CODEWITHSUNDEEP
javaandroidmultithreadingsleep
user1003910
user1003910

Reputation: 51

How can I get wait/sleep to work the way I want in java?

I'm trying to accomplish something very simple. First, load my layout (main.xml). Then wait 1 second, modify an image, wait 1 second and modify it to a third image. (My end goal is more complex, of course, but I can't even get this to work).

Basically, I get a black screen when the app loads. It stays that way until all the waiting is over, then it shows the final image. Here's my code:

super.onCreate(savedInstanceState);
setContentView(R.layout.main);        

ImageCard[0] = (ImageView)findViewById(R.id.imageView11);
Thread.sleep(1000);
ImageCard[0].setImageDrawable(getResources().getDrawable(R.drawable.secondimage));
Thread.sleep(1000);
ImageCard[0].setImageDrawable(getResources().getDrawable(R.drawable.thirdimage));

ImageCard[0] is the image I'm trying to change. It loads in main.xml and shows fine if I remove the rest of the code.

If I change the sleep time to 5000, it then takes 10 seconds before it finally comes away from the black screen and shows the third image. This is how I know it's not just loading slow, but that it's actually waiting.

It's like it's not running sequentially. I'm no java expert, so I'm assuming I'm doing something dumb...

Thanks for any help!

Upvotes: 1

Views: 3728

Answers (5)

kajacx
kajacx

Reputation: 12939

do you have that code in constructor or in init() function? if yes, draw just the first picture and the Thread.sleep() function move after the place which the constructor or the init() function was called from. then call repaint() function or something.

Upvotes: 0

Kirill Rakhman
Kirill Rakhman

Reputation: 43821

I think you are blocking the UI Thead. Try Handler.postDelayed on a static Handler object.

Upvotes: 3

John
John

Reputation: 74

Ok heres your problem, you can never do a sleep(...) when you are in the UIThread. The UIThread is never suppose to be locked up, it causes a lot of very bad things to happen in android. But there is a very easy way around it, just get off the UIThread and hop back on it when you need to. Heres what i would recommend:

public void onCreate(...)
{
    super.onCreate(...);
    myActivity.setContentView(R.layout.main);
    new Thread(this).start();
}

public void run()
{
    try
    {
        changeLayout(R.layout.main2);
        Thread.sleep(5000);
        changeLayout(R.layout.main3);
        Thread.sleep(10000)
        changeLayout(R.layout.main4);
    }catch(Exception e){}
}

public void changeLayout(int id)
{
    this.id = id;
    myActivity.post(new Runnable()
    {
        public void run()
        {
            myActivity.setContentView(id);
        }
    });
}

private int id;

Of course with this example your class must implement Runnable to work. Only the UIThread can access the UI, no other thread can. Thats why you have to hop on and off the UIThread. Hope this worked!

Upvotes: 2

Rob V
Rob V

Reputation: 376

I think Hovercraft Full of Eels is pointing you in the right direction. Essentially, you're not doing any multi-threading, you're telling the main thread to wait which means that it never completes the drawing. I'm not sure about Android, but Swing uses double-buffering by default (to avoid screen flashes), but that means that what is drawn, is actually drawn on to a buffer, not the window itself which is why you don't see anything. You could try disabling the double buffering (which Android is likely using) but that could cause other issues.

You might want to actually do multi-threading, or, I'm sure Android likely has a Timer component. If it does, I'd suggest you use it over Thread.sleep or actual multi-threading. Using a Timer you can have it fire an event after one second. That event will execute the other code.

Upvotes: 0

mamboking
mamboking

Reputation: 4637

Try adding ImageCard[0].invalidate() when you want it to draw.

Upvotes: 0

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