AnimatorUtils.java

import android.animation.Animator;
import android.animation.AnimatorSet;
import android.animation.Keyframe;
import android.animation.PropertyValuesHolder;
import android.animation.ValueAnimator;
import android.os.Build;
import android.support.annotation.Nullable;

import java.lang.reflect.Field;

public final class AnimatorUtils
{
    private static final boolean SUPPORTED;

    private static final Class<?> CLASS__INT_KEYFRAME_SET;
    private static final Class<?> CLASS__FLOAT_KEYFRAME_SET;

    private static final Field FIELD__PROPERTY_VALUES_HOLDER__KEYFRAME_SET;
    private static final Field FIELD__KEYFRAME_SET__FIRST_KEYFRAME;
    private static final Field FIELD__KEYFRAME__HAS_VALUE;
    private static final Field FIELD__INT_KEYFRAME_SET__FIRST_TIME;
    private static final Field FIELD__FLOAT_KEYFRAME_SET__FIRST_TIME;

    static
    {
        boolean supported = false;

        Class<?> class_IntKeyframeSet = null;
        Class<?> class_FloatKeyframeSet = null;
        Field field_PropertyValuesHolder_mKeyframeSet = null;
        Field field_KeyframeSet_mFirstKeyframe = null;
        Field field_Keyframe_hasValue = null;
        Field field_IntKeyframeSet_firstTime = null;
        Field field_FloatKeyframeSet_firstTime = null;

        if (Build.VERSION.SDK_INT < 21)
        {
            //noinspection TryWithIdenticalCatches
            try
            {
                final Class class_KeyframeSet = Class.forName("android.animation.KeyframeSet");
                class_IntKeyframeSet = Class.forName("android.animation.IntKeyframeSet");
                class_FloatKeyframeSet = Class.forName("android.animation.FloatKeyframeSet");

                field_PropertyValuesHolder_mKeyframeSet = PropertyValuesHolder.class.getDeclaredField("mKeyframeSet");
                field_PropertyValuesHolder_mKeyframeSet.setAccessible(true);

                field_KeyframeSet_mFirstKeyframe = class_KeyframeSet.getDeclaredField("mFirstKeyframe");
                field_KeyframeSet_mFirstKeyframe.setAccessible(true);

                field_Keyframe_hasValue = Keyframe.class.getDeclaredField("mHasValue");
                field_Keyframe_hasValue.setAccessible(true);

                field_IntKeyframeSet_firstTime = class_IntKeyframeSet.getDeclaredField("firstTime");
                field_IntKeyframeSet_firstTime.setAccessible(true);

                field_FloatKeyframeSet_firstTime = class_FloatKeyframeSet.getDeclaredField("firstTime");
                field_FloatKeyframeSet_firstTime.setAccessible(true);

                supported = true;
            }
            catch (NoSuchFieldException ignore)
            {
            }
            catch (ClassNotFoundException ignore)
            {
            }
        }

        SUPPORTED = supported;

        CLASS__INT_KEYFRAME_SET = class_IntKeyframeSet;
        CLASS__FLOAT_KEYFRAME_SET = class_FloatKeyframeSet;
        FIELD__PROPERTY_VALUES_HOLDER__KEYFRAME_SET = field_PropertyValuesHolder_mKeyframeSet;
        FIELD__KEYFRAME_SET__FIRST_KEYFRAME = field_KeyframeSet_mFirstKeyframe;
        FIELD__KEYFRAME__HAS_VALUE = field_Keyframe_hasValue;
        FIELD__INT_KEYFRAME_SET__FIRST_TIME = field_IntKeyframeSet_firstTime;
        FIELD__FLOAT_KEYFRAME_SET__FIRST_TIME = field_FloatKeyframeSet_firstTime;
    }

    private AnimatorUtils() {}

    public static void resetStartValues(@Nullable Animator animator)
    {
        // see https://github.com/android/platform_frameworks_base/commit/8619f48fb353740f7fd3f6eaa86fe493377e6cad

        if (!SUPPORTED || animator == null) { return; }

        if (animator instanceof AnimatorSet)
        {
            for (Animator childAnimator : ((AnimatorSet)animator).getChildAnimations())
            {
                resetStartValues(childAnimator);
            }
        }
        else if (animator instanceof ValueAnimator)
        {
            final PropertyValuesHolder[] values = ((ValueAnimator)animator).getValues();
            if (values != null)
            {
                try
                {
                    for (PropertyValuesHolder pvh : values)
                    {
                        final Object mKeyframeSet = FIELD__PROPERTY_VALUES_HOLDER__KEYFRAME_SET.get(pvh);
                        if (mKeyframeSet != null)
                        {
                            final Object mFirstKeyframe = FIELD__KEYFRAME_SET__FIRST_KEYFRAME.get(mKeyframeSet);
                            if (mFirstKeyframe != null)
                            {
                                FIELD__KEYFRAME__HAS_VALUE.set(mFirstKeyframe, false);
                            }
                            final Class<?> keyframeSetClass = mKeyframeSet.getClass();
                            if (CLASS__INT_KEYFRAME_SET.isAssignableFrom(keyframeSetClass))
                            {
                                FIELD__INT_KEYFRAME_SET__FIRST_TIME.set(mKeyframeSet, true);
                            }
                            else if (CLASS__FLOAT_KEYFRAME_SET.isAssignableFrom(keyframeSetClass))
                            {
                                FIELD__FLOAT_KEYFRAME_SET__FIRST_TIME.set(mKeyframeSet, true);
                            }
                        }
                    }
                }
                catch (IllegalAccessException ignore)
                {
                }
            }
        }
    }
}