我的 Xamarin 跨平臺應用程序在調試模式 (Android) 下運行良好，但是當我更改為發布時，它會拋出異常。我已經搜索過以糾正這種情況。大多數帖子顯示android.permission.INTERNET需要在 AndroidManifest.xml 文件中添加。但這對我的問題不起作用。另外，無論 Linker 是 Sdk Assembly only 還是發布模式下的 None，它仍然不起作用。（我的應用程序基于 Android Pie 9.0 構建）和例外：Unhandled Exception:04-21 22:37:08.972 E/mono    ( 5319): System.NullReferenceException: Object reference not set to an instance of an object.04-21 22:37:08.972 E/mono    ( 5319):   at .Views.LoginPage+<SigninProcedure>d__2.MoveNext () [0x001d6] in LoginPage.xaml.cs:56 04-21 22:37:08.972 E/mono    ( 5319): --- End of stack trace from previous location where exception was thrown ---04-21 22:37:08.972 E/mono    ( 5319):   at (wrapper dynamic-method) System.Object.31(intptr,intptr)04-21 22:37:08.972 E/mono    ( 5319):   at (wrapper native-to-managed) System.Object.31(intptr,intptr)04-21 22:37:08.973 E/mono-rt ( 5319): [ERROR] FATAL UNHANDLED EXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object.04-21 22:37:08.973 E/mono-rt ( 5319):   at Views.LoginPage+<SigninProcedure>d__2.MoveNext () [0x001d6] in LoginPage.xaml.cs:56 <uses-permission android:name="android.permission.INTERNET" />下面是我拋出異常時的代碼：public async Task<List<User>> FindExistUserAsync(string weburl, string username){    string url = weburl + username;    try    {        var response = await client.GetAsync(url);// throw exception after run this line.        if (response.StatusCode == System.Net.HttpStatusCode.OK)        {            var JsonResult = response.Content.ReadAsStringAsync().Result;            try            {                //Debug.WriteLine(JsonResult);                var contentResp = JsonConvert.DeserializeObject<List<User>>(JsonResult);                return contentResp;            }            catch (Exception ex) { Debug.WriteLine(ex.Message); return null; }        }    }    catch (Exception ex) { Debug.WriteLine(ex.Message); return null; }    return null;}