先看下一个点击的效果，我看到其他的分析博客里面没有谈到这一点，在这个代码中，我们一直看到是listview的第二项，而listview的第一项被遮挡了起来，滑动至第一项：
点击头条，头条会变成以下：
然后，过一段时间，刷新完成以后，listview又setSelection(1),增加一条数据，同时，把顶部给遮挡住：
这是点击刷新，然后是下拉刷新：
最后结果和点击刷新相同。那现在开始看下代码：
首先看下所用到的控件和变量：
// 状态
private static final int TAP_TO_REFRESH = 1;//点击刷新
private static final int PULL_TO_REFRESH = 2; //拉动刷新
private static final int RELEASE_TO_REFRESH = 3; //释放刷新
private static final int REFRESHING = 4; //正在刷新
// 当前滑动状态
private int mCurrentScrollState;
// 当前刷新状态
private int mRefreshState;
//头视图的高度
private int mRefreshViewHeight;
//头视图 原始的top padding 属性值
private int mRefreshOriginalTopPadding;
private int mLastMotionY;
// 监听对listview的滑动动作
private OnRefreshListener mOnRefreshListener;
//箭头图片
private static int REFRESHICON = R.drawable.goicon;
//listview 滚动监听器
private OnScrollListener mOnScrollListener;
private LayoutInflater mInflater;
private RelativeLayout mRefreshView;
//顶部刷新时出现的控件
private TextView mRefreshViewText;
private ImageView mRefreshViewImage;
private ProgressBar mRefreshViewProgress;
private TextView mRefreshViewLastUpdated;
// 箭头动画效果
//变为向下的箭头
private RotateAnimation mFlipAnimation;
//变为逆向的箭头
private RotateAnimation mReverseFlipAnimation;
//是否反弹
private boolean mBounceHack;
看下点击刷新的代码过程：
在init()方法中初始化各个控件及设置监听：
private void init(Context context) {
// Load all of the animations we need in code rather than through XML
mFlipAnimation = new RotateAnimation(0, -180,RotateAnimation.RELATIVE_TO_SELF,
0.5f,RotateAnimation.RELATIVE_TO_SELF, 0.5f);
mFlipAnimation.setInterpolator(new LinearInterpolator());
mFlipAnimation.setDuration(250);
mFlipAnimation.setFillAfter(true);
mReverseFlipAnimation = new RotateAnimation(-180, 0,RotateAnimation.RELATIVE_TO_SELF, 0.5f,RotateAnimation.RELATIVE_TO_SELF, 0.5f);
mReverseFlipAnimation.setInterpolator(new LinearInterpolator());
mReverseFlipAnimation.setDuration(250);
mReverseFlipAnimation.setFillAfter(true);
mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
mRefreshView = (RelativeLayout) mInflater.inflate(R.layout.pull_to_refresh_header, this, false);
mRefreshViewText =(TextView) mRefreshView.findViewById(R.id.pull_to_refresh_text);
mRefreshViewImage =(ImageView) mRefreshView.findViewById(R.id.pull_to_refresh_image);
mRefreshViewProgress =(ProgressBar) mRefreshView.findViewById(R.id.pull_to_refresh_progress);
mRefreshViewLastUpdated =(TextView) mRefreshView.findViewById(R.id.pull_to_refresh_updated_at);
mRefreshViewImage.setMinimumHeight(50);
mRefreshView.setOnClickListener(new OnClickRefreshListener());
mRefreshOriginalTopPadding = mRefreshView.getPaddingTop();
mRefreshState = TAP_TO_REFRESH;
//为listview头部增加一个view
addHeaderView(mRefreshView);
super.setOnScrollListener(this);
measureView(mRefreshView);
mRefreshViewHeight = mRefreshView.getMeasuredHeight();
}
我们看到，mRefreshView控件既是listview用于刷新的头控件，这里它设置了监听事件：
mRefreshView.setOnClickListener(new OnClickRefreshListener());
我们再来看下监听事件的定义：
private class OnClickRefreshListener implements OnClickListener {
@Override
public void onClick(View v) {
if (mRefreshState != REFRESHING) {
prepareForRefresh();
onRefresh();
}
}
}
调用了preparForRefresh()（准备刷新）和onRefresh()（刷新）两个方法，然后在查看这两个方法的定义：
public void prepareForRefresh() {
resetHeaderPadding(); // 恢复header的边距
mRefreshViewImage.setVisibility(View.GONE);
// We need this hack, otherwise it will keep the previous drawable.
