/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.animation;

This class holds a time/value pair for an animation. The Keyframe class is used by ValueAnimator to define the values that the animation target will have over the course of the animation. As the time proceeds from one keyframe to the other, the value of the target object will animate between the value at the previous keyframe and the value at the next keyframe. Each keyframe also holds an optional TimeInterpolator object, which defines the time interpolation over the intervalue preceding the keyframe. 
The Keyframe class itself is abstract. The type-specific factory methods will return
a subclass of Keyframe specific to the type of value being stored. This is done to improve
performance when dealing with the most common cases (e.g., float and
int values). Other types will fall into a more general Keyframe class that treats its values as Objects. Unless your animation requires dealing with a custom type or a data structure that needs to be animated directly (and evaluated using an implementation of TypeEvaluator), you should stick to using float and int as animations using those types have lower runtime overhead than other types.
/**
 * This class holds a time/value pair for an animation. The Keyframe class is used
 * by {@link ValueAnimator} to define the values that the animation target will have over the course
 * of the animation. As the time proceeds from one keyframe to the other, the value of the
 * target object will animate between the value at the previous keyframe and the value at the
 * next keyframe. Each keyframe also holds an optional {@link TimeInterpolator}
 * object, which defines the time interpolation over the intervalue preceding the keyframe.
 *
 * <p>The Keyframe class itself is abstract. The type-specific factory methods will return
 * a subclass of Keyframe specific to the type of value being stored. This is done to improve
 * performance when dealing with the most common cases (e.g., <code>float</code> and
 * <code>int</code> values). Other types will fall into a more general Keyframe class that
 * treats its values as Objects. Unless your animation requires dealing with a custom type
 * or a data structure that needs to be animated directly (and evaluated using an implementation
 * of {@link TypeEvaluator}), you should stick to using float and int as animations using those
 * types have lower runtime overhead than other types.</p>
 */
public abstract class Keyframe implements Cloneable {
    
Flag to indicate whether this keyframe has a valid value. This flag is used when an
animation first starts, to populate placeholder keyframes with real values derived
from the target object.
/**
     * Flag to indicate whether this keyframe has a valid value. This flag is used when an
     * animation first starts, to populate placeholder keyframes with real values derived
     * from the target object.
     */
    boolean mHasValue;

    
Flag to indicate whether the value in the keyframe was read from the target object or not.
If so, its value will be recalculated if target changes.
/**
     * Flag to indicate whether the value in the keyframe was read from the target object or not.
     * If so, its value will be recalculated if target changes.
     */
    boolean mValueWasSetOnStart;


    
The time at which mValue will hold true.
/**
     * The time at which mValue will hold true.
     */
    float mFraction;

    
The type of the value in this Keyframe. This type is determined at construction time,
based on the type of the value object passed into the constructor.
/**
     * The type of the value in this Keyframe. This type is determined at construction time,
     * based on the type of the <code>value</code> object passed into the constructor.
     */
    Class mValueType;

    
The optional time interpolator for the interval preceding this keyframe. A null interpolator
(the default) results in linear interpolation over the interval.
/**
     * The optional time interpolator for the interval preceding this keyframe. A null interpolator
     * (the default) results in linear interpolation over the interval.
     */
    private TimeInterpolator mInterpolator = null;



    
Constructs a Keyframe object with the given time and value. The time defines the
time, as a proportion of an overall animation's duration, at which the value will hold true
for the animation. The value for the animation between keyframes will be calculated as
an interpolation between the values at those keyframes.
Params:
fraction – The time, expressed as a value between 0 and 1, representing the fraction
of time elapsed of the overall animation duration.
value – The value that the object will animate to as the animation time approaches
the time in this keyframe, and the value animated from as the time passes the time in
this keyframe./**
     * Constructs a Keyframe object with the given time and value. The time defines the
     * time, as a proportion of an overall animation's duration, at which the value will hold true
     * for the animation. The value for the animation between keyframes will be calculated as
     * an interpolation between the values at those keyframes.
     *
     * @param fraction The time, expressed as a value between 0 and 1, representing the fraction
     * of time elapsed of the overall animation duration.
     * @param value The value that the object will animate to as the animation time approaches
     * the time in this keyframe, and the value animated from as the time passes the time in
     * this keyframe.
     */
    public static Keyframe ofInt(float fraction, int value) {
        return new IntKeyframe(fraction, value);
    }

