Android ListView实现下拉加载功能

 public class MyListView extends ListView implements OnScrollListener { private final static int RELEASE_To_REFRESH = 0;// 下拉过程的状态值 private final static int PULL_To_REFRESH = 1; // 从下拉返回到不刷新的状态值 private final static int REFRESHING = 2;// 正在刷新的状态值 private final static int DONE = 3; private final static int LOADING = 4; // 实际的padding的距离与界面上偏移距离的比例 private final static int RATIO = 3; private LayoutInflater inflater; // ListView头部下拉刷新的布局 private LinearLayout headerView; private TextView lvHeaderTipsTv; private TextView lvHeaderLastUpdatedTv; private ImageView lvHeaderArrowIv; private ProgressBar lvHeaderProgressBar; // 定义头部下拉刷新的布局的高度 private int headerContentHeight; private RotateAnimation animation; private RotateAnimation reverseAnimation; private int startY; private int state; private boolean isBack; // 用于保证startY的值在一个完整的touch事件中只被记录一次 private boolean isRecored; private OnRefreshListener refreshListener; private boolean isRefreshable; public MyListView(Context context) { super(context); init(context); } public MyListView(Context context, AttributeSet attrs) { super(context, attrs); init(context); } private void init(Context context) { inflater = LayoutInflater.from(context); headerView = (LinearLayout) inflater.inflate(R.layout.lv_header, null); lvHeaderTipsTv = (TextView) headerView .findViewById(R.id.lvHeaderTipsTv); lvHeaderLastUpdatedTv = (TextView) headerView .findViewById(R.id.lvHeaderLastUpdatedTv); lvHeaderArrowIv = (ImageView) headerView .findViewById(R.id.lvHeaderArrowIv); // 设置下拉刷新图标的最小高度和宽度 lvHeaderArrowIv.setMinimumWidth(70); lvHeaderArrowIv.setMinimumHeight(50); lvHeaderProgressBar = (ProgressBar) headerView .findViewById(R.id.lvHeaderProgressBar); measureView(headerView); headerContentHeight = headerView.getMeasuredHeight(); // 设置内边距，正好距离顶部为一个负的整个布局的高度，正好把头部隐藏 headerView.setPadding(0, -1 * headerContentHeight, 0, 0); // 重绘一下 headerView.invalidate(); // 将下拉刷新的布局加入ListView的顶部 addHeaderView(headerView, null, false); // 设置滚动监听事件 setOnScrollListener(this); // 设置旋转动画事件 animation = new RotateAnimation(0, -180, RotateAnimation.RELATIVE_TO_SELF, 0.5f, RotateAnimation.RELATIVE_TO_SELF, 0.5f); animation.setInterpolator(new LinearInterpolator()); animation.setDuration(250); animation.setFillAfter(true); reverseAnimation = new RotateAnimation(-180, 0, RotateAnimation.RELATIVE_TO_SELF, 0.5f, RotateAnimation.RELATIVE_TO_SELF, 0.5f); reverseAnimation.setInterpolator(new LinearInterpolator()); reverseAnimation.setDuration(200); reverseAnimation.setFillAfter(true); // 一开始的状态就是下拉刷新完的状态，所以为DONE state = DONE; // 是否正在刷新 isRefreshable = false; } @Override public void onScrollStateChanged(AbsListView view, int scrollState) { } @Override public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) { if (firstVisibleItem == 0) { isRefreshable = true; } else { isRefreshable = false; } } @Override public boolean onTouchEvent(MotionEvent ev) { if (isRefreshable) { switch (ev.getAction()) { case MotionEvent.ACTION_DOWN: if (!isRecored) { isRecored = true; startY = (int) ev.getY();// 手指按下时记录当前位置 } break; case MotionEvent.ACTION_UP: if (state != REFRESHING && state != LOADING) { if (state == PULL_To_REFRESH) { state = DONE; changeHeaderViewByState(); } if (state == RELEASE_To_REFRESH) { state = REFRESHING; changeHeaderViewByState(); onLvRefresh(); } } isRecored = false; isBack = false; break; case MotionEvent.ACTION_MOVE: int tempY = (int) ev.getY(); if (!isRecored) { isRecored = true; startY = tempY; } if (state != REFRESHING && isRecored && state != LOADING) { // 保证在设置padding的过程中，当前的位置一直是在head，否则如果当列表超出屏幕的话，当在上推的时候，列表会同时进行滚动 // 可以松手去刷新了 if (state == RELEASE_To_REFRESH) { setSelection(0); // 往上推了，推到了屏幕足够掩盖head的程度，但是还没有推到全部掩盖的地步 if (((tempY - startY) / RATIO  0) { state = PULL_To_REFRESH; changeHeaderViewByState(); } // 一下子推到顶了 else if (tempY - startY <= 0) {// 由松开刷新状态转变到done状态 state = DONE; changeHeaderViewByState(); } } // 还没有到达显示松开刷新的时候,DONE或者是PULL_To_REFRESH状态 if (state == PULL_To_REFRESH) { setSelection(0); // 下拉到可以进入RELEASE_TO_REFRESH的状态 if ((tempY - startY) / RATIO >= headerContentHeight) {// 由done或者下拉刷新状态转变到松开刷新 state = RELEASE_To_REFRESH; isBack = true; changeHeaderViewByState(); } // 上推到顶了 else if (tempY - startY <= 0) {// 由DOne或者下拉刷新状态转变到done状态 state = DONE; changeHeaderViewByState(); } } // done状态下 if (state == DONE) { if (tempY - startY > 0) { state = PULL_To_REFRESH; changeHeaderViewByState(); } } // 更新headView的size if (state == PULL_To_REFRESH) { headerView.setPadding(0, -1 * headerContentHeight + (tempY - startY) / RATIO, 0, 0); } // 更新headView的paddingTop if (state == RELEASE_To_REFRESH) { headerView.setPadding(0, (tempY - startY) / RATIO - headerContentHeight, 0, 0); } } break; default: break; } } return super.onTouchEvent(ev); } // 当状态改变时候，调用该方法，以更新界面 private void changeHeaderViewByState() { switch (state) { case RELEASE_To_REFRESH: lvHeaderArrowIv.setVisibility(View.VISIBLE); lvHeaderProgressBar.setVisibility(View.GONE); lvHeaderTipsTv.setVisibility(View.VISIBLE); lvHeaderLastUpdatedTv.setVisibility(View.VISIBLE); lvHeaderArrowIv.clearAnimation();// 清除动画 lvHeaderArrowIv.startAnimation(animation);// 开始动画效果 lvHeaderTipsTv.setText("松开刷新"); break; case PULL_To_REFRESH: lvHeaderProgressBar.setVisibility(View.GONE); lvHeaderTipsTv.setVisibility(View.VISIBLE); lvHeaderLastUpdatedTv.setVisibility(View.VISIBLE); lvHeaderArrowIv.clearAnimation(); lvHeaderArrowIv.setVisibility(View.VISIBLE); // 是由RELEASE_To_REFRESH状态转变来的 if (isBack) { isBack = false; lvHeaderArrowIv.clearAnimation(); lvHeaderArrowIv.startAnimation(reverseAnimation); lvHeaderTipsTv.setText("下拉刷新"); } else { lvHeaderTipsTv.setText("下拉刷新"); } break; case REFRESHING: headerView.setPadding(0, 0, 0, 0); lvHeaderProgressBar.setVisibility(View.VISIBLE); lvHeaderArrowIv.clearAnimation(); lvHeaderArrowIv.setVisibility(View.GONE); lvHeaderTipsTv.setText("正在刷新..."); lvHeaderLastUpdatedTv.setVisibility(View.VISIBLE); break; case DONE: headerView.setPadding(0, -1 * headerContentHeight, 0, 0); lvHeaderProgressBar.setVisibility(View.GONE); lvHeaderArrowIv.clearAnimation(); lvHeaderArrowIv.setImageResource(R.drawable.arrow); lvHeaderTipsTv.setText("下拉刷新"); lvHeaderLastUpdatedTv.setVisibility(View.VISIBLE); break; } } // 此方法直接照搬自网络上的一个下拉刷新的demo，此处是“估计”headView的width以及height private void measureView(View child) { ViewGroup.LayoutParams params = child.getLayoutParams(); if (params == null) { params = new ViewGroup.LayoutParams( ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT); } int childWidthSpec = ViewGroup.getChildMeasureSpec(0, 0 + 0, params.width); int lpHeight = params.height; int childHeightSpec; if (lpHeight > 0) { childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight, MeasureSpec.EXACTLY); } else { childHeightSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED); } child.measure(childWidthSpec, childHeightSpec); } public void setonRefreshListener(OnRefreshListener refreshListener) { this.refreshListener = refreshListener; isRefreshable = true; } public interface OnRefreshListener { public void onRefresh(); } public void onRefreshComplete() { state = DONE; lvHeaderLastUpdatedTv.setText("最近更新:" + new Date().toLocaleString()); changeHeaderViewByState(); } private void onLvRefresh() { if (refreshListener != null) { refreshListener.onRefresh(); } } public void setAdapter(LvAdapter adapter) { lvHeaderLastUpdatedTv.setText("最近更新:" + new Date().toLocaleString()); super.setAdapter(adapter); } } 

 public class MainActivity extends Activity { private List list; private MyListView lv; private LvAdapter adapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); lv = (MyListView) findViewById(R.id.lv); list = new ArrayList(); list.add("loonggg"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); list.add("我们都是开发者"); adapter = new LvAdapter(list, this); lv.setAdapter(adapter); lv.setonRefreshListener(new OnRefreshListener() { @Override public void onRefresh() { new AsyncTask() { protected Void doInBackground(Void... params) { try { Thread.sleep(1000); } catch (Exception e) { e.printStackTrace(); } list.add("刷新后添加的内容"); return null; } @Override protected void onPostExecute(Void result) { adapter.notifyDataSetChanged(); lv.onRefreshComplete(); } }.execute(null, null, null); } }); } }