如何在调用文件选取器后继续运行 Windows Phone 应用 (HTML)

[ 本文适用于编写 Windows 运行时应用的 Windows 8.x 和 Windows Phone 8.x 开发人员。如果你要针对 Windows 10 进行开发，请参阅 最新文档 ]

当你从 Windows Phone 应用商店应用调用文件选取器时，你的应用将停用，直到文件选取器返回用户做出的选择。但是，在低内存手机上，你的应用可能被终止。正因为如此，你必须在 Windows Phone 应用商店应用中调用不同于在 Windows 应用商店应用中调用的方法，才能在完成文件选取器操作后继续运行应用。下表显示了这些方法。

本主题中的示例演示了如何在使用 FileOpenPicker 时继续运行应用。当你调用其他文件和文件夹选取器方法时，请使用类似代码。

提示  若要查看此解决方案的示例，请参阅文件选取器示例。

说明

步骤 1: 调用 FileOpenPicker 并继续运行应用的步骤

以下示例假设用户通过使用 FileOpenPicker 选择了一个新照片。

1. 调用 PickSingleFileAndContinue 方法以使用文件选取器选取照片。

       function pickSinglePhoto() {
           // Clean scenario output
           WinJS.log && WinJS.log("", "sample", "status");
   
           // Create the picker object and set options
           var openPicker = new Windows.Storage.Pickers.FileOpenPicker();
           openPicker.viewMode = Windows.Storage.Pickers.PickerViewMode.thumbnail;
           openPicker.suggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.picturesLibrary;
           // Users expect to have a filtered view of their folders depending on the scenario.
           // For example, when choosing a documents folder, restrict the filetypes to documents for your application.
           openPicker.fileTypeFilter.replaceAll([".png", ".jpg", ".jpeg"]);
   
           // Open the picker for the user to pick a file
           openPicker.pickSingleFileAndContinue();
       }
   

2. 当应用继续时编写延续方法，以对由用户选取的照片采取所需的操作。

       // Called when app is activated from file open picker
       // eventObject contains the returned files picked by user
       function continueFileOpenPicker(eventObject) {
           var files = eventObject[0].files;
           var filePicked = files.size > 0 ? files[0] : null;
           if (filePicked !== null) {
               // Application now has read/write access to the picked file
               WinJS.log && WinJS.log("Picked photo: " + filePicked.name, "sample", "status");
           } else {
               // The picker was dismissed with no selected file
               WinJS.log && WinJS.log("Operation cancelled.", "sample", "status");
           }
       }
   

3. 侦听 activated 事件。

       ...
       app.addEventListener("activated", activated, false);
       app.start();
   

4. 当激活应用时，处理 activated 事件以捕获有关该激活的信息，并将其转发到调用文件选取器的页面。

       function activated(eventObject) {
           var activationKind = eventObject.detail.kind;
           var activatedEventArgs = eventObject.detail.detail;
   
           // Handle launch and continuation activation kinds
           switch (activationKind) {
               case activationKinds.launch:
               case activationKinds.pickFileContinuation:
               case activationKinds.pickSaveFileContinuation:
               case activationKinds.pickFolderContinuation:
               case activationKinds.webAuthenticationBrokerContinuation:
                   var p = WinJS.UI.processAll().
                       then(function () {
   
                           // Navigate to either the first scenario or to the last running scenario
                           // before suspension or termination.
                           var url = "/pages/home/home.html";
                           var initialState = {};
                           var navHistory = app.sessionState.navigationHistory;
                           if (navHistory) {
                               nav.history = navHistory;
                               url = navHistory.current.location;
                               initialState = navHistory.current.state || initialState;
                           }
                           initialState.activationKind = activationKind;
                           initialState.activatedEventArgs = activatedEventArgs;
                           nav.history.current.initialPlaceholder = true;
                           return nav.navigate(url, initialState);
                       });
   
                   ...
                   break;
   
               default:
                   break;
           }
   

5. 当用户导航到该页面时，检查 ActivationKind 属性。如果其值为 pickFileContinuation，则调用延续方法。

               if (options && options.activationKind === Windows.ApplicationModel.Activation.ActivationKind.pickFileContinuation) {
                   continueFileOpenPicker(options.activatedEventArgs);
   

相关主题

文件选取器示例