    
Constructs a Keyframe object with the given time. The value at this time will be derived from the target object when the animation first starts (note that this implies that keyframes with no initial value must be used as part of an ObjectAnimator). The time defines the time, as a proportion of an overall animation's duration, at which the value will hold true for the animation. The value for the animation between keyframes will be calculated as an interpolation between the values at those keyframes. 
Params:
fraction – The time, expressed as a value between 0 and 1, representing the fraction
of time elapsed of the overall animation duration./**
     * Constructs a Keyframe object with the given time. The value at this time will be derived
     * from the target object when the animation first starts (note that this implies that keyframes
     * with no initial value must be used as part of an {@link ObjectAnimator}).
     * The time defines the
     * time, as a proportion of an overall animation's duration, at which the value will hold true
     * for the animation. The value for the animation between keyframes will be calculated as
     * an interpolation between the values at those keyframes.
     *
     * @param fraction The time, expressed as a value between 0 and 1, representing the fraction
     * of time elapsed of the overall animation duration.
     */
    public static Keyframe ofInt(float fraction) {
        return new IntKeyframe(fraction);
    }

    
Constructs a Keyframe object with the given time and value. The time defines the
time, as a proportion of an overall animation's duration, at which the value will hold true
for the animation. The value for the animation between keyframes will be calculated as
an interpolation between the values at those keyframes.
Params:
fraction – The time, expressed as a value between 0 and 1, representing the fraction
of time elapsed of the overall animation duration.
value – The value that the object will animate to as the animation time approaches
the time in this keyframe, and the value animated from as the time passes the time in
this keyframe./**
     * Constructs a Keyframe object with the given time and value. The time defines the
     * time, as a proportion of an overall animation's duration, at which the value will hold true
     * for the animation. The value for the animation between keyframes will be calculated as
     * an interpolation between the values at those keyframes.
     *
     * @param fraction The time, expressed as a value between 0 and 1, representing the fraction
     * of time elapsed of the overall animation duration.
     * @param value The value that the object will animate to as the animation time approaches
     * the time in this keyframe, and the value animated from as the time passes the time in
     * this keyframe.
     */
    public static Keyframe ofFloat(float fraction, float value) {
        return new FloatKeyframe(fraction, value);
    }

    
Constructs a Keyframe object with the given time. The value at this time will be derived from the target object when the animation first starts (note that this implies that keyframes with no initial value must be used as part of an ObjectAnimator). The time defines the time, as a proportion of an overall animation's duration, at which the value will hold true for the animation. The value for the animation between keyframes will be calculated as an interpolation between the values at those keyframes. 
Params:
fraction – The time, expressed as a value between 0 and 1, representing the fraction
of time elapsed of the overall animation duration./**
     * Constructs a Keyframe object with the given time. The value at this time will be derived
     * from the target object when the animation first starts (note that this implies that keyframes
     * with no initial value must be used as part of an {@link ObjectAnimator}).
     * The time defines the
     * time, as a proportion of an overall animation's duration, at which the value will hold true
     * for the animation. The value for the animation between keyframes will be calculated as
     * an interpolation between the values at those keyframes.
     *
     * @param fraction The time, expressed as a value between 0 and 1, representing the fraction
     * of time elapsed of the overall animation duration.
     */
    public static Keyframe ofFloat(float fraction) {
        return new FloatKeyframe(fraction);
    }

    
Constructs a Keyframe object with the given time and value. The time defines the
time, as a proportion of an overall animation's duration, at which the value will hold true
for the animation. The value for the animation between keyframes will be calculated as
an interpolation between the values at those keyframes.
Params:
fraction – The time, expressed as a value between 0 and 1, representing the fraction
of time elapsed of the overall animation duration.
value – The value that the object will animate to as the animation time approaches
the time in this keyframe, and the value animated from as the time passes the time in
this keyframe./**
     * Constructs a Keyframe object with the given time and value. The time defines the
     * time, as a proportion of an overall animation's duration, at which the value will hold true
     * for the animation. The value for the animation between keyframes will be calculated as
     * an interpolation between the values at those keyframes.
     *
     * @param fraction The time, expressed as a value between 0 and 1, representing the fraction
     * of time elapsed of the overall animation duration.
     * @param value The value that the object will animate to as the animation time approaches
     * the time in this keyframe, and the value animated from as the time passes the time in
     * this keyframe.
     */
    public static Keyframe ofObject(float fraction, Object value) {
        return new ObjectKeyframe(fraction, value);
    }

