReceive(Context context, Intent intent) {
String name = intent.getStringExtra("name");
if (name != null && name.equalsIgnoreCase("home")) {
replaceFragment(Tag.HOME_FRAGMENT.getTag(), new HomeFragment(), R.id.main_frame);
mDrawerLayout.closeDrawer(Gravity.START);
return;
}
openMenuItemsFragment(name);
}
}
The good thing about this is that it is completely local to your app. External apps cant receive your broadcasts so its secure. You can find out more on how to use it on the Android developer site.
I would like to achieve the following behaviour, but I'm not sure how:
User start an activity
Activity starts an AsyncTask
User performs some action that creates a new activity
The AsyncTask finishes and somehow returns the result to the new activity
Is there a way of achieving this behaviour?
Thank you
Create a Service that itself spawns its own thread and does your background processing. You can bind your activities to the service so you can call back into an activity when your processing is complete.
I've been using a variation of what was suggested by Chris:
Start by creating an IntentService, which is the easiest kind of Service to create. Then use SharedPreferences to indicate the state of your IntentService and share values between your Service and Activities. Your Activity can register itself as an OnSharedPreferenceChangeListener in order to know when your Service is done doing work and/or another SharedPreference it cares about has changed.
With IntentService, all you need to do is override the onHandleIntent method. Everything inside onHandleIntent will run on a background thread.
This is a way to do exactly what you want, assuming that the result is an int. You can extend this property, using a parcelable object. Probably, using a Service is still the best choice.
1) Create a class, called Result, that is a wrapper for your result. It must implement the Parcelable interface:
public class Result implements Parcelable {
private int result;
public Result(int i) {
super();
result = i;
}
public void setResult(int result) {
this.result = result;
}
public int getResult() {
return result;
}
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(result);
}
public static final Parcelable.Creator<Result> CREATOR = new Parcelable.Creator<Result>() {
public Result createFromParcel(Parcel in) {
return new Result(in);
}
public Result[] newArray(int size) {
return new Result[size];
}
};
public Result(Parcel in) {
result = in.readInt();
}
}
2) Now, you can use a Result object as a private variable of the first activity:
public class FirstActivity extends Activity {
private Result result;
....
}
3) In your firstActivity, you can start an AsyncTask with a line like this:
new MyAsyncTask(result).execute();
4) Your AsyncTask can be made in this way:
class MyAsyncTask extends AsyncTask<Void, Void, Void> { // you can modify types as you want
Result result;
public MyAsyncTask(Result result) {
this.result = result;
}
....
public mySetResult() {
result.setResult(...); //set your value
}
....
}
5) When you start the second Activity, you can pass your result object to the second activity:
Intent i = new Intent(getApplicationContext(), SecondActivity.class);
i.putExtra("parc", result);
startActivity(i);
6) Finally, from the second activity, you can obtain the result using this code:
Result res = (Result) getIntent().getParcelableExtra("parc");
For more details about parcelable object, can see Android Developer
A Service is a component that allows some code to have a separate lifetime outside of activities without interacting with the user. As others have mentioned, that's certainly one option to consider. If you go with that, IntentService is the easiest way to make the work asynchronous.
However, you could continue to use AsyncTask and just add some code to signal that it's "complete". This is the case when the background work no longer matters if your application is killed, and you're OK with your app being killed before this work completes if the user leaves the application. Another way to see this is if the result of the AsyncTask only matters to either/both of these two activities and not outside. This is an important difference in requirements from needing a Service which again, provides a lifetime outside of activities.
To pass the data, take a look at this doc. There are a lot of ways you could tackle this, but for this kind of thing I prefer a pseudo-singleton approach. (I don't like to use SharedPreferences to pass data, because frankly I don't think that's what the class is for. I prefer this pseudo-singleton approach over a pure singleton because it's more testable. Android uses the singleton approach all over the place though.) I'd create a reference to some sort of AsyncTask registrar class in the Application object. As the Application object is accessible from both activities, the first one can register your AsyncTask with the registrar and the second one can get that AsyncTask and register to listen for completion if it hasn't already finished.
