Animated Sprite Using XML?

safibaba · May 4th, 2010, 07:19 AM

Hi all

The Android docs shows a way to create an XML definition of an animation like this:

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<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
    android:oneshot="false">
    <item android:drawable="@drawable/img1" android:duration="200" />
    <item android:drawable="@drawable/img2" android:duration="200" />
    <item android:drawable="@drawable/img3" android:duration="200" />
</animation-list>

I have been trying to create a Drawable from this XML like this

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Drawable sprite = (Drawable) getResources().getDrawable(R.anim.sprite);

And then draw it on my canvas in my SurfaceView like this

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sprite.draw(canvas);

It draws the first image - but it doesn't animate through the images specified in the XML.

I thought maybe I needed to make it an AnimationDrawable like this

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AnimationDrawable sprite = (AnimationDrawable) getResources().getAnimation(R.anim.sprite);

But it still didn't animate. So finally I thought maybe I need to call start() on it, but that gives me an error.

Am I just barking up the wrong tree here? Is it not possible to draw an animation to a canvas in this way? I have seen a tutorial which uses a sprite sheet and the setbounds method to do this, so maybe it's just not possible using the XML route?

Boogs · May 4th, 2010, 07:39 AM

You're not trying to call start in onCreate() are you?

safibaba · May 4th, 2010, 07:52 AM

Hi Boogs - actually yes I was. I didn't know I shouldn't be

.

So is this a valid way to draw animations when using a SurfaceView?

HOWEVER - the start() thing doesn't seem to be where it falls over, because I think it doesn't even get that far.

I am getting a classcastexception here

PHP Code:


			
AnimationDrawable sprite = (AnimationDrawable) getResources().getAnimation(R.anim.sprite);

I don't suppose you know where I could find an example of doing this correctly?

Boogs · May 4th, 2010, 08:38 AM

Well, it seems usually calling animation "start" or similar calls in onCreate can be problematic because all the views haven't finished their "setup". Check out the note at the bottom of the Android developer 2D graphics page which basically says the same thing.

As for an example, I don't have any great examples for you. But, you might want to check out the Android examples Jet Boy or Lunar Lander for some examples of drawing on a canvas SurfaceView. Then integrate your AnimationDrawable in a similar manner.

Boogs

safibaba · May 4th, 2010, 06:43 PM

Thanks for the tips Boogs..but I just can't get it to work at all.

I tried calling start from a separate thread, even calling start() from an onTouchEvent to make sure it gets called after the onCreate is finished..but I just can't get this damn thing to animate...

Is it something to do with the setBounds call?

res/anim/sprite.xml

PHP Code:


			
<?xml version="1.0" encoding="utf-8"?>
<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
    android:oneshot="false">
    <item android:drawable="@drawable/sprite1" android:duration="500" />
    <item android:drawable="@drawable/sprite2" android:duration="500" />
    <item android:drawable="@drawable/sprite3" android:duration="500" />
    <item android:drawable="@drawable/sprite4" android:duration="500" />
    <item android:drawable="@drawable/sprite5" android:duration="500" />
</animation-list>

SurfaceView

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public void surfaceCreated(SurfaceHolder holder) {
 sprite = (AnimationDrawable) getResources().getDrawable(R.anim.sprite);
 sprite.setBounds(0,0,sprite.getIntrinsicWidth(),sprite.getIntrinsicHeight());
}

public void startAnim(){
   Log.v("APPLET","Start Anim");
   sprite.start();
}

Main Activity class (which creates surface view)

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@Override
public boolean onTouchEvent(MotionEvent event){
   gameScreen.startAnim();
   return true;
}

It outputs the log message fine, but the animation never starts So frustrating

Boogs · May 5th, 2010, 05:19 PM

Safibaba,

Sorry that didn't work. To be honest, I don't know why it won't work. My only suggestion would be to put your animation into an ImageView in an Activity and see if that works. If it does, then at least you know that your XML file and the like are working fine...

safibaba · May 6th, 2010, 04:11 PM

I fixed it Boogs - I find the docs a bit obscure sometimes ...after googling for the best part of a day..it turned out I was missing the addCallback() method to make the parent thread schedule updates to the animation. I thought the animation handled its own frame updates!!

Boogs · May 6th, 2010, 05:14 PM

Wow, it seems like they should've made that easier, or at least documented it better if it's that hard. Either way, I'm glad it worked out for you.

anserran · June 23rd, 2010, 02:14 PM

Hi, safibaba

I have exactly the same problem... How did you add that callback? I've been stuck with this for 2 days...

Thanks!

Pabrick · September 6th, 2011, 07:19 AM

Use this:
AnimationDrawable sprite = (AnimationDrawable) sprite.Background(R.anim.sprite);