C# 从OnCreate重写方法启动异步方法时出现问题 OnCreate（）中的） 新线程（新线程开始（（）=>{ this.RunOnUiThread（异步（）=> { 等待设置数据（今天）； //等待FindNotesForDay（今天，今天。添加天数（+6））； 进步。解散（）； }); })).Start（）； 专用异步任务SetData（日期时间日期） { 等待任务。运行（（）=> { dicMyMap=null； dicMyMap=新字典（）； 列表组=新列表（）； 集团。添加（“星期一”）； 集团。添加（“星期二”）； 集团。添加（“星期三”）； 集团。添加（“星期四”）； 集团。添加（“星期五”）； 添加（组[0]，列表填充（date.ToString（“yyyy-MM-dd”，CultureInfo.InvariantCulture））； 日期=日期加天数（+1）； 添加（组[1]，列表填充（date.ToString（“yyyy-MM-dd”，CultureInfo.InvariantCulture））； 日期=日期加天数（+1）； 添加（组[2]，列表填充（date.ToString（“yyyy-MM-dd”，CultureInfo.InvariantCulture））； 日期=日期加天数（+1）； 添加（组[3]，列表填充（date.ToString（“yyyy-MM-dd”，CultureInfo.InvariantCulture））； 日期=日期加天数（+1）； 添加（组[4]，列表填充（date.ToString（“yyyy-MM-dd”，CultureInfo.InvariantCulture））； myAdapater=新的ExpandableListViewAdapter（此、组、dicMyMap）； SetAdapter（myAdapater）； }); } 私有列表列表填充（字符串日期） { string sql=“SELECT*FROM”使用（组）加入groupConvert，其中StartDate='“+date+”，court='“+User.court+”，Year='“+User.IntakeYear+”；”； 列表温度=新列表（）； //插入标题 临时添加（新的ClassInstance（“开始时间”、“结束时间”、“主题”、“位置”、“位置”）； 使用（MySqlCommand cmd=newmysqlcommand（sql，Connect.GetConnection（））） { MySqlDataReader=cmd.ExecuteReader（）； while（reader.Read（）） { ClassInstance c=新ClassInstance（读卡器[“开始时间”].ToString（），读卡器[“结束时间”].ToString（），读卡器[“主题”].ToString（），读卡器[“位置”].ToString（），读卡器[“基本”].ToString（），读卡器[“注释”].ToString（））； 温度添加（c）； } } 如果（临时计数==1） { 温度清除（）； 临时添加（新ClassInstance（“无类”、“无类”、“无类”、“无类”、“无类”、“无类”））； } 返回温度； }

你好

我目前正试图从AWS上托管的数据库填充ListView。正如您所想象的，加载需要一点时间。我的问题是我当前的代码抛出了一个错误。抛出的错误模棱两可，仅表示程序已崩溃，没有帮助

本质上，我想做的非常简单，我基本上只想在加载这些方法时显示一个对话框

任何关于我的代码的建议都是非常好的

编辑：我已经将错误消息缩小到代码的这个区域。在尝试使用线程之前，我能够加载此活动，但是由于没有加载消息，用户会觉得该活动已冻结，而不是正在加载

谢谢，

---

Joe

因此我设法修复了上面的代码以正确运行

如果您有任何反馈或意见，请让我知道，我希望有人觉得这有帮助

我完全错误地使用了异步方法，您也无法从oncreate调用异步方法，我相信您已经知道了。我的解决方案的一部分是将我错误地使异步的所有方法改回void（这意味着它们是同步的）

然后我创建了一个线程来运行这些命令，现在它们最终以正确的顺序运行：）

重要的是要注意，在线程中，任何受UI影响的元素都需要使用主UI线程运行，这同样适用于它们调用的方法

下面是我为解决问题而创建的代码区域

       Within OnCreate()
       new Thread(new ThreadStart(() => {
            this.RunOnUiThread(async () =>
            {
                await SetData(TodaysDate); ;
                //await FindNotesForDay(TodaysDate, TodaysDate.AddDays(+6));
                progress.Dismiss();
            });
        })).Start();



        private async Task SetData(DateTime date)
    {
        await Task.Run(() =>
        {
            dicMyMap = null;

            dicMyMap = new Dictionary<string, List<ClassInstance>>();

