There are two reasons for this: 1. Both screen rotation and keyboard shown/hidden are configuration changes, which means that after the state changes the application's resources can have any arbitrary new values -- anything from specific strings (for ex in a particular language you may need a abbreviation when in portrait mode) to layout resources and anything else. Trying to keep track of, and update, any of these values that could have changed would require a lot of work in the system, and a fair amount of effort from the developer to help the system, so it is far easier to just restart the entire activity with the new configuration.
2. To be a correct application, you already need to deal with saving and restoring state so you will always be returned to the user in your previous state after being in the background. By relying on this same mechanism for configuration changes, we get to take advantage of the work the developer has already done, and also further encourage them to actually do that work which otherwise often only causes problems in the application in obscure cases, so can often be missed. For the case of a thread running in the background that wants to communicate back with the current activity, an easy way to deal with this is to have a static variable that is the "current" activity, which you set in your onCreate() and clear in onDestroy(). Then instead of pointing to the activity that originally started it, the thread can just retrieve the current value in that variable when it needs it. (And of course it will need to deal with the race where it can temporarily be null between the old activity being destroyed and the new one created... but if you are doing multithreaded programming, this should be familiar territory!) On Fri, Jan 23, 2009 at 9:52 AM, Stanley.lei <[email protected]>wrote: > > I rather agree with you! > > In fact, I could not understand why Google designs like this. The > keyboard action could impact the rotation, but why changing rotation > impacts the activity? In my case, the thread is destroyed, which will > destroy all tasks in the thread. In worst case, the user will have to > re-create their data from scratch. > > stanley > > On Jan 24, 1:47 am, cindy <[email protected]> wrote: > > Then android's implementation has problem. > > > > For example, if my application needs to create account, of cause, the > > key board will open first. After user typed in user name and password, > > then he clickes the "create" button.Request sends to server in a > > thread. After that, he closes the keyboard, the activity will be > > destroyed. So the callback function in thread to update UI will > > crashed. > > > > It happens exactly in my application. > > > > On Jan 23, 7:20 am, "James Patillo" <[email protected]> wrote: > > > > > I think what happens is that the activity's state is saved, the > activity is > > > destroyed, and then it is recreated with its saved state. This is the > same > > > thing that happens when the home button is pressed and the app is > reopened. > > > > > This just what I have come to understand, and may be wrong. > > > > > -----Original Message----- > > > From: Stanley.lei [mailto:[email protected]] > > > Sent: Friday, January 23, 2009 9:04 AM > > > To: Android Developers > > > > > Cc: [email protected] > > > Subject: [android-developers] Activity Issue on G1 phone > > > > > Hi all, > > > > > I met a very strange issue when I tested my application on G1 phone. > > > > > As usual method, I started a thread in an activity, and stopped the > > > thread in the onDestroy method. But to my surprise, when I tried to > > > slide down the keypad, the onDestroy method was called and the thread > > > was stopped, and more surprising thing was that the activity was still > > > alive and visible. > > > > > From the activity's life cycle diagram, > http://code.google.com/android/reference/android/app/Activity.html, we > > > can see that onDestroy is called only before the activity is shut > > > down. But my activity is still active and visible!!! > > > > > Who could tell me what the hidden story is? > > > > > Any reply will be appreciated. > > > > > Thanks, > > > > > Stanley > > > > > > > -- Dianne Hackborn Android framework engineer [email protected] Note: please don't send private questions to me, as I don't have time to provide private support. All such questions should be posted on public forums, where I and others can see and answer them. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -~----------~----~----~----~------~----~------~--~---
