Android :: Avoid Non Static Inner Classes In Activity?
Jun 17, 2010
Since I seem to have caught two activity references in a heapdump, where the Activity is set to singleTask. Romain's advice on avoiding memory leaks includes: "Avoid non-static inner classes in an activity if you don't control their life cycle, use a static inner class and make a weak reference to the activity inside"
What does this mean exactly? I can't find any examples, positive, or negative for this rule. I do have some non static inner classes in my activity. Most of them are anonymous inner classes like this one. I see hundreds of them in the samples:....................
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Oct 28, 2009
I frequently run into the problem that I have to preserve state between several invocations of an activity (i.e. going through several onCreate()/onDelete() cycles). Unfortunately, Android's support for doing that is really poor. As an easy way to preserve state, I thought that since the class is only loaded once by the class loader, that it would be safe to store temporary data that's shared between several instances of an activity in a static Bundle field. However, occasionally, when instance A creates the static bundle and stores data in it, then gets destroyed, and instance B tries to read from it, the static field is suddenly NULL. Doesn't that mean that the class had been removed and reloaded by the classloader while the activity was going through a create/destroy cycle? How else could a static field suddenly become NULL when it was referencing an object before?
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Mar 9, 2009
I have been finding it convenient to extend Handler in many of my activities to handle messages specific to the activity. The handler sublass is an inner class of the activity and needs to access its state. I am wondering if there is any performance difference between making the handler subclass static and passing in the activity explicitly in its constructor or making the subclass an "instance class" and letting the vm worry about my accessing members of the containing activity.
The static approach:
CODE:.............................
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Jun 24, 2010
I see a lot of Java code where android prefers to have developers use static inner classes. Particularly for patterns like the ViewHolder Pattern in custom ListAdapters. I'm not sure what the differences are between static and non-static classes. I've read about it but it doesn't seem to make sense when concerned with performance or memory-footprint.
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Feb 14, 2009
I am having trouble running my application as every time i try to run it the simulator gives me a an error.
I looked through the Documentation but I couldn't find anything on user created classes.
CODE:.................
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Mar 3, 2010
I'm writing a game for Android. My GUI has the following basic screens (i.e. the information and interactions required on each of these would take up the whole display):
Main menu (let you start a new game, enter settings, see high scores, see about screen)
Game screen i.e. where the actual game is played.
Settings screen.
High scores screen.
About screen (i.e. credits and a back button)
Game over screen (arrived at when the game ends)
Pause screen (pauses game and can access settings)
The following are some example transitions the user might make between these screens:
1->2->7->2->6 (starts new game, pauses game, returns to game, finishes game)
1->5->1->4->1 (views about screen, goes back to main, views score screen, goes back to main)
I'm really confused about when to have just one activity that switches layouts and when to create new activity classes. For example, when my game loads, I have a "main" activity that loads the main menu layout. When you click the settings button, I launch a "settings" activity (which uses android's standard settings GUI). For the moment, when you start a game, I switch the layout of "main" to the game screen layout (which just contains one big surface view). I'm not really sure what the best way to integrate the game over screen, high score screen, about screen etc.
Creating a new activity for each seems really heavy weight to me. There's quite a lot of boiler plate code involved for each activity. Plus, communication between activities seems like a pain as you have to use bundles. Using just one activity means I can just share object fields directly. It seems that using layouts for the above would be more compact. Can anyone give me some recommendations?
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Oct 13, 2010
I have total 3 activities.
First activity(A) starts second activity(B). From Activity B, 3rd activity(C) is called.
Activity B, shows list with checkbox to select items and single OK button. On clicking OK button Activity C is called with selection.
When user clicks BACK button in Activity C, by default Activity B is displayed (with selected checkbox).
I want to display Activity A when BACK button is clicked in Activity C.
How to achieve that?
I have handled OnKeyDown() in Activity C to startactivity(A). it is working. But when user clicks BACK button on Activity A, again Activity C is displayed. while application should end.
In this direction how to skip Activity B is ever called?
