Android :: Activities Vs Views
Jul 8, 2010
I am working on an Android app that has multiple screens the user will need to navigate between and I am curious what the best practices are when switching between those screens. I am torn between creating a new Activity for each screen and simply changing the view (setContentView(R.layout.whatever)). The screens all share at least some variable values so I'm leaning toward changing views and using class level variables, but I'm worried a single activity could become very large and confusing with logic for multiple screens in a single file. I'd like to keep the code clean and separated, but I also don't want to be passing several variables around between views if that isn't needed.Being new to Android development, I'm hoping some more experienced members of the community could share their thoughts and let me know how best to handle it
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Aug 3, 2010
I start a browser and from the browser,I start a video which occupies only a small part of the screen,say the bottom right corner.
Now the browser will be pushed to the 2nd position in the window order and Video will come to the first position. Is it possible that browser can have the control for active window and receive the key events though the video is the Top Most window.
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Apr 24, 2009
I've got a activity showing the user a list of songs to play, and when he opens a song I launch an activity which embed a player.
My problem is that when i finish playing i call "this.finish()", but when the user reopen the player, the "onCreate" is launched and it seems that the GUI is building itself "again".
I've tried to not call "this.finish()" and call the Activity.startActivity on the father, but with this way, when I clic on the "back" button on the emulator, I get all the players playing in the same time (they still exist).
So my question, is there a way to make an activity "a singleton" or to freeze it to be retrieved later (It can't be able to retrieve it with "back" button) or a way to cache all the constructions so to not have to do it again ?
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Jul 16, 2010
I am developing a Music Player and I have a view flipper to control all the artist view, album view, so on and so forth. What I am doing now is that I have list view in each view of the view flipper. However, I do not want to put all my codes inside one activity but rather, to have different activities for each view. Is that possible to implement?
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Jul 31, 2010
My situation is the following: I have written one MapActivity class that is able to display a set of places as well as single places. On startup, the application creates an instance of this MapActivity and displays multiple places. If the user clicks on a certain place, then a new Activity is launched that shows the details of the selected place. This activity has a menu item that allows the user to view the place on a map - this causes that a new instance of the MapActivity is created, except that now only this single place is displayed.
The problem now is that if the user navigates back to the first MapActivity (the one that shows multiple places) the tiles won't be loaded anymore + sometimes OutOfMemoryErrors are encountered. According to the Android JavaDocs, it is only possible to have one MapActivity per process. However, I don't want to define my MapActivity as a singleInstance/singleTask, since the user should always be able to navigate back to the first MapActivity that shows multiple places. I have seen that the Google Places app (which has come with Google Map 4.4) for Android uses multiple MapActivity instances. How is this possible?
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Sep 13, 2010
Trying to understand the Android framework model. I have an application that needs to have several threads running. On thread gets GPS fixes, another picks up GPS fixes and pushes them to server, and yet another occasionally polls a server for dispatched orders. Some of these threads update status Views as well.
Since I am new to Android, the application framework model hasn't clicked for me. Where are these threads started? Right now I start the threads in the initial Activity, but if I understand it right, once that Activity goes invisible it is stopped. Furthermore, I have to track GPS and network statistics so that I can have a View which may (or may not) be the active View.
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Jun 10, 2010
I am attempting to learn how to develop on the Android platform but do not quite understand the relationship between Activities and Views, because according to the documentation an Activity is almost always linked to a UI object that the user can interact with, but if this is the case where does the whole idea of Views come in?
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Jan 15, 2010
I have developed some apps for Android, and this questions stays always:
How should I structure my UI? Should I launch activity after activity and leave the phone to make the "back" button, or should I choose more optimized, but more complex to implement, way with switching manually Views and then manually doing the "Back" button functionality?
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Mar 17, 2010
I've been programming in Android for two years now and just joined an Android project where they are using a TabActivity to host multiple Activities. It's unclear why this is better than rewriting the TabActivity to simply use Views instead.
TabActivity extends ActivityGroup which means TabActivity can host both Activities and Views. But what's the use of this capability? I was under the impression that Activities should be treated as individual screens of an application.
In short, what is an example use case where it's recommended that TabActivity should host multiple Activities rather than multiple Views?