    
Constructs a Keyframe object with the given time. The value at this time will be derived from the target object when the animation first starts (note that this implies that keyframes with no initial value must be used as part of an ObjectAnimator). The time defines the time, as a proportion of an overall animation's duration, at which the value will hold true for the animation. The value for the animation between keyframes will be calculated as an interpolation between the values at those keyframes. 
Params:
fraction – The time, expressed as a value between 0 and 1, representing the fraction
of time elapsed of the overall animation duration./**
     * Constructs a Keyframe object with the given time. The value at this time will be derived
     * from the target object when the animation first starts (note that this implies that keyframes
     * with no initial value must be used as part of an {@link ObjectAnimator}).
     * The time defines the
     * time, as a proportion of an overall animation's duration, at which the value will hold true
     * for the animation. The value for the animation between keyframes will be calculated as
     * an interpolation between the values at those keyframes.
     *
     * @param fraction The time, expressed as a value between 0 and 1, representing the fraction
     * of time elapsed of the overall animation duration.
     */
    public static Keyframe ofObject(float fraction) {
        return new ObjectKeyframe(fraction, null);
    }

    
Indicates whether this keyframe has a valid value. This method is called internally when an ObjectAnimator first starts; keyframes without values are assigned values at that time by deriving the value for the property from the target object. 
Returns:
boolean Whether this object has a value assigned./**
     * Indicates whether this keyframe has a valid value. This method is called internally when
     * an {@link ObjectAnimator} first starts; keyframes without values are assigned values at
     * that time by deriving the value for the property from the target object.
     *
     * @return boolean Whether this object has a value assigned.
     */
    public boolean hasValue() {
        return mHasValue;
    }

    
If the Keyframe's value was acquired from the target object, this flag should be set so that,
if target changes, value will be reset.
Returns:
boolean Whether this Keyframe's value was retieved from the target object or not./**
     * If the Keyframe's value was acquired from the target object, this flag should be set so that,
     * if target changes, value will be reset.
     *
     * @return boolean Whether this Keyframe's value was retieved from the target object or not.
     */
    boolean valueWasSetOnStart() {
        return mValueWasSetOnStart;
    }

    void setValueWasSetOnStart(boolean valueWasSetOnStart) {
        mValueWasSetOnStart = valueWasSetOnStart;
    }

    
Gets the value for this Keyframe.
Returns:
The value for this Keyframe./**
     * Gets the value for this Keyframe.
     *
     * @return The value for this Keyframe.
     */
    public abstract Object getValue();

    
Sets the value for this Keyframe.
Params:
value – value for this Keyframe./**
     * Sets the value for this Keyframe.
     *
     * @param value value for this Keyframe.
     */
    public abstract void setValue(Object value);

    
Gets the time for this keyframe, as a fraction of the overall animation duration.
Returns:
The time associated with this keyframe, as a fraction of the overall animation
duration. This should be a value between 0 and 1./**
     * Gets the time for this keyframe, as a fraction of the overall animation duration.
     *
     * @return The time associated with this keyframe, as a fraction of the overall animation
     * duration. This should be a value between 0 and 1.
     */
    public float getFraction() {
        return mFraction;
    }

    
Sets the time for this keyframe, as a fraction of the overall animation duration.
Params:
fraction – time associated with this keyframe, as a fraction of the overall animation
duration. This should be a value between 0 and 1./**
     * Sets the time for this keyframe, as a fraction of the overall animation duration.
     *
     * @param fraction time associated with this keyframe, as a fraction of the overall animation
     * duration. This should be a value between 0 and 1.
     */
    public void setFraction(float fraction) {
        mFraction = fraction;
    }

    
Gets the optional interpolator for this Keyframe. A value of null indicates
that there is no interpolation, which is the same as linear interpolation.
Returns:
The optional interpolator for this Keyframe./**
     * Gets the optional interpolator for this Keyframe. A value of <code>null</code> indicates
     * that there is no interpolation, which is the same as linear interpolation.
     *
     * @return The optional interpolator for this Keyframe.
     */
    public TimeInterpolator getInterpolator() {
        return mInterpolator;
    }

