Thank you for your help. It's great to learn some fundamental concepts. This is not just my first Android app, this is my first Java code.
On Jul 2, 11:35 pm, Bob Kerns <[email protected]> wrote: > First, don't rush to learn about threads and threading. There's a lot > to learn, it's subtle, mistakes are easy to make but hard to detect > and analyze. > > That's why so many frameworks, including Android, go out of their way > to make directly working with threads unnecessary for most people and > purposes. > > The mistake you are making here is not in your code, so much as it's > your expectations. > > You expect that when you set the background color, that something > happens immediately. That's not true. > > You are just recording what to use. Then you wait, and then you set it > back. > > Then, and only then, you return -- and then, and only then, the system > calls the methods that update the actual screen. That update does not > happen until you are done with your onClick() method, because you > don't want to see partial results. > > So all you've done by calling Thread.sleep() is to delay updating the > screen. > > A good rule of thumb in Android is that if you're calling > Thread.sleep(), you're doing it wrong. > > What you want to do instead, is to put your call > textResult.setBackgroundColor(Color.BLACK); where it is, and put the > call textResult.setBackgroundColor(Color.WHITE); in some code to run > later, after 500 ms. > > You can do this with a Handler object and a Runnable, like this: > > private Handler myHandler = new Handler(); > > protected void showNewDraw() { > textResult.setBackgroundColor(Color.BLACK); > textResult.setText("Before sleep"); > myHandler.postDelayed(500, new Runnable() { > public void run() { > textResult.setBackgroundColor(Color.WHITE); > textResult.setText("After sleep"); > } > } > > This will set the background to BLACK, and request that it run the > other code 500 ms later, and return. The screen will then be updated > with the new information, and 500 ms later, the Runnable will be > called and perform the change. > > By the way, this is also the case in most modern UI toolkits, not just > android. You should never do ANYTHING in your UI routines that takes a > long time, and especially not deliberately wait. There are things in > Android that are unique, but this is not one of them. So what you > learn here you can apply elsewhere as well. > > On Jul 2, 1:13 pm, Dmitri Snytkine <[email protected]> wrote: > > > Hello! > > I am new to android development, also new to java. I have many years > > of experience with OO PHP, so it's not hard for me to quickly learn > > Java and Android, but I still don't know many things like Thread > > class. > > > I just started developing a simple app. > > > What I want to do is that when a button is clicked, then the TextView > > is update in this way: > > the background is changed to black (by default it's set to white) > > > Then it should wait a half a second and then set the background back > > to white and update the text inside the TextView > > > Here is my code, it's inside my Activity class: > > > public synchronized void onClick(View v) { > > // TODO Auto-generated method stub > > switch (v.getId()) { > > case R.id.btnPlay: > > showNewDraw(); > > break; > > } > > > } > > > protected void showNewDraw() { > > textResult.setBackgroundColor(Color.BLACK); > > textResult.setText("Before sleep"); > > > try { > > Thread.sleep(500); > > } catch (Exception e) { > > textResult.setText("Something wrong"); > > } > > > textResult.setBackgroundColor(Color.WHITE); > > textResult.setText("After sleep"); > > } > > > The way it works now is that it seems to actually take 1/2 second from > > the time the button is pressed and text is updated, but the background > > is not reset to black and back to white - it always stays white. > > > Either it is being set to black and instantly reset to white or it's > > just never set to black. > > > What should I do in order for the "delay" effect to work? > > -- 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
