UWP Printing

Unity Engine
,
1

Hoping to get UWP print functionality in my Unity UWP app by following the steps in

stackoverflow question 9074684 - how-to-print-in-uwp-app

Here’s the relevant parts of my app:

#if (ENABLE_IL2CPP && UNITY_WSA_10_0)
    void InitializePrinting()
    {
        printMan = PrintManager.GetForCurrentView();
        printMan.PrintTaskRequested += PrintTaskRequested;
        printDoc = new PrintDocument();
        printDocSource = printDoc.DocumentSource;
......

void OnPrint()
{
UnityEngine.WSA.Application.InvokeOnUIThread(async () =>
            {
                InitializePrinting();
            }, true);

}

However program is hanging when new PrintDocument() is called…

Any ideas, anyone?

2

So, offhand I noticed your calling InvokeOnUIThread() with true for waitUntilDone parameter; this should be false.
This is blocking the calling thread and is probably causing the deadlock

3

Thanks for responding!

I did change the parameter to false, but still seems to hang when creating the PrintDoc object. Also I’m calling the InitializePrinting() function from an OnEnable

#if (ENABLE_IL2CPP && UNITY_WSA_10_0)
    void InitializePrinting()
    {
        printMan = PrintManager.GetForCurrentView();
        printMan.PrintTaskRequested += PrintTaskRequested;
        printDoc = new PrintDocument();
        printDocSource = printDoc.DocumentSource;
......
void OnEnable()
{
UnityEngine.WSA.Application.InvokeOnUIThread(async () =>
            {
                InitializePrinting();
            }, false);
}
4

I quickly tried this code out but wasn’t able to repro the deadlock. So a couple additional questions:

  • Are you building a “XAML Project” for UWP?
    Since PrintDocument is a XAML control, you’ll need to use the project type. I tried it with D3D and just got a RPC_E_WRONG_THREAD error (but didn’t deadlock).

  • What version of Unity are you using?

  • Are you using IL2CPP or .NET back end (if on a 217.4 or older release)?

5

sorry for the delay in responding…

I switched from a D3D to a XAML project
using Unity 2018.3.13f1
with IL2CPP backend

When printDoc = new PrintDocument(); is called, I’m getting an exception:

Exception: Exception of type ‘System.Exception’ was thrown.
at Windows.UI.Xaml.Printing.PrintDocument…ctor () [0x00000] in <00000000000000000000000000000000>:0
at ScreenShotPopUp.InitializePrinting2 () [0x00000] in <00000000000000000000000000000000>:0
at ScreenShotPopUp+d__65.MoveNext () [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) [0x00000] in <00000000000000000000000000000000>:0

#if (ENABLE_IL2CPP && UNITY_WSA_10_0)
void InitializePrinting()
{
// Printing
LogManager.mInstance.Log(“ScreenShotPopuUp.InitializePrinting”);

LogManager.mInstance.Log(“ScreenShotPopuUp.InitializePrinting getting printMan”);
printMan = PrintManager.GetForCurrentView();
LogManager.mInstance.Log(“ScreenShotPopuUp.InitializePrinting adding PrintTaskRequested”);
printMan.PrintTaskRequested += PrintTaskRequested;

LogManager.mInstance.Log(“ScreenShotPopuUp.InitializePrinting Done”);

InitializePrinting2();
}

void InitializePrinting2()
{
// Build a PrintDocument and register for callbacks
LogManager.mInstance.Log(“ScreenShotPopuUp.InitializePrinting2 creating printdocument”);
printDoc = new PrintDocument();

6

Are you calling InitializePrinting() on the UI thread? From this recent code you pasted it doesn’t seem like you are, whereas in your original post you did.

void Start()
{
#if (ENABLE_IL2CPP && UNITY_WSA_10_0)

UnityEngine.WSA.Application.InvokeOnUIThread(async () =>
{
    InitializePrinting();
}, false);
#endif

I tried the Printing APIs in a 2018.3 release of Unity using IL2PP (invoking them on the UI thread) and didn’t hit the exception or run into other issues creating a new PrintDocument.

7

Looks like I got it working. I think I was attempting to create printDoc a second time.

Really appreciate your help.