I am writing an Android App and i need to display some results from a non-activity class.
Basically my App gets the current location, activity and other things, and on those i run some functions, for example to check if the user has been at that place before.
Anyway, an intent triggers these functions, and at the end of the function I want to update a TextView with the result of these functions.
But it doesn't seem to work from anywhere besides MainActivity. I tried making the TextView static, but that doesn't seem to work, and returning the results to MainActivity is not possible either in since it is not called directly from MainActivity.
Does some have an idea on how to solve this problem?
This is my first android project, so there's still a lot of thing i don't know about. Thank you!
I don't know exactly what your code looks like, but do you have a model class that holds all your data (for example, some kind of singleton)? If so, you could just save the updated text there, and then update the TextView in a callback method.
If that doesn't fit what you're doing, I would considering refactoring your code so that the text you want is sent back to your MainActivity. You mentioned that the method is not called directly, but could your calculations pass the text to an intermediate class, which passes it to your MainActivity?
You should not update the ui drom background thread.
If you want to update the ui from background thread use Handlers,AsyncTask or use some other thread concepts.
If you want to update the UI fro Service or Broadcast receiver for eg you receive a message inside onReceive of broadcasrReceiver now to update the ui use sendBroadcast and inside your activity registet a dynamic Broadcast receiver and then update
Related
I'm confused regarding with some basic android development concepts, my question is not pointing at a particular code, thats why I dont include any.
Let's say that I have an activity inside of which I have a container in which I load a couple fragments (they are multiple instances of the same fragment), now the activity is populated, and inside one fragment I press a button that opens a new activity, it doesn't matter what may happen in that activity, the thing is that when I press a button it should take me back to the previos activity, I know that pressing the back button or using .finish(); will take me back to my already-populated activity, but I want to know, if that is the correct thing to do, or should I finish the activity as soon as i leave to the next one and when I want to go back create a new instance and repopulate it, if so, where should i store the variables?
Let's say that the fragments that I mentioned are "alarms" for an alarm application, and when I create it I call AlarmFragment newAlarm = new AlarmFragment(); and then I add that alarm to an arrayList in my alarms activity (java class) getListOfAlarms().add(getAlarmsAmount(), frag); which remains on the activity that has the fragment container, the question is, are these variables created in the right place? Because I am leaving them inside the activity itself right? What could happen if the activity is destroyed? I've been told that I should create an SQL database for storing those variables. I am not talking about long term saving but variables that I will be using at runtime
Can someone explain me these concepts a little bit? A link to a place where it is explained will be great too.
Your question seems like it has many parts.
In Part 1, this is what I think you are talking about:
1) how you decide to allow the user to get back to the first activity is really up to you. And 2) what you leave in the Back Stack is also up to you and what you want to define for the users' capabilities within your app. For example, if you want them to only be able to use a button that you define inside Activity 2 container, that is fine. However, you are not required to provide a button in Activity 2, and you are certainly allowed to use the Up Action in the App Bar for navigation. If I were you, I would read more about the Tasks and the Back Stack http://developer.android.com/guide/components/tasks-and-back-stack.html
You also mention this idea of having to "finish an Activity" with .finish(). I don't think that is usually necessary, but it is available to you if you want to use it based on what you decide for your app's logic (and what the user should and shouldn't be able to do).
With the Back button, Activity 1 will appear as if just initialized when you get back from Activity 2. Try it out. Also run some Log statements based on the simple diagram I provided and the Lifecycle "callbacks" (put these methods in your Activities and throw a Log statement in each to get a better sense of where you are in the Lifecycle) http://developer.android.com/guide/components/activities.html#Lifecycle
As for Part 2 of your question, I would try/set-up some of the above first, then start to experiment with a single variable to see what happens to it between Activities. There are a lot of "what ifs" to your question. You don't necessarily have to create a DB to store your variables, but that could certainly be an option. Take a look at the Developer Guide for most of the Data Storage options: http://developer.android.com/guide/topics/data/data-storage.html
If you are concerned about losing data when the Activity is destroyed, I might consider creating a database. Read the following for more info on recreating an Activity when you have gone elsewhere and are returning: http://developer.android.com/training/basics/activity-lifecycle/recreating.html In particular Saving Your Activity State: http://developer.android.com/training/basics/activity-lifecycle/recreating.html#SaveState
There's also an SO post on this: Saving Android Activity state using Save Instance State
I have an android app with one "home" or "main" activity that relies on fragments to accomplish several tasks. This data relies on information retrieved from a server (mine, and presumably a substantial amount by google maps).
I would like to structure my code such that several other activities (ie. preferences) can temporarily take focus before returning to the main activity.
Currently android destroys and recreates the main activity, which means bandwidth is wasted every time.
