Refactor new height manager

.vscode/launch.json

@@ -21,6 +21,13 @@
       "request": "launch",
       "type": "dart"
     },
+    {
+      "name": "example web",
+      "cwd": "example",
+      "request": "launch",
+      "type": "dart",
+      "args": ["-d", "chrome"]
+    },
     {
       "name": "example (profile mode)",
       "cwd": "example",

lib/src/effective_height_manager.dart

@@ -0,0 +1,222 @@
+import 'package:flutter/widgets.dart';
+
+import '../flutter_list_view.dart';
+import 'height_manager.dart';
+
+class HeightList {
+  final _indexList = <int>[];
+  final Map<int, double> _itemHeights = {};
+
+  get indexList => _indexList;
+
+  void setHeight(int index, double height) {
+    _itemHeights[index] = height;
+    // Maintain the orders
+    var length = _indexList.length;
+    if (length == 0) {
+      _indexList.add(index);
+    } else {
+      bool found = false;
+      int startIndex = 0;
+      int endIndex = length - 1;
+      int assertIndex = ((endIndex - startIndex) / 2).floor();
+      while (true) {
+        if (endIndex == startIndex) {
+          if (_indexList[startIndex] == index) {
+            found = true;
+            assertIndex = startIndex;
+          } else if (_indexList[startIndex] > index) {
+            found = false;
+            assertIndex = startIndex;
+          } else {
+            found = false;
+            assertIndex = startIndex + 1;
+          }
+          break;
+        }
+
+        if (_indexList[assertIndex] == index) {
+          found = true;
+          break;
+        } else if (_indexList[assertIndex] > index) {
+          endIndex = assertIndex - 1;
+          if (endIndex < startIndex) endIndex = startIndex;
+          assertIndex = startIndex + ((endIndex - startIndex) / 2).floor();
+        } else {
+          startIndex = assertIndex + 1;
+          if (startIndex > endIndex) startIndex = endIndex;
+          assertIndex = startIndex + ((endIndex - startIndex) / 2).floor();
+        }
+      }
+      if (!found) {
+        _indexList.insert(assertIndex, index);
+      }
+    }
+  }
+
+  double? getHeight(int index) {
+    return _itemHeights[index];
+  }
+
+  void clear() {
+    _indexList.clear();
+    _itemHeights.clear();
+  }
+}
+
+class EffectiveHeightManager implements HeightManager {
+  final HeightList _itemHeightObj = HeightList();
+
+  SliverChildDelegate? _delegate;
+
+  /// 总的item的高度
+  double _totalItemHeight = 0;
+  @override
+  double get totalItemHeight => _totalItemHeight;
+
+  @override
+  set delegate(SliverChildDelegate d) {
+    _delegate = d;
+  }
+
+  @override
+  SliverChildDelegate get delegate => _delegate ?? SliverChildListDelegate([]);
+
+  /// [_itemHeights]维护着已经layout的高度, 如果_itemHeights有，则取这个高度
+  /// 没有，则返回preferHeight或后面扩展的接口（要用户提供的Height）
+  @override
+  double getItemHeight(String key, int index) {
+    var existHeight = _itemHeightObj.getHeight(index);
+    if (existHeight != null) {
+      return existHeight;
+    } else {
+      if (delegate is FlutterListViewDelegate) {
+        var flutterListDelegate = delegate as FlutterListViewDelegate;
+        return flutterListDelegate.preferItemHeight;
+      }
+      return 50.0;
+    }
+  }
+
+  @override
+  setItemHeight(String key, int index, double height) {
+    _itemHeightObj.setHeight(index, height);
+  }
+
+  /// 只有当total count发生变化或第一次时，会调用
+  @override
+  void calcTotalItemHeight(
+      {required int childCount,
+      required String Function(int index) getKeyByItemIndex}) {
+    _itemHeightObj.clear();
+    var preferHeight = 50.0;
