Question

我有一个WPF应用程序，当有互联网连接时，它会从URL加载图像，并且在没有活动的互联网连接时，应从缓存中加载图像。

我的问题是-在没有任何有效的互联网连接的情况下，图像不会被缓存以显示在后续应用程序启动中。

我搜索了几个小时，并尝试了CreateOptions和CacheOption的几乎所有可能的组合，但是结果却有相同的问题。

XAML代码如下：

              <Image
                   Width="{Binding MY_TILE_W}" MaxWidth="380" 
                   Height="{Binding MY_TILE_H}" MaxHeight="240" 
                   Stretch="UniformToFill">

                    <Image.CacheMode>
                        <BitmapCache  EnableClearType="False"
                              RenderAtScale="1"
                              SnapsToDevicePixels="False" />
                    </Image.CacheMode>

                    <Image.Source>
                        <BitmapImage UriSource="{Binding ImageUrl}" 
                             CreateOptions="IgnoreImageCache"
                             CacheOption="OnLoad"/>
                    </Image.Source>

                </Image>

除了C#代码以外，没有其他Binding代码了。

是否有可能实现我正在尝试的目标？如果是，请如何？

编辑： 正如@Wilson的评论所示，我的问题与this SO post并不完全相同-因为在我的用例中每次下载图像都不相同，但是the accepted answer's mentioned CachedImage library已部分解决了该问题

我将此ui元素的Image块替换为the library's：

<cachedImage:Image Grid.Row="0" Grid.ColumnSpan="2"
        Width="{Binding MY_TILE_W}" MaxWidth="380" 
        Height="{Binding MY_TILE_H}" MaxHeight="240" 
        Stretch="UniformToFill"
        ImageUrl="{Binding ImageUrl}"/>

然后从VS 2017开始的直接构建可以在脱机图像缓存中正常工作，但是生成的安装文件（使用Inno-setup）崩溃并显示以下日志：

Set property 'System.Windows.Controls.ItemsControl.ItemTemplate' threw an exception.
Stack Trace:    at System.Windows.Markup.WpfXamlLoader.Load(XamlReader xamlReader, IXamlObjectWriterFactory writerFactory, Boolean skipJournaledProperties, Object rootObject, XamlObjectWriterSettings settings, Uri baseUri)
   at System.Windows.Markup.WpfXamlLoader.LoadBaml(XamlReader xamlReader, Boolean skipJournaledProperties, Object rootObject, XamlAccessLevel accessLevel, Uri baseUri)
   at System.Windows.Markup.XamlReader.LoadBaml(Stream stream, ParserContext parserContext, Object parent, Boolean closeStream)
   at System.Windows.Application.LoadComponent(Object component, Uri resourceLocator)
   at MyApp.MyWindow.InitializeComponent() in E:\w_Development\DotNet\MyApp\MyWindow.xaml:line 1
   at MyApp.MyWindow..ctor(Window window) in E:\w_Development\DotNet\MyApp\MyWindow.xaml.cs:line 54
   at MyApp.MainWindow.<NavigateWithDelay>d__3.MoveNext() in E:\w_Development\DotNet\MyApp\MainWindow.xaml.cs:line 35
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.CompilerServices.AsyncMethodBuilderCore.<>c.<ThrowAsync>b__6_0(Object state)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
   at MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(Object obj)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at MS.Internal.CulturePreservingExecutionContext.Run(CulturePreservingExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   at System.Windows.Application.RunDispatcher(Object ignore)
   at System.Windows.Application.RunInternal(Window window)
   at System.Windows.Application.Run(Window window)
   at MyApp.App.Main()

我已经发布了an issue regarding this crash in library's issue-board。

Answer 1

使用CachedImage library符合标准，如this SO answer所示。

我用库的ui元素替换了Image块：

<cachedImage:Image Grid.Row="0" Grid.ColumnSpan="2"
        Width="{Binding MY_TILE_W}" MaxWidth="380" 
        Height="{Binding MY_TILE_H}" MaxHeight="240" 
        Stretch="UniformToFill"
        ImageUrl="{Binding ImageUrl}"/>

然后使用InnoSetup脚本生成安装文件后出现异常，因为未在我的InnoSetup脚本中添加DLL reference。现在一切正常。

WPF中的脱机图像缓存

1 个答案: