Android :: Volatile Reference A Safe Way To Pass MotionEvents Between Threads?
Jun 29, 2010
I am curious about the safety of this method I have considered using for passing touch events in my Android application (and testing my understanding of concurrency in Java). Here's the basics:
I have a SurfaceView hooked up to SurfaceHolder.Callback to get user input events, mainly the onTouchEvent callback. After the onTouchEvent method is invoked, I see if event.getAction() == MotionEvent.ACTION_UP and, if so, call a method I have named postTouchEvent which is a member method of my app thread that updates the application's state and draws to the canvas. Code...
Now I understand that it is certainly not atomic, but since I treat it as immutable after receiving it from framework, won't this work? (Instead of synchronizing the post method and the if statement, which I have no problem doing, but I'm asking to learn.)
Here are my thoughts. I know I will have a valid reference to the object but I am unsure in what state I will actually see the object. While testing everything is working out just fine but I am aware of how uncommon threading exceptions can be, even if something is broken.
Also, I can see one problem with this: If another MotionEvent comes though, it's possible that inputEvent in the run() method will be set to a different event than the one that was referenced when this.mInputEvent != null was checked, but this really isn't an issue.
So, is there anything I am missing or, for my purposes, should this be ok?
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Sep 11, 2009
I decided to start pipelining input to increase responsiveness in my games. Basically what I do is when the activity receives a Key or Motion event, it sends it to a feed method in the game, which encapsulates it with a time and whatever else I need and puts it in a queue then immediately returns so the UI loop is never held up waiting for long. The main loop later processes the queue, applying the events in it at the appropriate times.
This works great and makes the games snappy, although now I'm starting to miss touch events intermittently. I realized that the events could be recycled objects and that could make them not safe to queue. Is this the case or is it safe to queue them for deferred processing like I'm doing?
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Nov 15, 2010
Let me give you the scenario.
Say that my first Activity that loads up, also creates a thread, which will run indefinitely in the background.
Now, if I move to another Activity, I assume that the thread that I initially created in the main activity will continue to run.
So, now to my main question - in order to manage this background thread from other Activities, is it safe to store a reference to that thread in a singleton object?
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Jan 9, 2010
Currently I have two threads, other than the UI thread, which need to communicate with each other. Thread one needs to be able to send messages directly to thread two, and vice versa. What is the best way to implement this?
At the minute, my code looks like this...
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Mar 9, 2009
I want to pass a class reference to an activity, and then the activity will construct the view according to the content of the class.
How could I implement this function?
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Jul 17, 2010
I'm using a timer which needs context..
Now i have the following code ...
Is this safe to use , or may i be leaking the context here?
btw. this is in a broadcastreceiver.
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Jun 24, 2009
I have a service running in the background.I have a background thread that gets a reference to the service from the application's main activity. But when the background thread calls a method in the service to display a toast, I get the "Looper not initialized exception".Why,if I have a valid, bound reference to a Service, does this still happen?
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Jan 27, 2009
If I setOnTouchListener for a view the only events I get are ACTION_DOWN events. What do I need to do to capture ACTION_MOVE events which should occur when the user drags a finger across the view?
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Apr 13, 2010
What are the advantages/disadvantages in placing a lengthy network access code in a thread in an activity or a thread in a service? How would it affect the application? I am writing a streaming audio player and from what I've read so far putting the code in a service will still end up blocking the application so a new thread is needed, does anyone know if it makes more sense to put this piece of code in a service.
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May 12, 2009
What I want to carry out is that the handle of the SlidingDrawer will be dragged by my finger, and when My finger leaves the screen, the handle of the SlidingDrawer will be just stop there and don't slide to top or bottom.
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Jul 13, 2010
I was just on there yesterday i go into browse tonight and now all of a sudden it says pass world invalid from last night till this morning i tried typing in the little letters they had and I cant read it so I go to the google site. I put the info in and it says sorry account has been terminated for terms and conditions I didnt even do any thing to violate them?
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Mar 1, 2009
To be plain, the android / xml widget reference material is poor at best.Rather than approaching the controls from an xml point of view, its all driven from a class point of view, which is clunky when you want to figure out how to build a good xml UI.Is there any decent documentation with design in mind (tag names, attribute names, etc) or is it just figure it out and struggle through the best you can? I'm on my 2nd android app and losing patience with hunting and pecking for the correct attributes / tags.
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Jul 15, 2010
Is there one? I have "Professional Android 2 Application Development" by Meier and "Teach Yourself Android Application Development in 24 Hours" by Darcy/Conder. Both are mediocre at best. Neither is a decent REFERENCE, but rather they are basically structured as tutorials, without nothing in the way of reasonably comprehensive API documentation (which also, BTW, is woefully inadequate on the android.com site). And no sort of in-depth discussion of the structure of the system, so one could perhaps understand it rather than simply using the (inadequate) cookbooks.
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Aug 31, 2009
Is there any sort of xml reference?
