Thanks, Dianne, and others. This is what I needed to know. I know I can async preload Drawables and Bitmaps (there is an official tutorial, too), but it seems that my custom View is so complex that it takes 1 second to instantiate (even if its drawables are preloaded). And I need to *instantly* appear when the Activity is displayed that uses it. This is the reason I preinstantiate my View to a static (yes, I take care to null it out, so there will be no leak).
Assume I have Activity A and B. Is the below solution allowed then (all in UI thread, just at different times): 1. From Activity A: sStaticVar = new MyCustomView(this.getApplicationContext()) 2. From Activity B onCreate(): mRootLayout.addChild(sStaticVar); // instead of "addChild(new MyCustomView(this))" or "new MyCustomView(getApplicationContext())" In this way, each time Activity B is must be displayed, it will display instantly. My SystemClock measurements seem to confirm this. On Jun 27, 12:23 am, Dianne Hackborn <[email protected]> wrote: > No, it is not safe. Don't do this. > > The documentation is very clear about > this:http://developer.android.com/reference/android/view/View.html > > "Note: The entire view tree is single threaded. You must always be on the > UI thread when calling any method on any view." > > This wasn't written to mislead people into thinking that it works a > different way than it does: it is because it is true, the view hierarchy is > single-threaded, and it is explicitly not designed to be used from multiple > threads. > > If you think that not seeing checks about which thread calls are being made > on indicates that something is safe to use from multiple threads, you > should probably stop whatever multi-threaded programming you are doing and > rethink it. :} > > Even instantiating a view from one thread and attaching it to a view > hierarchy in another is not safe, because many views will internally create > Handler objects that are bound to whatever thread they were created on, > causing you to have parts of your view hierarchy running on the wrong > thread with bad results. > > On Tue, Jun 26, 2012 at 2:00 PM, Tamás Kovács > <[email protected]>wrote: > > > > > > > > > > > It works seamlessly like a charm. It would be nice to know if this is > > supported/acceptable generally. > > > I hope we'll get an answer from the Android guys/ladies. > > > On Jun 26, 10:53 pm, Justin Anderson <[email protected]> wrote: > > > I'm not sure, but I doubt it... Have you tried it? Did it work? > > > > Thanks, > > > Justin Anderson > > > MagouyaWare Developerhttp://sites.google.com/site/magouyaware > > > > On Tue, Jun 26, 2012 at 2:27 PM, Tamás Kovács > > > <[email protected]>wrote: > > > > > I know that the UI elements (View hierarchy) may only be manipulated > > > > from the UI thread. For a background operation, the AsyncTask can be > > > > used, which offers event handers to reach the UI thread. > > > > > To be brief, is it allowed to instantiate a View (tied to > > > > getApplicationContext()) in a non-UI thread? This custom View > > > > descendant -- once instantiated -- is added to the view hierarchy from > > > > the UI thread. So only the constructor call is done inside an > > > > Asynctask.doInBackground; its attaching (addView(...))to the > > > > Activity's root layout hierarchy is still done in the UI thread. > > > > > (I pre-instantiate the View in an asynctask because when it's needed > > > > in an Activity, it must be instantly displayed.) > > > > > -- > > > > 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 > > > -- > > 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 > > -- > 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, and so won't reply to such e-mails. 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
