PullToRefreshScrollView踩坑经历以及源码分析

         目前下拉刷新已经满大街都是，在自己的应用如果不使用这个模式的话，出门都不好意思和人家打招呼

，该文章结合自己使用PullToRefreshScrollView过程中所遇到的问题，简单探讨下针对于github
上的这个开源项目的使用心得，具体的使用方法不做探究。

         首先描述下自己使用PullToRefreshScrollView所遇到的BUG现象吧：在ScrollView下拉刷新时去服务端获取数据并进行展示，获取数据的过程采用线程池管理线程（具体优点儿不做解释），进行到该步发现一个奇妙的问题，发现一下拉刷新APP就闪退了，查看Log错误显示ThreadPoolExecutor队列满了RejectedExecutionException，怀疑我的ThreadPoolExecutor容量不够大，虽扩大至20，再次测试依然闪退，并没有什么乱用，仍然是队列已满错误。之后层层源码追看，发现了端倪，onPullDownToRefresh该方法一直不断的在调用，所以导致ThreadPoolExecutor里面的任务一直变多，导致容量急剧增加，进而闪退。把自己的解决过程记录下来献给遇到同样问题的童鞋。

          →代表调用的意思

         当用户下拉刷新并松开手指时会调用PullToRefreshBase.java的onTouchEvent的case MotionEvent.ACTION_UP→PullToRefreshBase.java的final void setState(State state, final boolean... params)其PullToRefreshBase.java的中state=MANUAL_REFRESHING，params=[true]→PullToRefreshBase.java的protected
void onRefreshing(final boolean doScroll) 其中doScroll=true→PullToRefreshBase.java的protected final void smoothScrollTo(int scrollValue, OnSmoothScrollFinishedListener listener)→PullToRefreshBase.java的private final void smoothScrollTo(int newScrollValue, long
duration, long delayMillis,OnSmoothScrollFinishedListener listener)→PullToRefreshBase.java的public SmoothScrollRunnable(int fromY, int toY, long duration, OnSmoothScrollFinishedListener listener)实例化一个线程→PullToRefreshBase.java的post(mCurrentSmoothScrollRunnable);运行SmoothScrollRunnable线程从SmoothScrollRunnable内部源码

final class SmoothScrollRunnable implements Runnable
{
private final Interpolator mInterpolator;

private final int mScrollToY;

private final int mScrollFromY;

private final long mDuration;

private OnSmoothScrollFinishedListener mListener;

private boolean mContinueRunning = true;

private long mStartTime = -1;

private int mCurrentY = -1;

public SmoothScrollRunnable(int fromY, int toY, long duration, OnSmoothScrollFinishedListener listener)
{
Log.i("TTT", " SmoothScrollRunnable 实例化");
mScrollFromY = fromY;
mScrollToY = toY;
mInterpolator = mScrollAnimationInterpolator;
mDuration = duration;
mListener = listener;
}

@Override
public void run()
{

/**
* Only set mStartTime if this is the first time we're starting,
* else actually calculate the Y delta
*/
if (mStartTime == -1)
{
mStartTime = System.currentTimeMillis();
Log.i("TTT", " mStartTime=" + mStartTime);
}
else
{

/**
* We do do all calculations in long to reduce software float
* calculations. We use 1000 as it gives us good accuracy and
* small rounding errors
*/
long normalizedTime = (1000 * (System.currentTimeMillis() - mStartTime)) / mDuration;
normalizedTime = Math.max(Math.min(normalizedTime, 10
4000
00), 0);

final int deltaY =
Math.round((mScrollFromY - mScrollToY) * mInterpolator.getInterpolation(normalizedTime / 1000f));
mCurrentY = mScrollFromY - deltaY;
setHeaderScroll(mCurrentY);
Log.i("TTT",
" normalizedTime=" + normalizedTime + ", mContinueRunning=" + mContinueRunning + ",mScrollToY="
+ mScrollToY + ",mCurrentY=" + mCurrentY);
}

