flex-DataGrid列太多，横向滚动条特别卡的解决方法

做项目的时候遇到了DataGrid列太多，导致横向滚动条特别卡，界面反应非常慢。

在网上找了一下解决方法，最终只找到这一个

http://blogs.adobe.com/aharui/2008/11/faster_datagrid_horizontal_scr.html 

但是这里面的大师提供的例子代码是有问题的，不过细心的人仔细看评论有人修复了这些bug。

我在这里把修复后的代码贴出来，方便大家查看

package components{import flash.geom.Point;import mx.collections.CursorBookmark;import mx.controls.DataGrid;import mx.controls.dataGridClasses.DataGridColumn;import mx.controls.listClasses.IListItemRenderer;import mx.core.mx_internal;use namespace mx_internal;public class BetterDataGrid extends DataGrid{/**  *  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 renderervar 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 techniquecanUseScrollH = false;// call the base class.  If we can use our technique we'll trip that flagsuper.horizontalScrollPosition = value;// if the flag got tripped run our new techniqueif (canUseScrollH){scrollLeftOrRight();configureScrollBars();}// reset the flagitemsSizeChanged = lastItemsSizeChanged;}// remember the parameters to scrollHorizontally to be used in our new techniqueprivate 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 techniqueoverride 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 refreshitemsSizeChanged = 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 discardingvar discardCols:int = deltaPos;// measure how far we have to move by measuring the width of the columns we// are discardingmoveBlockDistance = sumColumnWidths(discardCols, true);// trace("moveBlockDistance = " + moveBlockDistance);//  shift rows leftward and toss the ones going awayfor (i = 0; i < rowCount; i++){numCols = listItems[i].length;if(numCols == 0) //empty rowcontinue;// move the positions of the row, the item renderers for the row,// and the indicators for the rowmoveRowHorizontally(i, discardCols, -moveBlockDistance, numCols);// move the renderers within the array of rowsshiftColumns(i, discardCols, numCols);truncateRowArray(i);}// generate replacement columnscursorPos = iterator.bookmark;var firstNewColumn:int = lastNumberOfColumns - deltaPos;curX = listItems[0][firstNewColumn - 1].x + listItems[0][firstNewColumn - 1].width;for (i = 0; i < rowCount; i++){if(iterator == null || iterator.afterLast || !iteratorValid)continue;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 columnswhile (listItems[i].length > visibleColumns.length){addToFreeItemRenderers(listItems[i].pop());}}iterator.seek(cursorPos, 0);           }else{numCols = listItems[0].length;if(deltaPos > visibleColumns.length)deltaPos = visibleColumns.length;moveBlockDistance = sumColumnWidths(deltaPos, false);// shift the renderers and slots in arrayfor (i = 0; i < rowCount; i++){numCols = listItems[i].length;if(numCols == 0)continue;moveRowHorizontally(i, 0, moveBlockDistance, numCols);// we add placeholders at the front for new renderersaddColumnPlaceHolders(i, deltaPos);}cursorPos = iterator.bookmark;for (i = 0; i < rowCount; i++){if(iterator == null || iterator.afterLast || !iteratorValid)continue;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 columnswhile (listItems[i].length > visibleColumns.length){addToFreeItemRenderers(listItems[i].pop());}}iterator.seek(cursorPos, 0);           }// force update the headerheader.headerItemsChanged = true;header.visibleColumns = visibleColumns;header.invalidateDisplayList();header.validateNow();// draw column lines and backgroundsdrawLinesAndColumnBackgrounds();}        // if moving left, add up old renderers// if moving right, add up new columnsprivate 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;}}elsefor (i = 0; i < num; i++){value += visibleColumns[i].width;}return value;}// shift position of renderers on screenprivate 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 arrayprivate function shiftColumns(rowIndex:int, shift:int, numCols:int):void{var item:IListItemRenderer;var uid:String = itemToUID(listItems[rowIndex][0].data);for (var i:int = 0; i < shift; i++){//rebuild the listContent.visibleData map entrylistContent.visibleData[uid] = listItems[rowIndex][0];item = listItems[rowIndex].shift();addToFreeItemRenderers(item);}}// add places in front of row for new columnsprivate function addColumnPlaceHolders(rowIndex:int, count:int):void{for (var i:int = 0; i < count; i++){listItems[rowIndex].unshift(null);}}// remove excess columnsprivate function truncateRowArray(rowIndex:int):void{while (listItems[rowIndex].length > visibleColumns.length){var item:IListItemRenderer;{item = listItems[rowIndex].pop();addToFreeItemRenderers(item);}}}}}

这下拖动速度还是比较快了，希望能帮助到正在苦恼这个问题的人