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Jul 25, 2010
I am using a TabActivity (Main) with 3 TabSpecs
I am using Intents for the content of the 3 Tabs
TabA, TabB, TabC for example.
All these tab activities use common data that is stored in SharedPreferences
In the Main TabActivity I have an options menu which has a refresh option.
CODE:.............
This refresh uses an AsyncTask (updateCommonDataFromWeb) to reload the common data from the web.
I need a way to tell the 3 tab activities to refresh their views and rebuild their content from the newly downloaded data.
When the tab activities are first created they load the data from SharedPreferences like so:
CODE:..............
I thought about making a common method on each of the tab activities
like.... reloadViewData()
I thought maybe I could use the activity manager from the Main TabActivity to get the activity of the current tab like so:
CODE:.............
Unfortunately i cant get this approach to work, whilst activity is the correct instance its an Activity instead of a TabA,TabB or TabC
Maybe i've completely taken the wrong approach to the whole thing.
I have also read alot about not using Activities for tab content instead using views.
However I dont know what view to use to replace my <RelativeLayout /> as i cant use my R.layout.* as views.
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Aug 16, 2010
Are there design guidelines to help decide if an application with multiple views should be designed with multiple activities or just one activity and control the back button itself.
I've tried both. My most complex applications using one activity per screen. However, now that I'm successfully written an app with just one activity and handling the back button myself, I don't see any compelling reason to use multiple activities. The one activity application is much simpler and more straightforward.
What advantages of multiple activities am I missing?
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Feb 18, 2010
I'm working on an application using xml layouts.
I wish to know which is better:
1. Use few activities and change its contentview
2. Use an activity for each 'view' needed
If both works, in which case which option would be better?
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Jan 6, 2010
I have a simple ListView and on that ListView I have placed a number of custom defined Views. The CustomView has ImageView and two TextViews.
The CustomView also has a "stateful drawable" as background, so that the background image (a 9-patch) changes if you press the Row in the ListView. When pressing the Row, the background image changes to a Red-ish thing.
The problem is that when the background changes from the default greyish, all the Views in the CustomView (ImageView and TextViews) still have their greyish background and thus creates very ugly greay boxes on top of the now redish background.
What is the best way to solve that problem? I hoped that such things were handled automatically (as it is done in for example .NET), but I was wrong it seems.
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Nov 16, 2010
I am implementing a music player application in Android. My play list selection screen is implemented as a tab selector widget which contains a ListActivity inside each of the tabs: Artist, Albums, Songs.
I want to update the ListView in each of the ListActivity when I delete an item from any of the lists.
i.e. When I long press an item in the Artists list a context menu is drawn with "Delete Artist"
And it should delete all the songs from this artist in the Songs ListView, delete all the albums by this artist in the Albums ListView, and finally delete the entry for the artist in the Artist ListView.
Each of the ListActivity has its own fillData() method, which updates the ListView when the button in the context menu is pressed.
How can I call the fillData() method of the Albums ListActivity after I update the ListView inside of the Artists ListActivity?
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Feb 28, 2010
I want to populate a table, defined in layout xml file through the programmatic way. I have define Table with a single row defining its header, with all the attributes set. Now i want to know a way so that i can just replicate that header row in the table with new content.
I tried using inflator inflate(int,view) method, but at runtime it showed up with error.
Here is the XML code for the layout file defining the table
CODE:.................
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Mar 6, 2010
I have the following XML code:.................
The idea is to change the views, whenever I press one of the radio buttons. When I press a button the first time everything works out fine, but the second time I press a button, I get an IllegalStateException, and I can't quite see why I'm getting this.
Also, the Activity seems to set all my global variables to null, which is why I have to create them every time I switch from portrait to landscape or vice versa. So I would like to know if there is a way I can save my views in the Bundle, or any other way in which I can permanently save my views, so I don't have to add or create them every time, I flip the phone. And whenever I flip the phone, it seems that it rereads the main XML file, causing the RadioGroup to be set to 2D even if the 3D button is checked. This is because I've said the 2D button to be checked from when the app is first created, but I would like to also save the state of that RadioGroup.
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Jun 16, 2010
How do you align views relative to the "middle" part of another view? I think it is best explained with a pic of the UI I'm trying to create in android.
