动画——插值器（interpolator）

java类	xml资源id	说明
AccelerateDecelerateInterpolator	@android:anim/accelerate_decelerate_interpolator	其变化开始和结束速率较慢，中间加速
AccelerateInterpolator	@android:anim/accelerate_interpolator	其变化开始速率较慢，后面加速
DecelerateInterpolator	@android:anim/decelerate_interpolator	其变化开始速率较快，后面减速
LinearInterpolator	@android:anim/linear_interpolator	其变化速率恒定
AnticipateInterpolator	@android:anim/anticipate_interpolator	其变化开始向后甩，然后向前
AnticipateOvershootInterpolator	@android:anim/anticipate_overshoot_interpolator	其变化开始向后甩，然后向前甩，过冲到目标值，最后又回到了终值
OvershootInterpolator	@android:anim/overshoot_interpolator	其变化开始向前甩，过冲到目标值，最后又回到了终值
BounceInterpolator	@android:anim/bounce_interpolator	其变化在结束时反弹
CycleInterpolator	@android:anim/cycle_interpolator	循环播放，其速率为正弦曲线
TimeInterpolator		一个接口，可以自定义插值器
pathInterpolator		path插值器，一般要自定义xml传入path

使用：

自定义

以accelerate_interpolator为例
在源码中，对应的文件是：

frameworks\base\core\res\res\anim\linear_accelerate.xml

frameworks\base\core\java\android\view\animation\AnimationUtils.java
private static Interpolator createInterpolatorFromXml(Resources res, Theme theme, XmlPullParser parser)
        throws XmlPullParserException, IOException {

    BaseInterpolator interpolator = null;

    // Make sure we are on a start tag.
    int type;
    int depth = parser.getDepth();

    while (((type = parser.next()) != XmlPullParser.END_TAG || parser.getDepth() > depth)
            && type != XmlPullParser.END_DOCUMENT) {

        if (type != XmlPullParser.START_TAG) {
            continue;
        }

        AttributeSet attrs = Xml.asAttributeSet(parser);

        String name = parser.getName();

        if (name.equals("linearInterpolator")) {
            interpolator = new LinearInterpolator();
        } else if (name.equals("accelerateInterpolator")) {
            interpolator = new AccelerateInterpolator(res, theme, attrs);
        } else if (name.equals("decelerateInterpolator")) {
            interpolator = new DecelerateInterpolator(res, theme, attrs);
        } else if (name.equals("accelerateDecelerateInterpolator")) {
            interpolator = new AccelerateDecelerateInterpolator();
        } else if (name.equals("cycleInterpolator")) {
            interpolator = new CycleInterpolator(res, theme, attrs);
        } else if (name.equals("anticipateInterpolator")) {
            interpolator = new AnticipateInterpolator(res, theme, attrs);
        } else if (name.equals("overshootInterpolator")) {
            interpolator = new OvershootInterpolator(res, theme, attrs);
        } else if (name.equals("anticipateOvershootInterpolator")) {
            interpolator = new AnticipateOvershootInterpolator(res, theme, attrs);
        } else if (name.equals("bounceInterpolator")) {
            interpolator = new BounceInterpolator();
        } else if (name.equals("pathInterpolator")) {
            interpolator = new PathInterpolator(res, theme, attrs);
        } else {
            throw new RuntimeException("Unknown interpolator name: " + parser.getName());
        }
    }
    return interpolator;
}

可见，最后调用的是new AccelerateInterpolator ()

frameworks\base\core\java\android\view\animation\AccelerateInterpolator .java
/*
 * Copyright (C) 2006 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.view.animation;

import android.content.Context;
import android.content.res.Resources;
import android.content.res.Resources.Theme;
import android.content.res.TypedArray;
import android.util.AttributeSet;

import com.android.internal.R;
import com.android.internal.view.animation.HasNativeInterpolator;
import com.android.internal.view.animation.NativeInterpolatorFactory;
import com.android.internal.view.animation.NativeInterpolatorFactoryHelper;

/**
 * An interpolator where the rate of change starts out slowly and
 * and then accelerates.
 *
 */
@HasNativeInterpolator
public class AccelerateInterpolator extends BaseInterpolator implements NativeInterpolatorFactory {
    private final float mFactor;
    private final double mDoubleFactor;

    public AccelerateInterpolator() {
        mFactor = 1.0f;
        mDoubleFactor = 2.0;
    }

    /**
     * Constructor
     *
     * @param factor Degree to which the animation should be eased. Seting
     *        factor to 1.0f produces a y=x^2 parabola. Increasing factor above
     *        1.0f  exaggerates the ease-in effect (i.e., it starts even
     *        slower and ends evens faster)
     */
    public AccelerateInterpolator(float factor) {
        mFactor = factor;
        mDoubleFactor = 2 * mFactor;
    }

    public AccelerateInterpolator(Context context, AttributeSet attrs) {
        this(context.getResources(), context.getTheme(), attrs);
    }

    /** @hide */
    public AccelerateInterpolator(Resources res, Theme theme, AttributeSet attrs) {
        TypedArray a;
        if (theme != null) {
            a = theme.obtainStyledAttributes(attrs, R.styleable.AccelerateInterpolator, 0, 0);
        } else {
            a = res.obtainAttributes(attrs, R.styleable.AccelerateInterpolator);
        }

        mFactor = a.getFloat(R.styleable.AccelerateInterpolator_factor, 1.0f);
        mDoubleFactor = 2 * mFactor;
        setChangingConfiguration(a.getChangingConfigurations());
        a.recycle();
    }

    public float getInterpolation(float input) {
        if (mFactor == 1.0f) {
            return input * input;
        } else {
            return (float)Math.pow(input, mDoubleFactor);
        }
    }

    /** @hide */
    @Override
    public long createNativeInterpolator() {
        return NativeInterpolatorFactoryHelper.createAccelerateInterpolator(mFactor);
    }
}

通过重写getInterpolation(float input)来控制动画播放

自定义