异步方法中的可观察集合

你好朋友们，我在我的Windows应用商店应用程序中以异步方法使用ObservableCollection遇到了非常奇怪的问题。我正在尝试以异步方法在可观察集合中添加项目，如果我在 await 关键字所在的行上方定义可观察集合，它工作正常，但我在此行下方初始化它不起作用。我已经为这个问题做了样本。我的 XAML 代码是..

<Page
x:Class="observableCollectionTest.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:observableCollectionTest"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Grid Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
    <ListView ItemsSource="{Binding SomeCollection}" Background="Pink" HorizontalAlignment="Left" Width="500" >
        <ListView.ItemTemplate>
            <DataTemplate>
                <Grid Width="200" Height="200" Background="Red" >
                    <Button Content="click me" Name="btn" ></Button>
                </Grid>
            </DataTemplate>
        </ListView.ItemTemplate>            
    </ListView>
</Grid>

我的主页反手工作代码是..

public sealed partial class MainPage : Page
{
    public ObservableCollection<string> SomeCollection { get; set; }
    public MainPage()
    {
        this.InitializeComponent();

        FillCollection();
        this.DataContext = this;
    }
    public async Task FillCollection()
    {
        SomeCollection = new ObservableCollection<string>(); // it is working..
        HttpClient client = new HttpClient();
        HttpResponseMessage message = await client.GetAsync("https://www.google.co.in/");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
    }

我的主页反手 FillCollection 代码不起作用。.

 public async Task FillCollection()
    {
        HttpClient client = new HttpClient();
        HttpResponseMessage message = await client.GetAsync("https://www.google.co.in/");
        SomeCollection = new ObservableCollection<string>(); // this is not working
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
        SomeCollection.Add("asd");
    }

我不明白为什么会这样。 我在这里缺少一些概念，请告诉我..感谢任何形式的帮助或建议。