在有些listview上面和ScrollView上，当滑动到底部的时候，在右下角会出现一个回到顶部的按钮，提供更好的用户体验。

效果图如下：

先说布局，可以用帧布局Framelayout，也可以用相对布局relativelayout.看下listview的布局文件：

<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:background="@android:color/white" ><ListViewandroid:id="@+id/my_listView"android:layout_width="fill_parent"android:layout_height="wrap_content"android:layout_marginLeft="10dp"android:layout_marginRight="10dp" /><Buttonandroid:id="@+id/top_btn"android:layout_width="50dp"android:layout_height="50dp"android:visibility="gone"android:layout_alignParentBottom="true"android:layout_alignParentRight="true"android:layout_marginBottom="6dp"android:layout_marginRight="6dp"android:background="@drawable/top_btn_bg"android:gravity="center"android:text="顶" /></RelativeLayout>

/*** 主界面* * @author zihao* @details 因为有些手机是有虚拟按键的（在计算屏幕分辨率的时候，有些可以去除掉虚拟区域的区域->如三星，有些不行->如MX3），为了计算的准确性，*          各位可以设置Activity为Theme*          .NoTitleBar.Fullscreen填满屏幕(解决类似MX3这种在计算过程中把虚拟键盘算入屏幕高度的)。*/
public class ListActivity extends Activity implements OnClickListener {private ListView listView;// List数据列表private Button toTopBtn;// 返回顶部的按钮private MyAdapter adapter;private boolean scrollFlag = false;// 标记是否滑动private int lastVisibleItemPosition = 0;// 标记上次滑动位置@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_list);initView();}/*** 初始化视图*/private void initView() {listView = (ListView) findViewById(R.id.my_listView);toTopBtn = (Button) findViewById(R.id.top_btn);adapter = new MyAdapter(this, getTitleDatas());listView.setAdapter(adapter);toTopBtn.setOnClickListener(this);listView.setOnScrollListener(new OnScrollListener() {@Overridepublic void onScrollStateChanged(AbsListView view, int scrollState) {// TODO Auto-generated method stubswitch (scrollState) {// 当不滚动时case OnScrollListener.SCROLL_STATE_IDLE:// 是当屏幕停止滚动时scrollFlag = false;// 判断滚动到底部if (listView.getLastVisiblePosition() == (listView.getCount() - 1)) {toTopBtn.setVisibility(View.VISIBLE);}// 判断滚动到顶部if (listView.getFirstVisiblePosition() == 0) {toTopBtn.setVisibility(View.GONE);}break;case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:// 滚动时scrollFlag = true;break;case OnScrollListener.SCROLL_STATE_FLING:// 是当用户由于之前划动屏幕并抬起手指，屏幕产生惯性滑动时scrollFlag = false;break;}}/*** firstVisibleItem：当前能看见的第一个列表项ID（从0开始）* visibleItemCount：当前能看见的列表项个数（小半个也算） totalItemCount：列表项共数*/@Overridepublic void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {// 当开始滑动且ListView底部的Y轴点超出屏幕最大范围时，显示或隐藏顶部按钮if (scrollFlag&& ScreenUtil.getScreenViewBottomHeight(listView) >= ScreenUtil.getScreenHeight(ListActivity.this)) {if (firstVisibleItem > lastVisibleItemPosition) {// 上滑toTopBtn.setVisibility(View.VISIBLE);} else if (firstVisibleItem < lastVisibleItemPosition) {// 下滑toTopBtn.setVisibility(View.GONE);} else {return;}lastVisibleItemPosition = firstVisibleItem;}}});}/*** 获取标题数据列表* * @return*/private List<String> getTitleDatas() {List<String> titleArray = new ArrayList<String>();for (int i = 0; i < 30; i++) {titleArray.add("这是第" + i + "个item");}return titleArray;}/*** 滚动ListView到指定位置* * @param pos*/private void setListViewPos(int pos) {if (android.os.Build.VERSION.SDK_INT >= 8) {listView.smoothScrollToPosition(pos);} else {listView.setSelection(pos);}}@Overridepublic void onClick(View v) {// TODO Auto-generated method stubswitch (v.getId()) {case R.id.top_btn:// 点击按钮返回到ListView的第一项setListViewPos(0);break;}}}