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Sep 8, 2010
I am new to android development and am currently working my way through the "Hello..." Tutorials on the developer website.
I got stuck on the Tab Layout walkthrough and the only way I could resolve it was to put each Activity Class in a separate .java file.
I was wondering if all Activities need to be in separate .java files, or am I missing something.
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Sep 13, 2010
I have a server socket bound to a port and I want to send notifications using NotificationManager when a client connects. This all works well.
What I want to avoid is sending notifications if a specific activity is currently being used by the user. E.g., I'm trying to avoid something like GMail notification if I'm already reading email.
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Nov 5, 2010
I go back and forth about how to name activity classes.Activity seems to imply a verb, like EditContact, for example.But that seems more like what one would call the Intent that triggers EditContact.Should the activity be named ContactEditor instead?
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Sep 1, 2010
Not sure how to figure out which android project on android.git.kernel.org corresponds to the classes extended in some of the app examples in the SDK such as Activity, Intent, and ContentProvider.
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Nov 17, 2010
Static Layout for whole app that must be in all Activity
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Sep 8, 2010
Why is the use of static final variables encouraged to declare constants over just final variables? The use of static sounds logical when there will be many instances of a class but is this argument correct when used for a Android activity. In fact, since the Class instance will be around even after the activity finishes and is eventually garbage collected, it seems like all these constants will still be in memory until the class loader is around. Also, does the compiler inline non-static final variables(ints and String) just like it does for static final variables?
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Jul 28, 2009
I have fixed the activity screen orientation to portrait on AndroidManifest.xml file. When I open or close the keyboard the activity gets restarted. How to avoid this restart?
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Aug 11, 2009
when i open my keyboard, it restarts the activity. i use only landscape mode and dont want the activity to restart.
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Jan 5, 2010
I am new to Android, and I haven't developed any app regarding databases on Android yet. So I have a few basic questions. I am after a good database class sample, that will let me to run the CRUD operations. I would like to use it as a static class
like: clsDB->Select("select * from clients");
or objClient->Delete(clientid);
I am wondering if someone, can share his database classes, if more people share the best. Also I have in mind to reuse this class in multiple ways, I will have services, activities etc...
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Jul 14, 2009
I just ran into a situation where it looks like a static variable reference is persisted across activity sessions. I didn't expect that because I thought that when an activity exits, it's de-referenced and garbage collected. I am wondering if anyone can shed some (more) light on when the VM eliminates object references for Activities and Services and in particular when static variables get reset to default values?
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Aug 26, 2010
I want to clear variable value when will i close activity.
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Jan 15, 2010
I wanted to create a static options menu for all my activity screens. I dont want to override onCreateOptionsMenu() in each activity. Since Menu class is an interface with a huge number of methods, its difficult to create a static object of the implementing class.
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Mar 30, 2010
i want to display a msg to the user (msg box or Toast) when exception happend in a static SQLite Database class that i use. the problem is that i cant call a non static method in a static class , how can i handle this. this is the class
private static SQLiteDatabase getDatabase(Context aContext) {
and i want to add something like this in the class when exception happen but context generates the problem of reference to non static in static class.
Context context = getApplicationContext();
CharSequence text = "Hello toast!";
int duration = Toast.LENGTH_SHORT;
Toast toast = Toast.makeText(context, text, duration);
toast.show();
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Feb 7, 2010
I'm having some issues with the old "Cannot make a static reference to a non-static method" error in my Android program. I am creating a sand falling game (similar to the Powder Game) and I created a class called Control to create a Control Bar at the bottom of the screen with a slider for brush size (that works fine) and a button to pop up a Dialog to allow users to pick the selected element. However, when I call DemoActivity.showDialog(2) from my code, it gives the static reference to non-static error (DemoActivity is the main activity of my application). I also tried changing it to just Activity.showDialog(2), but I got exactly the same error!
Here's my code:
CODE:................
I fixed it by adding the following to my Control.java code:
CODE:..........
