从源码角度理解android动画Interpolator类的使用

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最新推荐文章于 2024-03-28 01:41:37 发布

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本文详细解析了Android动画中的Interpolator类，特别是LinearInterpolator的作用，展示了如何通过自定义Interpolator实现动画匀速执行，并通过代码实例进行了说明。

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做过android动画的人对Interpolator应该不会陌生，这个类主要是用来控制android动画的执行速率，一般情况下，如果我们不设置，动画都不是匀速执行的，系统默认是先加速后减速这样一种动画执行速率。
android通过Interpolator类来让我们自己控制动画的执行速率，还记得上一篇博客中我们使用属性动画实现的旋转效果吗？在不设置Interpolator的情况下，这个动画是先加速后减速，我们现在使用android系统提供的类LinearInterpolator来设置动画的执行速率，LinearInterpolator可以让这个动画匀速执行，我们来看一个案例，我们有两个TextView重叠放在一起，点击旋转按钮后这两个TextView同时执行旋转动画，不同的是一个设置了LinearInterpolator，而另外一个什么都没有设置，代码如下：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">            LinearInterpolator ll = new LinearInterpolator()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            ObjectAnimator animator = ObjectAnimator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ofFloat</span>(tv, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"rotation"</span>,
                    <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>f, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">360</span>f)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            animator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setInterpolator</span>(ll)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            animator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setDuration</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5000</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            animator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.start</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            ObjectAnimator animator2 = ObjectAnimator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ofFloat</span>(tv2, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"rotation"</span>,
                    <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>f, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">360</span>f)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            animator2<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setDuration</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5000</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            animator2<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.start</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

效果图如下：

这里写图片描述

现在我们可以很清楚的看到这里的差异，一个TextView先加速后减速，一个一直匀速运动。

这就引起了我的好奇，究竟LinearInterpolator做了什么，改变了动画的执行速率。这里我们就要看看源码了。
当我们调用animator.setInterpolator(ll);的时候，调用的是ValueAnimator方法中的setInterpolator方法，源码如下：

<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> <span class="hljs-title" style="box-sizing: border-box;">setInterpolator</span>(TimeInterpolator <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span>) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span> != <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">null</span>) {
            mInterpolator = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">value</span>;
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
            mInterpolator = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> LinearInterpolator();
        }
    }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

我们看到这里有一个mInterpolator变量，如果我们不执行这个方法，那么mInterpolator 的默认值是多少呢？
我们找到了这样两行代码：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// The time interpolator to be used if none is set on the animation</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">final</span> TimeInterpolator sDefaultInterpolator =
            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> AccelerateDecelerateInterpolator();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">private</span> TimeInterpolator mInterpolator = sDefaultInterpolator;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li></ul>

这下明朗了，如果我们不设置，那么系统默认使用AccelerateDecelerateInterpolator，AccelerateDecelerateInterpolator又是什么呢？继续看源码：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">AccelerateDecelerateInterpolator</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">BaseInterpolator</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">NativeInterpolatorFactory</span> {</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">AccelerateDecelerateInterpolator</span>() {
    }

    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@SuppressWarnings</span>({<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"UnusedDeclaration"</span>})
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">AccelerateDecelerateInterpolator</span>(Context context, AttributeSet attrs) {
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">float</span> <span class="hljs-title" style="box-sizing: border-box;">getInterpolation</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">float</span> input) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">float</span>)(Math.cos((input + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>) * Math.PI) / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2.0</span>f) + <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0.5</span>f;
    }

    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @hide</span> */</span>
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> <span class="hljs-title" style="box-sizing: border-box;">createNativeInterpolator</span>() {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> NativeInterpolatorFactoryHelper.createAccelerateDecelerateInterpolator();
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>

