Android简洁的下拉放大刷新效果示例

allprojects {
 repositories {
  jcenter()
  maven { url 'https://jitpack.io' }
 }
}

compile 'com.github.xypmhxy:PullZoomLayout:1.1'

<com.ren.pullzoom.widget.PullZoomLayout
  android:id="@+id/pull"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical"
  app:image_height="200dp" 图片高度
  app:image_res="@mipmap/timg" 图片资源
  app:refresh_enable="true" 是否开启刷新
  app:scale_type="center_crop">//图片缩放方式

  <ListView
   android:id="@+id/listview"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:background="@android:color/white" />

 </com.ren.pullzoom.widget.PullZoomLayout>

/*实例化头部布局包含pullZoomImage 和 refreshProgress*/
protected void init(Context context) {
  RelativeLayout head = new RelativeLayout(context);
  ViewGroup.LayoutParams headParams = new ViewGroup.LayoutParams(-1, -2);
  head.setLayoutParams(headParams);
  /*实例化pullZoomImage*/
  ·······
  pullZoomImage.setImageResource(imageRes);
  originalParams = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, imageHeight);
  pullZoomImage.setLayoutParams(originalParams);
  head.addView(pullZoomImage);
  /*实例化refreshProgress*/
  refreshProgress = new ImageView(context);
  refreshProgress.setVisibility(GONE);
  refreshProgress.setImageResource(R.drawable.refresh);
  RelativeLayout.LayoutParams refreshParams = new RelativeLayout.LayoutParams(dip2px(context, 35), dip2px(context, 35));
  refreshParams.addRule(RelativeLayout.ALIGN_PARENT_END, RelativeLayout.TRUE);
  refreshProgress.setLayoutParams(refreshParams);
  head.addView(refreshProgress);
  /*将头部添加到此控件中*/
  addView(head, 0);
}

 @Override
 protected void onFinishInflate() {
  super.onFinishInflate();
  /*获取listview*/
  if (getChildAt(1) instanceof ListView) {
   listView = (ListView) getChildAt(1);
   listView.setOnScrollListener(scrollListener);
   listView.setOnTouchListener(touchListener);
  }
 }

 /*listview滑动监听*/
 protected AbsListView.OnScrollListener scrollListener = new AbsListView.OnScrollListener() {
  @Override
  public void onScrollStateChanged(AbsListView view, int scrollState) {
   /*判断是否滑动到顶部*/
   int firstVisibleItem = listView.getFirstVisiblePosition();
   if (firstVisibleItem == 0 && scrollState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
    View firstView = getChildAt(0);
    canZoom = firstView != null && firstView.getTop() == 0;
   } else
    canZoom = false;
  }

  @Override
  public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
  }
 };

/*listview touchListener监听*/
 protected OnTouchListener touchListener = new OnTouchListener() {
  @Override
  public boolean onTouch(View v, MotionEvent ev) {
   if (pullZoomImage == null) return false;
   switch (ev.getAction()) {
    case MotionEvent.ACTION_DOWN:
     pressY = ev.getY();//获取按下的Y坐标
     break;
    case MotionEvent.ACTION_MOVE:
     if (canZoom)//如果已经滑动到顶部并继续滑动则开始放大pullZoomImage
      return zoomView(ev);
     break;
    case MotionEvent.ACTION_CANCEL:
    case MotionEvent.ACTION_UP:
     if (canZoom)
      restroe();//还原pullZoomImage动画
     if (needRefresh && refreshListener != null) {//达到刷新条件并且实现刷新监听
      refreshListener.onRefresh();
      rotationProgress();//刷新时progress旋转动画
     } else
      refreshProgress.setVisibility(GONE);
     //重置变量
     needRefresh = false;
     canZoom = false;
     break;

   }
   return false;
  }
 };

 /*放大pullZoomImage*/
 protected boolean zoomView(MotionEvent ev) {
  float offY = ev.getY() - pressY;
  if (offY <= 0 || offY < 16)//滑动方向上滑或者滑动距离小于16则不管
   return false;
  /*如果开启下拉刷新判断滑动距离是否大于refrshSlop则显示refreshProgress*/
  if (refreshEnable) {
   needRefresh = offY >= refrshSlop;
   if (needRefresh)
    refreshProgress.setVisibility(VISIBLE);
  }
  ViewGroup.LayoutParams params = pullZoomImage.getLayoutParams();
  float height = originalParams.height + offY / damp;//根据滑动距离增加pullZoomImage的高度
  params.height = (int) height;
  scaleImage(height);//放大图片
  rotationProgress(offY);//旋转refreshProgress
  if (params.height >= originalParams.height)
   pullZoomImage.setLayoutParams(params);//为pullZoomImage设置改变后的params
  return true;
 }
 /*缩放imageview*/
 protected void scaleImage(float height) {
//  if (pullZoomImage.getScaleType() == ImageView.ScaleType.CENTER_CROP)
//   return;
  float scale = (height - originalParams.height) / originalParams.height;//根据滑动的大小判断缩放比例
  pullZoomImage.setScaleX(1 + scale);
  pullZoomImage.setScaleY(1 + scale);
 }

 /*放开后还原pullZoomImage*/
 protected void restroe() {
  ValueAnimator animator = ValueAnimator.ofFloat(pullZoomImage.getLayoutParams().height, originalParams.height);// 动画更新的监听
  animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {

   @Override
   public void onAnimationUpdate(ValueAnimator arg0) {
    float height = (float) arg0.getAnimatedValue();// 获取动画当前变化的值
    // 根据最新高度,更新布局高度
    ViewGroup.LayoutParams params = pullZoomImage.getLayoutParams();
    params.height = (int) height;
    scaleImage(height);
    pullZoomImage.setLayoutParams(params);
   }
  });
  animator.setDuration(200);// 动画时间
  animator.start();// 开启动画
 }