+    if (delegate is FlutterListViewDelegate) {
+      var flutterListDelegate = delegate as FlutterListViewDelegate;
+      preferHeight = flutterListDelegate.preferItemHeight;
+    }
+
+    _totalItemHeight = preferHeight * childCount;
+  }
+
+  @override
+  void increaseTotalItemHeight(double diff) {
+    _totalItemHeight += diff;
+  }
+
+  @override
+  MatchScrollOffsetResult? getFirstItemByScrollOffset(
+      {required int childCount,
+      required double scrollOffset,
+      required double cacheExtent,
+      required String Function(int index) getKeyByItemIndex}) {
+    var preferHeight = 50.0;
+    if (delegate is FlutterListViewDelegate) {
+      var flutterListDelegate = delegate as FlutterListViewDelegate;
+      preferHeight = flutterListDelegate.preferItemHeight;
+    }
+
+    // 估算Index
+    double startOffset = scrollOffset - cacheExtent;
+    if (startOffset < 0) {
+      startOffset = 0;
+    }
+
+    var estimateIndex = (startOffset / preferHeight).floor();
+    if (estimateIndex >= childCount) {
+      estimateIndex = childCount - 1;
+    }
+    // Estimate offset of estimateIndex
+    var estimateOffset = estimateIndex * preferHeight;
+
+    // Fixed estimate offset
+    for (var renderedItemIndex in _itemHeightObj._indexList) {
+      if (renderedItemIndex <= estimateIndex) {
+        var existHeight = _itemHeightObj.getHeight(renderedItemIndex);
+        if (existHeight != null) {
+          estimateOffset += (existHeight - preferHeight);
+        }
+      }
+    }
+
+    if (estimateOffset <= startOffset) {
+      for (var i = estimateIndex + 1; i < childCount; i++) {
+        var itemHeight = getItemHeight(getKeyByItemIndex(i), i);
+        if (estimateOffset <= startOffset &&
+            (estimateOffset + itemHeight) >= startOffset) {
+          return MatchScrollOffsetResult(index: i, accuHeight: estimateOffset);
+        }
+        estimateOffset += itemHeight;
+      }
+    } else {
+      for (var i = estimateIndex - 1; i >= 0; i--) {
+        var itemHeight = getItemHeight(getKeyByItemIndex(i), i);
+        if (estimateOffset - itemHeight <= startOffset &&
+            estimateOffset >= startOffset) {
+          return MatchScrollOffsetResult(
+              index: i, accuHeight: estimateOffset - itemHeight);
+        }
+        estimateOffset -= itemHeight;
+      }
+    }
+
+    return null;
+  }
+
+  @override
+  double getScrollOffsetByIndex(
+      {required int index,
+      required double offset,
+      required bool basedOnBottom,
+      required double viewportHeight,
+      required String Function(int index) getKeyByItemIndex}) {
+    var preferHeight = 50.0;
+    if (delegate is FlutterListViewDelegate) {
+      var flutterListDelegate = delegate as FlutterListViewDelegate;
+      preferHeight = flutterListDelegate.preferItemHeight;
+    }
+
+    // Estimate offset of estimateIndex
+    var estimateOffset = index * preferHeight;
+
+    // Fixed estimate offset
+    for (var renderedItemIndex in _itemHeightObj._indexList) {
+      if (renderedItemIndex <= index) {
+        var existHeight = _itemHeightObj.getHeight(renderedItemIndex);
+        if (existHeight != null) {
+          estimateOffset += (existHeight - preferHeight);
+        }
+      }
+    }
+
+    if (basedOnBottom) {
+      var itemHeight = getItemHeight(getKeyByItemIndex(index), index);
+      estimateOffset = estimateOffset - (viewportHeight - itemHeight - offset);
+    } else {
+      estimateOffset -= offset;
+    }
+
+    if (estimateOffset < 0) estimateOffset = 0;
+
+    return estimateOffset;
+  }
+}