想象一个并排显示两个内容区域的平板电脑应用程序。它们完全填满显示屏，高度为 100%，宽度为 50%。假设我们将一个列表添加到一个容器中。自然这个列表会占用整个显示空间的一半。
现在我的问题是，这种大小的列表是否可能无法实现高帧率滚动？我拥有最基本的 AS3 ItemRenderer，但在滚动期间仍然无法获得高于 30fps 的任何内容。现在奇怪的是，如果我在另一个容器中添加东西，比如说另一个列表或其他组件，列表滚动性能下降到 20 秒。因此，您在 MAX 节目中看到的 Adobe 广告远不及 40+ fps。
我正在 iPad2 和 3 上进行测试，即使使用静态值，滚动也不是很好。现在，如果我启用流式传输值以便set data调用 ItemRenderer 的方法，则帧速率会再下降 2 到 3 帧。
我的（几乎）完整的渲染器看起来像这样，但即使我将其剥离以仅显示单个文本字段，禁用其中正在进行的内容set data并仅设置 中的单个文本字段的大小layoutContents，性能如所述，大约 30如果列表单独显示，如果还显示其他内容，则低 20 秒。
//FCStyleableTextField is just a StyleableTextField with an additional ID
private var _textFields:Vector.<FCStyleableTextField>;
private var _oldValues:Dictionary;
private var _sym:Symbol;
public function GridRenderer() {
super();
_textFields = new Vector.<FCStyleableTextField>();
_oldValues = new Dictionary();
}
override protected function createChildren():void {
var _symLabel:FCStyleableTextField = new FCStyleableTextField();
_symLabel.editable = false;
_symLabel.selectable = false;
_symLabel.multiline = false;
_symLabel.id="sym";
_symLabel.setStyle("fontSize", fontSize);
_symLabel.textColor = 0xc0c0c0;
_textFields.push(_symLabel);
addChild(_symLabel);
var fidLen:int = fids.length;
for (var i:int = 0; i<fidLen; i++) {
var _fid_lbl:FCStyleableTextField = new FCStyleableTextField();
_fid_lbl.selectable = false;
_fid_lbl.editable = false;
_fid_lbl.multiline = false;
_fid_lbl.id = String(fids[i]);
_fid_lbl.textColor = 0xc0c0c0;
_fid_lbl.setStyle("textAlign", "right");
_fid_lbl.setStyle("fontSize", fontSize);
_fid_lbl.text = " ";
_textFields.push(_fid_lbl);
addChild(_fid_lbl);
if(i>visibleColumns) {
_fid_lbl.includeInLayout = false;
_fid_lbl.visible = false;
}
}
}
override public function set data(value:Object):void {
if(!value) return;
if(data) {
// check if the value's symbolName is different than the current
// data's symbolName, if so, the itemRenderer has been
// recycled, thus we need to reset the old fid values
if((value as Symbol).symbolName != (data as Symbol).symbolName)
_oldValues = new Dictionary();
}
super.data = value;
_sym = data as Symbol;
try {
var textLen:int = _textFields.length;
for (var i:int = 0; i<textLen;i++) {
var lbl:FCStyleableTextField = _textFields[i];
if(lbl.id == "sym") {
lbl.text = _sym.symbolName;
lbl.truncateToFit();
} else {
if(lbl.id == _sym.fidList.fidMap[lbl.id].fidId && lbl.text != _sym.fidList.fidMap[lbl.id].fieldValue) {
var time:int = new Date().time;
var timerName:String = _sym.symbolName+","+lbl.id+","+grid;
globalTimer.addTimer(timerName, time, "reset", lbl, null, null);
var _oldVal:* = _oldValues[lbl.id];
var _newVal:* = _sym.fidList.fidMap[lbl.id].fieldValue;
// basic color formatting
if(Number(_newVal) > Number(_oldVal))
lbl.textColor = 0x40c040;
else if(Number(_newVal) < Number(_oldVal))
lbl.textColor = 0xf05050;
// add + to change and changePercent fids if value is positive
if(lbl.id == "56") {
if(_newVal >0)
lbl.text = "+" + _newVal;
else
lbl.text = String(_newVal);
} else if(lbl.id == "11") {
if(_newVal >0)
lbl.text = "+" + _newVal;
else
lbl.text = String(_newVal);
} else
lbl.text = String(_newVal);
if(!_sym.fidList.fidMap[lbl.id].fieldValue)
lbl.text =" ";
_oldValues[lbl.id] = _newVal;
}
}
lbl.truncateToFit();
}
} catch (e:Error) { /* nothing to do here -> try/catch required due to async symbolassembly */ }
}
override protected function layoutContents(unscaledWidth:Number, unscaledHeight:Number):void {
var viewWidth:Number = unscaledWidth - paddingLeft - paddingRight;
var viewHeight:Number = unscaledHeight - paddingTop - paddingBottom;
var _previousLabel:FCStyleableTextField;
var textLen:int = _textFields.length;
for(var i:int =0; i<textLen;i++) {
var lbl:FCStyleableTextField = _textFields[i];
graphics.beginFill(0x808080, .3);
lbl.height = viewHeight;
lbl.y = paddingTop;
if(lbl.id=="sym") {
lbl.width = 95;
} else if (lbl.id == "35000") {
lbl.width = 24;
} else {
lbl.width = optimalColWidth;
}
_previousLabel ? lbl.x = (_previousLabel.x + _previousLabel.width): lbl.x = paddingLeft;
graphics.drawRect(lbl.x+lbl.width, 1, 1, unscaledHeight-1);
lbl.commitStyles();
_previousLabel = lbl;
graphics.endFill();
}
}
不过，我很确定不是项目渲染器导致了减速，因为正如我所说，与只显示单个文本字段的渲染器相比，它花费 2 帧，也许 3 帧。我宁愿认为 Flex 无法处理一次显示的矢量数量，这可能吗？有什么方法可以提高性能吗？一旦用户滚动列表，我已经禁用了实时流媒体值，因此 flex 基本上只需要滚动位图（因为 LabelItemRenderer 自动启用cacheasbitmap），但这可能会获得 4 帧。你们有什么技巧可以使滚动更顺畅？