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?
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