一、大致的实现思路
给ListView添加HeadView和FootView，当ListView滑动至列表第一项时使HeadView滑动出现，当ListView滑动至列表最后一项时使FootView滑动出现。HeadView和FootView的高度取决于用户手指滑动的距离（ACTION_MOVE初始时记录startPullDownY=event.getY()，startPullUpY=event.getY()，ACTION_MOVE结束时计算手指的总滑动距离moveDownY=event.getY()
- startPullDownY()，moveUpY=startPullUpY()-event.getY()），然后刷新HeadView和FootView的高度至moveDownY*0.5(moveUpY*0.5)，取值0.5是为了让用户感觉到视图滑动视差，形成一种平滑滑动的感觉。当用户滑动完毕放开手指时，调用任务调度类ScheduledExecutorService，实现HeadView和FootView的平滑回弹。
二、实现关键代码
添加HeadView和FootView
/**
* 初始化
*/
@SuppressWarnings("deprecation")
private void init(boolean isHeadViewNeed, boolean isTailViewNeed) {
Log.d(TAG, "isHeadViewNeed=" + isHeadViewNeed);
Log.d(TAG, "isTailViewNeed=" + isTailViewNeed);
if(isHeadViewNeed) {
// 监听滚动状态
setOnScrollListener(this);
// 创建PullListView的HeadView
mHeadView = new View(this.getContext());
// 默认白色背景,可以改变颜色, 也可以设置背景图片
mHeadView.setBackgroundColor(Color.parseColor("#4F9D9D"));
// 默认高度为0
mHeadView.setLayoutParams(new AbsListView.LayoutParams(
LayoutParams.FILL_PARENT, 0));
this.addHeaderView(mHeadView);
}
if(isTailViewNeed) {
// 监听滚动状态
setOnScrollListener(this);
// 创建PullListView的HeadView
mTailView = new View(this.getContext());
// 默认白色背景,可以改变颜色, 也可以设置背景图片
mTailView.setBackgroundColor(Color.parseColor("#4F9D9D"));
// 默认高度为0
mTailView.setLayoutParams(new AbsListView.LayoutParams(
LayoutParams.FILL_PARENT, 0));
this.addFooterView(mTailView);
}
}
重写ListView的onTouchEvent事件
/**
* 覆盖onTouchEvent方法,实现下拉回弹效果
*/
@SuppressWarnings("deprecation")
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
break;
case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
if (!isRecordPullDown && !isRecordPullUp) {
// it's not in pull down state or pull up state, break
Log.d(TAG, "ACTION_UP it's not in pull down state or pull up state, break");
break;
}
if(isPullDownState()) {
Log.d(TAG, "isRecordPullDown=" + isRecordPullDown);
// 以一定的频率递减HeadView的高度,实现平滑回弹
schedulor = Executors.newScheduledThreadPool(1);
schedulor.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
mHandler.sendEmptyMessage(PULL_DOWN_BACK_ACTION);
}
}, 0, PULL_BACK_TASK_PERIOD, TimeUnit.NANOSECONDS);
setPullDownState(!isRecordPullDown);
} else if(isPullUpState()) {
Log.d(TAG, "isRecordPullUp=" + isRecordPullUp);
// 以一定的频率递减HeadView的高度,实现平滑回弹
schedulor = Executors.newScheduledThreadPool(1);
schedulor.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
mHandler.sendEmptyMessage(PULL_UP_BACK_ACTION);
}
}, 0, PULL_BACK_TASK_PERIOD, TimeUnit.NANOSECONDS);
setPullUpState(!isRecordPullUp);
}
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG, "firstItemIndex=" + firstItemIndex);
if (!isRecordPullDown && firstItemIndex == 0) {
Log.d(TAG, "firstItemIndex=" + firstItemIndex + " set isRecordPullDown=true");
startPullDownY = (int) event.getY();
setPullType(PULL_DOWN_BACK_ACTION);
}else if (!isRecordPullUp && lastItemIndex == getCount()) {
Log.d(TAG, "lastItemIndex == getCount()" + " set isRecordPullUp=true");
startPullUpY = (int) event.getY();
setPullType(PULL_UP_BACK_ACTION);
}
if (!isRecordPullDown && !isRecordPullUp) {
// it's not in pull down state or pull up state, break
Log.d(TAG, "ACTION_MOVE it's not in pull down state or pull up state, break");
break;
}
if(isRecordPullDown) {
int tempY = (int) event.getY();
int moveY = tempY - startPullDownY;
if (moveY
使用Handler完成HeadView和FootView的回弹效果
/**
* 实现回弹效果的handler,用于递减HeadView的高度并请求重绘
*/
@SuppressLint("HandlerLeak")
private Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
switch(msg.what) {
case PULL_DOWN_BACK_ACTION:
AbsListView.LayoutParams headerParams = (LayoutParams) mHeadView
.getLayoutParams();
// 递减高度
headerParams.height -= PULL_BACK_REDUCE_STEP;
mHeadView.setLayoutParams(headerParams);
// 重绘
mHeadView.invalidate();
// 停止回弹时递减headView高度的任务
if (headerParams.height
重写ListView的onScroll方法和onScrollStateChanged方法
@Override
public void onScroll(AbsListView view, int firstVisiableItem,
int visibleItemCount, int totalItemCount) {
this.firstItemIndex = firstVisiableItem;
this.lastItemIndex = firstVisiableItem + visibleItemCount;
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
currentScrollState = scrollState;
Log.d(TAG, "scrollState: " + getScrollStateString(currentScrollState));
}
private String getScrollStateString(int flag) {
String str = "";
switch(flag) {
case OnScrollListener.SCROLL_STATE_IDLE:
str = "SCROLL_STATE_IDLE";
break;
case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
str = "SCROLL_STATE_TOUCH_SCROLL";
break;
case OnScrollListener.SCROLL_STATE_FLING:
str = "SCROLL_STATE_FLING";
break;
default:
str = "wrong state";
}
return str;
}三、实现效果图
