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问题:

I have a DataGrid component that I would like to update every 5 seconds. As rows are being added to this DataGrid I noticed that every update causes it to reset the scroll bar position to the top. How can I manage to keep the scroll bar at its previous position?

回答1:

make a variable to store your last scroll position and use that.

roughly something like:

var lastScroll:Number = 0;

private function creationCompleteHandler(event:FlexEvent):void{
stage.addEventListener(MouseEvent.MOUSE_UP, updateLastScroll);
}

private function updateLastScroll(event:MouseEvent):void{
lastScroll = myDataGrid.verticalScrollPosition
}
private function dataGridHandler(event:Event):void{
myDataGrid.verticalScrollPosition = lastScroll;
}

It's not the best code, but it illustrates the point, whenever someone finishes the scroll event, you store last position in a variable and you use that to restore the scroll position right after you've added new data.

回答2:

I wrote a little extension class to DataGrid based on this article. It seems to work great.

public final class DataGridEx extends DataGrid
{
    public var maintainScrollAfterDataBind:Boolean = true;

    public function DataGridEx()
    {
        super();
    }       

    override public function set dataProvider(value:Object):void {
        var lastVerticalScrollPosition:int = this.verticalScrollPosition;
        var lastHorizontalScrollPosition:int = this.horizontalScrollPosition;

        super.dataProvider = value;

        if(maintainScrollAfterDataBind) {
            this.verticalScrollPosition = lastVerticalScrollPosition;
            this.horizontalScrollPosition = lastHorizontalScrollPosition;
        }
}

回答3:

I haven't tested this code, but it should work:

var r:IListItemRenderer;
var len:Number = dataGrid.dataProvider.length;
var i:Number;
//indexToItemRenderer returns null for items that are not visible
for(i = 0; i < len; i++)
{
  r = dataGrid.indexToItemRenderer(i);
  if(r)
    break;
}
//now i contains the first visible item - store this in a variable
lastPos = i;

//update the dataprovider here.

//now scroll to the position
dataGrid.scrollToIndex(lastPos);