该效果是一名国外工程师（johannilsson）的代码，拿来研究了下，自己整合了一下，现在拿出来，跟大家一起分享。
再次感谢这位国外工程师（johannilsson），谢谢！
新浪微博，和QQ空间里面，都有那个下拉刷新的效果，另很多人眼前一亮，细细分析，原理原来如此。
在原作者的基础上，写了一些注释，和帮助大家更好的阅读理解，（可能其中有些地方注释不准，欢迎指正，谢谢）
下面，就亮出关键代码：
**** 自定义listivew （关键代码）
public class PullToRefreshListView extends ListView implements OnScrollListener {
private static final int TAP_TO_REFRESH = 1; // 初始状态
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
private static final String TAG = "PullToRefreshListView";
//刷新接口
private OnRefreshListener mOnRefreshListener;
//箭头图片
private static int REFRESHICON = R.drawable.goicon;
/**
* listview 滚动监听器
*/
private OnScrollListener mOnScrollListener;
//视图索引器
private LayoutInflater mInflater;
/**
* 头部视图 内容 -- start
*/
private RelativeLayout mRefreshView;
private TextView mRefreshViewText;
private ImageView mRefreshViewImage;
private ProgressBar mRefreshViewProgress;
private TextView mRefreshViewLastUpdated;
/**
* 头部视图 内容 -- end
*/
//当前listivew 的滚动状态
private int mCurrentScrollState;
//当前listview 的刷新状态
private int mRefreshState;
//动画效果
//变为向下的箭头
private RotateAnimation mFlipAnimation;
//变为逆向的箭头
private RotateAnimation mReverseFlipAnimation;
//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;
//是否反弹
private boolean mBounceHack;
public PullToRefreshListView(Context context) {
super(context);
init(context);
}
public PullToRefreshListView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public PullToRefreshListView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context);
}
private void init(Context context) {
// Load all of the animations we need in code rather than through XML
//初始化动画
//
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);//(R.layout.pull_to_refresh_header, null);
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;
addHeaderView(mRefreshView);
super.setOnScrollListener(this);
measureView(mRefreshView);
mRefreshViewHeight = mRefreshView.getMeasuredHeight(); //获取头文件的测量高度
}
@Override
protected void onAttachedToWindow() {
setSelection(1);
}
@Override
public void setAdapter(ListAdapter adapter) {
super.setAdapter(adapter);
setSelection(1);
}
/**
* Set the listener that will receive notifications every time the list
* scrolls.
*
* @param l The scroll listener.
*/
@Override
public void setOnScrollListener(AbsListView.OnScrollListener l) {
mOnScrollListener = l;
}
/**
* Register a callback to be invoked when this list should be refreshed.
*
* @param onRefreshListener The callback to run.
*/
public void setOnRefreshListener(OnRefreshListener onRefreshListener) {
mOnRefreshListener = onRefreshListener;
}
/**
* Set a text to represent when the list was last updated.
* @param lastUpdated Last updated at.
*/
public void setLastUpdated(CharSequence lastUpdated) {
if (lastUpdated != null) {
mRefreshViewLastUpdated.setVisibility(View.VISIBLE);
mRefreshViewLastUpdated.setText(lastUpdated);
} else {
mRefreshViewLastUpdated.setVisibility(View.GONE);
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
//当前手指的Y值
final int y = (int) event.getY();
//Log.i(TAG, "触屏的Y值"+y);
mBounceHack = false; //不反弹
switch (event.getAction()) {
case MotionEvent.ACTION_UP:
//将垂直滚动条设置为可用状态
if (!isVerticalScrollBarEnabled()) {
setVerticalScrollBarEnabled(true);
}
//如果头部刷新条出现，并且不是正在刷新状态
if (getFirstVisiblePosition() == 0 && mRefreshState != REFRESHING) {
if ((mRefreshView.getBottom() >= mRefreshViewHeight
|| mRefreshView.getTop() >= 0)
&& mRefreshState == RELEASE_TO_REFRESH) { //如果头部视图处于拉离顶部的情况
// Initiate the refresh
mRefreshState = REFRESHING; //将标量设置为，正在刷新
prepareForRefresh(); //准备刷新
onRefresh(); //刷新
} 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:
mLastMotionY = y; //跟踪手指的Y值
break;
case MotionEvent.ACTION_MOVE:
//更行头视图的toppadding 属性
applyHeaderPadding(event);
break;
}
return super.onTouchEvent(event);
}
/****
* 不断的头部的top padding 属性
* @param ev
*/
private void applyHeaderPadding(MotionEvent ev) {
//获取累积的动作数
int pointerCount = ev.getHistorySize();
// Log.i(TAG, "获取累积的动作数"+pointerCount);
for (int p = 0; p < pointerCount; p++) {
if (mRefreshState == RELEASE_TO_REFRESH) { //如果是释放将要刷新状态
if (isVerticalFadingEdgeEnabled()) {
setVerticalScrollBarEnabled(false);
}
//历史累积的高度
int historicalY = (int) ev.getHistoricalY(p);
//Log.i(TAG, "单个动作getHistoricalY值："+historicalY);
// Calculate the padding to apply, we divide by 1.7 to
// simulate a more resistant effect during pull.
int topPadding = (int) (((historicalY - mLastMotionY)
- mRefreshViewHeight) / 1.7);
mRefreshView.setPadding(
mRefreshView.getPaddingLeft(),
topPadding,
mRefreshView.getPaddingRight(),
mRefreshView.getPaddingBottom());
}
}
}
/**
* Sets the header padding back to original size.
