Rebound动画框架简单介绍
Android菜鸟一枚,有不对的地方希望大家指出，谢谢。
最近在接手了一个老项目，发现里面动画框架用的是facebook中的Rebound框架，由于以前没听说过，放假时闲得蛋痛，看看了源码，就顺手写这一篇吧。
写了一个小Demo，具体效果如下：
代码很简单，这是xml布局：
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="@+id/image"
android:src="@drawable/a1" />
</RelativeLayout>
这是MainActivity：
package com.micro.mytest_button;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;
import com.facebook.rebound.Spring;
import com.facebook.rebound.SpringListener;
import com.facebook.rebound.SpringSystem;
import com.nineoldandroids.view.ViewHelper;
public class MainActivity extends Activity {
private ImageView image;
private Spring spring;
private final float mScale = 1.0f;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
image = (ImageView) findViewById(R.id.image);
SpringSystem springSystem = SpringSystem.create();
spring = springSystem.createSpring();
spring.addListener(new SpringListener() {
@Override
public void onSpringUpdate(Spring spring) {
float value = (float) spring.getCurrentValue();
float scale = 1f - (value * mScale);
System.out.println("the value is " + value + "--the scale is --" + scale);
ViewHelper.setScaleX(image, scale);
ViewHelper.setScaleY(image, scale);
}
@Override
public void onSpringEndStateChange(Spring spring) {
}
@Override
public void onSpringAtRest(Spring spring) {
}
@Override
public void onSpringActivate(Spring spring) {
}
});
image.setOnTouchListener(new OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
spring.setEndValue(1.0f);
break;
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL:
spring.setEndValue(0.0f);
break;
}
return true;
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
现在主要是来分析下Rebound的源码，看看里面到底怎么走的，用法很简单（这是最简单的用法），就三句话：
SpringSystem springSystem = SpringSystem.create();
spring = springSystem.createSpring();
spring.addListener(new SpringListener() {}- 1
主要是创建了三个对象，SpringSystem/spring/SpringListener，对于动画的效果，就是这三个玩意搞出来的。具体的模式如下：
SpringSystem:继承自BaseSpringSystem，其中包含了Spring对象引用的容器，控制Spring对象的操作，存在一个SpringLooper（是一个抽象方法，只有start()/stop()方法），这也是facebook自定义的类，与android.os.Looper无关，只是模拟了android.os.Looper的方法，内存start(),end()方法。其构造方法：
public static SpringSystem create() {
return new SpringSystem(AndroidSpringLooperFactory.createSpringLooper());
}- 1
打开SpringSystem(SpringLooper sl)源码：
public BaseSpringSystem(SpringLooper springLooper) {
if (springLooper == null) {
throw new IllegalArgumentException("springLooper is required");
}
mSpringLooper = springLooper;
mSpringLooper.setSpringSystem(this);
}- 1
现在再看AndroidSpringLooperFactory.createSpringLooper()源码：
public static SpringLooper createSpringLooper() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
return ChoreographerAndroidSpringLooper.create();
} else {
return LegacyAndroidSpringLooper.create();
}
}- 1
可以看到为了兼容JDK,高低版本创建的SpringLooper容器不经相同，这个不是考虑的重点。
现在来看第二句：
spring = springSystem.createSpring();- 1
翻开SpringSytem.createSpring()源码：
public Spring createSpring() {
Spring spring = new Spring(this);
registerSpring(spring);
return spring;
}- 1
- 2
可以看到Spring类是一个对立的Java类，持有SpringSystem的引用，来看看Spring（SpringSystem ss)构造函数：
Spring(BaseSpringSystem springSystem) {
if (springSystem == null) {
throw new IllegalArgumentException("Spring cannot be created outside of a BaseSpringSystem");
}
mSpringSystem = springSystem;
mId = "spring:" + ID++;
setSpringConfig(SpringConfig.defaultConfig);
}再看setSpringConfig(SpringConfig.defaultConfig)源码：
public Spring setSpringConfig(SpringConfig springConfig) {
if (springConfig == null) {
throw new IllegalArgumentException("springConfig is required");
}
mSpringConfig = springConfig;
return this;