// 注意加上，否则仍然显示之前的图片
mRefreshViewImage.setImageDrawable(null);
mRefreshViewProgress.setVisibility(View.VISIBLE);
// Set refresh view text to the refreshing label
mRefreshViewText.setText(R.string.pull_to_refresh_refreshing_label);
mRefreshState = REFRESHING;
}
public void onRefresh() {
if (mOnRefreshListener != null) {
mOnRefreshListener.onRefresh();
}
}
其中，后者还是回调方法。
我们看下preparForRefresh()方法中，引用了resetHeadPadding()方法：
/**
* Sets the header padding back to original size.
* 将head的边距重置为初始的数值
*/
private void resetHeaderPadding() {
mRefreshView.setPadding(
mRefreshView.getPaddingLeft(),
mRefreshOriginalTopPadding,
mRefreshView.getPaddingRight(),
mRefreshView.getPaddingBottom());
}
从新设置下header距上下左右的距离。
最重要的方法应该是：onScroll()和onTouchEvent()方法，先看下onTouchEvent()方法：
@Override
public boolean onTouchEvent(MotionEvent event) {
//当前手指的Y值
final int y = (int) event.getY();
mBounceHack = false;
switch (event.getAction()) {
case MotionEvent.ACTION_UP:
//将垂直滚动条设置为可用状态
if (!isVerticalScrollBarEnabled()) {
setVerticalScrollBarEnabled(true);
}
if (getFirstVisiblePosition() == 0 && mRefreshState != REFRESHING) {
// 拖动距离达到刷新需要
if ((mRefreshView.getBottom() >= mRefreshViewHeight
|| mRefreshView.getTop() >= 0)
&& mRefreshState == RELEASE_TO_REFRESH) {
// 把状态设置为正在刷新
// Initiate the refresh
mRefreshState = REFRESHING; //将标量设置为，正在刷新
// 准备刷新
prepareForRefresh();
// 刷新
onRefresh();
} else if (mRefreshView.getBottom() < mRefreshViewHeight
|| mRefreshView.getTop() <= 0) {
// Abort refresh and scroll down below the refresh view
//停止刷新，并且滚动到头部刷新视图的下一个视图
resetHeader();
setSelection(1); //定位在第二个列表项
}
}
break;
case MotionEvent.ACTION_DOWN:
// 获得按下y轴位置
mLastMotionY = y;
break;
case MotionEvent.ACTION_MOVE:
//更行头视图的toppadding 属性
applyHeaderPadding(event);
break;
}
return super.onTouchEvent(event);
}
当按下的时候，记录按下y轴的位置，然后在move中调用了applyHeaderPadding()方法，我们再看下这个方法：
// 获得header距离
private void applyHeaderPadding(MotionEvent ev) {
//获取累积的动作数
int pointerCount = ev.getHistorySize();
for (int p = 0; p < pointerCount; p++) {
//如果是释放将要刷新状态
if (mRefreshState == RELEASE_TO_REFRESH) {
if (isVerticalFadingEdgeEnabled()) {
setVerticalScrollBarEnabled(false);
}
//历史累积的高度
int historicalY = (int) ev.getHistoricalY(p);
// Calculate the padding to apply, we divide by 1.7 to
// simulate a more resistant effect during pull.
// 计算申请的边距，除以1.7使得拉动效果更好
int topPadding = (int) (((historicalY - mLastMotionY)- mRefreshViewHeight) / 1.7);
mRefreshView.setPadding(
mRefreshView.getPaddingLeft(),
topPadding,
mRefreshView.getPaddingRight(),
mRefreshView.getPaddingBottom());
}
}
}
通过记录滑动距离，实时变化头部mRefreshView的上下左右的距离。
最后，看下手指松开的ACTION_UP：
case MotionEvent.ACTION_UP:
//将垂直滚动条设置为可用状态
if (!isVerticalScrollBarEnabled()) {
setVerticalScrollBarEnabled(true);
}
if (getFirstVisiblePosition() == 0 && mRefreshState != REFRESHING) {
// 拖动距离达到刷新需要
if ((mRefreshView.getBottom() >= mRefreshViewHeight
|| mRefreshView.getTop() >= 0)
&& mRefreshState == RELEASE_TO_REFRESH) {
// 把状态设置为正在刷新
// Initiate the refresh
mRefreshState = REFRESHING; //将标量设置为：正在刷新
// 准备刷新
prepareForRefresh();
// 刷新
onRefresh();
} else if (mRefreshView.getBottom() < mRefreshViewHeight
|| mRefreshView.getTop() <= 0) {
// Abort refresh and scroll down below the refresh view
//停止刷新，并且滚动到头部刷新视图的下一个视图
resetHeader();
setSelection(1); //定位在第二个列表项
}
}
break;
当滑动距离大于一个item的距离时，添加一个item，否则，弹回。
看完onTouchEvent()，然后再看一下onScroll()方法：
@Override
public void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {
// When the refresh view is completely visible, change the text to say
// "Release to refresh..." and flip the arrow drawable.
