Animation Drawable Won't Resize Properly

Question

I have a walking dinosaur that I animate using an animation drawable

<animation-list xmlns:android="http://schemas.android.com/apk/res/android"
    android:oneshot="false">
    <item android:drawable="@drawable/dino1" android:duration="@integer/dino_dino" />
    <item android:drawable="@drawable/dino2" android:duration="@integer/dino_dino" />
    <item android:drawable="@drawable/dino3" android:duration="@integer/dino_dino" />
</animation-list>

I want to establish its width using guidelines and calculate its height automatically. I'm accustomed to scaleType doing that for me normal pictures. Like this:

<ImageView
    android:id="@+id/dino"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:scaleType="fitCenter"
    android:adjustViewBounds="true"
    android:layout_marginBottom="6dp"
    app:layout_constraintLeft_toLeftOf="@+id/guidelineDinoStart"
    app:layout_constraintRight_toRightOf="@+id/guidelineDinoEnd"
    app:layout_constraintBottom_toBottomOf="parent" />

Indeed, if I add the following line to the above ImageView definition (that is, set its src to be the first frame in the animation):

android:src="@drawable/dino_1"

then I get the properly proportioned image:

If I do the following as code though (and remove the src line from the ImageView definition), the image appears stretched:

_dino = view.findViewById(R.id.dino);

_dino.setBackgroundResource(R.drawable.dino_anim);

AnimationDrawable anim = (AnimationDrawable) _dino.getBackground();

_dino.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View view) {
        anim.start();
    }
});

And if I comment out the _dino.setBackgroundResource(R.drawable.dino_anim); and set the ImageView definition's src to be the animation:

android:src="@drawable/dino_anim"

then the app crashes when I click (try to start) the animation, saying:

Attempt to invoke virtual method 'void android.graphics.drawable.AnimationDrawable.start()' on a null object reference

How can I set the ImageView to have a properly-proportioned AnimationDrawable (using guidelines for the width but not the height) the way it naturally does if it's just a still picture?

ianovir · Accepted Answer · 2022-09-18T14:22:01.530

0

you need to use background OR src for an ImageView. I suggest to use the src, since the resource will be displayed in its original aspect ratio.

Using ImageView's Resource

Just set the resource:

android:src="@drawable/dino_anim"

In the code get the animationDrawable reference from getDrawable() instead of getBackground():

AnimationDrawable anim = (AnimationDrawable) _dino.getDrawable();

Why the crash?

The crash is caused by anim.start();, since the imageView's background is not set when you commented out _dino.setBackgroundResource(R.drawable.dino_anim);.

edited Sep 18 '22 at 14:22

answered Sep 17 '22 at 15:31

ianovir

31
4

Hi, thanks for your answer, I don't think it's quite right though. For instance, setting width to "wrap_content" makes the proportion right but the size way too big (it's the original image size rather than the size defined by the constraints). You also suggest setting the src, but give the same code that I did to set src (#3 thing that I tried). The crash happened with src set. The setBackgroundResource is commented out because I set src in the xml instead for that variant, rendering it unnecessary. – Elliptica Sep 18 '22 at 02:56
Forget the background with ImageView, use the src only. Your third try is ok, except for the `anim` object which must point to the src (getDrawable()) instead of the background (getBackground()). See my answer for the complete line. – ianovir Sep 18 '22 at 10:48
I see! I need to use `getDrawable` not `getBackground` with my third try and then it works! Can you remove the "Using Background Resource" part of your answer that says to use "wrap_content"? That's not correct because it causes the image to be too big and not respect the guidelines. The width should be 0dp to respect guidelines (wrap_content is fine for height, which has none). Then I can accept the answer! – Elliptica Sep 18 '22 at 11:44
Done! Yes, background resource can be tricky to resize properly. – ianovir Sep 18 '22 at 14:27

Animation Drawable Won't Resize Properly

1 Answers1

Using ImageView's Resource

Why the crash?