I just tested the code I had posted earlier and it does not work. I think it has to do with making DataGridColumn changes. I will try editing the columns property and rebinding it with the change.

sorry, I'm brand new to flex. How do I use this function on the datagrid?
thanks

I also encountered this problem during my training.
I tried your code, actually it worked just when the first item(one record in XMLList)'s text length is the longest of all the items. You can try modifying your dataProvider, to that the second or third of text's length in record is the longest and you will find the problem rise.
I'm a brand new but In my view, the head line of datagrid also contain a datagridcolumn, so if we can also set the hearcolumn's width to properly width, we will solve this problem perfectly.
Best Regard!
Cai

How about this?

private function optimizeColumnWidths (dg:DataGrid):void
{
var dgCol:DataGridColumn;
var renderer:UITextField;
var tf:TextFormat;
var col:int;

if (dg.columnCount > 0 && dg.dataProvider != null)
{
// initialize widths array
var widths:Array = new Array (dg.columnCount);
for (col = 0; col < widths.length; ++col)
{
widths[col] = -1;
}

// go through each data item in the grid, estimate
// the width of the text in pixels
for each (var item:Object in dg.dataProvider)
{
for (col = 0; col < widths.length; ++col)
{
// TODO: it's ok to reuse renderer, but I chose not
// to for safety reasons. Optimize if needed.
renderer = new DataGridItemRenderer();

// Must add to datagrid as child so that it inherits
// properties essential for text width estimation,
// such as font size
dg.addChild(renderer);

dgCol = dg.columns[col] as DataGridColumn;
renderer.text = dgCol.itemToLabel(item);
widths[col] = Math.max(renderer.measuredWidth + 10, widths[col]);

// remove renderer from datagrid when we're done
dg.removeChild(renderer);
}
}

// go through headers in the grid, estimate the width of
// the text in pixels, assuming the text is bold
for (col = 0; col < widths.length; ++col)
{
// TODO: it's ok to reuse renderer, but I chose not
// to for safety reasons. Optimize if needed.
renderer = new DataGridItemRenderer();

// Must add to datagrid as child so that it inherits
// properties essential for text width estimation,
// such as font size
dg.addChild(renderer);

dgCol = dg.columns[col] as DataGridColumn;
renderer.text = dgCol.headerText;

tf = renderer.getTextFormat();
tf.bold = true;
renderer.setTextFormat (tf);

widths[col] = Math.max(renderer.measuredWidth + 25, widths[col]);

// remove renderer from datagrid when we're done
dg.removeChild(renderer);
}

// set width of columns to determined values
for (col = 0; col < widths.length; ++col)
{
if (widths[col] != -1)
{
trace ("Optimized width of col " + col + " to " + widths[col]);
dg.columns[col].width = widths[col];
}
}
}
}

Dude, create a text field, fill it with the longest string and measure its length.

If you populate your datagrid from the results of an HTTPService, you can call the function in the handler function for the result event of the HTTPService. Flex 3 is event driven so try to think of an event that will always occur before the datagrid will have data and call the function from that event handler.

Thanks for the code! However, I get errors when I try to execute the code and I have more columns than are visible on the screen in the Datagrid. Here is the error:

Optimized width of col 14 to 165
TypeError: Error #1010: A term is undefined and has no properties.
at mx.controls::DataGrid/ http://www.adobe.com/2006/flex/mx/internal::resizeColumn()[C:\dev\GMC\ sdk\frameworks\mx\controls\DataGrid.as:2379
at mx.controls.dataGridClasses::DataGridColumn/set width()[C:\dev\GMC\sdk\frameworks\mx\controls\dataGridClasses\DataGri dColumn.as:1048]
at view.forms::securitysetup/optimizeColumnWidths()[C:\Documents and Settings\Misc\Desktop\MPR\MPRPro\view\forms\securitysetup.mxml:417]
at view.forms::securitysetup/dataHandler()[C:\Documents and Settings\Misc\Desktop\MPR\MPRPro\view\forms\securitysetup.mxml:116]
at view.forms::securitysetup/___Operation1_result()[C:\Documents and Settings\Misc\Desktop\MPR\MPRPro\view\forms\securitysetup.mxml:432]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at mx.rpc::AbstractOperation/ http://www.adobe.com/2006/flex/mx/internal::dispatchRpcEvent()[C:\dev\ enterprise_gmc\frameworks\mx\rpc\AbstractOperation.as:179
at mx.rpc::AbstractInvoker/ http://www.adobe.com/2006/flex/mx/internal::resultHandler()[C:\dev\ent erprise_gmc\frameworks\mx\rpc\AbstractInvoker.as:167
at mx.rpc::Responder/result()[C:\dev\enterprise_gmc\frameworks\mx\rpc\Re sponder.as:48]
at mx.rpc::AsyncRequest/acknowledge()[C:\dev\enterprise_gmc\frameworks\m x\rpc\AsyncRequest.as:82]
at DirectHTTPMessageResponder/completeHandler()[C:\dev\enterprise_gmc\fr ameworks\mx\messaging\channels\DirectHTTPChannel.as:359]
at flash.events::EventDispatcher/dispatchEventFunction()
at flash.events::EventDispatcher/dispatchEvent()
at flash.net::URLLoader/onComplete()

It shoots me to the code in the DataGrid.as in the ResizeColumns function and I think the error occurs because the code is trying to resize a column that is not visible in the datagrid (i.e. you have to horizontally scroll to find it).

Here is where it stops in DataGrid.as: if (w < visibleColumns[col].minWidth)

Please help me troubleshoot this because the code is awesome and I really need it to work.

Thanks

angie_mc-

To resolve the issue of column widths not binding correctly simply set the dg.horizontalScroll = "on" before binding widths and then back to dg.horizontalScroll = "off" once completed.