extjs.net 按钮执行并显示Mask代码

<ext:Button ID="ButtonTest" runat="server"  Width="65" Text="同步"
ToolTip="点击同步">
<DirectEvents>
<Click OnEvent="btnSync_Click" Timeout="300000" Before=" if(!confirm('执行等待，继续吗？')) return false;">
<EventMask Msg="同步中.." ShowMask="true" />
</Click>
</DirectEvents>
</ext:Button>