Develop Reference

How to solve Java.Lang.RuntimeException: 'getParameters failed (empty parameters)'

I have a mobile app in Xamarin where a QR-code scanner is needed. Scanning the code works fine... After scanning a code, the user is redirected to another page. After checking out this page, the user is redirected to the page where the scanner is located. So, when this redirection happens, I get the error Java.Lang.RuntimeException: 'getParameters failed (empty parameters)'... I googled for hours but couldn't find any solution for this problem. BTW, it also happens when I use the 'back' button on the emulator or real word Android device...

--SOLVED--
Changing the PushAsync(pageX()) to PopAsync(); worked in my case. Found out that the problem is bases around getting the camera parameters. These are not available, because the camera is already using it in the former screen. So closing the camera/ending the camera activity is also a solution!

Error android.app.ServiceConnectionLeaked when InApp purchase

I am developing an Android App with Xamarin Android.
I'm using the InAppBilling Plugin from James Montemagno.
When I call PurchaseAsync Method the PlayStore dialog opens. But in the background my app freezes and I dont get any result.
var purchase = await CrossInAppBilling.Current.PurchaseAsync(productId, ItemType.Subscription, "apppayload");
In the Sys Log theres a android.app.ServiceConnectionLeaked error:
02-17 22:13:05.434 LENOVO YT3-X50L Error 8031 ActivityThread android.app.ServiceConnectionLeaked: Activity md5742c3bd4cdfedb6330d25c53207d662c.ShopActivity has leaked ServiceConnection md57a6f08dbc6561d468b2675b2ac9edab2.InAppBillingImplementation_InAppBillingServiceConnection#2277a40 that was originally bound here
at android.app.LoadedApk$ServiceDispatcher.<init>(LoadedApk.java:1092)
at android.app.LoadedApk.getServiceDispatcher(LoadedApk.java:986)
at android.app.ContextImpl.bindServiceCommon(ContextImpl.java:1303)
at android.app.ContextImpl.bindService(ContextImpl.java:1286)
at android.content.ContextWrapper.bindService(ContextWrapper.java:604)
at mono.android.view.View_OnClickListenerImplementor.n_onClick(Native Method)
at mono.android.view.View_OnClickListenerImplementor.onClick(View_OnClickListenerImplementor.java:30)
at android.view.View.performClick(View.java:5205)
at android.view.View$PerformClick.run(View.java:21164)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
I only get this error on LENOVO YT3-X50L. On Samsung phones it works fine...

ServiceConnectionLeaked
The CrossInAppBilling code does not take into consideration that your Activity can be killed/flushed from memory due to memory pressure/requirements and does not directly do anything to try to prevent it, it is up the app developer to determine when they need to take special action.
This is something I see a lot of in lower-end Android devices and the the new Android Oreo Go (<=1MB) test devices, but can happen on any device, but mostly noticeable on 2GB and lower devices.
Before calling any external code flush/release as much memory as possible
Focusing on releasing images is usually the largest payoff for memory reduction (restore them after the purchase is completed)
In cases of the Oreo Go 512MB devices I have had to go the extra mile and finish the current Activity, create a new blank/empty transient Activity and then call the external code (app billing, camera, etc) and upon completion, restore the original activity and bring it up to date with the new information externally obtained.
Note: profile your app and the activity first in order to focus your time.
Use your own Keep-Alive Service
Using Start/StopService and not Bind/UnBindService
Make it a Foreground Service
Note: This does not prevent the OS from killing/flushing your Activities/Services, it just provides a "hint" that it should not...
Note: Monitor the Importance state within the RunningAppProcessInfo to determine if your app is entering ReasonServiceInUse before you execute the external code.

Performance considerations when getting license information for WP app

Introduction
I have a Windows Phone 8.1 Silverlight (WP8.1 SL) based app in the store. Some users complain about performance issues when they have a bad network connection. I searched a bit and came up with the idea that it might be related to new LicenseInformation() that gives me the information of whether the app is running in Trial mode or not. The question is, whether this requires network information or not, and whether CurrentApp.LicenseInformation is a suitable replacement for a WP8.1 SL app.
Background and What I did so far
In general, the app does not need a network connection (no data to load, no advertisements, ...). To confirm that I used Fiddler to watch over the network sent by my phone. The result was that no network traffic is generated. However, the problem still persists.
After a lot of research and playing around I got the feeling that this issue might be related to the code part that checks on whether the app is in trial mode or not. I use the following code to check that.
var li = new LicenseInformation();
if (li.IsTrial()) {
...
}
I do this a couple of times during startup. So in case IsTrial() requires a network connection this could be the actual issue when there is only a bad connection available. But again, I couldn't find anything using Fiddler. The documentation (see here) for LicenseInformation does not mention whether a network connection is required or not.
Searching around I found that there is an updated interface available for both WP 8.1 SL and also W10M UWP.
var li = CurrentApp.LicenseInformation;
if (li.IsTrial) {
...
}
Its documentation clearly states that there is no network connection required for that (see here).
Even though the docs say that CurrentApp.LicenseInformation is also available on WP8 I also found some references that say that you only get a reliable answer for the IsTrial-question when using new LicenseInformation() (e.g. here).
Actual Questions
Is new LicenseInformation() required on WP8.1 SL, or can I use CurrentApp.LicenseInformation as well?
Does new LicenseInformation() require a network connection compared to CurrentApp.LicenseInformation?