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Jun 30, 2010
how to call BarCodeScanner, and return the value to a field.so now, i have a toast that says "successful scan" and then i want to pass the result to a new activity. when i comment out my intent, everything works (minus the passing of data/switching of screen, obviously) but when i run my project as is, it FC's no errors reported by eclipse in code or xml. any insights?
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Jan 25, 2010
Is there any way to query a root view of an activity for all of its child views even before the root view or its children have been inflated? I guess what I'm looking for is whether a view knows ahead of time what children it will have before it gets inflated, and can I get that list in some way. Bizarre I realize, but I think it will help me with some unconventional automation testing I'm working on. I haven't found anything in the API like this.
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Mar 7, 2010
Let's say I have a LinearLayout, and I want to add a View to it, in my program from the Java code. What method is used for this? I'm not asking how it's done in XML, which I do know, but rather, how can I do something along the lines of (One View).add(Another View) Like one can do in Swing.
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Jan 2, 2010
I'm new at this, I have not seen any examples on changing Views, what I want to do is when a user presses a button I want to show a map view based on their input on the first view.
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Aug 16, 2010
im having a problem getting a custom view that i created on the xml layout file. i have a class named DrawingLayout which extends FrameLayout. it is found in the package Drawing
as stated on this page http://developer.android.com/guide/topics/ui/custom-components.html i used the following decleration in xml
<Drawing.DrawingLayout ... />
but whenever i run the program with that decleration i get a runtime exception error on SetContentView( ... )
is there something im not doing well? If you need any more details please tell me because i cant seem to figure this one out.
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Feb 18, 2009
I 'm beginner in Android ,To start with i was asked to do a simple task ,i need to make blue and red screen appear on the screen alternatively , to achieve this i wrote two layout files 1. main.xml -- for to display red screen 2. sub1.xml -- for to display blue screen
In oncreate() i wrote
for(int i=0;i<20;i++) { setContentView(R.layout.main); try { Thread.sleep(500); }catch(Exception e){} setContentView(R.layout.sub1); }
but this doesn't work ,why ? Please help to understand the concept
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Apr 13, 2010
I currently have one Scrollview which contains a table layout and one list in my activity. Now my problem is that I wanted to move both of them(Scrollview and list) together and with proper synchronization... So if scrollview is being scrolled then listview should also scroll with the same distance, and vice versa...
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Mar 16, 2009
whats the exact differences between 1. LinearLayout lin = LinearLayout.inflate (ctxt, R.layout.bla, null); parent.addView(lin); and 2. LinearLayout.inflate(ctxt, R.layout.bla, lin);? Both doing the same thing, or?
I got sometimes a different behavior.
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Aug 27, 2009
I am using 5 views in one LinearLayout my app.While going to each view i am removing previous view by calling linearlayout.removeAllView(). But I think this is not removing my previous view becoz when i checked memory usage.My app memory is keep on growing.and Becoz of this i am getting low memory :no more background process error and after sometime app is getting hang and then it is exiting.Please help me to solve this problem.How can we clear memory or how can we remove view.Its very urgent.I am using system.gc() and also i cleared object also but no use... I tried to use different activity for each View but at that time low memory is coming immediately.
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Aug 30, 2010
I have a login page which has a Advanced button. The button sets a view where a user can add some information. When I click save, it goes back to my main view (loginpage) and all info is cleared? How can I save the state of the first view when navigating away and then back to it?
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Jul 13, 2009
I have the instance to my activity, and I want to get all the views that are in this activity. I need to add a listener to each view, for any activity. That means I can't user findViewById. Is there any way to do this? I was hoping for a activity.getViews() or something, but it doesn't exist.
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Jul 10, 2010
Is there a way to get every view that is inside my activity? I have over 200 views including buttons, and images, so i want to be able to access them by using a loop.
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Oct 3, 2010
I have a set of views that are populated with data from an online database. The context menu has a "refresh" choice that re-reads the online database and updates some attributes of the views, like setText and setChecked for some buttons. After the various setTexts and such, I invalidate the Views. However, they are not immediately redrawn. In fact, they don't get redrawn at all unless something like a rotation happens to cause a redraw of the screen. How can I initiate an immediate redraw after the refresh is complete?
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