// If we're not at the target Y, keep going...
if (mContinueRunning && mScrollToY != mCurrentY)
{
ViewCompat.postOnAnimation(PullToRefreshBase.this, this);
}
else
{
if (null != mListener)
{
Log.i("TTT", "mListener.onSmoothScrollFinished(),isSmoothScrollFinished=" + isSmoothScrollFinished);
mListener.onSmoothScrollFinished();
}
}
}

public void stop()
{
Log.i("TTT", " stop()");
mContinueRunning = false;
removeCallbacks(this);
}
}

首先将HeaderView采用postOnAnimation慢慢的隐藏掉，直到HeaderView隐藏掉之后mScrollToY == mCurrentY然后调用mListener.onSmoothScrollFinished()，该方法最终调用onPullDownToRefresh方法，如果onPullDownToRefresh里面开启一个线程去服务端获取数据，因为获取数据和SmoothScrollRunnable不在一个线程中，那么此时SmoothScrollRunnable获得时间片它的run方法会不断的运行，因此mListener.onSmoothScrollFinished()会不断的运行，所以会导致不停地向ThreadPoolExecutor提交任务，所以ThreadPoolExecutor容量会瞬间变满导致异常。因此考虑在SmoothScrollRunnable当中增加一个标志位，标志我当次已经在初始化中，具体代码如下，红色是新增的逻辑。

final class SmoothScrollRunnable implements Runnable
{
private final Interpolator mInterpolator;

private final int mScrollToY;

private final int mScrollFromY;

private final long mDuration;

private OnSmoothScrollFinishedListener mListener;

private boolean mContinueRunning = true;

private long mStartTime = -1;

private int mCurrentY = -1;

<span style="color:#FF0000;">private boolean isSmoothScrollFinished = false;</span>

public SmoothScrollRunnable(int fromY, int toY, long duration, OnSmoothScrollFinishedListener listener)
{
Log.i("TTT", " SmoothScrollRunnable 实例化");
mScrollFromY = fromY;
mScrollToY = toY;
mInterpolator = mScrollAnimationInterpolator;
mDuration = duration;
mListener = listener;
}

@Override
public void run()
{

/**
* Only set mStartTime if this is the first time we're starting,
* else actually calculate the Y delta
*/
if (mStartTime == -1)
{
mStartTime = System.currentTimeMillis();
Log.i("TTT", " mStartTime=" + mStartTime);
}
else
{

/**
* We do do all calculations in long to reduce software float
* calculations. We use 1000 as it gives us good accuracy and
* small rounding errors
*/
long normalizedTime = (1000 * (System.currentTimeMillis() - mStartTime)) / mDuration;
normalizedTime = Math.max(Math.min(normalizedTime, 1000), 0);

final int deltaY =
Math.round((mScrollFromY - mScrollToY) * mInterpolator.getInterpolation(normalizedTime / 1000f));
mCurrentY = mScrollFromY - deltaY;
setHeaderScroll(mCurrentY);
Log.i("TTT",
" normalizedTime=" + normalizedTime + ", mContinueRunning=" + mContinueRunning + ",mScrollToY="
+ mScrollToY + ",mCurrentY=" + mCurrentY);
}

// If we're not at the target Y, keep going...
if (mContinueRunning && mScrollToY != mCurrentY)
{
ViewCompat.postOnAnimation(PullToRefreshBase.this, this);
}
else
{
if (null != mListener)
{
Log.i("TTT", "mListener.onSmoothScrollFinished(),isSmoothScrollFinished=" + isSmoothScrollFinished);
<span style="color:#FF0000;">if (!isSmoothScrollFinished)</span>
<span style="color:#FF0000;">{</span>
mListener.onSmoothScrollFinished();
<span style="color:#FF0000;">}</span>
<span style="color:#FF0000;">isSmoothScrollFinished = true;</span>
}
}
}

public void stop()
{
Log.i("TTT", " stop()");
mContinueRunning = false;
<span style="color:#FF0000;">isSmoothScrollFinished = true;</span>
removeCallbacks(this);
}
}

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