    
Sets the optional interpolator for this Keyframe. A value of null indicates
that there is no interpolation, which is the same as linear interpolation.
Returns:
The optional interpolator for this Keyframe./**
     * Sets the optional interpolator for this Keyframe. A value of <code>null</code> indicates
     * that there is no interpolation, which is the same as linear interpolation.
     *
     * @return The optional interpolator for this Keyframe.
     */
    public void setInterpolator(TimeInterpolator interpolator) {
        mInterpolator = interpolator;
    }

    
Gets the type of keyframe. This information is used by ValueAnimator to determine the type of TypeEvaluator to use when calculating values between keyframes. The type is based on the type of Keyframe created. 
Returns:
The type of the value stored in the Keyframe./**
     * Gets the type of keyframe. This information is used by ValueAnimator to determine the type of
     * {@link TypeEvaluator} to use when calculating values between keyframes. The type is based
     * on the type of Keyframe created.
     *
     * @return The type of the value stored in the Keyframe.
     */
    public Class getType() {
        return mValueType;
    }

    @Override
    public abstract Keyframe clone();

    
This internal subclass is used for all types which are not int or float.
/**
     * This internal subclass is used for all types which are not int or float.
     */
    static class ObjectKeyframe extends Keyframe {

        
The value of the animation at the time mFraction.
/**
         * The value of the animation at the time mFraction.
         */
        Object mValue;

        ObjectKeyframe(float fraction, Object value) {
            mFraction = fraction;
            mValue = value;
            mHasValue = (value != null);
            mValueType = mHasValue ? value.getClass() : Object.class;
        }

        public Object getValue() {
            return mValue;
        }

        public void setValue(Object value) {
            mValue = value;
            mHasValue = (value != null);
        }

        @Override
        public ObjectKeyframe clone() {
            ObjectKeyframe kfClone = new ObjectKeyframe(getFraction(), hasValue() ? mValue : null);
            kfClone.mValueWasSetOnStart = mValueWasSetOnStart;
            kfClone.setInterpolator(getInterpolator());
            return kfClone;
        }
    }

    
Internal subclass used when the keyframe value is of type int.
/**
     * Internal subclass used when the keyframe value is of type int.
     */
    static class IntKeyframe extends Keyframe {

        
The value of the animation at the time mFraction.
/**
         * The value of the animation at the time mFraction.
         */
        int mValue;

        IntKeyframe(float fraction, int value) {
            mFraction = fraction;
            mValue = value;
            mValueType = int.class;
            mHasValue = true;
        }

        IntKeyframe(float fraction) {
            mFraction = fraction;
            mValueType = int.class;
        }

        public int getIntValue() {
            return mValue;
        }

        public Object getValue() {
            return mValue;
        }

        public void setValue(Object value) {
            if (value != null && value.getClass() == Integer.class) {
                mValue = ((Integer)value).intValue();
                mHasValue = true;
            }
        }

        @Override
        public IntKeyframe clone() {
            IntKeyframe kfClone = mHasValue ?
                    new IntKeyframe(getFraction(), mValue) :
                    new IntKeyframe(getFraction());
            kfClone.setInterpolator(getInterpolator());
            kfClone.mValueWasSetOnStart = mValueWasSetOnStart;
            return kfClone;
        }
    }

    
Internal subclass used when the keyframe value is of type float.
/**
     * Internal subclass used when the keyframe value is of type float.
     */
    static class FloatKeyframe extends Keyframe {
        
The value of the animation at the time mFraction.
/**
         * The value of the animation at the time mFraction.
         */
        float mValue;

        FloatKeyframe(float fraction, float value) {
            mFraction = fraction;
            mValue = value;
            mValueType = float.class;
            mHasValue = true;
        }

        FloatKeyframe(float fraction) {
            mFraction = fraction;
            mValueType = float.class;
        }

        public float getFloatValue() {
            return mValue;
        }

        public Object getValue() {
            return mValue;
        }

        public void setValue(Object value) {
            if (value != null && value.getClass() == Float.class) {
                mValue = ((Float)value).floatValue();
                mHasValue = true;
            }
        }

        @Override
        public FloatKeyframe clone() {
            FloatKeyframe kfClone = mHasValue ?
                    new FloatKeyframe(getFraction(), mValue) :
                    new FloatKeyframe(getFraction());
            kfClone.setInterpolator(getInterpolator());
            kfClone.mValueWasSetOnStart = mValueWasSetOnStart;
            return kfClone;
        }
    }
}