}- 1
也只是初始化一些参数，并没有有我们想要的源码(这里的意思就是我点击图片时，它为什么会有动画的意思)，再看第三个方法吧：
spring.addListener(new SpringListener() {}- 1
添加监听器，用的多的人就会有感觉，这个也不会有关键代码可以使我们图片有缩放效果，那么问题来了，看到facebook写的三句话，我们并没有找到动画缩放的想过函数啊，是不是有配置文件或者静态/动态代码块呢？？找了很久，没有啊。那只有接下来再看image的代码了，在看到Image的绑定的onTouch事件上，看到了这句话：
spring.setEndValue(1.0f);- 1
啥也不说，进去看看再说吧：
public Spring setEndValue(double endValue) {
if (mEndValue == endValue && isAtRest()) {
return this;
}
mStartValue = getCurrentValue();
mEndValue = endValue;
mSpringSystem.activateSpring(this.getId());
for (SpringListener listener : mListeners) {
listener.onSpringEndStateChange(this);
}
return this;
}- 1
其他没啥好看的，看到了这句话：
mSpringSystem.activateSpring(this.getId());- 1
活了二十几年，立马感觉这句话有问题，进入看看：
void activateSpring(String springId) {
Spring spring = mSpringRegistry.get(springId);
if (spring == null) {
throw new IllegalArgumentException("springId " + springId + " does not reference a registered spring");
}
mActiveSprings.add(spring);
if (getIsIdle()) {
mIdle = false;
mSpringLooper.start();
}
}解释一下，刚才说的SpringSystem包含了Spring对象的引用，mSpringRegistry.get(springId)是找到SpringSystem中注册的Spring， mActiveSprings.add(spring)是将该spring添加到活动的spring队列中，那现在就看看这句话吧： mSpringLooper.start()，刚才说SpringLooper是一个抽象类，那好随便找个其子类看看里面的方法吧，
private static class LegacyAndroidSpringLooper extends SpringLooper {}- 1
刚才的兼容性代码中，JELLY_BEAN(也就是4.1之前的代码)，那我们就看看mSpringLooper.start()是个什么鬼了吧：
private static class LegacyAndroidSpringLooper extends SpringLooper {
private final Handler mHandler;
private final Runnable mLooperRunnable;
private boolean mStarted;
private long mLastTime;
/**
* @return an Android spring looper using a new {@link Handler} instance
*/
public static SpringLooper create() {
return new LegacyAndroidSpringLooper(new Handler());
}
public LegacyAndroidSpringLooper(Handler handler) {
mHandler = handler;
mLooperRunnable = new Runnable() {
@Override
public void run() {
if (!mStarted || mSpringSystem == null) {
return;
}
long currentTime = SystemClock.uptimeMillis();
mSpringSystem.loop(currentTime - mLastTime);
mHandler.post(mLooperRunnable);
}
};
}
@Override
public void start() {
if (mStarted) {
return;
}
mStarted = true;
mLastTime = SystemClock.uptimeMillis();
mHandler.removeCallbacks(mLooperRunnable);
mHandler.post(mLooperRunnable);
}
@Override
public void stop() {
mStarted = false;
mHandler.removeCallbacks(mLooperRunnable);
}
}对，没错我们看到了 mHandler.post(mLooperRunnable);金典的方法啊，那我们看看这mLooperRunnable方法里面在干嘛吧，
long currentTime = SystemClock.uptimeMillis();
mSpringSystem.loop(currentTime - mLastTime);废话不多说，立马去找我们想要看到的SpringSystem.loop方法了：
public void loop(double ellapsedMillis) {
for (SpringSystemListener listener : mListeners) {
listener.onBeforeIntegrate(this);
}
advance(ellapsedMillis);
if (mActiveSprings.isEmpty()) {
mIdle = true;
}
for (SpringSystemListener listener : mListeners) {
listener.onAfterIntegrate(this);
}
if (mIdle) {
mSpringLooper.stop();
}
}
对了，我们好像看到了advance(ellapsedMillis)啊，这个看起来比较吊，不说了进去看看再说啊：
void advance(double deltaTime) {
for (Spring spring : mActiveSprings) {
// advance time in seconds
if (spring.systemShouldAdvance()) {
spring.advance(deltaTime / 1000.0);
} else {
mActiveSprings.remove(spring);
}
}
}尼玛啊，我看到了
spring.advance(deltaTime / 1000.0);哈哈，我感觉快要找到了，不说，赶快进去找：
void advance(double realDeltaTime) {
boolean isAtRest = isAtRest();
if (isAtRest && mWasAtRest) {
/* begin debug
Log.d(TAG, "bailing out because we are at rest:" + getName());
end debug */
return;
}
// clamp the amount of realTime to simulate to avoid stuttering in the UI. We should be able
// to catch up in a subsequent advance if necessary.