And then calling control.setActivity(this); from my onResume section of DemoActivity.java!
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May 26, 2010
I am modifying the source code here: http://thinkandroid.wordpress.com/2009/12/30/getting-response-body-of-httpresponse/
I get this error:
code:.............
This error is line 13 on the second box.
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Mar 18, 2013
I have Eclipse Juno and I'm working on an app with that.
The main activity will have a scrollable menu that takes you to all the other activities.
So the general structure/outline right now:[HIGH]Relative Layout ImageView (header logo type thing) ListView (the actual scrollable menu)[/HIGH]Here's the problem though... I can't find any simple list tutorials. I can easily make a single line list work but I need to make a two line list and one that is static, not dynamic and no examples are out there for that. It's like if you want to make a 2 line list, you can only learn how to do it in the most code-heavy ridiculous way possible.
Essentially what I am looking for with the list is this: Item one: Centred, bold, non selectable title (Resources)
- Item two-??: two line list items, click-able to a new activity, title of the section on first line, description on the second line.
- Item ??: Centred, bold, non selectable title (Tools)
- Item ??-??: two line list items, click-able to a new activity, title of the section on first line, description on the second line.
Nothing dynamic that is ever going to change, no super complex wonkey calculations, just to simply have the data set in stone (preferably via XML) and to call it into the list.
I experimented with some of the other list views and no matter what I did, I could get, via editing the resources and NOT using Java, more that one item on a single line but it wouldn't format it properly according to the layout I guess because I haven't got the ID correct or whatever I don't know.
I mean, all the examples I've seen for a 2 line list are extraordinarily over-coded and just bloated. I mean I have a website I am still working on in C#/ASP.net that has far more complex things in it with half the code that I've seen for the examples of the two line lists.
I tried on my own to figure it out (I am decent with C# and vaguely familiar with Java, self taught, and programming for some other systems like Python, again all self-taught), but like ALL coding references, they're organised by the actual code you implement (that you don't know) instead of by what you want it to do (so you have to search the whole code base to find something that you don't know what it's called but know what it does). >:C
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Sep 15, 2010
Why should a static method in java accept only final or non final variables within its method, but not static?
For example I have the following method:
CODE:.................
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Oct 29, 2010
I want to use the accessibility classes, but I'm a begginer in android programming and i can't understando how to use them. I don't find any example using these classes. Somebody can give me some use examples? Another thing Can I set enable the Accessility mode in the emulator?
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May 18, 2009
I am writing a app, which has sort of plugin framework. public abstract class AbstractService {public abstract AbstractService getInstance(String name)..
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May 29, 2009
I have an apk installed in /data/app. I want to use the class methods in there. Here is what I tried. code...
I got "ClassNotFoundException". By peeking into the apk, I don't see class files but classes.dex. I would assume SystemProperties class is in classes.dex. Why can I load it?
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Apr 7, 2009
I am developing sample Video Recorder for Android.Following is My code snippet.
CODE:............
But when i am trying to run in eclipse,am getting following errors. MediaRecorder.VideoSource can't be resolved. MediaRecorder.VideoEncoder can't be resolved.
I am using android-sdk-windows-1.1_r1 as my android SDK,and didn update this from 1.0 instead i installed it freshly.
I guess there might be some problem with the SDK.
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Mar 19, 2010
I am looking for the implementation of the IAlarmManager.I am interested in the scheduling done by the AlarmManager.setInexactRepeating method and so I started looking for the implementation but I haven't been able to find anything.Internally to AlarmManager, I can see that the actual work is being done by an android.app.IAlarmManager interface.After googling around for a bit there seems to reference to an implementing class called android.app.IAlarmManager.Stub but that is as far I get.I am working with Android 1.6.
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Oct 7, 2010
I have an app I am working on and being new to Android Dev I am running into a situation. I have a Scores class not extended from anything (Activity,Service, etc) but in the same package that needs to access SharedPreferences
public class Scores {
Context ctcx;
public Scores(Context context) { ctcx = context;
}
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