PropertyValuesHolder实现机制

一.使用

二.实现
/*
该类维护一个属性和该属性对应的一堆的KeyframeSet
*/
PropertyValuesHolder {

String mPropertyName;
KeyframeSet mKeyframeSet = null;

protected Property mProperty;

Method mSetter = null;

private Method mGetter = null;

Class mValueType;

}

public abstract class Property<T, V> {
private final String mName;
private final Class<V> mType;
}

/*
维护Keyframe的链表
*/
class KeyframeSet {

int mNumKeyframes;

Keyframe mFirstKeyframe;
Keyframe mLastKeyframe;
TimeInterpolator mInterpolator; // only used in the 2-keyframe case
ArrayList<Keyframe> mKeyframes; // only used when there are not 2 keyframes
TypeEvaluator mEvaluator;

public KeyframeSet(Keyframe... keyframes) {
mNumKeyframes = keyframes.length;
mKeyframes = new ArrayList<Keyframe>();
mKeyframes.addAll(Arrays.asList(keyframes));
mFirstKeyframe = mKeyframes.get(0);
mLastKeyframe = mKeyframes.get(mNumKeyframes - 1);
mInterpolator = mLastKeyframe.getInterpolator();
}

public static KeyframeSet ofInt(int... values) {
int numKeyframes = values.length;
IntKeyframe keyframes[] = new IntKeyframe[Math.max(numKeyframes,2)];
if (numKeyframes == 1) {
// 传进来的只有最终动画的值(1个value)-->保存0和结束的值
keyframes[0] = (IntKeyframe) Keyframe.ofInt(0f);
keyframes[1] = (IntKeyframe) Keyframe.ofInt(1f, values[0]);
} else {
keyframes[0] = (IntKeyframe) Keyframe.ofInt(0f, values[0]);
for (int i = 1; i < numKeyframes; ++i) {
keyframes[i] =
(IntKeyframe) Keyframe.ofInt((float) i / (numKeyframes - 1), values[i]);
}
}
return new IntKeyframeSet(keyframes);
}
}

/*
维护两个成员:mFraction, mValue的Item
*/
public abstract class Keyframe implements Cloneable {
/**
* 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 <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.
*/
private TimeInterpolator mInterpolator = null;

public static Keyframe ofInt(float fraction, int value) {
return new IntKeyframe(fraction, value);
}
}

/**

     * 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.

         */

        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;

            }

        }

    }

三.总结