double adjustedDeltaTime = realDeltaTime;
if (realDeltaTime > MAX_DELTA_TIME_SEC) {
adjustedDeltaTime = MAX_DELTA_TIME_SEC;
}
/* begin debug
long startTime = System.currentTimeMillis();
int iterations = 0;
end debug */
mTimeAccumulator += adjustedDeltaTime;
double tension = mSpringConfig.tension;
double friction = mSpringConfig.friction;
double position = mCurrentState.position;
double velocity = mCurrentState.velocity;
double tempPosition = mTempState.position;
double tempVelocity = mTempState.velocity;
double aVelocity, aAcceleration;
double bVelocity, bAcceleration;
double cVelocity, cAcceleration;
double dVelocity, dAcceleration;
double dxdt, dvdt;
// iterate over the true time
while (mTimeAccumulator >= SOLVER_TIMESTEP_SEC) {
/* begin debug
iterations++;
end debug */
mTimeAccumulator -= SOLVER_TIMESTEP_SEC;
if (mTimeAccumulator < SOLVER_TIMESTEP_SEC) {
// This will be the last iteration. Remember the previous state in case we need to
// interpolate
mPreviousState.position = position;
mPreviousState.velocity = velocity;
}
// Perform an RK4 integration to provide better detection of the acceleration curve via
// sampling of Euler integrations at 4 intervals feeding each derivative into the calculation
// of the next and taking a weighted sum of the 4 derivatives as the final output.
// This math was inlined since it made for big performance improvements when advancing several
// springs in one pass of the BaseSpringSystem.
// The initial derivative is based on the current velocity and the calculated acceleration
aVelocity = velocity;
aAcceleration = (tension * (mEndValue - tempPosition)) - friction * velocity;
// Calculate the next derivatives starting with the last derivative and integrating over the
// timestep
tempPosition = position + aVelocity * SOLVER_TIMESTEP_SEC * 0.5;
tempVelocity = velocity + aAcceleration * SOLVER_TIMESTEP_SEC * 0.5;
bVelocity = tempVelocity;
bAcceleration = (tension * (mEndValue - tempPosition)) - friction * tempVelocity;
tempPosition = position + bVelocity * SOLVER_TIMESTEP_SEC * 0.5;
tempVelocity = velocity + bAcceleration * SOLVER_TIMESTEP_SEC * 0.5;
cVelocity = tempVelocity;
cAcceleration = (tension * (mEndValue - tempPosition)) - friction * tempVelocity;
tempPosition = position + cVelocity * SOLVER_TIMESTEP_SEC;
tempVelocity = velocity + cAcceleration * SOLVER_TIMESTEP_SEC;
dVelocity = tempVelocity;
dAcceleration = (tension * (mEndValue - tempPosition)) - friction * tempVelocity;
// Take the weighted sum of the 4 derivatives as the final output.
dxdt = 1.0/6.0 * (aVelocity + 2.0 * (bVelocity + cVelocity) + dVelocity);
dvdt = 1.0/6.0 * (aAcceleration + 2.0 * (bAcceleration + cAcceleration) + dAcceleration);
position += dxdt * SOLVER_TIMESTEP_SEC;
velocity += dvdt * SOLVER_TIMESTEP_SEC;
}
mTempState.position = tempPosition;
mTempState.velocity = tempVelocity;
mCurrentState.position = position;
mCurrentState.velocity = velocity;
if (mTimeAccumulator > 0) {
interpolate(mTimeAccumulator / SOLVER_TIMESTEP_SEC);
}
// End the spring immediately if it is overshooting and overshoot clamping is enabled.
