[W8App][C#] Task Cancellation

若想要讓產生的Task具有可取消的機制，則必需透過以下static methods取得task handle與傳入cancel token來達成
Task.Run(Action, CancellationToken)
Task.Run(Func<Task>, CancellationToken)
Task.Run<TResult>(Func<Task<TResult>>, CancellationToken)
Task.Run<TResult>(Func<TResult>, CancellationToken)

這個範例是我設計的一個對話盒控制項，當對話盒產生時呼叫InitItemsAsync以非同步的方式產生圖片對載入UI的list控制項中，使用者可以不必等待所有的圖片都產生即按下OK(或Cancel)按來關閉這個對話盒。因此我必需讓InitItemsAsync具有可被取消的機制。

   1: public sealed partial class MyDialog : UserControl

   2: {

   3:     private CancellationTokenSource _cts;

   4:     private CancellationToken _token; 

   5:     private Task _opInit;

#3-5 我們的物件必需儲存CancellationTokenSource、CancellationToken與Task方便在動作的對應函式中取消

   1: private async Task InitItemsAsync()

   2: {

   3:     for(int i=0 ; i<24 ; i++)

   4:     {

   5:         if (_token.IsCancellationRequested) break;

   6:  

   7:         await LoadImageAsync(i);

   8:     }

   9: }

#5 非同步的InitItemsAsync函式，當_token收到取消的要求時(IsCancellationRequested)提前結束迴圈

   1: _cts = new CancellationTokenSource();

   2: _token = _cts.Token;

   3: _opInit = Task.Run(async () =>

   4: {

   5:     await InitItemsAsync();

   6: },

   7: _token);

透過Task.Run來執行非同步的函式，並載入cancel token。
#5 InitItemAsync是非同步的函式，因此必需有async / await來載明

PS: 我嘗試過不用Lambda的寫法，而是直接以函式指標的方式來使用Task.Run，但在VS2013編譯時期會有函式型別模糊(error CS0121: The call is ambiguous between the following methods or properties)的錯誤，目前還不知道解決的方式。

   1: private bool TryCancelInitItems()

   2: {

   3:     if (_opInit.IsCompleted == false)

   4:     {

   5:         try

   6:         {

   7:             _cts.Cancel();

   8:  

   9:             _opInit.Wait(_token);

  10:  

  11:             return true;

  12:         }

  13:         catch(System.OperationCanceledException)

  14:         {

  15:             return true;

  16:         }

  17:         catch (Exception e)

  18:         {

  19:             Debug.WriteLine(@"{0}", e);

  20:  

  21:             return false;

  22:         }

  23:     }

  24:  

  25:     return true;

  26: }

當使用者按下結束對話盒的按鈕時，呼叫我的TryCancelInitItems函式來取消InitItemsAsync。

#3 先檢查task是否已經完成，若尚未完成才需使用取消機制
#7 呼叫取消並等待_token
#13 若InitItemsAsync被取消了，會丟出System.OperationCanceledException

[W8App] 8.0 “Snapped” to 8.1– with LayoutAwarePage

Windows 8.1的一個德政是取消了原本的Snappped View限制，App除了FullScreen外還可以有任意的大小(只是有最小限制)。不過對於已經開發好的8.0 App，就要花時間重新調整不同視窗大小時Layout。

我的懶人改法是，除了FullScreen外一律視為Snapped。依這樣的邏輯其實只要改動一個function – LayoutAwarePage的DetermineVisualState：

   1: protected virtual string DetermineVisualState(ApplicationView appView)

   2: {

   3:     if(appView.IsFullScreen)

   4:     {

   5:         return @"FullScreen" + appView.Orientation.ToString();

   6:     }

   7:     else

   8:     {

   9:         return @"Snapped";

  10:     }

  11: }

1. 原本參數為ApplicationViewState (編譯時有warning)，改為ApplicationView
3-10. 原本view state可以直接吐回字串的部份用邏輯修正

當然呼叫端也要調整為

   1: string visualState = DetermineVisualState(ApplicationView.GetForCurrentView());

1.  原本呼叫端是傳入ApplicationView.Value (編譯時有warning)，改為ApplicationView.GetForCurrentView()

[W8App] In W8.1, DirectWrite must create font with IDWriteFactory2

升上8.1第一天後, 我的App發生DirectWrite繪製文字有時會繪製不出來的問題。最後才發現改IDWriteFactory改為IDWriteFactory2後就一切正常，不過IDWriteFactory2只支援8.1以上，所以結論是App必做二個版本了。。。

[W8App] D2DERR_WRONG_FACTORY (0x88990012)

最近在學習W8App的Direct2D與DirectWrite時發生了一個例外的錯誤，當呼叫D2D的EndDraw來更新繪圖結果是產生了0x88990012 (D2DERR_WRONG_FACTORY)的例外錯誤。

這個錯誤發生的原因是我的DirectWrite Render物件預先儲存了D2D factory，而透過SurfaceImageSource來連結W8App與Direct2D時，D2DContext所使用的D2D factory似乎有自已獨立的產生方式。

目前的解決方式是透過GetFactory直接從D2DContext物件中取得D2DFactory，至於是否有更好的作法，就需要再研究。

   1: IFACEMETHODIMP CustomTextRenderer::DrawGlyphRun(

   2:     _In_opt_ void* clientDrawingContext,

   3:     FLOAT baselineOriginX,

   4:     FLOAT baselineOriginY,

   5:     DWRITE_MEASURING_MODE measuringMode,

   6:     _In_ DWRITE_GLYPH_RUN const* glyphRun,

   7:     _In_ DWRITE_GLYPH_RUN_DESCRIPTION const* glyphRunDescription,

   8:     IUnknown* clientDrawingEffect

   9:     )

  10: {

  11:     HRESULT hr = S_OK;

  12:  

  13:     Microsoft::WRL::ComPtr<ID2D1Factory> d2dFactory;

  14:     m_d2dContext->GetFactory(&d2dFactory);

  15:  

  16:     // Create the path geometry.