I found this which turned out to be invaluable for me http://groups.google.com/group/android-developers/msg/d334017d72909c79
but I can't figure out how I was supposed to know how to do that, had I not found that post.
I know that the api reference has xml attributes listed for many of the classes... but what about xml tags? Where is it documented that I could build a shape using <padding>, <corners>, <solid> tags?
I'd really like to know where I can find such documentation.
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Oct 19, 2010
I want to write an application that will log down whatever I type using the Android keyboard.
The purpose is to have a backup of all the keyboard entries.
Is it possible?
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Oct 28, 2009
I have a custom view that needs a reference to the activity that created it.Dianne Hackborn said in another thread: >Give your view a reference to the activity (or a Java interface it implements) and call back through that. >Much much MUCH more efficient than sending a broadcast. >See all of the standard view and view subclass callbacks for examples.
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Apr 28, 2009
How i can get a reference to the digital keyboard? is the keyboard added to the activity? how i can set a other style to the keyboard? Where i get a documentation of the digital keyboard?
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Aug 25, 2010
I have a jar that I need to reference from my Android project. I also have the src of the jar, so I could include it in the project itself. I was wondering if referencing a jar vs. compiling it in with the project using Dalvik makes any difference in terms of final Dalvik package size that gets generated.
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Jul 29, 2010
I have an object that is used for calling callback functions ----- static jobject o;
I have assigned the callback function to that object through a pointer, env -----
o=env->NewGlobalRef(callback);
The same pointer, env, points towards the function CallVoidMethod( ) that uses JNI to reach to the java code.
env->CallVoidMethod(o, methodId, pDeviceId, deviceStatus, statusReason, connectionProgressInfo);
However on calling this function, the system is getting crashed, and VM says that it's an invalid reference to static jobject o and then it crashes.
My code is as follows :
CODE:..........................
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Nov 3, 2010
Object getThisObjName= new Object();
I'd like to get the name of an object reference.
Is this possible via reflection in Android?
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Aug 20, 2009
I have a tab with an activitygroup as the intent of tab1.
My code of the activity(group):
CODE:..................
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Jun 19, 2010
Where can i find a Reference Chooser like this: http://www.vogella.de/articles/Android/images/first46.gif
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Feb 23, 2010
I am trying to get a reference to the android internal class PhoneWindow (android.policy.PhoneWindow) object from an application. I would like to call a method on it (specifically I would like to call getDecorView on PhoneWindow). How do I do this?
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Apr 2, 2010
I have a Timer in my application, and would like to allow the user to set the timer, and maybe cancel it in another execution of the application. To do that, I need to have a reference to the Timer created in the first execution. How can I obtain that? Is there a way of storing/retrieving memory addressed?
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Apr 30, 2010
I've created a class that extends drawable that I'd like to reference inside a resource xml.
I happen to need it in a selector, like so:
CODE:.................................
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Jun 25, 2010
I am developing a study project using the mosembro (mobile semantic browser) project inside my Android project. I am using Eclipse and I created my project, downloaded / imported mosembro and included in my project's build path.
So now my code needs to refer to a resource in the mosembro's project. I want to do something like this: String commonJS = getScript(R.raw.common);
In this snippet, I want to load a javascript file from mosembro's project: res -> raw -> common.js so I need the java syntax to get "R" (precompiled resource-class) of Mosembro from my HelloGoogle project.
What is the syntax to replace the R-class of this with the included project's R-class.
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May 4, 2010
How do you get a reference to the window from outside of an Activity or from the context? Is it possible to access the window without having a reference to an activity?
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Dec 3, 2009
instead of referring the custom widget by a fully qualified class name, is it possible to map with a shorter name. Like it happens in ant custom tasks (though properties file).
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Mar 9, 2009
In my layout xml, I have: <TabHost android:id="@+id/tabhost" android:layout_width="fill_parent" android:layout_height="fill_parent">
<TabWidget android:id="@android:id/tabs" android:layout_width="fill_parent" android:layout_height="wrap_content"/>
</TabHost>
My question is how can I get a reference to TabWidget object. I tried this: mTabWidget = (TabWidget) findViewById(com.android.internal.R.id.tabs); but this won't compile since 'com.android.internal.R is not visible. And then I try change the id to android:id="@+id/tabs" but I get a run time error saying: "Your TabHost must have a TabWidget whose id attribute is 'android.R.id.tabs'"
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Jan 25, 2010
how will you know that this thumbnail points to which actual image in the SD card. I have a problem with MediaStore.Images.Thumbnails displaying blank previews. Though I followed mihai fonoage part 2 on how to load it properly by using scaling. Still, I got duplicate images. So instead of using MediaStore.Images.Thumbnails I used MediaStore.Images.Media instead but it loads the actual image but oading is too slow even if bitmap is scaled. That's why I was wondering if there's a way to know which actual image is the thumbnail pointing or is there a way to know the exact location of the thumbnail for this actual image (The other way around).
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