* 使头部视图的toppadding 恢复到初始值
*/
private void resetHeaderPadding() {
mRefreshView.setPadding(
mRefreshView.getPaddingLeft(),
mRefreshOriginalTopPadding,
mRefreshView.getPaddingRight(),
mRefreshView.getPaddingBottom());
}
/**
* Resets the header to the original state.
* 初始化头部视图 状态
*/
private void resetHeader() {
if (mRefreshState != TAP_TO_REFRESH) {
mRefreshState = TAP_TO_REFRESH; //初始刷新状态
//使头部视图的toppadding 恢复到初始值
resetHeaderPadding();
// Set refresh view text to the pull label
//将文字初始化
mRefreshViewText.setText(R.string.pull_to_refresh_tap_label);
// Replace refresh drawable with arrow drawable
//设置初始图片
mRefreshViewImage.setImageResource(REFRESHICON);
// Clear the full rotation animation
// 清除动画
mRefreshViewImage.clearAnimation();
// Hide progress bar and arrow.
//隐藏头视图
mRefreshViewImage.setVisibility(View.GONE);
//隐藏进度条
mRefreshViewProgress.setVisibility(View.GONE);
}
}
//测量视图的高度 private void measureView(View child) { //获取头部视图属性 ViewGroup.LayoutParams p = child.getLayoutParams(); if (p == null) { p = new ViewGroup.LayoutParams( ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT); } int childWidthSpec = ViewGroup.getChildMeasureSpec(0, 0 + 0, p.width); int lpHeight = p.height; int childHeightSpec; //不懂MeasureSpec------------------------------------------------------------------------------------------ if (lpHeight > 0) { //如果视图的高度大于0 childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight, MeasureSpec.EXACTLY); } else { childHeightSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED); } child.measure(childWidthSpec, childHeightSpec); //不懂MeasureSpec------------------------------------------------------------------------------------------ } /**** * 滑动事件 */ @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. if (mCurrentScrollState == SCROLL_STATE_TOUCH_SCROLL //如果是接触滚动状态,并且不是正在刷新的状态 && 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); if ((mRefreshView.getBottom() >= mRefreshViewHeight + 20 || mRefreshView.getTop() >= 0) && mRefreshState != RELEASE_TO_REFRESH) { //如果下拉了listiview,则显示上拉刷新动画 mRefreshViewText.setText(R.string.pull_to_refresh_release_label); mRefreshViewImage.clearAnimation(); mRefreshViewImage.startAnimation(mFlipAnimation); mRefreshState = RELEASE_TO_REFRESH; Log.i(TAG, "现在处于下拉状态"); } else if (mRefreshView.getBottom() < mRefreshViewHeight + 20 && mRefreshState != PULL_TO_REFRESH) { //如果没有到达，下拉刷新距离，则回归原来的状态 mRefreshViewText.setText(R.string.pull_to_refresh_pull_label); if (mRefreshState != TAP_TO_REFRESH) { mRefreshViewImage.clearAnimation(); mRefreshViewImage.startAnimation(mReverseFlipAnimation); Log.i(TAG, "现在处于回弹状态"); } mRefreshState = PULL_TO_REFRESH; } } else { mRefreshViewImage.setVisibility(View.GONE); //隐藏刷新图片 resetHeader(); //初始化，头部 } } else if (mCurrentScrollState == SCROLL_STATE_FLING //如果是自己滚动状态+ 第一个视图已经显示+ 不是刷新状态 && firstVisibleItem == 0 && mRefreshState != REFRESHING) { setSelection(1); mBounceHack = true; //状态为回弹 Log.i(TAG, "现在处于*滚动到顶部的状态"); } else if (mBounceHack && mCurrentScrollState == SCROLL_STATE_FLING) { setSelection(1); Log.i(TAG, "现在处于*滚动到顶部的状态"); } if (mOnScrollListener != null) { mOnScrollListener.onScroll(view, firstVisibleItem, visibleItemCount, totalItemCount); } } //滚动状态改变 @Override public void onScrollStateChanged(AbsListView view, int scrollState) { mCurrentScrollState = scrollState; if (mCurrentScrollState == SCROLL_STATE_IDLE) { //如果滚动停顿 mBounceHack = false; } if (mOnScrollListener != null) { mOnScrollListener.onScrollStateChanged(view, scrollState); } } //准备刷新 public void prepareForRefresh() { resetHeaderPadding(); //初始化，头部文件 mRefreshViewImage.setVisibility(View.GONE); // We need this hack, otherwise it will keep the previous drawable. 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; } //刷新 public void onRefresh() { Log.d(TAG, "执行刷新"); if (mOnRefreshListener != null) { mOnRefreshListener.onRefresh(); } } /** * 刷新完成 的回调函数 * Resets the list to a normal state after a refresh. * @param lastUpdated Last updated at. */ public void onRefreshComplete(CharSequence lastUpdated) { setLastUpdated(lastUpdated); onRefreshComplete(); } /** * 刷新完成回调函数 * Resets the list to a normal state after a refresh. */ public void onRefreshComplete() { Log.d(TAG, "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); } } /** * Invoked when the refresh view is clicked on. This is mainly used when * there's only a few items in the list and it's not possible to drag the * list. */ private class OnClickRefreshListener implements OnClickListener { @Override public void onClick(View v) { if (mRefreshState != REFRESHING) { //准备刷新 prepareForRefresh(); //刷新 onRefresh(); } } } /** * 刷新方法接口 */ public interface OnRefreshListener { public void onRefresh(); }
---------
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* 如果你还是没有弄明白的话，那就点击下面的链接，来下载整个demo项目:
http://download.csdn.net/detail/zjl5211314/3775209
原作者：johannilsson
选自：https://github.com/johannilsson/android-pulltorefresh