Force close on second start of application

I am developing an Android application, and when I star开发者_如何转开发t my application 2nd time I am getting force close error. Following is my logcat:

06-07 16:08:12.763: ERROR/AndroidRuntime(3293): Uncaught handler: thread  exiting due to uncaught exception06-07 
16:08:12.773: ERROR/AndroidRuntime(3293): java.lang.NullPointerException06-07   
16:08:12.773: ERROR/AndroidRuntime(3293):     at com.androidpeople.tab.MobiintheMorningActivity$t2.run(MobiintheMorningActivity.java:209)06-07    

16:08:12.773: ERROR/AndroidRuntime(3293): at java.lang.Thread.run(Thread.java:1060)

Your logcat capture is telling you that in your source file MobiintheMorningActivity.java, at line 209, you're using an object which is null. Seems pretty straight forward.

To prevent the application from crashing place try{//insert code} catch(Exception e){//todo when something fails}

On the NullPointer, try debugging your program and locating the null

Huh, I feel that I should give some more useful comments than those stupid answers from Captain Obvious fellows. Usually such problems happen because developer doesn't fully understand Android Application life cycle. When you start application second time, actually you re-starting an Activity, not whole Application, so for example static data may remain from previous activity launch, even you received onDestroy() event for that activity. If you created any threads, they may remain alive (if you don't take special actions to stop them gracefully, which is not often a trivial thing - for example in my case a thread was reading data from InputStream.read(), a blocked call ending somewhere in native code, and it was not possible to interrupt it, either via Thread.interrupt() or via InputStream.close() called in other thread. But it is another story).

So, from design point of view, if you're using threads, you must keep in mind that you may be attempting to start a new thread while the old one hasn't finished yet.

Whole application will be fully destroyed when OS decides so, when it will need to recycle memory. If your app is running some threads in background, the app may be considered alive, even you do not have open activities at the moment, and the app may avoid recycling, causing some sort of memory leak. This is considered as a bad coding style.

In your case the thread seems to reuse some old data, which you probably expected to be re-initialized by Activity re-start. Or you may have another thread concurrently running from previous launch and sharing data with Activity being started second time, and it reads/writes data while you're initializing them in the second start of the Activity, for the second start of the thread.

So you need to make sure that you do not start another thread before the first one quits. You may consider using a Local Service for such purposes, but you would need to launch threads for background activities (to not perform them in main event thread of the application, which is common for services and activities in the same Application instance), or in AsyncTask. A Service simplifies things a bit because it is not interrupted by Activities start/end, so you can somehow handle an async process (in your thread) between activities restarts. So activities should put requests to service to perform long jobs, and query its state from service (or receive notifications, for example via listeners, which quite OK for local services). So, starting an activity, you should check what the server is doing - probably it already performs a job from previous activity start. Your activity may request to stop the job (if you already didn't do so when previous activity finished), and wait for job cancelation, which generally may be not a quick thing, and should be made asynchronously). Of course you may implement the same approach without a service, just in that thread.