Graphics.CopyFromScreen() and GetDC(0) fail with "The handle is invalid"

I have an application that takes screenshots from the local computer.
This works since many years correctly until suddenly a colleague reported me that he got an "The handle is invalid" error from my application.
This error came from inside the .NET framework from Graphics.CopyFromScreen().
To work around this I replaced this function with C++ code using GetDC(GetDesktopWindow()) / GetDC(NULL) and BitBlt() to copy the screen into a bitmap. Now I got ERROR_INVALID_HANDLE.
This happens on Windows 7.
What is going on there ?
I can not investigate this problem on my own because I cannot reproduce it and my colleague is in another country.
I searched in Google and lots of people report this error.
But all posts that I found were from people who tried to take a screenshot from a client computer through ASP code on a server. I don't understand how people can have the strange desire to capture the client's computer from a website. It is obvious that this will not work.
But I could not find one single case where someone reports this problem from an application that cannot capture the screen of the SAME computer in the SAME session where the application itself is running.

After investigating more with my colleague and giving him ideas what he can try, he told me that he starts my application through a remote desktop session.
The remote desktop session creates a virtual desktop (you see for example that the desktop wallpaper is missing).
I told my colleague to install a VNC client to remote control the computer instead of a remote desktop session and now all works fine. He installed TightVNC which uses the REAL desktop user session instead of creating a virtual session and locking the screen of the machine.
So if anyone gets reports of "The handle is invalid" while taking a screen capture, ask your users if they use a remote desktop session.
To detect a remote desktop session in code you can write:
in C++:
if (GetSystemMetrics(SM_REMOTESESSION) > 0)
{
MessageBox(m_hWnd, L"This application may not work correctly in a remote desktop session", "Error", MB_ICONSTOP);
}
or in C#:
if (System.Windows.Forms.SystemInformation.TerminalServerSession)
{
Messagebox.Show("This application may not work correctly in a remote desktop session");
}
Note that the problem is not reproducible on all computers. When I test on my own Windows 7 it works. So there are probably any additional system settings or other factors that trigger the "The handle is invalid" error (service packs / hotfixes...?).
But my colleague reports that he has never seen the error again after he stopped using the remote desktop connection.

There are a few reasons this can happen but the underlying theme is that the desktop window isn't available when this method is called.
In addition to the reasons mentioned above, another reason this can happen is if this method is being called when the screen is locked.
The code for CopyFromScreen has this section:
int result = SafeNativeMethods.BitBlt(targetDC, destinationX, destinationY, destWidth, destHeight, screenDC, sourceX, sourceY, (int) copyPixelOperation);
//a zero result indicates a win32 exception has been thrown
if (result == 0) {
throw new Win32Exception();
}
It would seem to me that the safest course of action would be that if you make use of this function, make sure that you also write your code assuming that receiving a Win32Exception or an unavailable Desktop Window is a use case which must be handle so the application doesn't crash.

Programmatically enabling Windows 8 Pro mobile broadband device

Background
The company I work on is developing a kiosk-like application for tablets running Windows 8 Pro (on desktop mode). The user shouldn't be able to access anything that isn't the application itself: charms will be disabled, the taskbar will be hidden behind the application, etc.
This also means the user shouldn't be able to change network settings, leaving the responsability to keep the device always connected to us. Up to now, I had success using the Mobile Broadband API to assure the device is connected whenever there's a mobile network available. It'll detect disconnect events and try to connect again.
The Problem
Although the user shouldn't be able to do it, I'm considering the case where the user follows this steps:
User opens right-side charm,
clicks on Settings,
clicks on Network,
clicks on More PC Settings,
clicks on Wireless, and
disables the mobile broadband device.
I would like to be able to revert this programmatically and enable it again.
The Attempts
I have tried some different ways to force 3G being reenabled. Most of them give me the same result: they supposedly enable the device without errors, but I still cannot use it. Enable-NetAdapter in Powershell doesn't throw errors, and the Enable method of Win32_NetworkAdapter appears to work, but no dice.
I thought maybe the method IMbnRadio::SetSoftwareRadioState could be what I'm after, but I can't get to it when the device is disabled. The method IMbnInterfaceManager::GetInterfaces throws a COMException claiming the element could not be found (HRESULT = 0x80070490).
MbnInterfaceManager mbnInterfaceManager = new MbnInterfaceManager();
IMbnInterfaceManager interfaceManager = (IMbnInterfaceManager)mbnInterfaceManager;
// The following line throws a COMException:
IMbnInterface[] interfaces = (IMbnInterface[])interfaceManager.GetInterfaces();
mobileInterface = interfaces[0];
mobileRadio = (IMbnRadio)mobileInterface;
uint requestId;
mobileRadio.SetSoftwareRadioState(MBN_RADIO.MBN_RADIO_ON, out requestId);
Is there a way to override user preferences set on "More PC Settings?"

I found a sketchy way to solve this. Keep in mind this is undocumented, wrong, shameless and immoral, and will probably break eventually. The client is aware of this, but prefers to keep the access to the OS limited.
The setting in case is saved in the Registry. At least in the computers I've checked, it's stored in HKLM\SYSTEM\CurrentControlSet\Control\Class\{4d36e972-e325-11ce-bfc1-08002be10318}\0022 in a key named RadioOff.
The Airplane Mode setting is also stored in the Registry, but in a different place. It's at HKLM\SYSTEM\CurrentControlSet\Control\RadioManagement\SystemRadioState in a key named (Default).
After changing these keys and rebooting, everything seems to work fine. I'll repeat though: you really shouldn't be doing this, especially the Airplane Mode thing.