MICROSOFT_PRESS_EBOOK_PROGRAMMING_WINDOWS_8_APPS_WITH_HTML_CSS_AND_JAVASCRIPT_PDF

function pickSinglePhoto() {
// Verify that we are currently not snapped, or that we can unsnap to open the picker
var currentState = Windows.UI.ViewManagement.ApplicationView.value;
if (currentState === Windows.UI.ViewManagement.ApplicationViewState.snapped &&
!Windows.UI.ViewManagement.ApplicationView.tryUnsnap()) {
// Fail silently if we can't unsnap
return;
}
// 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.pickSingleFileAsync().done(function (file) {
if (file) {
// Application now has read/write access to the picked file
} else {
// The picker was dismissed with no selected file
}
});
As you can see, you should not try to invoke the File Picker when in snapped view; this will, like the
Settings Pane, cause an exception. You can check for such a condition ahead of time, as shown here, or
you can add an error handler within the done at the end. 44 In any case, to invoke the picker we create
an instance of Windows.Storage.Pickers.FileOpenPicker, configure it, and then call its
pick-SingleFileAsync method. The result of pickSingleFileAsync is the file argument given to the
completed handler, which will be either a StorageFile object for the selected file or null if the user
canceled. This is why you must always check that the picker’s result is not null.
With the configuration, here we’re setting the picker’s viewMode to thumbnail (from the enumeration
Windows.Storage.Pickers.PickerViewMode), resulting in the view of Figure 8-7. The other possibility
here is list, which gives a view like Figure 8-10.
We also set the suggestedStartLocation to the picturesLibrary, which is a value from the
Windows.Storage.Pickers.PickerLocationId enumeration; other possibilities are documentsLibrary,
computerFolder, desktop, downloads, homeGroup, musicLibrary, and videosLibrary, basically all the other
locations you see in Figure 8-8. Note that using these locations does not require you to declare
capabilities in your manifest because by using the picker, the user is giving consent for you to access
44 The sample, it should be noted, uses then instead of done on that last async call; while then works, it should actually be
done especially if you’re going to handle exceptions there.
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