            List<string> group = new List<string>();

            group.Add("Monday");
            group.Add("Tuesday");
            group.Add("Wednesday");
            group.Add("Thursday");
            group.Add("Friday");

            dicMyMap.Add(group[0], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));

            date = date.AddDays(+1);

            dicMyMap.Add(group[1], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));

            date = date.AddDays(+1);

            dicMyMap.Add(group[2], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));

            date = date.AddDays(+1);

            dicMyMap.Add(group[3], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));

            date = date.AddDays(+1);

            dicMyMap.Add(group[4], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));


            myAdapater = new ExpandableListViewAdapter(this, group, dicMyMap);

            expandableListView.SetAdapter(myAdapater);
        });
    }

    private List<ClassInstance> ListsPopulation(String date)
    {
        string sql = "SELECT * FROM lectures join groupConvert using (Groups) where StartDate = '" + date + "' AND Cohort = '" + User.Cohort + "' AND Year = '" + User.IntakeYear + "';";

        List<ClassInstance> Temp = new List<ClassInstance>();

        //Insert Header
        Temp.Add(new ClassInstance("Start Time", "End   Time", "Subject", "Location", "", ""));

        using (MySqlCommand cmd = new MySqlCommand(sql, Connect.GetConnection()))
        {
             MySqlDataReader reader = cmd.ExecuteReader();

            while (reader.Read())
            {
                ClassInstance c = new ClassInstance(reader["StartTime"].ToString(), reader["EndTime"].ToString(), reader["Theme"].ToString(), reader["Location"].ToString(), reader["Essential"].ToString(), reader["Notes"].ToString());
                Temp.Add(c);
            }
        }

        if (Temp.Count == 1)
        {
            Temp.Clear();
            Temp.Add(new ClassInstance("No Classes", "", "", "", "", ""));
        }


        return Temp;
    }

下面是我的完整课程，供其他用户参考。我还没有记录这段代码，因为它在这个评论中足够大

    // Try catch attempt to catch all errors, the error dialog thrown within 
    //the catch is fairly simple 
    try
        {
            //Start loading spinner
            var LoadingProgressDialog = ProgressDialog.Show(this, "Loading", "Loading", false);

            //Start loading thread, this thread will carry out the functions 
            // in the order you requested
            Thread LoadingThread = new Thread(() =>
            {
                //Line below only relevant to my code
                StartMonday.Text = "Week Commencing On " + TodaysDate.ToLongDateString();
                // Call this method first
                SetData(TodaysDate);
                // call this method second
                FindNotesForWeek(TodaysDate, 7);
                //Update the UI on the main thread but call third this will close the loading dialog message
                RunOnUiThread(() => LoadingProgressDialog.Hide());
            // End of thread
            });
            //Run the thread
            LoadingThread.Start();
        }
        catch (Exception e)
        {
            var ErrorMessageDialog = ProgressDialog.Show(this, "Loading", e.ToString(), false);
        }

命名空间MedicalHubaApplication
{
[活动（Label=“时间表”，NoHistory=true）]
公开课时间表：活动
{
ClassInstance populateClass=新ClassInstance（）；
UserInstance User=new UserInstance（）；
GetConnectionClass Connect=新建GetConnectionClass（）；
字典dicMyMap；
TextView DateHeaderTV；
TextView NoteHeaderTV；
可扩展列表视图适配器myAdapater；
ExpandableListView ExpandableListView；
//需要列表的实例
NotesListViewAdapter MyNoteAdapter；
列表视图注释列表视图；
滚动视图滚动视图列表；
TextView StartMonday；
按钮选择日期按钮；
创建时受保护的覆盖无效（Bundle savedInstanceState）
{
base.OnCreate（savedInstanceState）；
//在此处创建应用程序
SetContentView（Resource.Layout.timeline）；
expandableListView=FindViewById（Resource.Id.ListViewExpanded）；
StartMonday=FindViewById（Resource.Id.TextViewStartDateMonday）；
SelectDateButton=FindViewById（Resource.Id.SelectDateButton）；
NotesListView=FindViewById（Resource.Id.NotesListView）；
DateHeaderTV=FindViewById（Resource.Id.DateHeader）；
NoteHeaderTV=FindViewById（Resource.Id.NoteHeader）；
ScrollViewList=FindViewById（Resource.Id.ScrollView）；
//填充用户
User=JsonConvert.DeserializeObject（Intent.GetStringExtra（“用户”）；
//星期一
DateTime TodaysDate=DateTime.Now；
而（TodaysDate.DayOfWeek！=DayOfWeek.Monday）今天
        namespace MedicalHubApplication
        {
        [Activity(Label = "TimeTable", NoHistory = true)]
        public class TimeTable : Activity
        {
       ClassInstance populateClass = new ClassInstance();
       UserInstance User = new UserInstance();
       GetConnectionClass Connect = new GetConnectionClass();
       Dictionary<string, List<ClassInstance>> dicMyMap;

