Creating a Drawable animation in Android.

This is a simple example of how to animate a drawable in Android.
This example is from the official android demo applications.

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Here we have 5 java classes.
AnimateDrawable.java
AnimateDrawables.java
GraphicsActivity.java
PictureLayout.java
ProxyDrawable.java

AnimateDrawable.java

package com.coderzheaven.animatedrawable;

import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.view.animation.Transformation;

public class AnimateDrawable extends ProxyDrawable {

    private Animation mAnimation;
    private Transformation mTransformation = new Transformation();

    public AnimateDrawable(Drawable target) {
        super(target);
    }

    public AnimateDrawable(Drawable target, Animation animation) {
        super(target);
        mAnimation = animation;
    }

    public Animation getAnimation() {
        return mAnimation;
    }

    public void setAnimation(Animation anim) {
        mAnimation = anim;
    }

    public boolean hasStarted() {
        return mAnimation != null && mAnimation.hasStarted();
    }

    public boolean hasEnded() {
        return mAnimation == null || mAnimation.hasEnded();
    }

    @Override
    public void draw(Canvas canvas) {
        Drawable dr = getProxy();
        if (dr != null) {
            int sc = canvas.save();
            Animation anim = mAnimation;
            if (anim != null) {
                anim.getTransformation(
                                    AnimationUtils.currentAnimationTimeMillis(),
                                    mTransformation);
                canvas.concat(mTransformation.getMatrix());
            }
            dr.draw(canvas);
            canvas.restoreToCount(sc);
        }
    }
}

AnimateDrawables.java

package com.coderzheaven.animatedrawable;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.TranslateAnimation;

public class AnimateDrawables extends GraphicsActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new SampleView(this));
    }

    private static class SampleView extends View {
        private AnimateDrawable mDrawable;

        public SampleView(Context context) {
            super(context);
            setFocusable(true);
            setFocusableInTouchMode(true);

            Drawable dr = context.getResources().getDrawable(R.drawable.ic_launcher);
            dr.setBounds(0, 0, dr.getIntrinsicWidth(), dr.getIntrinsicHeight());

            Animation an = new TranslateAnimation(0, 100, 0, 200);
            an.setDuration(2000);
            an.setRepeatCount(-1);
            an.initialize(10, 10, 10, 10);

            mDrawable = new AnimateDrawable(dr, an);
            an.startNow();
        }

        @Override
        protected void onDraw(Canvas canvas) {
            canvas.drawColor(Color.WHITE);

            mDrawable.draw(canvas);
            invalidate();
        }
    }
}

GraphicsActivity.java

package com.coderzheaven.animatedrawable;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;

class GraphicsActivity extends Activity {
    // set to true to test Picture
    private static final boolean TEST_PICTURE = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public void setContentView(View view) {
        if (TEST_PICTURE) {
            ViewGroup vg = new PictureLayout(this);
            vg.addView(view);
            view = vg;
        }

        super.setContentView(view);
    }
}

PictureLayout.java

package com.coderzheaven.animatedrawable;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Picture;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;

public class PictureLayout extends ViewGroup {
    private final Picture mPicture = new Picture();

    public PictureLayout(Context context) {
        super(context);
    }

    public PictureLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public void addView(View child) {
        if (getChildCount() > 1) {
            throw new IllegalStateException("PictureLayout can host only one direct child");
        }

        super.addView(child);
    }

    @Override
    public void addView(View child, int index) {
        if (getChildCount() > 1) {
            throw new IllegalStateException("PictureLayout can host only one direct child");
        }

        super.addView(child, index);
    }

    @Override
    public void addView(View child, LayoutParams params) {
        if (getChildCount() > 1) {
            throw new IllegalStateException("PictureLayout can host only one direct child");
        }

        super.addView(child, params);
    }

    @Override
    public void addView(View child, int index, LayoutParams params) {
        if (getChildCount() > 1) {
            throw new IllegalStateException("PictureLayout can host only one direct child");
        }

        super.addView(child, index, params);
    }

    @Override
    protected LayoutParams generateDefaultLayoutParams() {
        return new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        final int count = getChildCount();

        int maxHeight = 0;
        int maxWidth = 0;

