this.ComboBox7.Disabled =true;

 <ext:RadioGroup ID="RadioG_sfzg" runat="server" GroupName="RadioGroup" FieldLabel="是否第一<font color=red>*</font>" Cls="x-check-group-alt" Visible="false">使用的是Visible="false" 这个属性,后台没找到类似的设置 .

  <ext:RadioGroup ID="RadioG" runat="server" GroupName="RadioGroup" FieldLabel="是否第一<font color=red>*</font>" Cls="x-check-group-alt" >       <Items>              <ext:Radio ID="Radio1" runat="server" BoxLabel="是" InputValue=http://www.mamicode.com/"1">                        <DirectEvents>                                      <Check OnEvent="Radio1_check" />                         </DirectEvents>               </ext:Radio>               <ext:Radio ID="Radio2" runat="server" BoxLabel="否" InputValue=http://www.mamicode.com/"0" Checked="true">                           <DirectEvents>                                         <Check OnEvent="Radio2_check" />                           </DirectEvents>               </ext:Radio>        </Items>   </ext:RadioGroup>

<ext:ComboBox ID="ComboBox7" runat="server" FieldLabel="第一名<font color=red>*</font>" EmptyText="请选择..." TypeAhead="true" ForceSelection="false" Mode="Local" StoreID="Store6" DisplayField="Name" ValueField="Id" MinChars="0" ListWidth="150" AnchorHorizontal="92%" />

        protected void Radio1_check(object sender, DirectEventArgs e){            if (this.Radio1.Checked)            {                this.ComboBox7.Disabled = false;             }                   }        protected void Radio2_check(object sender, DirectEventArgs e)        {            if (this.Radio2.Checked)            {                this.ComboBox7.Disabled = true;            }        }