C# code to change lockscreen and assign file to IStorage

There is example code available at the MSDN page[^]. Just download the C# source and give it a go.

In order to keep the stuff availabe when the Link should fail I wrote you a quick example up - Adjust it for yourself as ever needed.

using SDKTemplate;
using System;
using Windows.Storage;
using Windows.Storage.Pickers;
using Windows.Storage.Streams;
using Windows.System.UserProfile;

private async void SetLockScreen()
{
    rootPage.NotifyUser("", NotifyType.StatusMessage); 
    FileOpenPicker imagePicker = new FileOpenPicker 
    { 
       ViewMode = PickerViewMode.Thumbnail, 
       SuggestedStartLocation = PickerLocationId.PicturesLibrary, 
       FileTypeFilter = { ".jpg", ".jpeg", ".png", ".bmp" } 
     }; 
 
     StorageFile imageFile = await imagePicker.PickSingleFileAsync(); 
     if (imageFile != null) 
     { 
         try 
         { 
            // Application now has access to the picked file, setting image to lockscreen.  This will fail if the file is an invalid format. 
            await LockScreen.SetImageFileAsync(imageFile); 
 
            // Retrieve the lock screen image that was set 
            IRandomAccessStream imageStream = LockScreen.GetImageStream(); 
            if (imageStream != null) 
            { 
               BitmapImage lockScreen = new BitmapImage(); 
               lockScreen.SetSource(imageStream); 
               LockScreenImage.Source = lockScreen; 
               LockScreenImage.Visibility = Visibility.Visible; 
             } 
             else 
             { 
               LockScreenImage.Visibility = Visibility.Collapsed; 
               rootPage.NotifyUser("Setting the lock screen image failed.  Make sure your copy of Windows is activated.", NotifyType.StatusMessage); 
             } 
           } 
           catch (Exception) 
           { 
               LockScreenImage.Visibility = Visibility.Collapsed; 
               rootPage.NotifyUser("Invalid image selected or error opening stream.", NotifyType.ErrorMessage); 
           } 
    } 
    else 
    { 
         LockScreenImage.Visibility = Visibility.Collapsed; 
         rootPage.NotifyUser("No file was selected using the picker.", NotifyType.StatusMessage); 
    }
}

[Edit - Marco Bertschi: Added clarification and a solution to avoid the use of a FilePicker]

Please not that Windows 8 Apps which are using the new Win 8 API are only capable of accesing a previously defined list of locations on your computer. The list of currently accesible directories can be found at the MSDN[^]. Whatsoever, if you now would like to open a file located in your applications base directory, you would need to replace the folder picker with the following lines:

StorageFolder storageFolder = KnownFolders.DocumentsLibrary;
StorageFile file = await storageFolder.GetFileAsync("yourdesiredimage.jpg");

this would lead to let your code look somewhat like this:

using SDKTemplate;
using System;
using Windows.Storage;
using Windows.Storage.Pickers;
using Windows.Storage.Streams;
using Windows.System.UserProfile;

private async void SetLockScreen()
{
    rootPage.NotifyUser("", NotifyType.StatusMessage); 
    StorageFolder storageFolder = KnownFolders.DocumentsLibrary;
    StorageFile imageFile= await storageFolder.GetFileAsync("yourdesiredimage.jpg");
 
     if (imageFile != null) 
     { 
         try 
         { 
            // Application now has access to the picked file, setting image to lockscreen.  This will fail if the file is an invalid format. 
            await LockScreen.SetImageFileAsync(imageFile); 
 
            // Retrieve the lock screen image that was set 
            IRandomAccessStream imageStream = LockScreen.GetImageStream(); 
            if (imageStream != null) 
            { 
               BitmapImage lockScreen = new BitmapImage(); 
               lockScreen.SetSource(imageStream); 
               LockScreenImage.Source = lockScreen; 
               LockScreenImage.Visibility = Visibility.Visible; 
             } 
             else 
             { 
               LockScreenImage.Visibility = Visibility.Collapsed; 
               rootPage.NotifyUser("Setting the lock screen image failed.  Make sure your copy of Windows is activated.", NotifyType.StatusMessage); 
             } 
           } 
           catch (Exception) 
           { 
               LockScreenImage.Visibility = Visibility.Collapsed; 
               rootPage.NotifyUser("Invalid image selected or error opening stream.", NotifyType.ErrorMessage); 
           } 
    } 
    else 
    { 
         LockScreenImage.Visibility = Visibility.Collapsed; 
         rootPage.NotifyUser("No file was selected using the picker.", NotifyType.StatusMessage); 
    }
}

In reply to a comment on this solution, using hard-coded full paths as "C:\Temp\Img.jpeg" is considered bad coding practice and should be avoided whenever possible. Especially Windows 8, but also Windows 7 and Vista have a way to directly access a folder by either using a framework enumeration or accessing local computer variables (such as %APPDATA%) directly to get the path of a folder.

[Edit]