In my Android Application, I have two activities.
One Activity lets the user take a picture. This picture is saved, and then uploaded to the server. The server returns some info and displays it in a list.
The other Activity is a gallery. The user can select a picture, upload it and get the same info in a list (the same as the first activity)
The way I've implemented is this:
upload and Info task is a seperate AsyncTask called WebServiceTask. Both Activities execute this task.
I created a WebServiceTaskInvoker interface so that each activity could specify what happens on preExecute, postExecute, progressUpdate.
The problem is that the two activities pretty much do the exact same thing on preExecute, postExecute and progressUpdate so there's code repetition between the two activities.
OnPreExecute: Both Activities check internet connectivity
OnProgressUpdate: Both Activities change a TextView's text
OnPostExecute: Both Activities create a dynamic ListView and populate
it with results.
How can I fix this?
I know one way would be to combine the two activities into one but form past experience, I've known this to be troublesome and messy.
I could put the UI code in the WebServiceTask but that would lead to tight cohesion.
Implement a base class for the two activities that executes common code. Implement the activities as subclasses of your base class to execute different code.
An alternate to Catherine's suggestion is to create an activity mode enumeration.
Pass this mode as an extra when launching your activity.
If the mode is MODE_GALLERY then load the gallery.xml layout and populate it, if not then load the other layout.
Just make sure that you use the same id's for the common views, an easy way to do this is to use the include tag in your layout files.
The advantage of this is that you only have one activity file instead of three which would be required for the subclassing method.
You may also be able use fragments, but I don't have any experience with these so I can't advise ou further.
One last note, I would avoid putting UI code into a task.
Related
I'm writing my first android app, and it's going very well so far, but my code is getting obtuse and I'd like to reorganize it in a way that allows me to reuse portions, and add things more easily.
Based on my previous experience writing simple command line programs that call methods, this is how I THINK I should organize my code:
(some code in MainActivity)
Call a void method of the object DoStuff:
Launch Activity1 and write some values to SharedPreferences file, THEN
Launch Activity2 and write some values to SharedPreferences file, THEN
continue running code from MainActivity
Right now Activity1 and Activity2 both launch at the same time. Is there a different way I should be writing/organizing my code? I guess I'm trying to do thing with Activities that I'm used to doing with methods. But I'm aware that my thinking might be wrong on this. I hope this makes sense.
Thank you for your help!
Your understanding of Activities is wrong. Activities do have methods that you can very well use.
An Activity is basically one screen that you see in your app. It can be started, stopped, resumed, etc. You can have different screens shown in one Activity (e. g. with Fragments).
If for example you have a list of notes in one Activity, you could have the detail of one note shown in another DetailActivity.
Only in rare cases, for example if you want to check on startup what Activity to show you could have another activity that does not have a layout but only does some checks and launches another one.
In each of your activities you can have methods to execute what you want on user interaction. Of course this can also go into other classes.
I would recommend you to start with a basic Android tutorial to gain a better understanding of the concepts.
I am new to android programming. I would like to get some advices about AsyncTask. I have created a main activity and one fragment in which i will display content. The use for AsyncTask in my program is to download data from internet. So, the question would be: where it should be? In the fragment's class or activity's?
You have three choices:
You can make it an inner class inside of the Fragment. This is probably OK if this asynchronous task is only specific to the fragment and you won't ever reuse it
You can make it an inner class inside of the Activity. The is better if you have one activity that controls many Fragments that may reuse the same asynchronous task.
You can make it a class of its own if you plan to reuse it in man places in your application or even if you just want it neater. If you do plan on reusing it but the places that are reusing it may need some slight differences, then you might want to abstract it to make it flexible.
Hope that helps.
I am still searching for the best solution howto use a layout with a menu and a toolbar and inflate or start activities in android. My question may sound confusing, but im trying to explain it in an example.
Lets say im programming an android app (surprise.. i really do)
My app can do following:
User can log in [3] or register [2]. If he logs in, a new activity starts and his dashboard will be shown. If he registers: an activity for the registrationprocess starts.
Registrationprocess: user puts in his desired username and password and presses a button to accept. His data will be formvalidated and if valid, a new activity starts where he can choose his settings. Backbutton works and data can be passed to the new activity. After the last registrationwindow data will be saved and dashboard started. Starting new Activities is fun!
Now THATS where it gets complicated. Dasboard has an 'actionbar'(top) and a 'toolbar' (bottom, like tabs). So everything should be viewed in the middle part of the viewport(from now called main view). No more activity switching :(, tho.
Currently each tabclick removes all views from the main view and adds its new view. Look great, can be animated and works like a charm. Except: its currently not dynamic.
So... i don't know how to solve it the best way. For example: i fetch data from a webservice, create a listview out of it and it's extending listactivity. This activity i can't start but this data need to be put into the main view. How can i do it the best way?
And is it efficient?
I'm practicing and it's actually my first small discussion i want to start. So... FIGHT! ;)
UPDATE:
I've seen an interesting way to start activities and get results.
Launching activity through intents
. Is it possible to insert new/ update views after activity started? I would then generate my results in a separate activity. Update the view. Return back to 'dashboard' and load the view that was just updated. Possible? Or inefficient? And how can i update a view out of another activity? There is so much i need to learn :/
UPDATE2:
A good example of an app that has done it: Google+
Too bad i don't have their sourcecode ;)
UPDATE3:
What is best?
load a new activity, disable animation and set selected toolbox tab +
disable backbutton functionality
startActionForResults, fetch results and update current view (still don't really know how that would be possible)
viewFlipper onflip changing+updating data in flipped view.