    TextView DateHeaderTV;
    TextView NoteHeaderTV;

    ExpandableListViewAdapter myAdapater;
    ExpandableListView expandableListView;

    // Need Instance of List 
    NotesListViewAdapter myNoteAdapater;
    ListView NotesListView;
    ScrollView ScrollViewList;

    TextView StartMonday;
    Button SelectDateButton;

    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);

        // Create your application here
        SetContentView(Resource.Layout.TimeTable);

        expandableListView = FindViewById<ExpandableListView>(Resource.Id.ListViewExpanded);
        StartMonday = FindViewById<TextView>(Resource.Id.TextViewStartDateMonday);
        SelectDateButton = FindViewById<Button>(Resource.Id.SelectDateButton);
        NotesListView = FindViewById<ListView>(Resource.Id.NotesListView);
        DateHeaderTV = FindViewById<TextView>(Resource.Id.DateHeader);
        NoteHeaderTV = FindViewById<TextView>(Resource.Id.NoteHeader);
        ScrollViewList = FindViewById<ScrollView>(Resource.Id.ScrollView);

        // Populate User 
        User = JsonConvert.DeserializeObject<UserInstance>(Intent.GetStringExtra("User"));

        //Find Monday 
        DateTime TodaysDate = DateTime.Now;
        while (TodaysDate.DayOfWeek != DayOfWeek.Monday) TodaysDate = TodaysDate.AddDays(-1);

        try
        {
            var LoadingProgressDialog = ProgressDialog.Show(this, "Loading", "Loading", false);

            Thread LoadingThread = new Thread(() =>
            {
                StartMonday.Text = "Week Commencing On " + TodaysDate.ToLongDateString();
                SetData(TodaysDate);
                FindNotesForWeek(TodaysDate, 7);
                RunOnUiThread(() => LoadingProgressDialog.Hide());

            });

            LoadingThread.Start();
        }
        catch (Exception e)
        {
            var ErrorMessageDialog = ProgressDialog.Show(this, "Loading", e.ToString(), false);
        }

        SelectDateButton.Click += delegate
        {
            DateSelectOnClick();  
        }; 
    }

    private void DateSelectOnClick()
    {
        DatePickerFragment frag = DatePickerFragment.NewInstance(delegate (DateTime SelectedDate)
        {
            while (SelectedDate.DayOfWeek != DayOfWeek.Monday) SelectedDate = SelectedDate.AddDays(-1);

            try
            {
                var LoadingProgressDialog = ProgressDialog.Show(this, "Loading", "Loading", false);

                Thread LoadingThread = new Thread(() =>
                {
                    RunOnUiThread(() => StartMonday.Text = "Week Commencing On " + SelectedDate.ToLongDateString());
                    SetData(SelectedDate);
                    FindNotesForWeek(SelectedDate, 7);
                    RunOnUiThread(() => LoadingProgressDialog.Hide());

                });

                LoadingThread.Start();
            }
            catch (Exception e)
            {
                var ErrorMessageDialog = ProgressDialog.Show(this, "Loading", e.ToString(), false);
            }
        });
        frag.Show(FragmentManager, DatePickerFragment.TAG);
    }

    private void SetData(DateTime date)
    {

        dicMyMap = null;

        dicMyMap = new Dictionary<string, List<ClassInstance>>();

