Android如何实现一个上拉刷新下拉加载的ListView
2019-12-20
关键字:自定义上下拉ListView
在 APK 开发中,一个具备在列表顶部下拉刷新、在列表尾部上拉加载功能的 ListView 的需求还是比较多的。
具备这种功能的优秀开源代码同样也有很多。
但今天,笔者就非要自己实现一个这样的控件不可。
以下是成品效果图:
这个控件的结构很简单:
1、一个LinearLayout容器打底;
2、一个ListView置于中间;
3、一个用于标识头部“下拉刷新”标语的控件;
4、一个用于标识尾部“上拉加载”标语的控件;
仅此而已。
所以,笔者这个上下拉列表控件其实是需要自定义一个LinearLayout容器控件。然后在这个容器控件里根据规则来处理触摸事件、点击事件并通知上下拉事件等。
public class PullingListView extends LinearLayout
这里有几个难点:
1、如何监听列表滚动到头部还是尾部亦或正处于中间?
2、上在列表上的上、下滑事件应如何响应成滑出对应的提示标语?
3、首尾提示标语应如何随手势滑出来?
关于第 1 点,直接通过监听 ListView 的 onScrollListener 即可勉强达到目的。
listview.setOnScrollListener(this);
为什么说是勉强呢?因为这个监听会在ListView滚动时回调,虽然它会告诉我们当前ListView中第 1 个可见Item的标号与最后一个可见Item的标号以及总Item数量。但它会在Item刚一加载时就通知,而不是在Item真正展示出来或者真正展示完全以后才通知。这就会存在一个“超前通知”的问题。就是实际上我们还没有看到第 1 个Item,但你却在回调方法中告诉我它已经展示出来了。这会让我们误判。关于这个问题,笔者目前还没有找到解决办法。
而关于第 2 点,则是通过监听ListView的触摸事件,并根据前面 onScrollListener 中得到的当前列表位置,再根据手势方向来决定是该滑出提示语还是让其滚动ListView。
listview.setOnTouchListener(this);
第 3 点其实也不难,只需要在 onTouch 中判断出当前是要滑出头提示还是尾提示,然后再根据手势滑动的垂直距离来实时改变头尾控件的高度,再调用容器中的更新子布局方法即可。
head.setLayoutHeight((int) distanceVertical); requestLayout();
整个控件的核心就这些东西。整体代码量不多,能实现上面效果图中的功能,但同样也存在一些问题。具体问题就是在列表中数量超过一屏幕容量时,上、下滑动未及端点即开始响应滑出提示语的现象。这个现象的原因笔者在上面已经分析过了。
以下贴出完整源码:
/** * 一个具备上拉刷新与下拉加载功能的ListView * */ public class PullingListView extends LinearLayout implements View.OnTouchListener, AdapterView.OnItemClickListener, AbsListView.OnScrollListener { private static final String TAG = "PullingListView"; private static final int LISTVIEW_SCROLL_STATUS_IN_HEAD = 0; private static final int LISTVIEW_SCROLL_STATUS_IN_MIDDLE = 1; private static final int LISTVIEW_SCROLL_STATUS_IN_TAIL = 2; private float y0; private float lastDisHeight; //上次垂直移动的高度。 private int listViewPos; private ListView listview; private Header head; private Header foot; private OnPullingListViewListener listener; private ListAdapter adapter; public PullingListView(Context context){ super(context); init(); } private void init(){ Logger.v(TAG, "init()"); setLayoutParams(new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT)); setOrientation(VERTICAL); listview = new ListView(getContext()); LinearLayout.LayoutParams llp = new LinearLayout.LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT); llp.weight = 1; listview.setLayoutParams(llp); head = new Header(true); foot = new Header(false); listview.setOnTouchListener(this); listview.setOnItemClickListener(this); listview.setOnScrollListener(this); addView(head.getView()); addView(listview); addView(foot.getView()); } @Override public boolean onTouch(View v, MotionEvent event){ // Logger.v(TAG, "onTouch,action:" + event.getAction() + ",listViewPos:" + listViewPos); switch(event.getAction()){ case MotionEvent.ACTION_DOWN:{ y0 = event.getY(); lastDisHeight = 0; listview.scrollTo(0, 0); head.setLayoutHeight(0); foot.setLayoutHeight(0); requestLayout(); }break; case MotionEvent.ACTION_MOVE:{ float distanceVertical = (event.getY() - y0) / 2.0f; //为了避免响应过于灵敏,垂直滑动距离应延缓5倍。 switch(listViewPos){ case LISTVIEW_SCROLL_STATUS_IN_MIDDLE:{ Logger.d(TAG, "MIDDLE"); return false; } case LISTVIEW_SCROLL_STATUS_IN_HEAD:{ Logger.d(TAG, "HEAD"); if(distanceVertical > 0){ //往下滑动。 head.setLayoutHeight((int) distanceVertical); requestLayout(); }else{ //往上滑动,要看有没有填满。 if(adapter.getCount() > 0){ int shownHeight = listview.getChildCount() * (listview.getChildAt(0).getHeight() + listview.getDividerHeight()); if(shownHeight <= listview.getHeight()){ // Logger.d(TAG, "None fill out."); //没填满. foot.setLayoutHeight((int) distanceVertical); requestLayout(); if(foot.getView().getLayoutParams().height >= foot.HEAD_LAYOUT_HEIGHT_MAX){ lastDisHeight = distanceVertical; listview.scrollTo(0, foot.getView().getLayoutParams().height); }else{ listview.scrollBy(0, (int) (distanceVertical - lastDisHeight) * -1); } lastDisHeight = distanceVertical; }else{ // Logger.d(TAG, "filled out."); //填满了,要滑动item。 return false; } }else{ // Logger.d(TAG, "No records"); //没有数据,则忽略掉滑动事件。 return true; } } }break; case LISTVIEW_SCROLL_STATUS_IN_TAIL:{ Logger.d(TAG, "TAIL"); if(distanceVertical < 0){ //往上滑动,加载。 