fix(android): waterfall preloadItemNumber not working

android/sdk/src/main/java/com/tencent/mtt/hippy/views/waterfalllist/HippyWaterfallView.java

@@ -158,6 +158,14 @@ public void setListData() {
         @Override
         public void run() {
           dispatchLayout();
+          // check end reached
+          int itemCount = mLayout.getItemCount();
+          boolean hasContent = itemCount > 1
+                  || (itemCount == 1 && !(mAdapter.getItemNode(0) instanceof PullFooterRenderNode));
+          if (hasContent) {
+            mEndChecker.reset();
+            mEndChecker.check(HippyWaterfallView.this);
+          }
         }
       };
     }
@@ -264,7 +272,7 @@ public void onScrollStateChanged(int oldState, int newState) {
   @Override
   public void onScrolled(int x, int y) {
     super.onScrolled(x, y);
-    mEndChecker.onScroll(this, y);
+    mEndChecker.check(this);
   }
 
   public void startRefresh(int type) {

android/sdk/src/main/java/com/tencent/mtt/hippy/views/waterfalllist/WaterfallEndChecker.java

@@ -1,7 +1,23 @@
+/* Tencent is pleased to support the open source community by making Hippy available.
+ * Copyright (C) 2018 THL A29 Limited, a Tencent company. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
 package com.tencent.mtt.hippy.views.waterfalllist;
 
 import android.view.View;
 import com.tencent.mtt.hippy.views.waterfalllist.HippyWaterfallView.HippyWaterfallEvent;
+import com.tencent.mtt.supportui.views.recyclerview.RecyclerViewBase;
 
 /**
  * @author hengyangji
@@ -10,18 +26,28 @@
 public class WaterfallEndChecker {
 
   private boolean isVerticalEnd = false;
-  public void onScroll(HippyWaterfallView waterfallView, int y) {
-    boolean currentVerticalEnd = checkVerticalEnd(waterfallView, y);
+  public void reset() {
+    isVerticalEnd = false;
+  }
+
+  public void check(HippyWaterfallView waterfallView) {
+    boolean currentVerticalEnd = checkVerticalEnd(waterfallView);
     if (!isVerticalEnd && currentVerticalEnd) {
       new HippyWaterfallEvent("onEndReached").send(waterfallView, null);
     }
     isVerticalEnd = currentVerticalEnd;
   }
 
-  private boolean checkVerticalEnd(HippyWaterfallView waterfallView, int y) {
+  private boolean checkVerticalEnd(HippyWaterfallView waterfallView) {
     HippyWaterfallLayoutManager layoutManager = (HippyWaterfallLayoutManager)waterfallView.getLayoutManager();
     int lastVisibleItemPosition = layoutManager.findLastVisibleItemPosition();
-    boolean scrollToLastItem = lastVisibleItemPosition == layoutManager.getItemCount() - 1;
+    RecyclerViewBase.Adapter adapter = waterfallView.getAdapter();
+    int preloadItemNumber = adapter == null ? 0 : adapter.getPreloadThresholdInItemNumber();
+    int endPosition = layoutManager.getItemCount() - 1;
+    if (lastVisibleItemPosition > endPosition - preloadItemNumber) {
+      return true;
+    }
+    boolean scrollToLastItem = lastVisibleItemPosition == endPosition;
     if (scrollToLastItem) { //滑到最后一位了
       View lastView = waterfallView.findViewByPosition(lastVisibleItemPosition);
       return lastView.getBottom() <= waterfallView.getBottom();