如何在Android上修复"Only the original thread that created a view hierarchy can touch its views" Xamarin表单

Question

我正在用Xamarin Forms构建一个应用程序，但只在android上。当我运行应用程序时，我得到这个错误"只有创建视图层次结构的原始线程才能触摸它的视图"。我在我的应用程序中有类似的页面，但这是我第一次收到这个错误。我知道这是关于UI线程的事情，但我不知道我到底在哪里使用了错误的线程。

这是错误产生的代码:

ViewModel,

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
using Xamarin.Forms;
using XamarinApp.Services;
using XamarinApp.Views.Month;
namespace XamarinApp.ViewModels.Month
{
public class HistoryViewModel : BaseViewModel
{
private readonly IMonthService _monthService;
private ObservableCollection<int> years;
private ObservableCollection<int> months;
public int year;
public int month;
public HistoryViewModel(IMonthService monthService)
{
_monthService = monthService;
Years = new ObservableCollection<int>();
Months = new ObservableCollection<int>();
Title= "History";
FindCommand = new Command(async () => await GoToYearHistory());
}
private async Task GoToYearHistory()
{
if (year == 0)
return;
await Shell.Current.GoToAsync($"{nameof(YearHistoryPage)}?{nameof(YearHistoryViewModel.Year)}={year}");
}

public async void GetYearsAndMonths()
{
Years.Clear();
Months.Clear();
var years = await _monthService.GetYears().ConfigureAwait(false);
foreach (var year in years)
{
Years.Add(year);
}
for (int i = 0; i < 12; i++)
{
Months.Add(i+1);
}

}

public ObservableCollection<int> Years
{
get => years;
set
{
years = value;
OnPropertyChanged(nameof(Years));
}
}
public ObservableCollection<int> Months
{
get => months;
set
{
months = value;
OnPropertyChanged(nameof(Months));
}
}

public int Year
{
get => year;
set
{
year = value;
OnPropertyChanged(nameof(Year));
}
}
public int Month
{
get => month;
set
{
month = value;
OnPropertyChanged(nameof(Month));
}
}
public ICommand FindCommand { get; }
}
}

Xaml文件,

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" xmlns:month="clr-namespace:XamarinApp.ViewModels.Month" x:DataType="month:HistoryViewModel"
x:Class="XamarinApp.Views.Month.HistoryPage"
BackgroundColor="{StaticResource BackgroundColor}">
<ContentPage.Content>
<StackLayout Orientation="Vertical" Padding="30,24,30,24" Spacing="10">
<Label Text="History" 
FontSize="Title" 
TextColor="{StaticResource Primary}" 
FontAttributes="Bold"
HorizontalTextAlignment="Center"
VerticalTextAlignment="Center" />
<StackLayout Orientation="Horizontal">
<Picker Title="Select Year" ItemsSource="{Binding Years}"
SelectedItem="{Binding Year}"  HorizontalOptions="FillAndExpand"/>
<Picker Title="Select Month" ItemsSource="{Binding Months}"
SelectedItem="{Binding Month}"  HorizontalOptions="FillAndExpand"/>
</StackLayout>
<Button Text="Find" Command="{Binding FindCommand}" Margin="20,40,20,0" CornerRadius="10" HorizontalOptions="FillAndExpand"/>
</StackLayout>
</ContentPage.Content>
</ContentPage>

——Xaml.cs文件

using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using XamarinApp.ViewModels.Month;
namespace XamarinApp.Views.Month
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class HistoryPage : ContentPage
{
private readonly HistoryViewModel _historyViewModel;
public HistoryPage()
{
InitializeComponent();
_historyViewModel = Startup.Resolve<HistoryViewModel>();
BindingContext = _historyViewModel;
}
protected override void OnAppearing()
{
Device.BeginInvokeOnMainThread(() =>
{
_historyViewModel?.GetYearsAndMonths();
});

}
}
}

Answer 1

所以我通过删除ConfigureAwait(false)修复了这个问题从这一行"var years = await _monthService.GetYears().ConfigureAwait(false)">因为ConfigureAwait(false)让我不能呆在UI线程上