foot.setLayoutHeight((int) distanceVertical); requestLayout(); listview.scrollTo(0, 0); }else{ //往下滑动 return false; } }break; } }break; case MotionEvent.ACTION_UP:{ if(head.canLoad()){ head.load(); if(listener != null) { listener.onRefresh(); } }else if(foot.canLoad()){ foot.load(); if(listener != null) { listener.onLoad(); } }else{ foot.setLayoutHeight(0); head.setLayoutHeight(0); requestLayout(); listview.scrollTo(0, 0); } }break; }//switch(event.getAction()) -- end return false; }//onTouch() -- end @Override public void onItemClick(AdapterView<?> parent, View view, int position, long id) { if(listener != null) { listener.onItemClick(parent, view, position, id); } } @Override public void onScrollStateChanged(AbsListView view, int scrollState) { // do nothing. Logger.d(TAG, "onScrollStateChanged,scrollState:" + scrollState); } @Override public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { Logger.d(TAG, "onScroll,firstVisibleItem:" + firstVisibleItem + ",visibleItemCount:" + visibleItemCount + ",totalItemCount:" + totalItemCount); if (firstVisibleItem == 0) { listViewPos = LISTVIEW_SCROLL_STATUS_IN_HEAD; }else if (visibleItemCount + firstVisibleItem == totalItemCount) { listViewPos = LISTVIEW_SCROLL_STATUS_IN_TAIL; }else{ listViewPos = LISTVIEW_SCROLL_STATUS_IN_MIDDLE; } } public void setDivider(Drawable divider){ listview.setDivider(divider); } public void setDividerHeight(int height){ listview.setDividerHeight(height); } public void setAdapter(ListAdapter adapter){ this.adapter = adapter; listview.setAdapter(adapter); } public void setOnPullingListViewListener(OnPullingListViewListener listener){ this.listener = listener; } public void refreshed(){ Logger.v(TAG, "refreshed"); listview.post(new Runnable() { @Override public void run() { foot.loadFinished(); head.loadFinished(); requestLayout(); listview.scrollTo(0, 0); } }); } public void setSelction(int selection){ Logger.v(TAG, "setSelction:" + selection); listview.setSelection(selection); } /** * 上下两个页眉的布局管理。 * */ private class Header extends BaseLayoutManager { private final int HEAD_LAYOUT_HEIGHT_MAX = UnitManager.px2dp(60); private final int STATUS_NORMAL = 0; private final int STATUS_TIP = 1; private final int STATUS_LOADING = 2; private int status; private boolean isTop; private TextView tv; private Header(boolean isTop){ super(null); this.isTop = isTop; LinearLayout linearLayout = new LinearLayout(PullingListView.this.getContext()); LinearLayout.LayoutParams llp = new LinearLayout.LayoutParams(-1, 0); linearLayout.setLayoutParams(llp); linearLayout.setBackgroundColor(ResourcesManager.getColor(R.color.activity_base_bg)); linearLayout.setOrientation(LinearLayout.HORIZONTAL); linearLayout.setGravity(Gravity.CENTER); view = linearLayout; ProgressBar pb = new ProgressBar(getContext()); llp = new LinearLayout.LayoutParams(UnitManager.px2dp(35), UnitManager.px2dp(35)); pb.setLayoutParams(llp); tv = new TextView(getContext()); if(isTop) { tv.setText("刷新列表"); }else { tv.setText("加载更多"); } tv.setGravity(Gravity.CENTER_VERTICAL); llp = new LinearLayout.LayoutParams(-2, -1); llp.leftMargin = UnitManager.px2dp(15); tv.setLayoutParams(llp); linearLayout.addView(pb); linearLayout.addView(tv); } private void setLayoutHeight(int height){ height = Math.abs(height); if(height < HEAD_LAYOUT_HEIGHT_MAX){ view.getLayoutParams().height = height; if(height > (HEAD_LAYOUT_HEIGHT_MAX * 0.7)){ if(status != STATUS_TIP){ status = STATUS_TIP; if(isTop) { tv.setText("松开以刷新"); }else{ tv.setText("松开以加载"); } } }else { if(status != STATUS_NORMAL){ status = STATUS_NORMAL; if(isTop) { tv.setText("刷新列表"); }else{ tv.setText("加载更多"); } } } }else{ view.getLayoutParams().height = HEAD_LAYOUT_HEIGHT_MAX; } } private boolean canLoad(){ return status == STATUS_TIP; } private void load(){ status = STATUS_LOADING; if(isTop) { tv.setText("刷新中,请稍候"); }else{ tv.setText("加载中,请稍候"); } } private void loadFinished(){ status = STATUS_NORMAL; view.getLayoutParams().height = 0; if(isTop) { tv.setText("刷新列表"); }else { tv.setText("加载更多"); } } }// class Header -- end public interface OnPullingListViewListener { void onRefresh(); void onLoad(); void onItemClick(AdapterView<?> parent, View view, int position, long id); } }