        List<string> group = new List<string>();

        group.Add("Monday");
        group.Add("Tuesday");
        group.Add("Wednesday");
        group.Add("Thursday");
        group.Add("Friday");

        dicMyMap.Add(group[0], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));

        date = date.AddDays(+1);

        dicMyMap.Add(group[1], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));

        date = date.AddDays(+1);

        dicMyMap.Add(group[2], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));

        date = date.AddDays(+1);

        dicMyMap.Add(group[3], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));

        date = date.AddDays(+1);

        dicMyMap.Add(group[4], ListsPopulation(date.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)));


        myAdapater = new ExpandableListViewAdapter(this, group, dicMyMap);

        RunOnUiThread(() => expandableListView.SetAdapter(myAdapater));

    }

    private List<ClassInstance> ListsPopulation(String date)
    {
        string sql = "SELECT * FROM lectures join groupConvert using (Groups) where StartDate = '" + date + "' AND Cohort = '" + User.Cohort + "' AND Year = '" + User.IntakeYear + "';";

        List<ClassInstance> Temp = new List<ClassInstance>();

        //Insert Header
        Temp.Add(new ClassInstance("Start Time", "End   Time", "Subject", "Location", "", ""));

        using (MySqlCommand cmd = new MySqlCommand(sql, Connect.GetConnection()))
        {
             MySqlDataReader reader = cmd.ExecuteReader();

            while (reader.Read())
            {
                ClassInstance c = new ClassInstance(reader["StartTime"].ToString(), reader["EndTime"].ToString(), reader["Theme"].ToString(), reader["Location"].ToString(), reader["Essential"].ToString(), reader["Notes"].ToString());
                Temp.Add(c);
            }
        }

        if (Temp.Count == 1)
        {
            Temp.Clear();
            Temp.Add(new ClassInstance("No Classes", "", "", "", "", ""));
        }


        return Temp;
    }

    private void FindNotesForWeek(DateTime StartDate, int DaysInMonth)
    {
        List<NotesInstance> WeekNotes = new List<NotesInstance>();

        WeekNotes.AddRange(FindNotesForDay(StartDate, StartDate.AddDays(+DaysInMonth)));

        if (WeekNotes.Count != 0)
        {
            RunOnUiThread(() => NoteHeaderTV.Visibility = ViewStates.Visible);
            RunOnUiThread(() => NotesListView.Visibility = ViewStates.Visible);
            RunOnUiThread(() => DateHeaderTV.Text = "Date:");

            myNoteAdapater = new NotesListViewAdapter(this, WeekNotes);

            RunOnUiThread(() => NotesListView.Adapter = myNoteAdapater);
        }
        else
        {
            RunOnUiThread(() => NoteHeaderTV.Visibility = ViewStates.Invisible);
            RunOnUiThread(() => NotesListView.Visibility = ViewStates.Invisible);
            RunOnUiThread(() => DateHeaderTV.Text = "No Notifications");
        }

        // Set up Adapter 
        myNoteAdapater = new NotesListViewAdapter(this, WeekNotes);

        RunOnUiThread(() => NotesListView.Adapter = myNoteAdapater);
    }

    private List<NotesInstance> FindNotesForDay(DateTime StartDate, DateTime EndDate)
    {
        string sql = "SELECT *  FROM Notes WHERE dates between '" + StartDate.ToString("yyyy-MM-dd") + "' AND '" + EndDate.ToString("yyyy-MM-dd") + "' AND yearGroup = '" + User.IntakeYear.ToString() + "';";

        List<NotesInstance> Temp = new List<NotesInstance>();

        using (MySqlCommand cmd = new MySqlCommand(sql, Connect.GetConnection()))
        {

            MySqlDataReader reader = cmd.ExecuteReader();

            while (reader.Read())
            {
                NotesInstance c = new NotesInstance(reader.GetDateTime("dates").ToString("dd-MM-yyyy"), reader["Notes"].ToString());
                Temp.Add(c);
            }
        }

        return Temp;
    }
}