// Also make sure that if the spring was considered within a resting threshold that it's now
// snapped to its end value.
if (isAtRest() || (mOvershootClampingEnabled && isOvershooting())) {
// Don't call setCurrentValue because that forces a call to onSpringUpdate
mStartValue = mEndValue;
mCurrentState.position = mEndValue;
setVelocity(0);
isAtRest = true;
}
/* begin debug
long endTime = System.currentTimeMillis();
long elapsedMillis = endTime - startTime;
Log.d(TAG,
"iterations:" + iterations +
" iterationTime:" + elapsedMillis +
" position:" + mCurrentState.position +
" velocity:" + mCurrentState.velocity +
" realDeltaTime:" + realDeltaTime +
" adjustedDeltaTime:" + adjustedDeltaTime +
" isAtRest:" + isAtRest +
" wasAtRest:" + mWasAtRest);
end debug */
// NB: do these checks outside the loop so all listeners are properly notified of the state
// transition
boolean notifyActivate = false;
if (mWasAtRest) {
mWasAtRest = false;
notifyActivate = true;
}
boolean notifyAtRest = false;
if (isAtRest) {
mWasAtRest = true;
notifyAtRest = true;
}
for (SpringListener listener : mListeners) {
// starting to move
if (notifyActivate) {
listener.onSpringActivate(this);
}
// updated
listener.onSpringUpdate(this);
// coming to rest
if (notifyAtRest) {
listener.onSpringAtRest(this);
}
}
}- 1
代码精简一下，就变成这样了：
void advance(double realDeltaTime) {
boolean isAtRest = isAtRest();
if (isAtRest && mWasAtRest) {
return;
}
double adjustedDeltaTime = realDeltaTime;
if (realDeltaTime > MAX_DELTA_TIME_SEC) {
adjustedDeltaTime = MAX_DELTA_TIME_SEC;
}
mTimeAccumulator += adjustedDeltaTime;
while (mTimeAccumulator >= SOLVER_TIMESTEP_SEC) {
/**
inner change
**/
}
mTempState.position = tempPosition;
mTempState.velocity = tempVelocity;
mCurrentState.position = position;
mCurrentState.velocity = velocity;
for (SpringListener listener : mListeners) {
// starting to move
if (notifyActivate) {
listener.onSpringActivate(this);
}
// updated
listener.onSpringUpdate(this);
// coming to rest
if (notifyAtRest) {
listener.onSpringAtRest(this);
}
}
}- 1
这下看得十分清楚了吧，在while循环里面变换之后，我们得到了 ：
mCurrentState.position = position;
mCurrentState.velocity = velocity;然后在接口回调中我们使用到了这些参数，
spring.addListener(new SpringListener() {
@Override
public void onSpringUpdate(Spring spring) {
float value = (float) spring.getCurrentValue();
float scale = 1f - (value * mScale);
ViewHelper.setScaleX(image, scale);
ViewHelper.setScaleY(image, scale);
}
@Override
public void onSpringEndStateChange(Spring spring) {}
@Override
public void onSpringAtRest(Spring spring) {}
@Override
public void onSpringActivate(Spring spring) {}
});
就这样我么的变换终于就成功了，我们也就走通了相关的流程了，是不是很好玩呢？？？主要是facebook这个Rebound框架很小，类很少，我们可以在很短的时间对它通读，是不是感觉到分析源码很好玩呢？我也是一名android菜鸟，很多时候不敢去分析源码，很为很多的东西都看不懂看不透，那就慢慢来吧，先从简单的开始吧，呵呵。
最后，代码地址