I still don't know any efficient solution. Or am i missing something essential? I've just finished my ListActivity to fetch data from my webservice. But it still runs in a separate activity. How can i implement it into my "main view" now? Ofcourse... i could set a list my custom adapter. But currently im updating and fetching data from the server when i create the listactivity.
Im afraid this could be the only answer i'll get: Embed external Intent in main Activity
UPDATE4: I'm trying something.
Based on nininho's answer (thank you!) im trying the following approach:
Start Dashboardactivity and create a ViewFlipper.
Each Toolbarclick represents a certain ViewFlipper page.
Each Page has a Listadapter implemented and shows different results (different webservice queries). (ListView, GridView, with profileimage, without profileimage)
On Toolbarclick start AsyncTask or Service and notify List in current Page that data has changed. (ofcourse IF data has changed). Switch to page that was clicked.
Implement updatefeature. On scroll to bottom of list = fetch more data and add it. Update other lists automatically after 5min. or update list on update-button click.
PROs so far: Backbutton standalone for whole activity. Page-flip-animation possible. Async updating of lists and still possible to switch to another list.
CONs: ... someone has any? What about efficiency of such an approach? Does the ViewFlipper carry all the information so the performance would go down or does the viewflipper recycle its Views (like ListView)?
UPDATE5:
If i have some time i will make everything here more read- and discussable. Don't be mad at me for reading my rubbish ;)
From what I understand you want your app to start, fetch some data from the internet and after show this data on the main screen.
I don't see the need of a second activity to fetch the data because from your explanation you want to use it only to fetch the data, so the best approach would be:
Create one Activity (your dashboard)
Start an AsyncTask or Service on the background to fetch the data.
When the fetch ends, notify the activity that it ended.
Change your dashboard to show the list (you can use a ViewSwitcher if you want some animation or just create a layout with the list invisible and then change to visible).
ps: you can use a ListView outside of a ListActivity, just create a ListAdapter to create the ListView items and add this as the adapter for the ListView.
I have an app with multiple activities and multiple layouts. However, one piece of layout is included on several activities. I also have a thread which updates this layout. However, when i switch activity it doesn't work. Since the layout is included the elements have the same ID's, shouldn't it just work? Or do I really need to fetch an object for each element in the layout and feed it into my thread in order to make it update the elements in a new activity?
You should run the update code for each Activity/View, although the XML included is the same, each is a different instance.
My suggestion is on Restart verify is there is any modification to do in each activity, a simple way is to each Activity extend a BaseActivity that has this code.
I include a layout for adverts in my app, but on each activity that uses it, the adverts need to be reloaded.
If I call an activity from one that is using the same included layout when I go back to the previous activity it's still there.
I guess this is what you are seeing....
So you can also save that data inside sharedPreferences (if it is little data and primitive objets or parceable objects).
Also you can extend the Application class and store the data there and update every activity inside the onResume() method. that i believe is the best way to handle this. and this is quite simple to do.
Ask google about extending the application class and he will provide tons of results on how to do it. its an easy way to pass data between activities and/or keep a reference to a single object which you will use throughout the app. Just be carefull to clear it when you wont need it anymore because it will stay in existance untill the application is finished() (which comes with the application extension living thru the whole application lifetime).
I have a similar issue with this one:
Android: Multiple activity instances launched by same intent. Bring one uniquely to foreground?
I need to create a stack of activities, all created by using the same class: it is a class defining a news list, only there needs to be multiple children activities that are also news lists, but from different categories. (I do need to have these activities in a stack)
The trouble is I need to change data on each of these activities after they are shown, but I can't find a way to access each one of these activities separately, since they are all using the same class, so if I used static methods, I would change the data on all these activities at the same time. Ideally, there could be a way to use references of each activity, so that I can access methods on each one separately, but I don't think there is a way of doing this.
I might as well pass parameter IDs when starting each activity, and instantiate objects at the same time, for each activity, and using these IDs later access the respective objects' methods...
Edit to clarify: Let me use an example to what I am trying to achieve. I have an A class and I am using this same class to instantiate multiple activities, in a stack. After the creation of these activities, I need to alter data, say, on one of these activities statically, so by calling A.alterData(); , but not when the activities are created, so there is no way of doing this by starting the activities with different data.. Since there are multiple instances of this class, if I do so, this will result on altering the data on all these activities, that are using the A class. Would I be able to somehow use objects and methods to these objects to alter data on different activities that are using the same class?
any other ideas?
You could use an ActivityGroup. It basically holds a list of activities and you need to control the navigation around them. It sounds like it suits your situation. There are many examples of them that can be found through google.
How I would approach changing the data on the other screens is by using shared preferences. You can store whatever data you need in there, and then (through your activity group) when you change screen, the data is refreshed. This is faster and a little more efficient than restarting the intent every time.
Another way is to change the data in the background without the user noticing. This can be done because an Activity group loads all of the Activity it holds and they are always there in the background, running, unless the developer states otherwise.
You could grab a a hold of the appropriate instance of the class you want to change the data on and then just change it.
Does any of this make sense?
I can elaborate more if needed.
I would supply the parameters to each activity, such as:
intent.putExtra("category", categoryId);
That way you aren't managing too much global state.
About changing the data - if you are talking about refreshing the data from its original source, then you should probably be doing this in the onResume() method of the Activity. Check out the Activity Lifecycle.
This has a few benefits:
you will have access to all of the context of that Activity
you won't have to do something nasty like access another Activity's data
you won't waste time refreshing data the user isn't looking at
Even if you have to make updates to the data, there are ways to make sure each Activity "minds its own business".