How to continue your Windows Phone app after calling a file picker (HTML)

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[This article is for Windows 8.x and Windows Phone 8.x developers writing Windows Runtime apps. If you’re developing for Windows 10, see the latest documentation]

When you call a file picker from a Windows Phone Store app, your app is deactivated until the file picker returns the selection made by the user. On low-memory phones, however, your app may be terminated. Because of this possibility, you have to call different methods in a Windows Phone Store app than you call in a Windows Store app to continue your app after a file picker operation. The following table shows these methods.

Task Method to call from a Windows Store app Method to call from a Windows Phone Store app
Pick a file to open PickSingleFileAsync PickSingleFileAndContinue
Pick a location and filename to save a file PickSaveFileAsync PickSaveFileAndContinue
Pick a folder PickSingleFolderAsync PickFolderAndContinue

 

The example in this topic demonstrates how to continue your app when you use a FileOpenPicker. Use similar code when you call other file and folder picker methods.

Tip  To see an example of this solution, see the File picker sample.

 

Instructions

Step 1: To call a FileOpenPicker and continue your app

The following example assumes that the user is selecting a photo by using a FileOpenPicker.

  1. Call the PickSingleFileAndContinue method to pick a photo by using a file picker.

        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. Write a continuation method to take the desired action with the photo picked by the user when the app continues.

        // 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. Listen for the activated event.

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

  4. When the app is activated, handle the activated event to capture information about the activation and forward it to the page that called the file picker.

        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. When the user navigates to the page, check the ActivationKind property. If its value is pickFileContinuation, call the continuation method.

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

File picker sample