android编程之下拉刷新实现方法分析

public class MyListView extends ListView implements OnScrollListener { private static final String TAG = "listview"; private final static int RELEASE_To_REFRESH = 0; private final static int PULL_To_REFRESH = 1; private final static int REFRESHING = 2; 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; private LinearLayout headView; private TextView tipsTextview; private TextView lastUpdatedTextView; private ImageView arrowImageView; private ProgressBar progressBar; private RotateAnimation animation; private RotateAnimation reverseAnimation; // 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 int headContentWidth; private int headContentHeight; private int startY; private int firstItemIndex; private int state; private boolean isBack; 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) {  setCacheColorHint(context.getResources().getColor(R.color.transparent));  inflater = LayoutInflater.from(context);  headView = (LinearLayout) inflater.inflate(R.layout.head, null);  arrowImageView = (ImageView) headView    .findViewById(R.id.head_arrowImageView);  arrowImageView.setMinimumWidth(70);  arrowImageView.setMinimumHeight(50);  progressBar = (ProgressBar) headView    .findViewById(R.id.head_progressBar);  tipsTextview = (TextView) headView.findViewById(R.id.head_tipsTextView);  lastUpdatedTextView = (TextView) headView    .findViewById(R.id.head_lastUpdatedTextView);  measureView(headView);  headContentHeight = headView.getMeasuredHeight();  headContentWidth = headView.getMeasuredWidth();  headView.setPadding(0, -1 * headContentHeight, 0, 0);  headView.invalidate();  Log.v("size", "width:" + headContentWidth + " height:"    + headContentHeight);  addHeaderView(headView, null, false);  setOnScrollListener(this);  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);  state = DONE;  isRefreshable = false; } public void onScroll(AbsListView arg0, int firstVisiableItem, int arg2,   int arg3) {  firstItemIndex = firstVisiableItem; } public void onScrollStateChanged(AbsListView arg0, int arg1) { } public boolean onTouchEvent(MotionEvent event) {  if (isRefreshable) {   switch (event.getAction()) {   case MotionEvent.ACTION_DOWN:    if (firstItemIndex == 0 && !isRecored) {     isRecored = true;     startY = (int) event.getY();     Log.v(TAG, "在down时候记录当前位置‘");    }    break;   case MotionEvent.ACTION_UP:    if (state != REFRESHING && state != LOADING) {     if (state == DONE) {      // 什么都不做     }     if (state == PULL_To_REFRESH) {      state = DONE;      changeHeaderViewByState();      Log.v(TAG, "由下拉刷新状态，到done状态");     }     if (state == RELEASE_To_REFRESH) {      state = REFRESHING;      changeHeaderViewByState();      onRefresh();      Log.v(TAG, "由松开刷新状态，到done状态");     }    }    isRecored = false;    isBack = false;    break;   case MotionEvent.ACTION_MOVE:    int tempY = (int) event.getY();    if (!isRecored && firstItemIndex == 0) {     Log.v(TAG, "在move时候记录下位置");     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 < headContentHeight)        && (tempY - startY) > 0) {       state = PULL_To_REFRESH;       changeHeaderViewByState();       Log.v(TAG, "由松开刷新状态转变到下拉刷新状态");      }      // 一下子推到顶了      else if (tempY - startY <= 0) {       state = DONE;       changeHeaderViewByState();       Log.v(TAG, "由松开刷新状态转变到done状态");      }      // 往下拉了，或者还没有上推到屏幕顶部掩盖head的地步      else {       // 不用进行特别的操作，只用更新paddingTop的值就行了      }     }     // 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 >= headContentHeight) {       state = RELEASE_To_REFRESH;       isBack = true;       changeHeaderViewByState();       Log.v(TAG, "由done或者下拉刷新状态转变到松开刷新");      }      // 上推到顶了      else if (tempY - startY <= 0) {       state = DONE;       changeHeaderViewByState();       Log.v(TAG, "由DOne或者下拉刷新状态转变到done状态");      }     }     // 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) {      headView.setPadding(0, -1 * headContentHeight        + (tempY - startY) / RATIO, 0, 0);     }     // 更新headView的paddingTop     if (state == RELEASE_To_REFRESH) {      headView.setPadding(0, (tempY - startY) / RATIO        - headContentHeight, 0, 0);     }    }    break;   }  }  return super.onTouchEvent(event); } // 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:   arrowImageView.setVisibility(View.VISIBLE);   progressBar.setVisibility(View.GONE);   tipsTextview.setVisibility(View.VISIBLE);   lastUpdatedTextView.setVisibility(View.VISIBLE);   arrowImageView.clearAnimation();   arrowImageView.startAnimation(animation);   tipsTextview.setText("松开刷新");   Log.v(TAG, "当前状态，松开刷新");   break;  case PULL_To_REFRESH:   progressBar.setVisibility(View.GONE);   tipsTextview.setVisibility(View.VISIBLE);   lastUpdatedTextView.setVisibility(View.VISIBLE);   arrowImageView.clearAnimation();   arrowImageView.setVisibility(View.VISIBLE);   // 是由RELEASE_To_REFRESH状态转变来的   if (isBack) {    isBack = false;    arrowImageView.clearAnimation();    arrowImageView.startAnimation(reverseAnimation);    tipsTextview.setText("下拉刷新");   } else {    tipsTextview.setText("下拉刷新");   }   Log.v(TAG, "当前状态，下拉刷新");   break;  case REFRESHING:   headView.setPadding(0, 0, 0, 0);   progressBar.setVisibility(View.VISIBLE);   arrowImageView.clearAnimation();   arrowImageView.setVisibility(View.GONE);   tipsTextview.setText("正在刷新...");   lastUpdatedTextView.setVisibility(View.VISIBLE);   Log.v(TAG, "当前状态,正在刷新...");   break;  case DONE:   headView.setPadding(0, -1 * headContentHeight, 0, 0);   progressBar.setVisibility(View.GONE);   arrowImageView.clearAnimation();   arrowImageView.setImageResource(R.drawable.arrow);   tipsTextview.setText("下拉刷新");   lastUpdatedTextView.setVisibility(View.VISIBLE);   Log.v(TAG, "当前状态，done");   break;  } } public void setonRefreshListener(OnRefreshListener refreshListener) {  this.refreshListener = refreshListener;  isRefreshable = true; } public interface OnRefreshListener {  public void onRefresh(); } public void onRefreshComplete() {  state = DONE;  lastUpdatedTextView.setText("最近更新:" + new Date().toLocaleString());  changeHeaderViewByState(); } private void onRefresh() {  if (refreshListener != null) {   refreshListener.onRefresh();  } } // 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 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;  if (lpHeight > 0) {   childHeightSpec = MeasureSpec.makeMeasureSpec(lpHeight,     MeasureSpec.EXACTLY);  } else {   childHeightSpec = MeasureSpec.makeMeasureSpec(0,     MeasureSpec.UNSPECIFIED);  }  child.measure(childWidthSpec, childHeightSpec); } public void setAdapter(BaseAdapter adapter) {  lastUpdatedTextView.setText("最近更新:" + new Date().toLocaleString());  super.setAdapter(adapter); }}