解决DataGrid大数据量滚动轴卡的问题

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package { import flash.geom.Point; import mx.collections.CursorBookmark; import mx.controls.listClasses.IListItemRenderer; import mx.controls.dataGridClasses.DataGridColumn; import mx.controls.DataGrid; import mx.core.mx_internal; use namespace mx_internal; /** * A DataGrid subclass that has faster horizontal scrolling */ public class BetterDataGrid extends DataGrid { public function BetterDataGrid() { super(); } /** * remember the number of columns in case it changes */ private var lastNumberOfColumns:int; /** * a flag as to whether we can use the optimized scrolling */ private var canUseScrollH:Boolean; /** * when the horizontal scrollbar is changed it will eventually set horizontalScrollPosition * This value can be set programmatically as well. */ override public function set horizontalScrollPosition(value:Number):void { // remember the setting of this flag. We will tweak it in order to keep DataGrid from // doing its default horizontal scroll which essentially refreshes every renderer var lastItemsSizeChanged:Boolean = itemsSizeChanged; // remember the current number of visible columns. This can get changed by DataGrid // as it recomputes the visible columns when horizontally scrolled. lastNumberOfColumns = visibleColumns.length; // reset the flag for whether we use our new technique canUseScrollH = false; // call the base class. If we can use our technique we'll trip that flag super.horizontalScrollPosition = value; // if the flag got tripped run our new technique if (canUseScrollH) scrollLeftOrRight(); // reset the flag itemsSizeChanged = lastItemsSizeChanged; } // remember the parameters to scrollHorizontally to be used in our new technique private var pos:int; private var deltaPos:int; private var scrollUp:Boolean; // override this method. If it gets called that means we can use the new technique override protected function scrollHorizontally(pos:int, deltaPos:int, scrollUp:Boolean):void { // just remember the args for later; this.pos = pos; this.deltaPos = deltaPos; this.scrollUp = scrollUp; if (deltaPos < visibleColumns.length) { canUseScrollH = true; // need this to prevent DG from asking for a full refresh itemsSizeChanged = true; } } /** * The new technique does roughly what we do vertically. We shift the renderers on screen and in the * listItems array and only make the new renderers. * Because we can't get internal access to the header, we fully refresh it, but that's only one row * of renderers. There's significant gains to be made by not fully refreshing the every row of columns * * Key thing to note here is that visibleColumns has been updated, but the renderer array has not * That's why we don't do this in scrollHorizontally as the visibleColumns hasn't been updated yet * But because of that, sometimes we have to measure old renderers, and sometimes we measure the columns */ private function scrollLeftOrRight():void { // trace("scrollHorizontally " + pos); var i:int; var j:int; var numCols:int; var uid:String; var curX:Number; var rowCount:int = rowInfo.length; var columnCount:int = listItems[0].length; var cursorPos:CursorBookmark; var moveBlockDistance:Number = 0; var c:DataGridColumn; var item:IListItemRenderer; var itemSize:Point; var data:Object; var xx:Number; var yy:Number; if (scrollUp) // actually, rows move left { // determine how many columns we're discarding var discardCols:int = deltaPos; // measure how far we have to move by measuring the width of the columns we // are discarding moveBlockDistance = sumColumnWidths(discardCols, true); // trace("moveBlockDistance = " + moveBlockDistance); // shift rows leftward and toss the ones going away for (i = 0; i < rowCount; i++) { numCols = listItems[i].length; // move the positions of the row, the item renderers for the row, // and the indicators for the row moveRowHorizontally(i, discardCols, -moveBlockDistance, numCols); // move the renderers within the array of rows shiftColumns(i, discardCols, numCols); truncateRowArray(i); } // generate replacement columns cursorPos = iterator.bookmark; var firstNewColumn:int = lastNumberOfColumns - deltaPos; curX = listItems[0][firstNewColumn - 1].x + listItems[0][firstNewColumn - 1].width; for (i = 0; i < rowCount; i++) { data = iterator.current; iterator.moveNext(); uid = itemToUID(data); xx = curX; yy = rowInfo[i].y; for (j = firstNewColumn; j < visibleColumns.length; j++) { c = visibleColumns[j]; item = setupColumnItemRenderer(c, listContent, i, j, data, uid); itemSize = layoutColumnItemRenderer(c, item, xx, yy); xx += itemSize.x; } // toss excess columns if (listItems[i].length > visibleColumns.length) { addToFreeItemRenderers(listItems[i].pop()); } } iterator.seek(cursorPos, 0); } else { numCols = listItems[0].length; moveBlockDistance = sumColumnWidths(deltaPos, false); // shift the renderers and slots in array for (i = 0; i < rowCount; i++) { numCols = listItems[i].length; moveRowHorizontally(i, 0, moveBlockDistance, numCols); // we add placeholders at the front for new renderers addColumnPlaceHolders(i, deltaPos); } cursorPos = iterator.bookmark; for (i = 0; i < rowCount; i++) { data = iterator.current; iterator.moveNext(); uid = itemToUID(data); xx = 0; yy = rowInfo[i].y; for (j = 0; j < deltaPos; j++) { c = visibleColumns[j]; item = setupColumnItemRenderer(c, listContent, i, j, data, uid); itemSize = layoutColumnItemRenderer(c, item, xx, yy); xx += itemSize.x; } // toss excess columns if (listItems[i].length > visibleColumns.length) { addToFreeItemRenderers(listItems[i].pop()); } } iterator.seek(cursorPos, 0); } // force update the header header.headerItemsChanged = true; header.visibleColumns = visibleColumns; header.invalidateDisplayList(); header.validateNow(); // draw column lines and backgrounds drawLinesAndColumnBackgrounds(); } // if moving left, add up old renderers // if moving right, add up new columns private function sumColumnWidths(num:int, left:Boolean):Number { var i:int; var value:Number = 0; if (left) { for (i = 0; i < num; i++) { value += listItems[0][i].width; } } else for (i = 0; i < num; i++) { value += visibleColumns[i].width; } return value; } // shift position of renderers on screen private function moveRowHorizontally(rowIndex:int, start:int, distance:Number, end:int):void { for (;start < end; start++) listItems[rowIndex][start].x += distance; } // shift renderer assignments in listItems array private function shiftColumns(rowIndex:int, shift:int, numCols:int):void { var item:IListItemRenderer; for (var i:int = 0; i < shift; i++) { item = listItems[rowIndex].shift(); addToFreeItemRenderers(item); } } // add places in front of row for new columns private function addColumnPlaceHolders(rowIndex:int, count:int):void { for (var i:int = 0; i < count; i++) { listItems[rowIndex].unshift(null); } } // remove excess columns private function truncateRowArray(rowIndex:int):void { while (listItems[rowIndex].length > visibleColumns.length) { var item:IListItemRenderer; { item = listItems[rowIndex].pop(); addToFreeItemRenderers(item); } } } } }

 

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