通用Windows平臺（UWP）相當於獲取主應用程序UI

Question

我正在嘗試將Windows Phone 8.1 Silverlight應用程序遷移到UWP。我在獲取Main Application UI時出錯。

這是Windows Windows Phone 8.1 Silverlight代碼：

Storage storage = ((App.Current.RootVisual as PhoneApplicationFrame).DataContext as Storage); 

這就是我的UWP版本進行：

Storage storage = ((Window.Current.Content as Frame).DataContext as Storage); 

我得到了NullPointerException。有任何想法嗎？

在此先感謝。

編輯

這是我的XAML：

<Page 
x:Class="windows_phone.MainPage" 
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768" 
FontFamily="{StaticResource PhoneFontFamilyNormal}" 
FontSize="20" 
Foreground="#FF000000"> 

<!--LayoutRoot is the root grid where all page content is placed--> 
<Grid x:Name="LayoutRoot" Background="Transparent"> 
    <Grid.RowDefinitions> 
     <RowDefinition Height="Auto"/> 
     <RowDefinition Height="*"/> 
    </Grid.RowDefinitions> 

    <!--TitlePanel contains the name of the application and page title--> 

    <!--ContentPanel - place additional content here--> 
    <Grid x:Name="ContentPanel" Grid.Row="1" Margin="0,0,0,0"> 
     <WebView 
      x:Name="webView" 
      Margin="0,0,0,0" 
      Grid.Row="1" 
      /> 
    </Grid> 
</Grid> 

這是我的類存儲，保存最後的URI：

namespace windows 
{ 
public class Storage 
{ 
    #region Properties 
    private Uri _lastUri = null; 
    public Uri lastUri 
    { 
     get {return _lastUri;} 
     set 
     { 
      _lastUri = value; 
     } 
    } 
    #endregion 
} 
} 

第二個編輯

代碼，我使用的存儲類：

public sealed partial class MainPage : Page 
{ 

    private Storage storage = null; 

.... 

protected override void OnNavigatedTo(NavigationEventArgs e) 
    { 
     storage = (((Window.Current.Content as Frame).Content as Page).DataContext as Storage); 
     if (Storage.lastUri != null) webView.Navigate(Storage.lastUri); 
     base.OnNavigatedTo(e); 
    } 

    void webView_LoadCompleted(object sender, NavigationEventArgs e) 
    { 
     if (webView.Source.ToString().Contains("login")) 
     { 
      string id = LoadUserIdFromIsolatedStorage(); 
      String[] data = new String[1]; 
      data[0] = id; 
      if (id != null) 
       webView.InvokeScript("WinHelp", data); 
     } 
     progressIndicator.Visibility = Visibility.Collapsed; 
     Storage.lastUri = e.Uri; 
    } 

Answer 1

框架的DataContext的確實是NULL。這是因爲框架將視圖放在另一個內容變量中。那一個將包含您的DataContext。

您需要將內容聲明爲頁面。下面是一個例子：

((Window.Current.Content as Frame).Content as Page).DataContext;