这里的一个核心函数就是getInterpolation，使用了反余弦函数，input传入的值在0-1之间，因此这里返回值的变化速率就是先增加后减少，对应的动画执行速率就是先增加后减速。有兴趣的童鞋可以使用MatLab来画一下这个函数的图像。而当我们实现了LinearInterpolator之后，情况发生了变化：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">LinearInterpolator</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">extends</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">BaseInterpolator</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">NativeInterpolatorFactory</span> {</span>

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">LinearInterpolator</span>() {
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-title" style="box-sizing: border-box;">LinearInterpolator</span>(Context context, AttributeSet attrs) {
    }

    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">float</span> <span class="hljs-title" style="box-sizing: border-box;">getInterpolation</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">float</span> input) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> input;
    }

    <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**<span class="hljs-javadoctag" style="color: rgb(102, 0, 102); box-sizing: border-box;"> @hide</span> */</span>
    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">long</span> <span class="hljs-title" style="box-sizing: border-box;">createNativeInterpolator</span>() {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> NativeInterpolatorFactoryHelper.createLinearInterpolator();
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>

这里干净利落直接返回了input，没有经过任何计算。input返回的值是均匀的，因此动画得以匀速执行。
看到这里，大家应该就明白了，如果我们想要控制动画的执行速率，应该重写getInterpolation方法就能实现。为了证实我们的猜想，我们继续看源码。

大部分时候，我们使用的系统提供的各种各样的**Interpolator，比如上文说的LinearInterpolator，这些类都是继承自Interpolator，而Interpolator则实现了TimeInterpolator接口，我们来看看一个继承结构图：

这里写图片描述

那么这个终极大Boss TimeInterpolator究竟是什么样子呢？

<code class="hljs applescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">package android.animation;

/**
 * A <span class="hljs-property" style="box-sizing: border-box;">time</span> interpolator defines <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> rate <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> change <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> an animation. This allows animations
 * <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> have non-linear motion, such <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">as</span> acceleration <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> deceleration.
 */
public interface TimeInterpolator {

    /**
     * Maps a value representing <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> elapsed fraction <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> an animation <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> a value <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">that</span> represents
     * <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interpolated fraction. This interpolated value <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">then</span> multiplied <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">by</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> change <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span>
     * value <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> an animation <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> derive <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> animated value <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">at</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> current elapsed animation <span class="hljs-property" style="box-sizing: border-box;">time</span>.
     *
     * @param input A value <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">between</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1.0</span> indicating our current point
     *        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> animation <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">where</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> represents <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> start <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1.0</span> represents
     *        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">end</span>
     * @<span class="hljs-constant" style="box-sizing: border-box;">return</span> The interpolation value. This value can be more than <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1.0</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span>
     *         interpolators which overshoot their targets, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">or</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">less than</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span>
     *         interpolators <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">that</span> undershoot their targets.
     */
    float getInterpolation(float input);
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li></ul>

源码还是很简单的，只有一个方法，就是getInterpolation，看来没错，就是它了，如果我们想要自定义Interpolator，只需要实现TimeInterpolator接口的getInterpolation方法就可以了，getInterpolation方法接收的参数是动画执行的百分比，这个值是均匀的。
我们来个简单的案例：

<code class="hljs java has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">class</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">TanInterpolator</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">implements</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">TimeInterpolator</span> {</span>

    <span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@Override</span>
    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">float</span> <span class="hljs-title" style="box-sizing: border-box;">getInterpolation</span>(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">float</span> t) {
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">float</span>) Math.sin((t / <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>) * Math.PI);
    }
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>

在动画中使用：

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">            TanInterpolator tl = new TanInterpolator()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            ObjectAnimator animator = ObjectAnimator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ofFloat</span>(tv, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"rotation"</span>,
                    <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>f, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">360</span>f)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            animator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setInterpolator</span>(tl)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            animator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.setDuration</span>(<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5000</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
            animator<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.start</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

咦？这是什么效果？这是一开始速度很大，然后逐渐减小到0的动画效果.
原因如下：
看下图，这是sin函数图象：
这里写图片描述