Despite similar question was asked, I have differnet situation:
My app consists mostly of a background Service. I want to start external activities and get results back.
I see several options:
Create dummy Activity and keep reference to it for using its startActivityForResult. This consumes quite a lot of memory, as we know.
Use Broadcast Intents instead of Android's results infrastructure: ask client activities to broadcast their results before closing. This kind of breaks the idea and not so performance-efficient.
Use Instrumentation directly - try to copy code from startActivityForResult into my Service.
Use Service interfaces - serialize and add AIDL connection to the Intent for starting an Activity. In this case Activity should call Service directly instead of providing result.
The third approach feels closer to Android for me, but I'm not sure if it's possible to do - Service does not have its Instrumentation, and default implementation seems to always return null.
Maybe you have any other ideas?
I’ve been thinking about this recently when implementing account authenticators with three-legged authorisation flows. Sending a result back to the service for processing performs better than processing it in the activity. It also provides a better separation of concerns.
It’s not that clearly documented, but Android provides an easy way to send and receive results anywhere (including services) with ResultReceiver.
I’ve found it to be a lot cleaner than passing activities around, since that always comes with the risk of leaking those activities. Additionally, calling concrete methods is less flexible.
To use ResultReceiver in a service, you’ll need to subclass it and provide a way to process the received result, usually in an inner class:
public class SomeService extends Service {
/**
* Code for a successful result, mirrors {#link Activity.RESULT_OK}.
*/
public static final int RESULT_OK = -1;
/**
* Key used in the intent extras for the result receiver.
*/
public static final String KEY_RECEIVER = "KEY_RECEIVER";
/**
* Key used in the result bundle for the message.
*/
public static final String KEY_MESSAGE = "KEY_MESSAGE";
// ...
/**
* Used by an activity to send a result back to our service.
*/
class MessageReceiver extends ResultReceiver {
public MessageReceiver() {
// Pass in a handler or null if you don't care about the thread
// on which your code is executed.
super(null);
}
/**
* Called when there's a result available.
*/
#Override
protected void onReceiveResult(int resultCode, Bundle resultData) {
// Define and handle your own result codes
if (resultCode != RESULT_OK) {
return;
}
// Let's assume that a successful result includes a message.
String message = resultData.getString(KEY_MESSAGE);
// Now you can do something with it.
}
}
}
When you start an activity in the service, create a result receiver and pack it into the intent extras:
/**
* Starts an activity for retrieving a message.
*/
private void startMessageActivity() {
Intent intent = new Intent(this, MessageActivity.class);
// Pack the parcelable receiver into the intent extras so the
// activity can access it.
intent.putExtra(KEY_RECEIVER, new MessageReceiver());
startActivity(intent);
}
And finally, in the activity, unpack the receiver and use ResultReceiver#send(int, Bundle) to send a result back.
You can send a result at any time, but here I've chosen to do it before finishing:
public class MessageActivity extends Activity {
// ...
#Override
public void finish() {
// Unpack the receiver.
ResultReceiver receiver =
getIntent().getParcelableExtra(SomeService.KEY_RECEIVER);
Bundle resultData = new Bundle();
resultData.putString(SomeService.KEY_MESSAGE, "Hello world!");
receiver.send(SomeService.RESULT_OK, resultData);
super.finish();
}
}
I think option 2 is the most idiomatic way on android. Using startActivityForResult from an Activity is a synchronous/blocking call, i.e., the parent activity waits and does not do anything until the child is done. When working from a Service and interacting with activities your primarily doing asynchronous/non-blocking calls, i.e., the service calls out for some work to be done and then waits for a signal to tell it that it can continue.
If you are using the android local service pattern then you can have your activities acquire a reference of the Service and then call a specific function after it has performed its work. Attempting your option 3 would be counter to what the framework provides for you.