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Change Windows 8.1 lock screen image via WPF application

I'm trying to change Windows 8.1 (desktop) lock screen image from WPF application.
I've found solution with Windows SDK approach, but it uses runtime application as example (actually, all information I've found was regarding to WinRT apps). But I don't want to use WinRT - all I want is to use LockScreen class in plain old WPF.
After all I have managed to do this in the WPF app several times. This included:
1) manually adding <TargetPlatformVersion/>8.1</TargetPlatformVersion> into .csproj as suggested here;
2) adding references to Windows and System.Runtime.WindowsRuntime as suggested ibid;
3) following these steps to change lock screen background
Then I've faced the problem with platform - application does what it should only with x64 platform (not anyCPU). And not each time (I could not determine consistency yet).
Any way I think that I am over-complicating the solution. Does anyone have other suggestions? Is there any other simpler/cleaner way to change Windows 8.1 lock screen image via WPF application?

Open Camera Application From My App in Windows 8.1

Is there any way to open Windows 8.1 native camera application programatically in c#.

Basically WinRT doesn't allow that, Metro Apps run in the highly sandboxed environment, you can't open a a Metro nor a desktop one directly, you may find using the Launcher class from Windows.System.Launcher somehow helpful , take a look at this thread :
http://social.msdn.microsoft.com/Forums/windowsapps/en-US/b38bb2de-2a05-4f7d-8547-48b9759d72d4/can-i-use-windowssystemlauncherlauncherdefaultprogramuri-to-invoke-another-metro-style-app?forum=winappswithhtml5

Minimize Windows 8 Store App while tracking location with GPS

I'm working on a metro app and am having trouble finding how not to show the application.
We recently deployed tablets to our field reps, and need to add gps tracking. GPS is much easier to deal with in the metro libs (it's like 4 lines of code vs. unmanaged) so we're hoping to be able to push a metro app instead of spending time coding a winforms/wpf desktop app (the tablets are full version windows, so it's an option if we can't hide a metro app. I feel like it should be possible though as the start screen tiles update automatically without opening the main program).
In WPF, it's fairly simple to make a window invisible. I'm creating the metro app in wpf, but it uses different libs than desktop and I may just not know how to do it.
In desktop programs, it's fairly simple. You do something along the lines of:
<Page
x:Class = xxxxxxxx
..
Visibility="Hidden">
Unfortunately, with metro, the only options I have are collapsed and visible. Collapsed doesn't seem to have any effect, unless it's just because it's not deployed and visual studio shows it anyway...
So basically I'm trying to figure out if there's a way to start the program minimized or hidden so that it doesn't interrupt the field reps every time it takes their location.

If you really want to make a metro app and want it to run "minimised" you will need to look at background task. To start the background task the user would still need to start the app at least once, futhermore background task have limitation how how often and how long they can run. Also there is a lot of constraint on deploying a windows store app if you cannot publish it in the store.
If your goal is to just have access to GPS through C# apis, the GPS is actually one of the winRT api you can use from the desktop, you can find a tutorial on how to access winRT api from the desktop here
Here is the complete list of winRT api accessible from the desktop (You can find Geoposition class among them).

Have you looked into creating a background task that transmits GPS? The background task can run without the app running.

I am not entirely certain you can voluntarily minimize a Windows Store App on a user's behalf. I see nothing in IntelliSense about it, nor have I found anything online or see any app do it.
However, be aware that deploying the app without using the Windows Store -- sideloading -- requires Windows 8 Enterprise edition computers joined to the domain OR Windows 8 Pro with a sideloading key ($30 per key, purchased in packs of at least 100.) Perhaps a WPF app with unmanaged code is worth the money and effort.

How to use a monitor which is not part of desktop (Windows 7)

I would like to use a monitor which is actually marked "disconnected" in the windows control panel under "Change display settings". (I do NOT mean a physically disconnected monitor.)
I know how to add a second monitor in Windows and make it part of desktop. I also know how to make my application run on a primary or on secondary monitor when they are part of desktop.
I have a piece of equipment attached to the PC which has a touch screen on it. The touchscreen is connected to the PC over USB looking as an ordinary USB-Monitor and I can make it part of my Windows desktop. But that is not what I want.
What I would like to do is make sure that only one special application can run on this monitor. I also do not want to have a windows desktop on it because than the user could move any window to it which is not what I want. The idea behind all this is to use the touch screen to have an application on it which can control this external piece of equipment. The user would only have to run the PC but not to login. I was thinking about starting the app from a windows service before the windows desktop is loaded. And once the user logs in I do not want him to be able to use the touch screen for anything else except this special application. That is why the touch screen must not be part of the windows desktop but ”deactivated”.
I am using . NET 4.0 and C# for my application, but I will use C++ or whatever comes handy.
Any help or idea is appreciated. Thank you!

It seems WDDM does not support independent displays any more. Here are a few links in case somebody wishes to take a look for himself:
(old MSDN link) = /windows/win32/gdi/multiple-display-monitors
(old MSDN link) = /windows/win32/gdi/using-multiple-monitors-as-independent-displays
The important part is this note from the second link:
ⓘ Note
Using other monitors as independent displays isn't supported on drivers that are implemented to the Windows Display Driver Model (WDDM).

Accessing other processes in Win8 Metro-style app

I am trying to build a Windows 8 "metro-style" app that will operate as a "app killer". For those of you who have used Win8 (Tech Preview) you'll notice that once you open a metro-style app you cannot close it (without going into Task Manager and ending the process).
My challenge is that I cannot access 'System.Diagnostics.Process' from my metro-style app, nor do I know if there is an comparable alternative within the WinRT. I also thought of building a separate app that hosts a service for my metro app to interface with, but I'd like to do this with a single app.
Fundamentally, I am looking for a pattern for building Metro-style apps that leverage .NET 4.0 components, specifically to be able to enumerate and kill other processes running on the PC.
CLARIFICATION: I am less concerned with this specific application than I am with access that type of .NET functionality within a Metro-style app
Thanks

To your specific question, this functionality is not available. Apps are not allowed to interact or interfere with other apps.
To answer your more general question, the APIs available to Metro style applications is limited compared to what is available to desktop applications. C# has a subset of the .Net library available, much like Silverlight does. The same is true for C++ where a subset of the desktop Win32/COM APIs are available.

From what I understand (watching Build2011 videos) a Metro App won't be able to do that...
Interaction between processes is severally limited to specific Contracts (the charms on the right: Search, Send-to).
Think Phone, not Desktop.
You might be able to build a non-Metro Win8 app though.

Don't waste too much time on this. I expect that in a beta a close option (perhaps even a charm) will be included. Until then use a keyboard Alt-F4 or the Task Manager

C++:
Window::Current->CoreWindow->Close();
or
Window::Current->Close();
I haven't explored the difference between these two (more precisely, I don't know how CoreWindow differs from Current. I could assume though...
I'm using an Oracle VBox with Win8 on my Win7 machine to develop a C++ Metro App using VS 11. I used both of the above methods. I verified in Task Manager the app was not running on both Win8 and the Simulator.