public class ScrollViewActivity extends Activity implements OnClickListener {private ScrollView scrollView;// scrollView数据列表private Button toTopBtn;// 返回顶部的按钮private int scrollY = 0;// 标记上次滑动位置private View contentView;private final String TAG="test";@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_scroll);initView();}/*** 初始化视图*/private void initView() {scrollView = (ScrollView) findViewById(R.id.my_scrollView);if (contentView == null) {contentView = scrollView.getChildAt(0);}toTopBtn = (Button) findViewById(R.id.top_btn);toTopBtn.setOnClickListener(this);//http://blog.csdn.net/jiangwei0910410003/article/details/17024287/******************** 监听ScrollView滑动停止 *****************************/scrollView.setOnTouchListener(new OnTouchListener() {private int lastY = 0;private int touchEventId = -9983761;Handler handler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);View scroller = (View) msg.obj;if (msg.what == touchEventId) {if (lastY == scroller.getScrollY()) {handleStop(scroller);} else {handler.sendMessageDelayed(handler.obtainMessage(touchEventId, scroller), 5);lastY = scroller.getScrollY();}}}};public boolean onTouch(View v, MotionEvent event) {if (event.getAction() == MotionEvent.ACTION_UP) {handler.sendMessageDelayed(handler.obtainMessage(touchEventId, v), 5);}return false;}/*** ScrollView 停止* * @param view*/private void handleStop(Object view) {Log.i(TAG,"handleStop");ScrollView scroller = (ScrollView) view;scrollY = scroller.getScrollY();doOnBorderListener();}});/***********************************************************/}/*** ScrollView 的顶部，底部判断：* http://www.trinea.cn/android/on-bottom-load-more-scrollview-impl/* * 其中getChildAt表示得到ScrollView的child View， 因为ScrollView只允许一个child* view，所以contentView.getMeasuredHeight()表示得到子View的高度,* getScrollY()表示得到y轴的滚动距离，getHeight()为scrollView的高度。* 当getScrollY()达到最大时加上scrollView的高度就的就等于它内容的高度了啊~* * @param pos*/private void doOnBorderListener() {Log.i(TAG,ScreenUtil.getScreenViewBottomHeight(scrollView) + "  "+ scrollView.getScrollY()+" "+ ScreenUtil.getScreenHeight(ScrollViewActivity.this));// 底部判断if (contentView != null&& contentView.getMeasuredHeight() <= scrollView.getScrollY()+ scrollView.getHeight()) {toTopBtn.setVisibility(View.VISIBLE);Log.i(TAG,"bottom");}// 顶部判断else if (scrollView.getScrollY() == 0) {Log.i(TAG,"top");}else if (scrollView.getScrollY() > 30) {toTopBtn.setVisibility(View.VISIBLE);Log.i(TAG,"test");}}/*** 下面我们看一下这个函数: scrollView.fullScroll(ScrollView.FOCUS_DOWN);滚动到底部* scrollView.fullScroll(ScrollView.FOCUS_UP);滚动到顶部* * * 需要注意的是，该方法不能直接被调用 因为Android很多函数都是基于消息队列来同步，所以需要一部操作，* addView完之后，不等于马上就会显示，而是在队列中等待处理，虽然很快， 但是如果立即调用fullScroll，* view可能还没有显示出来，所以会失败 应该通过handler在新线程中更新* * http://blog.csdn.net/t12x3456/article/details/12799825* http://www.tuicool.com/articles/zayIjq*/@Overridepublic void onClick(View v) {// TODO Auto-generated method stubswitch (v.getId()) {case R.id.top_btn :scrollView.post(new Runnable() {@Overridepublic void run() {scrollView.fullScroll(ScrollView.FOCUS_UP);}});toTopBtn.setVisibility(View.GONE);break;}}}

很多细节都注释在代码里面了，参考链接也已经加上。大家下载下代码执行一下看看。