There are several notable intent flags which 'solve' this problem (Intent.FLAG_ACTIVITY_REORDER_TO_FRONT and Intent.FLAG_ACTIVITY_CLEAR_TOP), however they only appear to be useful when transitioning back to the main activity, which means I have to #override the system behaviour for both onKeyDown() and onBackPressed(). I would really prefer not to do this in case it causes other issues or eventually becomes deprecated.
Is this safe? Or is the better solution to force my application to create a serialization (savedInstanceState) of the main activity and all fragments anytime another activity temporarily takes the foreground?
Using saved instance state is the proper approach here. That will let you persist the information retrieved from the server when the activity gets re-created.
You only need to implement code to save / restore the instance state in the fragment or activity that holds the data. If you want to share that data across all your fragments, you can place it in the activity and add code to save the instance state of the activity. Then you can access the data that's stored in the activity from your fragments with ((MainActivity)getActivity()).getData().
For code to save and restore instance state, take a look at:
http://developer.android.com/training/basics/activity-lifecycle/recreating.html#SaveState
http://developer.android.com/training/basics/activity-lifecycle/recreating.html#RestoreState
If the data you need to persist is really large, you can use a retained fragment instead, as explained here:
http://developer.android.com/guide/topics/resources/runtime-changes.html#RetainingAnObject
Another trick for large data objects is to use a singleton class to store the data while the orientation change takes place.
We have been learning how to open new Activities, in class, but so far the second activity runs its logic from the OnCreate() class.
I am wanting to return directly to activity one, from activity two, but run a function in its java when I do so.
All I've been able to find on the matter is how to effectively write my own "back" button.
I am needing to pass a string, as well as an int, that was originally sent from activity one to activity two. I need to compare the received int with the sent int to confirm it is coming from the same source.
My biggest problem is that we were taught to use OnCreate(). This will not work on returning to an Activity, as OnCreate only runs when the instance is first created. If I am creating the instance as I move back, my other function will not work.
You can just use an startActivityForResult method.
Here is a topic of that: How to manage `startActivityForResult` on Android?
Hope it helps :)
I am trying to write an Android application which uses Bluetooth but ran into some problems. I succeeded in getting things working by following the guide on Android Developers portal. But i want to organize my code a bit and move everything related to Bluetooth to a separate class/src file. I run into a problem already when trying to turn on Bluetooth. As per above mentioned guide this is done with:
Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
However my class is not an activity and startActivityForResult is not defined. I can pass my main activity's context to my Bluetooth class and call startActivityForResult on that. This works. But result is then returned to my main activity and again I have to write code into it, instead of my Bluetooth dedicated class.
Alternatively I can make my Bluetooth class extend the Activity class. But then startActivityForResult returns a nullPointer exception (I take it because my "Activity" is not initialized).
I am completely new in Android app development so I am hoping for some pointers about what to look at to help me solve my problem. I would really like to have everything related to Bluetooth in one class/src file so that I can reuse it in any future apps.
All ideas in how to achieve that will be greatly appreciated.
Thank you.
Composition, not inheritance.
Pass the Activity to your BluetoothGodClass as a contructor, store it in an instance variable, and use that to call the respective method. BUT.
What do you really need to do? Does the UI need to control bluetooth? Create a method turnOnBluetooth(Activity activity) and use that. Do you really need to receive the specific result of the activity you called? If not, use a Context or a BroadcastReceiver.
I'm a little confused by the difference between Java and Android Java. Let's say I have an Activity class AndroidX. There is no main function and there is no AndroidX() constructor as we know it. I realize that onCreate() most probably initializes the AndroidX Activity, but why is there no main? What's the difference?
Consider that your activities are many *main*s and your manifest directs the execution to one of them.
Also consider that the constructor as we know it before is hidden and now it is always called onCreate()
Fair enough to keep going?
This graphic may help some.
http://developer.android.com/images/activity_lifecycle.png
In the Activity documentation they elaborate on what each function is meant for (i.e. onCreate(), onResume(), etc).
http://developer.android.com/reference/android/app/Activity.html
There is no "main" because that assumes that your app is either running or not running. But on android there are many other possible states your app could be in paused, stopped, started, etc...
Check out this link for an excellent overview of the Android Activity lifecycle.
How onCreate works is described in the Activity page of the Android Developer Reference. Specifically here:
onCreate(Bundle) is where you initialize your activity. Most importantly, here you will usually call setContentView(int) with a layout resource defining your UI, and using findViewById(int) to retrieve the widgets in that UI that you need to interact with programmatically.
In a sense you can consider this method the constructor for your Activity, as the initialization is handled there (see the Activity Lifecycle).
As for main, consider it hidden from you. Generally what you do is register listeners for UI elements such as buttons or text fields, then act on input from those UI elements. These listeners handle calls to your methods which might manipulate data or change how the UI displays.