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                measureChild(child, widthMeasureSpec, heightMeasureSpec);
            }
        }

        maxWidth += getPaddingLeft() + getPaddingRight();
        maxHeight += getPaddingTop() + getPaddingBottom();

        Drawable drawable = getBackground();
        if (drawable != null) {
            maxHeight = Math.max(maxHeight, drawable.getMinimumHeight());
            maxWidth = Math.max(maxWidth, drawable.getMinimumWidth());
        }

        setMeasuredDimension(resolveSize(maxWidth, widthMeasureSpec),
                resolveSize(maxHeight, heightMeasureSpec));
    }

    private void drawPict(Canvas canvas, int x, int y, int w, int h,
                          float sx, float sy) {
        canvas.save();
        canvas.translate(x, y);
        canvas.clipRect(0, 0, w, h);
        canvas.scale(0.5f, 0.5f);
        canvas.scale(sx, sy, w, h);
        canvas.drawPicture(mPicture);
        canvas.restore();
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(mPicture.beginRecording(getWidth(), getHeight()));
        mPicture.endRecording();

        int x = getWidth()/2;
        int y = getHeight()/2;

        drawPict(canvas, 0, 0, x, y,  1,  1);
		drawPict(canvas, x, 0, x, y, -1,  1);
		drawPict(canvas, 0, y, x, y,  1, -1);
		drawPict(canvas, x, y, x, y, -1, -1);
    }

    @Override
    public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
        location[0] = getLeft();
        location[1] = getTop();
        dirty.set(0, 0, getWidth(), getHeight());
        return getParent();
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        final int count = super.getChildCount();

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                final int childLeft = getPaddingLeft();
                final int childTop = getPaddingTop();
                child.layout(childLeft, childTop,
                        childLeft + child.getMeasuredWidth(),
                        childTop + child.getMeasuredHeight());

            }
        }
    }
}

ProxyDrawable.java

package com.coderzheaven.animatedrawable;

import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.PixelFormat;
import android.graphics.drawable.Drawable;

public class ProxyDrawable extends Drawable {

    private Drawable mProxy;
    private boolean mMutated;

    public ProxyDrawable(Drawable target) {
        mProxy = target;
    }

    public Drawable getProxy() {
        return mProxy;
    }

    public void setProxy(Drawable proxy) {
        if (proxy != this) {
            mProxy = proxy;
        }
    }

    @Override
    public void draw(Canvas canvas) {
        if (mProxy != null) {
            mProxy.draw(canvas);
        }
    }

    @Override
    public int getIntrinsicWidth() {
        return mProxy != null ? mProxy.getIntrinsicWidth() : -1;
    }

    @Override
    public int getIntrinsicHeight() {
        return mProxy != null ? mProxy.getIntrinsicHeight() : -1;
    }

    @Override
    public int getOpacity() {
        return mProxy != null ? mProxy.getOpacity() : PixelFormat.TRANSPARENT;
    }

    @Override
    public void setFilterBitmap(boolean filter) {
        if (mProxy != null) {
            mProxy.setFilterBitmap(filter);
        }
    }

    @Override
    public void setDither(boolean dither) {
        if (mProxy != null) {
            mProxy.setDither(dither);
        }
    }

    @Override
    public void setColorFilter(ColorFilter colorFilter) {
        if (mProxy != null) {
            mProxy.setColorFilter(colorFilter);
        }
    }

    @Override
    public void setAlpha(int alpha) {
        if (mProxy != null) {
            mProxy.setAlpha(alpha);
        }
    }

    @Override
    public Drawable mutate() {
        if (mProxy != null && !mMutated && super.mutate() == this) {
            mProxy.mutate();
            mMutated = true;
        }
        return this;
    }
}

Download the complete source code from here

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