  17:     Microsoft::WRL::ComPtr<ID2D1PathGeometry> pathGeometry;

  18:     hr = d2dFactory->CreatePathGeometry(&pathGeometry);

  19:  

  20:     // Write to the path geometry using the geometry sink.

  21:  

  22:     Microsoft::WRL::ComPtr<ID2D1GeometrySink> sink;

  23:     if (SUCCEEDED(hr))

  24:     {

  25:         hr = pathGeometry->Open(&sink);

  26:     }

  27:  

  28:     // Get the glyph run outline geometries back from DirectWrite and place them within the

  29:     // geometry sink.

  30:     if (SUCCEEDED(hr))

  31:     {

  32:         hr = glyphRun->fontFace->GetGlyphRunOutline(

  33:             glyphRun->fontEmSize,

  34:             glyphRun->glyphIndices,

  35:             glyphRun->glyphAdvances,

  36:             glyphRun->glyphOffsets,

  37:             glyphRun->glyphCount,

  38:             glyphRun->isSideways,

  39:             glyphRun->bidiLevel %2,

  40:             sink.Get()

  41:             );

  42:     }

  43:  

  44:     // Close the geometry sink

  45:     if (SUCCEEDED(hr))

  46:     {

  47:         hr = sink.Get()->Close();

  48:     }

  49:  

  50:     // Initialize a matrix to translate the origin of the glyph run.

  51:     D2D1::Matrix3x2F const matrix = D2D1::Matrix3x2F(

  52:         1.0f, 0.0f,

  53:         0.0f, 1.0f,

  54:         baselineOriginX, baselineOriginY

  55:         );

  56:  

  57:     // Create the transformed geometry

  58:     Microsoft::WRL::ComPtr<ID2D1TransformedGeometry> transformedGeometry;

  59:     if (SUCCEEDED(hr))

  60:     {

  61:         hr = d2dFactory->CreateTransformedGeometry(

  62:             pathGeometry.Get(),

  63:             &matrix,

  64:             &transformedGeometry

  65:             );

  66:     }

  67:  

  68:     // Draw the outline of the glyph run

  69:     if(SUCCEEDED(hr))

  70:     {

  71:         m_d2dContext->DrawGeometry(transformedGeometry.Get(),m_brushOutline.Get());

  72:         m_d2dContext->FillGeometry(transformedGeometry.Get(),m_brushFill.Get());

  73:     }

  74:  

  75:     return hr;

  76: }

13-14 透過目前的D2DContext來取得D2DFactory

[W8App] Hide / Show cursor

隱藏滑鼠指標

   1: if (Window.Current.CoreWindow.PointerCursor != null) Window.Current.CoreWindow.PointerCursor = null;

顯示滑鼠指標

   1: if (Window.Current.CoreWindow.PointerCursor == null)

   2: {

   3:     Window.Current.CoreWindow.PointerCursor = new CoreCursor(CoreCursorType.Arrow, 1);

   4: }

CoreCursor的id可以自已隨意的指派並不一定是1。

Reference:

1. CoreCursorType enumeration

如何取消訂閱行事曆

有網友問已訂閱的行事曆如何取消，所以就多了這一篇。和訂閱行事曆一樣必需透過瀏覽器進入SkyDrive的行事曆設定。進入SkyDrive的行事曆後，點選右邊的小齒輪，進入選項頁

選擇想要取消訂閱的行事曆

 刪除

相關文章
整合Windows 8與google行事曆

[W8App] XAML/C# Hex string

XAML的Hex string表示是以&#x開頭，如：

   1: <Button Content="&#xE114;" FontFamily="Segoe UI Symbol"/>

但C#的Hex string是以\x開頭，如：

   1: btn.Content = "\xE114";

[W8App] Custom Control – Access template component

Step 1. XAML，給予要存取元件名稱

   1: <Style TargetType="local:WaitReadyButton">

   2:     <Setter Property="Template">

   3:         <Setter.Value>

   4:             <ControlTemplate TargetType="local:WaitReadyButton">

   5:                 <Grid>

   6:                     <TextBlock x:Name="txtSymbol" Text=""/>

   7:                 </Grid>

   8:             </ControlTemplate>

   9:         </Setter.Value>

  10:     </Setter>

  11: </Style>

Step 2. C#，宣告存取元件

   1: public sealed class WaitReadyButton : Control

   2: {

   3:     private TextBlock _txtSymbol;

Step 3. C#，在OnApplyTemplate()中取得元件

   1: protected override void OnApplyTemplate()

   2: {

   3:     base.OnApplyTemplate();

   4:  

   5:     _txtSymbol = GetTemplateChild(@"txtSymbol") as TextBlock;

   6: }

成功取得元件後即可在程式碼中使用該元件。

Reference

1. Creating a WPF Custom Control