I have got 2 activities - "A" contains fragment with a list of conversations, "B" represents a conversation (shows it's messages), in B I can also send a new message.
I would like to be able to update A's list of conversations every time a message is sent in B, so when I click android's back button, A activity's view is updated.
The core of the problem for me, is that I'm not starting A through an Intent when I click the android's back button, so I don't know how to get this effect.
Thank you for your help!
When A is on the backstack, there's no guarantee that an instance of A even exists in memory. The answer to the question of how to manipulate A from B is don't.
Some correct ways of doing it:
If your model (the list of conversations) is Parcelable or Serializable, you can pass it between activities via Intent. You can pass it back from B to A if you start B for result and retrieve it from the Intent returned to A's onActivityResult.
Make the model persistent, like in a database or SharedPreferences file.
Put the model in a bound Service. This would be faster than having each activity load it from persistent storage, but you may still need to make it persistent so you don't lose it when the Service shuts down.
Related
I am noob in Android. Suppose I have two Activity in my android app.
Activity A and B, currently I am on Activity A then on click on one button I am now Activity B. Here From Activity B I want to update some view with updated data that is in Activity A. I got updated data in Activity B so Should I use here LocalBroadCastReceiver for this or anything ?? so that When I press back then app should show me updated data in Activity A
Should we use our custom callback here to update the UI view data of Activity A from Activity B ??
No, you shouldn't use BroadcastReceiver for that. The method depends on the size of data you want to transfer from Activity B to Activity A. If it's quite small, you can start Activity B with startActivityForResult and then get data back at the onActivityResult method (in Activity B you should use setResult once you are done). If the size of data is quite big, it's better to use DB for storing it instead of keeping it in memory.
okay , there are multiple ways to do it :-
you can use a static variable to store you data that too of application level ( might not be a good approach ) check the value of vairable in onResume() and set it to the view.
you can use sharedpreferences if your data is not that large , store the data in Activity B and fetch it on onResume() method of activity A.
as #nikis has told you
if your data is too large store it in db.
I dont think broadcastreceiver fits right in your scenario !!
Considering the following scenario. There's an Activity_1, which creates another Activity_2, in Activity_1, some data are produced which needs to be recorded, and Activity_2 starts another Activity_1.
a) Will Activity_1 be brought to the top of calling stack, or will there be another instance Activity_3 that's the same class with Activity_1?
b) How do I recover the data generated in Activity_1, and make the show in Acitivity_3(or Activity_1 if it's simply brought to top). i.e., maintain the historical data in Activity_1
Well the answer is what flags you are setting during the start of new activity or calling an old activity. Below link will answer your question.
Tasks and Back Stack and SharedPreference
Would suggest to read the whole article and you will never have any problems.
Let say that I have two Activity to develop in Android. Upon the end user click a button in Activity A, the application supposed to pull data off a JSON API and present that information on Activity B.
So my question is, what's the best practice or pattern? i.e.
Activity A will call an AsyncTask and perform JSON call. Pull the data, push it into the Intent via putExtra, and call Activity B?
Activity A will call Activity B, Activity B onCreate will call an AsyncTask and perform the JSON call?
Other suggestions?
Which one is the prefer pattern?
And which gives better user experience? (e.g. imagine where the error dialog will be if connection fail to the server.)
I think normally something of your #2 approach is done. In most cases, though, you need to tell Activity B what type of information to request from the JSON API. So say in Activity A you are choosing an item from a list, and Activity B will get more information about that item. In this example Activity A will simply pass a reference to which item was selected, and then Activity B can use that reference to make a JSON request for more information about that item. Does that make sense?
I usually try to pass as little information as I can in Intent extras so I would steer clear of your first solution.
Lets say I have 2 activities:
A: A ListView displaying articles titles. Data is fetched from a web server and converted from XML to a list of ArticleSummary. Only user titles and id are returned by the server. Click on a title starts activity B.
B: A form to edit an article. Article is fetched from server. When the user hits OK, modifications are sent to the server and activity closed.
When the user go back to activity A, I would like to update the article title without any additional web request.
I was thinking about the following solution:
When article is modified, send a broadcast event with article id and new attributes values.
Listen for this event on activity A
Update the ArticleSummary object
notify data changed on ListView
Is there a better approach ?
If you want to have a shared data model between different Activities, you can place it in an extension of the Application class. Or, you can use a singleton. Just reload the data from the shared location when the ListView activity is restarted.
As Fredley alluded to, if you have are communicating with a server you should be sure to do so in a separate background thread.
you can also use startActivityForResult() to launch activity and managed returned data.
Check the "Returning a Result from a Screen" section in the part below.
http://developer.android.com/guide/appendix/faq/commontasks.html
I'd like the activity stack for my app to contain multiple instances of the same activity, each working on different data. So I'd have activity A working with data a, b, c and d in my activity stack ad I'd have 4 instances of activity A that I'd call A(a), A(b), A(c) & A(d). I'd also like to arrange it so that if the user asks to work with data c again then it won't start a new activity, but rather will just bring the already running activity A(c) to the front.
Any suggestions on the best way to achieve this?
So I'd have activity A working with
data a, b, c and d in my activity
stack ad I'd have 4 instances of
activity A that I'd call A(a), A(b),
A(c) & A(d).
That will happen by default.
I'd also like to arrange it so that if
the user asks to work with data c
again then it won't start a new
activity, but rather will just bring
the already running activity A(c) to
the front.
I do not believe that is possible unless you create distinct activities for each letter.
I'm not sure you can do it the way you have it described because fiddling with the activity stack like that is not supported AFAIK.
What you could do instead is just use a tab based activity. Each tab could be another instance of activity A working on a different dataset.
I agree with Falmarri (comment), you cant "switch between activities" in the way you are describing. You can however store that data somewhere (file, database, service, global variable, ext.). Where you choose to store that data (a, b, c, d) is up to you and depends on what kinds of functionality you need your data to have.
As for how you "switch" from one to the other, that is somewhat easier than you might think. you dont actually have to "switch" from one activity to the other, you can just swap our all the data. its is perfectly legal (though not always recommended) to have your entire app exist in ONE activity, and merely switch layouts over and over.
My suggestion would be to swap out the data within one activity. you could even specify which data set you want to load initially in your intent filter.