// 在refreshview完全可见时，设置文字为松开刷新，同时翻转箭头
//如果是接触滚动状态,并且不是正在刷新的状态
if (mCurrentScrollState == SCROLL_STATE_TOUCH_SCROLL&& mRefreshState != REFRESHING) {
if (firstVisibleItem == 0) {
//如果显示出来了第一个列表项，显示刷新图片
mRefreshViewImage.setVisibility(View.VISIBLE);
//如果下拉了listiview,则显示上拉刷新动画
if ((mRefreshView.getBottom() >= mRefreshViewHeight + 20|| mRefreshView.getTop() >= 0)
&& mRefreshState != RELEASE_TO_REFRESH) {
mRefreshViewText.setText(R.string.pull_to_refresh_release_label);
mRefreshViewImage.clearAnimation();
mRefreshViewImage.startAnimation(mFlipAnimation);
mRefreshState = RELEASE_TO_REFRESH;
//如果下拉距离不够，则回归原来的状态
} else if (mRefreshView.getBottom() < mRefreshViewHeight + 20
&& mRefreshState != PULL_TO_REFRESH) {
mRefreshViewText.setText(R.string.pull_to_refresh_pull_label);
if (mRefreshState != TAP_TO_REFRESH) {
mRefreshViewImage.clearAnimation();
mRefreshViewImage.startAnimation(mReverseFlipAnimation);
}
mRefreshState = PULL_TO_REFRESH;
}
} else {
mRefreshViewImage.setVisibility(View.GONE);
resetHeader();
}
//如果是滚动状态+ 第一个视图已经显示+ 不是刷新状态
} else if (mCurrentScrollState == SCROLL_STATE_FLING && firstVisibleItem == 0
&& mRefreshState != REFRESHING) {
setSelection(1);
mBounceHack = true;
} else if (mBounceHack && mCurrentScrollState == SCROLL_STATE_FLING) {
setSelection(1);
}
if (mOnScrollListener != null) {
mOnScrollListener.onScroll(view, firstVisibleItem,visibleItemCount, totalItemCount);
}
}
该方法是在滑动过程中，各种状况的处理。
onScroll()方法和onTouchEvent()方法的执行过程应该是，先onTouchEvent()的ACTION_DOWN，然后是ACTION_MOVE和onScroll()方法同时进行，最后是onTouchEvent()的ACTION_UP。也可以自己打log看一下。这样在onTouchEvent()处理header，就是mRefreshView的外部的各个熟悉，onScroll()里面处理header（mRefreshView）里面内部的控件变化，从逻辑上来说比较清晰。
在onScroll()中，引用方法resetHeader()方法：
/**
* Resets the header to the original state.
* 重置header为之前的状态
*/
private void resetHeader() {
if (mRefreshState != TAP_TO_REFRESH) {
mRefreshState = TAP_TO_REFRESH;
resetHeaderPadding();
// 将刷新图标换成箭头
// Set refresh view text to the pull label
mRefreshViewText.setText(R.string.pull_to_refresh_tap_label);
// Replace refresh drawable with arrow drawable
// 清除动画
mRefreshViewImage.setImageResource(REFRESHICON);
// Clear the full rotation animation
mRefreshViewImage.clearAnimation();
// Hide progress bar and arrow.
// 隐藏图标和进度条
mRefreshViewImage.setVisibility(View.GONE);
mRefreshViewProgress.setVisibility(View.GONE);
}
}
resetHead就是header（mRefreshView）的内部的具体操作。
当一切都完成以后，就可以调用onRefreshComplete()方法：
/**
* Resets the list to a normal state after a refresh.
* 重置listview为普通的listview
* @param lastUpdated
* Last updated at.
*/
public void onRefreshComplete(CharSequence lastUpdated) {
setLastUpdated(lastUpdated);
onRefreshComplete();
}
/**
* Resets the list to a normal state after a refresh.
* 重置listview为普通的listview，
*/
public void onRefreshComplete() {
resetHeader();
// If refresh view is visible when loading completes, scroll down to
// the next item.
if (mRefreshView.getBottom() > 0) {
invalidateViews(); //重绘视图
setSelection(1);
}
}
重新绘制listivew,然后setSelection(1)。
