Android :: Caching Views And Activities
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 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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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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Nov 5, 2010
My app makes several calls to getFromLocationName from the android.location.Geocoder; class, this is currently handled in my activity which also displays some data depedant on the results of that call.
This can be quite slow, for example before the activity can load it first has to complete the various calls, and that is reliant on a network connection.
Once I have the results, I don't really need to refresh that (I mean how often do locations and geo coordinates change?)
My question : How can I best avoid having to query for this data each time my app runs. Should I do something with a service that loads them all on startup? (could be quite slow if it has to query 50+ times). OR should I make the call, store results in SQL, then only query next time if I don't currently hold the results?
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Feb 2, 2009
I am performing hundreds of calls to a single content provider to perform various insertions, updates and deletions. After profiling my application, I have noticed that the ContentResolver class takes approx. 30ms to retrieve the corresponding content provider object for each call. Is there anyway to retrieve a reference to the content provider rather then going through the ContentResolver every time?
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Apr 27, 2010
I am retrieving a list of images and text from a web service.The images are getting displayed in the list view. But the problem is, when i scroll down the list the entire images are getting loaded once again. When i scroll twice or thrice there is a OutofMemory occuring.Can anyone tell me how to cache the images and also to avoid the loading of the images that are already loaded when i scroll down. I have tried to increase inSampleSize but it didnt work.
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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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Apr 19, 2010
That is the only thing I can think of. When I generate a random number (for the radius of a ball), after a while, the radius goes to one number and sticks that way. I've even tried setting the random number value to 0 before getting the random number, and java.util.Random must be at fault, it still gives the same random number. Here is an apk if you would like to try it yourself: http://74.118.194.50:84/Balls.apk
Here is a snippet of the code (I would rather not release the full source): <code> Random randomizer = new Random(System.currentTimeMillis()); int hw; hw = randomizer.nextInt(95-15+1)+15; </code>
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Nov 24, 2008
I don't currently have a data plan. Since I'm on WiFi 95% of the time, I don't plan on getting one. The only thing I haven't been able to do easily (without a data plan) is use Google Maps while driving/walking.If I load the maps before leaving a WiFi hotspot, my location is tracked and I can pan around the map. Of course, as soon as I want to view another uncached portion of the map, I can't.Maps are small, and it would be perfect if I could cache maps for a certain area - say everything within 100 mi of my house. Any ideas?
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May 6, 2010
I am trying to cache my viewgroup to a bitmap and blit this to screen instead of calling dispatchDraw on the group while scrolling for performance reasons. This works quite well on 1.5, but has ugly scaling artefacts on 1.6 and newer for high density screens. Because of my 1.5 compatibility I can't find a way to set the density of my cached bitmap.
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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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Jan 14, 2014
I'm trying to employ HttpResponseCache to cache each HTTP-request sent with HttpURLConnection.
why I get hit count always zero?
Code:
HttpResponseCache.getInstalled().getHitCount()
Usage:
Code:
for(int i = 0; i < 2; i++){
try {
HttpURLConnection connection = (HttpURLConnection) new URL("http://www.google.com").openConnection();
connection.setUseCaches(true);
if(i == 1){
try {
[code]....
On 2'nd run I have "NOT cached" in console and hit count == 0.
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Jul 25, 2010
I really like the new Google Navigation, and it would be really handy for when I go abroad cycling, apart from the roaming charges. Any apps that can cashe the maps and store them, or must I always be connected?
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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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Nov 9, 2010
Opera Mobile 10.1 Beta Brings Turbo-Powered Browsing to Android.This is supposedly different than what's in the market.This forum is stale lately, so let's mix it up.I still like XScope, but Firefox is promising, and though I have NEVER been a fan of Opera, I am gonna try it.The one touch pinch zoom on Xscope is really tough to give up
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Jul 28, 2009
Im currently developing a system where the user will end up having large arrays( using android). However the JVM memory is at risk of running out, so in order to prevent this I was thinking of creating a temporary database and store the data in there. However, one of the concerns that comes to me is the SDcard limited by read and write. Also another problem that comes to mind is the overhead of such an operation. Can anyone clear up my concerns, as well as also suggest a possibly good alternative to handling large arrays ( in the end these arrays will be uploaded to a website by writing a csv file and uploading it).
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