EXT.NET window中动态加载网址

前台代码：

<form id="form1" runat="server">
    <ext:ResourceManager ID="ResourceManager1" runat="server">
    </ext:ResourceManager>
    <ext:Button ID="Button1" runat="server" Text="点我" Icon="Accept">
        <DirectEvents>
            <Click OnEvent="Button_OnClick">
            </Click>
        </DirectEvents>
    </ext:Button>
    <ext:Window ID="Window1" runat="server" Title="Hello World" Icon="Application" Height="600"
        Width="850" BodyStyle="background-color: #fff;" BodyPadding="5" Modal="true" Hidden="true">
        <Loader ID="Loader_Body" runat="server" Url="http://www.baidu.com" Mode="Frame">
            <LoadMask ShowMask="true" />
        </Loader>
    </ext:Window>
    </form>

后台代码：

string str = "http://windows.microsoft.com/zh-cn/windows/home";
            Window1.LoadContent(new ComponentLoader()
            {
                Url = str,
                Mode = LoadMode.Frame,
                DisableCaching = true
            });
            Window1.Show();

注：前台代码中必须指定loader的URL的初值，要不会报错