react-native-refresh-loadmore-recyclerlistview/core/layoutmanager/LayoutManager.js

The listview that you need and deserve. It was built for performance, uses cell recycling to achieve smooth scrolling.

import CustomError from "../exceptions/CustomError";
export default class LayoutManager {
    constructor(layoutProvider, dimensions, isHorizontal = false, cachedLayouts) {
        this._layoutProvider = layoutProvider;
        this._window = dimensions;
        this._totalHeight = 0;
        this._totalWidth = 0;
        this._layouts = cachedLayouts ? cachedLayouts : [];
        this._isHorizontal = isHorizontal;
    }
    getLayoutDimension() {
        return { height: this._totalHeight, width: this._totalWidth };
    }
    getLayouts() {
        return this._layouts;
    }
    getOffsetForIndex(index) {
        if (this._layouts.length > index) {
            return { x: this._layouts[index].x, y: this._layouts[index].y };
        }
        throw new CustomError({
            message: "No layout available for index: " + index,
            type: "LayoutUnavailableException",
        });
    }
    overrideLayout(index, dim) {
        const layout = this._layouts[index];
        if (layout) {
            layout.isOverridden = true;
            layout.width = dim.width;
            layout.height = dim.height;
        }
    }
    setMaxBounds(itemDim) {
        if (this._isHorizontal) {
            itemDim.height = Math.min(this._window.height, itemDim.height);
        }
        else {
            itemDim.width = Math.min(this._window.width, itemDim.width);
        }
    }
    reLayoutFromIndex(startIndex, itemCount) {
        let startIndexTMp = this._locateFirstNeighbourIndex(startIndex);
        let startX = 0, startY = 0, maxBound = 0;
        const startVal = this._layouts[startIndexTMp];
        if (startVal) {
            startX = startVal.x;
            startY = startVal.y;
            this._pointDimensionsToRect(startVal);
        }
        const oldItemCount = this._layouts.length, itemDim = { height: 0, width: 0 };
        let itemRect = null, oldLayout = null;
        for (let i = startIndexTMp; i < itemCount; i++) {
            oldLayout = this._layouts[i];
            if (oldLayout && oldLayout.isOverridden) {
                itemDim.height = oldLayout.height;
                itemDim.width = oldLayout.width;
            }
            else {
                this._layoutProvider.setLayoutForType(this._layoutProvider.getLayoutTypeForIndex(i), itemDim, i);
            }
            this.setMaxBounds(itemDim);
            while (!this._checkBounds(startX, startY, itemDim, this._isHorizontal)) {
                if (this._isHorizontal) {
                    startX += maxBound;
                    startY = 0;
                    this._totalWidth += maxBound;
                }
                else {
                    startX = 0;
                    startY += maxBound;
                    this._totalHeight += maxBound;
                }
                maxBound = 0;
            }
            maxBound = this._isHorizontal ? Math.max(maxBound, itemDim.width) : Math.max(maxBound, itemDim.height);
            if (i > oldItemCount - 1) {
                this._layouts.push({ x: startX, y: startY, height: itemDim.height, width: itemDim.width });
            }
            else {
                itemRect = this._layouts[i];
                itemRect.x = startX;
                itemRect.y = startY;
                itemRect.width = itemDim.width;
                itemRect.height = itemDim.height;
            }
            if (this._isHorizontal) {
                startY += itemDim.height;
            }
            else {
                startX += itemDim.width;
            }
        }
        if (oldItemCount > itemCount) {
            this._layouts.splice(itemCount, oldItemCount - itemCount);
        }
        this._setFinalDimensions(maxBound);
    }
    _pointDimensionsToRect(itemRect) {
        if (this._isHorizontal) {
            this._totalWidth = itemRect.x;
        }
        else {
            this._totalHeight = itemRect.y;
        }
    }
    _setFinalDimensions(maxBound) {
        if (this._isHorizontal) {
            this._totalHeight = this._window.height;
            this._totalWidth += maxBound;
        }
        else {
            this._totalWidth = this._window.width;
            this._totalHeight += maxBound;
        }
    }
    _locateFirstNeighbourIndex(startIndex) {
        if (startIndex === 0) {
            return 0;
        }
        let i = startIndex - 1;
        for (; i >= 0; i--) {
            if (this._isHorizontal) {
                if (this._layouts[i].y === 0) {
                    break;
                }
            }
            else if (this._layouts[i].x === 0) {
                break;
            }
        }
        return i;
    }
    _checkBounds(itemX, itemY, itemDim, isHorizontal) {
        return isHorizontal ? (itemY + itemDim.height <= this._window.height) : (itemX + itemDim.width <= this._window.width);
    }
}
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